When a textile material is tested certain things are expected from the results. Some of these are explicit but other requirements are implicit. The explicit requirements from the results are either that they will give an indication of how the material will perform in service or that they will show that it meets its specification. The implicit requirement from a test is that it is reproducible, that is if the same material is tested either at another time, or by another operator or in a different laboratory the same values will be obtained. In other words the test measures some ‘true’ or correct value of the property being assessed. If the test results vary from laboratory to laboratory then the test is not measuring anything real and it is pointless carrying it out. However, the values that are obtained from testing textile materials are not expected to be exactly the same, so that appropriate statistical criteria should be applied to the results to see whether they fall within the accepted spread of values.
The lack of reproducibility of test results can be due to a number of causes.
Most textile materials are variable, natural fibres having the most variation in their properties. The variation decreases as the production progresses from fibres to yarns to fabrics, since the assembly of small variable units into larger units helps to smooth out the variation in properties. The problem of variable material can be dealt with by the proper selection of representative samples and the use of suitable statistical methods to analyse the results.
Variation caused by the test method
It is important that any variations due to the test itself are kept to the minimum. Variability from this source can be due to a number of causes:
1 The influence of the operator on the test results. This can be due to differences in adherence to the test procedures, care in the mounting of specimens, precision in the adjustment of the machine such as the zero setting and in the taking of readings.
2 The influence of specimen size on the test results, for instance the effect of specimen length on measured strength.
3 The temperature and humidity conditions under which the test is carried out. A number of fibres such as wool, viscose and cotton change their properties as the atmospheric moisture content changes.
4 The type and make of equipment used in the test. For instance pilling tests can be carried out using a pilling box or on the Martindale abrasion machine. The results from these two tests are not necessarily comparable.
5 The conditions under which the test is carried out such as the speed, pressure or duration of any of the factors.
It is therefore necessary even within a single organisation to lay down test procedures that minimise operator variability and set the conditions of test and the dimensions of the specimen. Very often in such cases, factors such as temperature, humidity and make of equipment are determined by what is available.
However, when material is bought or sold outside the factory there are then two parties to the transaction, both of whom may wish to test the material. It therefore becomes important in such cases that they both get the same result from testing the same material. Otherwise disputes would arise which could not be resolved because each party was essentially testing a different property.
This requires that any test procedures used by more than one organisation have to be more carefully specified, including, for instance, the temperature and humidity levels at which the test takes place. The details in the procedure have to be sufficient so that equipment from different manufacturers will produce the same results as one another. This need for standard written test methods leads to the setting up of national standards for test procedures so making easier the buying and selling of textiles within that country. Even so certain large organisations, such as IWS or Marks and Spencer, have produced their own test procedures to which suppliers have to conform if they wish to carry the woolmark label or to sell to Marks and Spencer.
Next to wool and cotton, flax is used most largely in our textile manufactures. The linen fiber consists of the bast cells of certain species of flax grown in Europe, Africa, and the United States. All bast fibers are obtained near the outer surface of the plant stems. The pith and woody tissues are of no value. The flax plant is an annual and to obtain the best fibers it must be gathered before it is fully ripe. To obtain seed from which the best quality of linseed oil can be made it is usually necessary to sacrifice the quality of the fibers to some extent.
The Flax Must Be Pulled Up by the Roots to Give Fibres with Tapered Ends.
Treatment of Flax
Unlike cotton, flax is contaminated by impurities from which it must be freed before it can be woven into cloth. The first process to which the freshly pulled flax is submitted is that of “rippling” or the removal of the seed capsules. Retting, next in order, is the most important operation. This is done to remove the substances which bind the bast fibers to each other and to remove the fiber from the central woody portion of the stem. This consists of steeping the stalks in water.
(1) Cold water retting, either running or stagnant water.
(2) Dew retting.
(3) Warm water retting.
A—Inlet; B—Undisturbed Water; C—Bundles of Flax.
Cold water retting in running water is practiced in Belgium. Retting in stagnant water is the method usually employed in Ireland and Russia. The retting in stagnant water is more rapidly done, but there is danger of over-retting on account of the organic matter retained in the water which favours fermentation. In this case the fiber is weakened.
In dew retting, the flax is spread on the field and exposed to the action of the weather for several weeks without any previous steeping. This method of retting is practiced in Germany and Russia. Warm water retting and chemical retting have met with limited success.
When the retting is complete, the flax is set up in sheaves to dry. The next operations consist of “breaking,” “scutching,” and “hackling” and are now done by machinery.
Breaking removes the woody center from the retted and dried flax by being passed through a series of fluted rollers. The particles of woody matter adhering to the fibers are detached by scutching.
Hackling or combing still further separates the fibers into their finest filaments—”line” and “tow.” The “flax line” is the long and valuable fiber; the tow, the short coarse tangled fiber which is spun and used for weaving coarse linen.
A, Unthrashed Straw; B, Retted; C, Cleaned or Scutched; D, Hackled or Dressed.
HACKLING FLAX BY HAND
The “Tow” Is Seen at the Left and a Bunch of “Flax line” on the Bench.
When freed from all impurities the chief physical characteristics of flax are its snowy whiteness, silky luster and great tenacity. The individual fibers may [Pg 50]be from ten to twelve inches in length; they are much greater in diameter than cotton. It is less pliant and elastic than cotton and bleaches and dyes less readily. Linen cloth is a better conductor of heat than cotton and clothing made from it is cooler. When pure, it is, like cotton, nearly pure cellulose.
Besides the linen, there is a great number of bast fibers fit for textile purposes, some superior, some inferior. India alone has over three hundred plants that are fiber yielding. One-third of these furnish useful fibers for cordage and fabrics. The next in importance to linen is ramie or rhea, and China grass. China grass comes from a different plant but is about the same as ramie. The staple is longer and finer than linen. The great strength of yarn made from it is due to length of the staple.
The variety and great value of the ramie fibers has long been recognized, but difficulties attending the separation and degumming of the fibers have prevented its employment in the manufactures to any great extent. The native Chinese split and scrape the plant stems, steeping them in water. The common retting process used for flax is not effective on account of the large amount of gummy matter, and although easy to bleach it is difficult to dye in full bright shades without injuring the luster of the fibers.
Jute and Hemp
Jute and hemp belong to the lower order of bast fibers. The fiber is large and is unfit for any but the coarsest kind of fabrics. Jute is mainly cultivated in Bengal. The fiber is separated from the plant by retting, beating, etc.
JUTE GROWING IN LOUISIANA.
DRYING HEMP IN KENTUCKY
Olona, the textile fiber of Hawaii, is found to have promising qualities. This plant resembles ramie and belongs to the nettle family also, but it is without the troublesome resin of the ramie. The fiber is fine, light, strong, and durable.
The Philippines are rich in fiber producing plants. The manila hemp is the most prominent, of which coarse cloth is woven, besides the valuable cordage. The sisal hemp, pineapple, yucca, and a number of fiber plants growing in the southern part of the United States are worthy of note. These fiber industries are conducted in a rude way, the fiber being cleaned by hand, except the pineapple.
The word wool is restricted to the description of the curly hairs that form the fleece produced by sheep (Rogers, 2006:931). The sheep’s fleece is removed once a year by power-operated clippers. The soiled wool at the edges is removed before the fleeces are graded and baled. The price of raw wool is influenced by fineness and length. This is representative of the yarn into which it can be spun. The average fibre length will also determine the type of fabric for which it will be used (Collier, 1974:24).
Newly removed wool is known as raw wool and contains impurities such as sand, dirt, grease and dried sweat. Altogether, these can represent between 30 and 70% of the wool’s weight (Kadolph, 2002:51). The wool is sorted by skilled workers who are experts in distinguishing quality by touch and sight. The grade is determined by type, length, fineness, elasticity and strength (Corbman, 1983:271).
Long wool fibres will be combed and made into worsteds, while short wools are described as carding, or clothing wools. When the quality has been determined, the wool is offered for sale as complete fleeces or as separate sections (Collier, 1974:24).
When the wool arrives at the mill it is dirty and contain many impurities that must be removed before processing. The raw wool is scoured with a warm alkaline solution containing warm water, soap and a mild solution of alkali, before being squeezed between rollers (Corbman, 1983:272). This procedure is repeated three to four times, after which the wool is rinsed in clean water and dried.
The quality and characteristics of the fibre and fabric depend on a number of factors, such as the kind of sheep, its physical condition, the part of the sheep from which the wool is taken, as well as the manufacturing and finishing processes (Corbman, 1983:273).
The chemical composition of wool:
The protein of the wool fibre is keratin (Azoulay, 2006:26), which contains carbon, hydrogen, oxygen and nitrogen, but in addition wool also contains sulphur. These are combined as amino acids in long polypeptide chains (Kadolph, 2002:54). Wool contains 18 amino acids, of which 17 are present in measurable amounts (Joseph, 1986:48). These are glycine, alanine, valine, leucine, isoleucine, phenylalanine, proline, serine, threonine, tyrosine, aspartic, glutamic, arginine, lysine, histidine, tryptophan, cystine and methionine (Stout, 1970:107). In addition to the long-chain polyamide structure, wool has cross-linkages called cystine or sulphur linkages, plus ion-to-ion bonds called salt bridges and hydrogen bonds (Tortora, 1978:74).
The cross-linkages in the chains permit the ends to move up and down, which provides the resiliency of the fibre (Labarthe, 1975:51). Keratin reacts with both acids and bases, which makes it an amphoretic substance (Hollen and Saddler, 1973:17).
When keratin is in a relaxed state it has a helical, or spiral structure called alpha-keratin (Gohl and Vilensky, 1983:75), which is responsible for wool’s high elongation property (Kadolph, 2002:54). When the fibre is stretched it tends to unfold its polymers and this unfolded configuration is known as beta-keratin (Gohl and Vilensky, 1983:78).
Helical arrangement of the wool molecule (Wool Bureau, Inc. as cited in Kadolph, 2002:56).
The tenacity of wool is improved by the presence of the hydrogen bonding between the oxygen and hydrogen atoms of alternate spirals of the helix. This strengthens the structure and a greater force is required to stretch the molecules (Smith and Block, 1982:91).
The physical structure of wool:
The fibre consists of three layers – an outer layer of scales called the cuticle, a middle layer called the cortex and an inner core, called the medulla Joseph, 1986:49).
The wool fibre is a cylinder, tapered from root to tip and covered with scales (Ito et al, 1994:440). The scales are irregular in shape and overlap each other towards to the tip of the fibre. These then have a directional effect that influences the frictional behaviour of wool because of its resistance to deteriorating influences (Joseph, 1986; Hall, 1969:15). These scales are responsible for wool textile’s tendency to undergo felting and shrinking as a consequence of the difference of friction in the ‘with-scale’ and ‘against scale’ directions (Silva et al, 2006:634; Cortez et al, 2004:64). Each cuticle cell contains an inner region of low sulphur content, known as the endocuticle, plus a central sulphur rich band, known as the exocuticle. Around the scales is a shield, a membrane called the epicuticle (Maxwell and Hudson, 2005:127), which acts as a diffusive barrier and can also affect the surface properties of the fibre. The epicuticle is present as an envelope that bounds the entire inner surface of the cell (Swift and Smith, 2001:204). The sub-cuticle membrane is a thin layer between the cuticle and the cortex (Morton and Hearle, 1975:59).
fig:-Physical structure of a wool fibre (Gohl and Vilensky, 1983:73).
The cortex is the bulk of the fibre and the hollow core at the centre is called the medulla. The cortex consists of millions of long and narrow cells, held together by a strong binding material. These cells consist of fibrils, which are constructed from small units and lie parallel to the long axis of the long narrow cells. The wool fibre gets its strength and elasticity from the arrangement of the material composing the cortex (Collier, 1974:25). The medulla resembles a honeycomb, i.e. contains empty space that increases the insulating power of the fibre (Hollen and Saddler, 1973:19).
Wool appears to be divided longitudinally into halves because of its bilateral structure, with one side called the paracortex and the other the orthocortex. The chemical composition of the cells of the ortho- and paracortex is different, i.e. the paracortex contains more cystine groups that cross-link the chain molecules and is therefore more stable. It is this difference between the ortho- and paracortex that brings about the spiral form of the fibre and explains why the paracortex is always found on the inside of the curve as the fibre spirals around in its crimped form. In addition, these two parts react differently to changes in the environment, which leads to the spontaneous curling and twisting of wool (Gohl and Vilensky, 1983:74).
fig:-Three-dimensional crimp of the wool fibre (Gohl and Vilensky, 1983:75).
The fibres have a natural crimp, i.e. a built in waviness, which increases the elasticity and resiliency of the fibre. The spiral formed by the crimp is three-dimensional and does not only move above and below the central axis, but also to its left and right (Joseph, 1986:49).
The cross-section of the wool fibre is nearly circular and in some cases even oval in shape (Joseph, 1986:49). The longitudinal view shows both the scale structure, plus the striations on the epicuticle that can occur on the original undamaged fibres. These arise from an interaction in the follicle with the cuticle of the inner root sheath. When the fatty acids are stripped from the surface, the striations have been shown to reflect a corresponding irregularity of the epicuticle’s surface (Swift and Smith, 2001:203).
Wool fibres vary in length between 2cm to 38cm, depending on various factors such as the breed of the sheep and the part of the animal from where it was removed (Joseph, 1986:50; Smith and Block, 1982:92). The diameters of the wool also vary. Fine fibres have a diameter of 15 to 17μm, medium fibres have a diameter 24 to 34μm and coarse wool has a diameter of about 40μm (Joseph, 1986:50). Hollen and Saddler (1973) differ in as much that they claim the diameter of a wool fibre varies from 15 to 50μm, with Merino lamb’s wool averaging 15 μm in diameter.
The colour of the natural wool depends on the breed of sheep, but most wool is an ivory colour, although it can also be grey, black, tan and brown (Joseph, 1986:50).
Physical properties of wool:
The lustre of a fibre depends on the amount and pattern of light reflected from the fibre (Hopkins, 1950:593).
The lustre of wool varies, but it is not generally considered to be a lustrous fibre. Nevertheless, lustre also depends on factors such as the specific breed of sheep, conditions of living and the part of the animal from which it was taken (Tortora, 1978:76). Fine and medium wools have more lustre than coarse fibres (Joseph, 1986:50) because lustre is due to the nature and transparency of the scale structure (Stout, 1970:113).
Wool is a weak natural textile fibre (Corbman, 1983:280). It has a large amorphous area containing bulky molecules that can’t be packed close enough together to allow strong hydrogen bonding. Thus wool has many weak bonds and a few strong cystine linkages. Moisture weakens the hydrogen bonds, which makes the fibre even weaker when wet (Hollen and Saddler, 1973:20). When a garment is wet, the weight of the water puts strain on the weakened fibre and the shape can be distorted (Hollen and Saddler, 1973:21).
The strength of a fibre is dependent on the cross-sectional area of the fibre being tested. The smallest fibre diameter and the rate of change in diameter are important determinants of strength. There are a variety of environmental and physiological factors that influence the strength of wool fibres. The nutrient supply has a great influence as it provides amino acids, trace elements and vitamins. The fibre strength is also influenced by pregnancy and lactation through competition for essential nutrients (Reis, 1992:1337). During wear, however, resistance to abrasion is more important than tensile strength. The scale structure of the wool fibre gives excellent abrasion resistance, which makes wool fabric very durable (Smith and Block, 1982:93).
Wool fibres are very elastic and, when stretched, they quickly return to their original size (Smith and Block, 1982:92). This is due to the crimp, or waviness, of the fibre which enables it to be stretched out and then relaxed to the crimp form, like a spring (Collier, 1974:26). The molecules are in a folded state, but become straightened when stretched. The cross-linkages between the molecules, plus the disulphide and salt linkages tend to resist any permanent alteration in shape (Collier, 1974:27).
Disulphide linkage (Collier, 1974:27)
Salt linkage (Collier, 1974:27)
Wool fibres can be stretched from 25 to 30% of their original length before breaking, which also reduces the chances of tearing under tension (Corbman,1983:280).
Wool’s recovery is excellent and after a 2% extension the fibre has an immediate regain in length of 99% (Joseph, 1986:50). Elasticity is a valuable characteristic because it leads to the easy shedding of wrinkles. Wrinkles will easily hang out of wool garments, especially when hung in a damp atmosphere (Tortora, 1978:76).
The molecules in the wool fibre are arranged in long parallel chains, which are held together by cross-linkages. When the fibres are stretched or distorted, these cross-linkages will force the fibre back to shape (Cowan and Jungerman, 1969:9). This shows that the fibres will recover quickly from creasing (Thiry, 2005:19; Azoulay, 2006:26), but through the application of heat, moisture and pressure, pleats and creases can be put into the fabric. This is a result of the molecular adjustment and the formation of new crosslinkages in the polymer.
The resilience of the wool fibre also contributes to the fabrics’ loft, which can either produce open porous fabrics with good covering power, or thick and warm fabrics that are also light in weight (Joseph, 1986:50).
Wool is classified as a resilient fibre. Therefore a bunch of irregular fibres should: a) offer moderate resistance to compression, and; b) spring back vigorously upon relaxation (Demiruren and Burns, 1955:666).
Wool and silk have the ability to resist the formation of wrinkles (Buck and McCord, 1949).
Absorption and moisture regain:
Water is usually shed by the wool fibres because of a combination of factors that include, for instance, the protection by the scales and the membrane, interfacial surface tension, uniform distribution of pores and low bulk density (Joseph, 1986:51).
However, once the moisture seeps between the scales, the high degree of capillarity within the fibre will cause ready absorption (Ito et al., 1994:440). Wool can absorb 20% of its own weight in water without feeling wet (Corbman, 1983:282). According to Cowan and Jungerman (1969:9) wool is a hygroscopic fibre because it absorbs water vapour. Most of the moisture is absorbed into the spongy matrix, which then causes the rupture of hydrogen bonds and leads to the swelling of the fibre. The absorbent nature is due to the polarity of the peptide groups, salt linkages and amorphous polymer system (Cook and Fleischfresser, 1990:43). Wool dries very slowly (Corbman, 1983:282).
Hydrogen bonds are broken by moisture and heat, so the wool structure can be reshaped by mechanical action like that of an iron. While the heat dries the wool, new hydrogen bonds are formed in the structure as the water escapes in the form of steam. The new hydrogen bonds maintain the new shape while humidity is low. When the wool is dampened or in a high humidity atmosphere, the new bonds are broken and the structure returns to its original shape.
This is why garments shaped with ironing lose their creases and flatness, and show relaxation shrinkage on wetting (Hollen and Saddler, 1973: 21) Wool produces heat as part of the absorption function (Azouly, 2005:25), which is known as heat of wetting. This is due to the energy generated by the collision of water molecules and the polar groups in the wool polymers. The polymer system will continue to give off heat until it becomes saturated. As wool begins to dry, the evaporation causes the heat to be absorbed by the fibre and a chill may be experienced (Joseph, 1986:51).
The behaviour of wool in relation to moisture can be summarized by saying that wool is water repellent, but with prolonged exposure to moisture the fibre does absorb large quantities of water. Since the moisture is held inside the fibre, the surface still feels dry (Tortora, 1978:77; Etters, 1999). Wool is hydrophilic and contains various amounts of absorbed water depending on the conditions (Cook and Fleischfresser, 1990:43). The standard moisture regain of wool is set at 16 to 30% (Hollen and Saddler, 1973:22), but according to Lyle (1976:29) and Hunter (1978:46) it is only 15%. Cowan and Jungerman (1969:9) and Joseph (1986) report a regain of 13 to 16%.
The structure of wool fibres contributes to its non stability (Joseph, 1986:51). All fabrics made of wool are subject to shrinkage (Corbman, 1983:282). Two kinds of shrinkage occur: felting shrinkage and relaxation shrinkage. Felting shrinkage occurs as a result of combined agitation, heat and moisture (Lenting et al., 2006:711; Cortez et al., 2004:64).
When wet, untreated wool fabric is agitated, the fibres will tend to move in a root ward direction and the root curls upon itself (Gohl and Vilensky, 1983:71). The scales interlock and hook together, causing the fibres to become entangled (Silva et al., 2006:634).
When the felting is not properly controlled, the fabric will become stiff and thick, and it will shrink considerably (Joseph, 1986:52). Felting is enhanced by heat, which causes the fibre to become more elastic and thus more likely to move. This, in turn, will make it distort and entangle itself with other fibres. Heat also causes the fibre to swell, a condition that is enhanced by acid or alkaline conditions. Swelling leads to more inter-fibre contact and inter-fibre friction (Gohl and Vilensky, 1983:71).
Relaxation shrinkage occurs as a result of the elasticity of the fibre. Fibres are stretched and extended during the construction of fabrics, and when the fibre is exposed to moisture, the yarns return to their original length that causes the fabric to shrink (Joseph, 1986:52; Garcia et al., 1994:466). This also includes exposure to steam, which causes shrinkage (Lyle, 1976:103). The felting shrinkage of wool is progressive. Wool will continue to shrink if it is not washed in cold water with a neutral pH and minimum handling to
minimize felting (Tortora, 1978:77).
The warmth of wool is due to its spongy structure and scales that incorporate many extremely small pockets of air (Miller, 1992:26).
Stationary air is a bad conductor of heat and therefore wool is a good heat insulator and feels warm (Corbman, 1983:281).
cool absorbs atmospheric moisture and through the heat of absorption makes the wearer feel warmer (Cowan and Jungerman, 1969:9), and the fibre is protein and therefore doesn’t transmit heat quickly (Miller, 1992:29).
Thermal properties of wool:
Wool is not a very flammable fibre. Dry wool will burn slowly with a sputtering smoky flame, and will self-extinguish when removed from the source of flame (Smith and Block, 1982:94). Wool fibres scorch at 204°C and will eventually turn to char at 300°C. During combustion it will give off a smell similar to burning feathers. When removed from the flame each fibre will form a charred black knob (Cook, 1984:90).
Chemical properties of wool:
Effect of alkalis:
Wool is easily attacked by alkalis. Weak alkalis like soap, sodium phosphate, ammonia, borax and sodium silicate will not damage wool if the temperatures are low (Labarthe, 1975:63). Alkaline solutions can open the disulphide cross-links of wool, while hot alkalis may even dissolve it (Chapman, 1974:56). Wool dissolves when boiled in a 5% solution of
sodium hydroxide (Labarthe, 1975:63). Caustic soda will completely destroy wool. Wool turns yellow as it disintegrates, then it become slick and turn into a jelly-like mass, and goes into solution (Hollen and Saddler, 1973:22).
Weak solutions of sodium carbonate can damage wool when used hot, or for a long period (Hall, 1969:17).
Concentrated alkalis below 31°C gives wool increased lustre and strength, by fusing the scales together; it is called mercerized wool (Labarthe, 1975:63).
Effect of acids:
Wool is more resistant to acids. This is because they hydrolyse the peptide groups but leave the disulfide bonds intact, which cross-link the polymers. Although this weakens the polymer system, it doesn’t dissolve the fibre (Gohl and Vilensky, 1984:81).
Wool is only damaged by hot sulphuric acid (Corbman, 1983:282) and nitric acid (Joseph, 1986). Acids are used to activate the salt linkages in the wool fibre, making it available to the dye (Hollen and Saddler, 1973:22). Concentrated mineral acids will destroy wool if the fabric is soaked in it for more than a few minutes. It will also destroy wool when it dries on the fabric (Labarthe, 1975:63).
Effect of bleach:
Bleaches that contain chlorine compounds will damage wool. Products with hypochlorite will cause wool to become yellow and dissolve it at room temperature. Various forms of chlorine are used to make ‘unshrinkable wool’, by destroying the scales. This wool is weaker, less elastic and has no felting properties (Labarthe, 1975:63).
Bleaches containing hydrogen peroxide, sodium perborate, sodium peroxide (Corbman, 1983:282) and potassium permanganate won’t harm wool and are safe to use for stain removal (Wingate and Mohler, 1984:308).
Effect of sunlight:
Wool will weaken when exposed to sunlight for long periods (Schmidt and Wortmann, 1994). The ultraviolet rays will cause the disulfide bonds of cystine to break, which leads to photochemical oxidation. This will cause fibre degradation and eventual destruction (Joseph, 1986:53). Wet fabrics exposed to ultraviolet light are more severely faded and weakened than dry fabrics (Labarthe, 1975:62).
Effect of perspiration:
As already stated, wool is easily deteriorated by alkalis and therefore perspiration which is alkaline will weaken wool as a result of hydrolysis of peptide bonds and amide side chains (Maclaren and Milligan, 1981:89). Perspiration in general will lead to discoloration (Corbman, 1983:283).
Effect of water:
Wool loses 10 to 25% of its strength when wet, although it is regained upon drying (Stout, 1970:113). Prolonged boiling will dissolve and decompose small amounts of the fibre. Boiling water will reduce lustre and promote felting (Labarthe, 1975:63). The heat makes the fibre more elastic and plastic which makes it easier to move and entangle itself with other fibres (Gohl and Vilenski, 1983:72).
Biological properties of wool:
Wool is vulnerable to the larvae of moths and carpet beetles (Corbman, 1983:282), as they are attracted by the chemical structure of the cystine cross-linkages in wool (Tortora, 1978:78).
Raw wool may contain inactive spores, which becomes active when wet. Mildew will develop when wool is left in a damp condition for a long period (Labarthe, 1975:59).
Dry cleaning is the recommended care method for wool items (Kadolph, 2002:56), because the solvents do not harm wool and create less wrinkling, fuzzing and shrinkage (Hollen and Saddler, 1973:22). Wool fabrics should not be tumble dried, because the tumbling of the damp fabrics may cause excessive felting shrinkage. The dryer will provide all of the conditions necessary for felting, namely heat, moisture and friction (Tortora, 1978:78). Wool items should be dried flat to prevent strain on any part of the garment. Heat has a negative effect on wool fibres and therefore it is necessary to keep ironing temperatures low, and to use a press cloth (Tortora, 1978:78). Steaming will partially shrink and condition the fabric, so should be done with care (Wingate and Mohler, 1984:319).
Silks can be defined as externally spun fibrous protein secretions. Of all the natural fibers, silks represent the only ones that are spun. Silk fibers have been used in textiles for thousands of years, owing to their unique visual luster, tactile properties, and durability. These fibers are remarkable materials displaying unusual mechanical properties. Strong, extensible, and mechanically compressible, silks display interesting electromagnetic responses, particularly in the UV range for insect entrapment; form liquid crystalline phases related to processing; and exhibit piezoelectric properties. Silks were used in optical instruments as late as the mid-1900s because of their fine diameter and high strength and stability over a range of temperatures. Spider silks are reportedly used in the South Pacific for gill nets, dip nets, and fishing lures, as well as in weaving and ceremonial dress.
Types of Silk
These are just some of the more common forms of silk
Raw silk – Silk in its natural form is covered with a gum called Sericin. Raw silk still has all the gum which is dull & stiff and can be in many colours. Various processes can be used to remove the sericin to reveal the lustrous fibre beneath.
Wild Silk – This is usually not white and is from the tannins from eating plants other than the mulberry tree. It can be courser than cultivated silk, making it better for high wear items. It is cheaper. Wild silk cocoons are usually gathered after the moth has emerged, therefore the staples or fibres will have been cut, making it only suitable for spinning. It is also known as Tussah Silk
Tussah Silk – Courser than cultivated silk and correspondingly, more robust. It usually has small black flecks throughout. See also Wild Silk Cultivated Silk – This has become a highly technical and controlled industry where silk worms are raised and fed mainly on mulberry leaves to produce a near white coloured silk. Often the chrysalis or grub is destroyed before it has a chance to eat its way out of the cocoon, so that the fibre can be reeled off in one long fibre. See also Reeled Silk & Thrown Silk
Thrown Silk – Made from the long filaments of silk up to 1500 mts long, and is nearly always made from cultivated silk. It is more expensive due to the extra work required in reeling off the single filaments. It requires very little twist so retains more lustrousness, and can be woven into fabric that are almost transparent. Also called Reeled silk. Some types of thrown silk fabrics include: voile, georgette, organza and crepe.
Dupion Silk – This is silk which retains the lumps where two threads join. It is a characteristic which is admired and should not be considered a flaw.
Noil Silk – Made from very short staple and contains little tangle balls of fibre
Reeled Silk – See also Thrown Silk and Cultivated Silk
Spun Silk – Shorter staples can be carded and woven, much the same way as cotton or wool. Includes varieties such as Shantung, Mutka and Noil.
Cut Silk – See Spun Silk
Table 2 summarizes the amino acid composition of various silk proteins. The silkworm cocoon silk contains two structural proteins, the fibroin heavy chain (mol. wt. ca 350,000) and fibroin light chain (mol. wt. ca
25,000), plus the family of sericin proteins (mol wt 20,000–310,000) to hold the fibroin chains together in the final cocoon fiber and accessory proteins. Other silks, such as the caddis fly and aquatic midge, which spin silks underwater to form sheltered tubes, have also been characterized and consist of a family of proteins having high cysteine content and running from low to very high (>106) molecular weights. Some silkworm silks from wild strains have been reported to contain up to 95% alanine. The consensus crystalline amino acid repeat in the B. mori silkworm cocoon silk fibroin heavy chain is the 59mer: GAGAGSGAAG[SGAGAG]8Y. More detailed analysis of these repeats indicates that the fibroin contains alternate arrays of repeating GAGAGS and GAGAGY. Valine or tyrosine replacements for alanine exist in the second repeat. These core repeats are surrounded by homogenous nonrepetitive amorphous domains. The repetitive structures in the protein are thought to be the result of genetic level continuous unequal crossovers or genetic recombination events during evolution. The spider dragline silk from the principal ampullate gland contains at least one protein, called MaSp1, for major ampullate silk protein, previously termed spidroin 1; molecular weight is around 275,000. It remains unclear whether additional proteins play a significant role in the dragline silk fiber. There is no sericin or glue-like protein associated with the dragline fiber. MaSp1 contains amino acid repeats considerably shorter than those found in the silkworm fibroin and not as highly conserved. The repeats contain polyalanine domains consisting of six to nine residues, and a 15-amino acid region showing a GGX repeat motif, where X = alanine, tyrosine, leucine, or glutamine.
The silkworm cocoon and spider dragline silks are characterized as an antiparallel β-pleated sheet wherein the polymer chain axis is parallel to the fiber axis. Other silks are known to form α-helical (bees,wasps, ants) or cross- β-sheet (many insects) structures. The cross- β-sheets are characterized by a polymer chain axis perpendicular to the fiber axis and a higher serine content. Most silks assume a range of different secondary structures during processing from soluble protein in the glands to insoluble spun fibers. The crystalline structure of silk was first described in the 1950s as an antiparallel, hydrogen-bonded β-sheet based on the characterization of B. mori fibroin, and further modifications to this early model have been made over the years. Two crystalline forms for silk have been characterized on the basis of X-ray diffraction and 13C-cross-polarization/magic-angle spinning (CP/MAS) NMR spectroscopy. The random coil or silk I, ie, the prespun pseudocrystalline form of silk present in the gland in a water-soluble state, is predominant in the
gland; silk II, ie, the spun form of silk which is insoluble in water, becomes predominant once the protein is spun into fiber. The unit cell parameters in the silk II structure are 940 pm (a, interchain), 697 pm (b, fiber axis), and 920 pm (c,intersheet). The chains run antiparallel with interchain hydrogen bonds roughly perpendicular to the chain axis between carbonyl and amine groups. Van derWaal forces stabilize intersheet interactions owing to the predominance of short sidechain amino acids (glycine, alanine, serine) in these crystalline regions. Solid-state 13C NMR studies of N. clavipes dragline silk have concluded that the polyalanine runs in the MaSp1 are in a β-sheet conformation.
The structure of silk I remains incompletely understood. This structure is unstable and upon shearing, drawing, heating, spinning, or exposure in an electric field or exposure to polar solvents, such as methanol or acetone, converts to silk II. The change in unit cell dimensions during the transition from silk I to silk II during fiber spinning is most significant in the intersheet plane, where an 18.3% decrease in distance occurs between overlying sheets. This change results in the exclusion of water, thus reducing solubility of the protein. Silk II is more energetically stable than silk I and the energy barrier for the transition is low, whereas the return barrier is high and considered essentially irreversible. Because the instability or metastable nature of the silk I conformation leads to difficulty in obtaining an orientated sample for fiber diffraction analysis and detailed structural characterization, different models have been proposed to describe the silk I structure.
Generally, spider dragline and silkworm cocoon silks are considered semicrystalline materials having less crystalline flexible chains reinforced by strong stiff crystals. The orb web fibers are Composite Materials (qv) in the sense that they are composed of crystalline regions immersed in less crystalline regions, which have estimates of 30–50% crystallinity. Earlier studies by X-ray diffraction analysis indicated 62–65% crystallinity in cocoon silk fibroin from the silkworm, 50–63% in wild-type silkworm cocoons, and lesser amounts in spider silk.
Structure of the Spider Orb Web.
The construction of the orb web is a feat of engineering involving material tailoring, optimization of material interfaces, and conservation of resources to promote survival of the spider. In addition, the web absorbs water from the atmosphere, and ingestion by the spider may provide a significant contribution to water intake needs. Around 70% of the energy is dissipated through viscoelastic processes upon impact by a flying insect into the web. Thus the web balances stiffness and strength against extensibility, both to keep the web from breaking and the insect from being ejected from the web by elastic recoil. The ability to dissipate the kinetic energy of a flying insect impacting the web is based on the hysteresis of radial threads and also aerodynamic damping by the web.Some orb webs appear to be at least in part recycled by ingestion as a conservation tool, and some of the amino acids are reused in new webs.
In Vivo Processing.
Silks are synthesized in specialized glands within the organism. Initially, some degree of self-organization or assembly occurs as a result of protein–protein interactions among the crystalline repeats in the protein chains. In the spider gland, changes in physiological conditions such as pH and salt concentrations accompany the processing and, presumably, help maintain solubility, despite increasing protein concentration during passage through the various regions of the gland. In silkworm there are three distinct regions to the glands and two sets of these organs feeding into one final thread. The fibroin is synthesized in the posterior region of the gland and the protein moves by peristalsis to the middle region of the gland where it is stored as a viscous aqueous solution until needed for spinning. The protein concentration is 12–15% in the posterior region of the gland where fibroin chain synthesis occurs, increases to around 20–30% in the middle region of the gland where the fibroin is stored and sericin is synthesized, and is significantly higher in the anterior region of the gland where spinning is initiated. The two lobes of the gland join just before the spinnerettes in the anterior region and the fiber is spun into air. Aside from binding together the fibroin chains in the final spun fiber, sericin in this process may function in plasticization to ease the flow through the spinneret, as a reservoir for divalent cations, or as a water-holding medium to promote plasticization of the fiber after spinning.
Rheological experiments indicate that crystallinity in the fiber correlates positively with shear and draw rates, and an extrusion rate of around 50 cm/min was found to be a minimum threshold for the appearance of birefringence and the conversion of the soluble silk solution in the gland to the β-sheet found in the spun fiber. In the posterior region of the gland, 0.4–0.8mmin diameter, the silk solution is optically featureless; a range of secondary structures are present, including random coil and silk I; and the shear rate is low. In the middle region of the gland, the diameter is 1.2–2.5 mm, streaming birefringence is observed, and the shear rate is also low. In the anterior region of the gland, the diameter is narrow (0.05–0.3 mm), the shear rate is high, water appears to be actively transported out of the gland, the pH decreases, and active ion exchange occurs. Viscosity also increases but presumably decreases prior to spinning as a result of the liquid crystalline phase. At this point the characteristic silk II structure forms. In the pair of major ampullate glands in the spider, which are the location of dragline protein synthesis, a similar process occurs as summarized for the silkworm. This gland is smaller, however, and there is no sericin contribution in the middle region of the gland. A lyotropic nematic liquid crystalline phase of the protein forms prior to spinning in both the spider and the silkworm, as well as in many of the different glands of the spider responsible for the different silks . Recent studies also suggest that silk fibroin forms into micelles and then gel states in the gland as a mode to optimize protein concentration within the aqueous processing environment.
Commercial and Artificial Processing.
Commercially, silkworm cocoons are extracted in hot soapy water to remove the sticky sericin protein. The remaining fibroin or structural silk is reeled onto spools, yielding approximately 300–1200 m of usable thread per cocoon. These threads can be dyed or modified for textile applications. Production levels of silk textiles in 1992 were 67,000 t worldwide. The highest levels were in China, at 30,000 t, followed by Japan, at 17,000 t, and other Asian and Oceanian countries, at 14,000 t. Less than 3000 t are produced annually in each of eastern Europe, western Europe, and Latin America; almost no production exists in North America, the Middle East, or Africa. The 1993 projections were for a continued worldwide increase in silk textile production to 75,000 t by 1997 and 90,000 t by 2002. Most solvents used to solubilize globular proteins do not suffice for silks owing to extensive hydrogen bonding and van der Waals interactions, and the exclusion of water from the intersheet regions. Silks are insoluble in water, dilute acids and alkali, and most organic solvents; they are resistant to most proteolytic enzymes. Silkworm fibroin can be solubilized by first degumming or removing the sericin using boiling soap solution or boiling dilute sodium bicarbonate solution, followed by immersion of the fibroin in high concentration salt solutions such as lithium bromide, lithium thiocyanate, or calcium chloride. These salt solutions can also be used to solubilize spider silk, as can high concentrations of propionic acid–hydrochloric acid mixtures and formic acid. After solubilization in these aggressive solvents, dialysis into water or buffers can be used to remove the salts or acids, although premature reprecipitation is a common problem. Ternary-phase diagrams of silk, water, and chaotropic salt for processing windows have been published for native silkworm silks and for genetically engineered versions of silkworm silk.
Films or membranes of silkworm silk have been produced by air-drying aqueous solutions prepared from the concentrated salts, followed by dialysis.The films, which arewater-soluble, generally contain silk in the silk I conformation with a significant content of random coil. Many different treatments have been used to modify these films to decrease their water solubility by converting silk I to silk II in a process found useful for enzyme entrapment. Silk membranes have also been cast from fibroin solutions and characterized for permeation properties. Oxygen and water vapor transmission rates were dependent on the exposure conditions to methanol to facilitate the conversion to silk II. Thin monolayer films have been formed from solubilized silkworm silk using Langmuir techniques to facilitate structural characterization of the protein. Resolubilized silkworm cocoon silk has been spun into fibers, as have recombinant silkworm silks.Recent studies have included the formation of electrospun nanometerdiameter fibers, hydrogels, and 3D porous scaffolds prepared from these proteins.
The mechanical properties of silks are an intriguing combination of high strength, extensibility, and compressibility (Table 3). Resistance to axial compressive deformation is another interesting property of the silk fibers. Based on microscopic evaluations of knotted single fibers, no evidence of kink-band failure on the compressive side of a knot curve has been observed. Synthetic high performance fibers fail by this mode even at relatively low strain levels. This is a principal limitation of synthetic fibers in some structural applications.
B. mori cocoon silk ranges from 10 to 25 μm in diameter; dragline silk from N. clavipes from 2.5 to 4.5 μm in diameter.Web fibers from some spiders have diameters as low as 0.01 μm. A silking rate of ∼1 cm/s is considered equivalent to natural spinning rates for the spider. Some spider silks have been observed to supercontact up to around 50% when unconstrained and exposed to high moisture; other silks such as the silkworm cocoon silk do not contract under similar experimental conditions. A skin core has been reported using light microscopy and electron microscopy. However, more recent data using dragline silk from N. clavipes refute this finding.
Spider dragline silk was thermally stable to about 230◦C based on thermal gravimetric analysis (TGA). Two thermal transitions were observed by dynamic mechanical analysis (DMA), one at −75◦C, presumed to represent localized mobility in the noncrystalline regions of the silk fiber, and the other at 210◦C, indicative of a partial melt or a glass transition. Data from thermal studies on B. mori silkworm cocoon silk indicate a glass-transition temperature, Tg, of 175◦C and stability to ∼250◦C. The Tg for wild silkworm cocoon silks was slightly higher, from 160 to 210◦C.
An understanding of the genetics of silk production in silkworms and spiders should help in developing processes for higher levels of silk expression generated by recombinant deoxyribonucleic acid (DNA) methods. The ability of the silkworm to produce large amounts of protein, around 300 μg of fibroin per epithelial cell lining the silk producing gland, has generated a great amount of interest from molecular biologists and developmental biologists in elucidating the genetic regulation of this system. Genetically engineered or recombinant DNA silkworm and spider silks have been produced using either native genes or synthetic genes. It is interesting to note that studies of variations in native silkworm populations indicate differences in sizes of the crystalline-encoding domains resulting from a high degree of polymorphism in length and organization of the fibroin gene and thus the encoded proteins . A significant degree of variation in protein size, apparently, can be tolerated in native populations of silkworms and, possibly, spiders. Owing to the highly repetitive nature of the genes and the encoded proteins, the deletion or addition of repeats has little impact on secondary structure and functional performance within a certain window of sizes.
Because of the advent of improved analytical techniques, together with the tools of biotechnology, a new generation of products is envisioned with silk. The ability to tailor polymer structure to a precise degree leads to interesting possibilities in the control of macroscopic functional properties of fibers, membranes, and coatings, as well as improved control of processing windows. Biotechnology offers the tools with which to solve limitations in spider silk production that have not been overcome with traditional domestication and breeding approaches, such as those used successfully with the silkworm. This is of interest because of the variety of silk structures available and the higher modulus and strength as compared to silkworm silk.
Hybrid silk fibers containing synthetic fiber cores having silk coextruded or grafted have been synthesized. Cosmetics and consumer products, such as hair replacements and shampoos containing silk, have also been marketed. Sutures (qv), biomaterials for tissue repairs, wound coatings, artificial tendons, bone repair, and related needs may be possible applications, since immunological responses to the silks are controllable (see TISSUE ENGINEERING). It is also reasonable to speculate on the use of silk webbing for tissue cell growth, nerve cell growth, and brain repair applications such as temporary scaffolding during regrowth and reinfusion after surgery. Cell culture Petri plates having genetically engineered silkworm silks containing cell binding or adhesive domains have already been produced and are sold commercially. These recombinant silks are stable during injection molding with polystyrene. The demonstration of fiber spinning from resolubilized silkworm silk provides further opportunities in material fabrication using native
and genetically engineered silk proteins.
The burn test is a simple, somewhat subjective test based on the knowledge of how particular fibers burn. Be prepared to note the following when testing your fibers:
• Do the fibers melt and/or burn?
• Do the fibers shrink from the flame?
• What type of odor do the fumes have?
• What is the characteristic(s) of any smoke?
• What does the residue of the burned fibers look like?
The burn test is normally made on a small sample of yarns or thread which are twisted together. Since the fiber content of yarns used in one direction of a fabric are not always made up of the same fibers used in the other direction, warp and filling yarns should be burned separately to determine the entire fiber content of the fabric. This test is very helpful in determining whether a fabric is made from synthetic or natural fibers, but it is not foolproof and the characteristics observed during the burning test can be affected by several things. If the fabric /yarn contains blends of fibers, identification of individual fibers can be difficult. Two or three different kinds of fibers burned together in one yarn may also be difficult to distinguish. The odor and burning characteristics exhibited may be that of several fibers, thus making your results difficult to analyze. Finishes used on the fabric can also change the observed characteristics.
Pull a small sample of at least six to eight yarns from your fabric about 4 inches long, and twist them together into a bundle about 1/8 inch in diameter. You can also use a small snippet of the fabric if you only need to determine whether it is a synthetic or natural fiber fabric and you are not seeking to determine the specific fiber(s) that make up the fabric.
Hold one end of the bundle with tweezers over a sink or a sheet of aluminum foil (about 10 to 12 inches square) to protect your working area. If the sample ignites it can be dropped into the sink or on the foil without damage. Use either a candle or a match (automatic lighters work well) as your flame.
Potential Test Results
Natural, Organic & Manmade Fibers
In general, if the ash is soft and the odor is of burning hair or paper, the fabric is a natural fiber. Cellulosic fibers (cotton, linen and rayon) burn rapidly with a yellow flame. When the flame is removed, there is an afterglow, then soft gray ash.
• Cotton: Ignites on contact with flames; burns quickly and leaves a yellowish to orange afterglow when put out. Does not melt. It has the odor of burning paper, leaves, or wood. The residue is a fine, feathery, gray ash. • Hemp: Same as cotton • Linen: Same as cotton • Ramie : Same as cotton • Rayon : Same as cotton, but burns slowly without flame with slight melting; leaves soft black ash. • Silk: Burns slowly, but does not melt. It shrinks from the flame. It has the odor of charred meat (some say like burned hair). The residue is a black, hollow irregular bead that can be easily to a gritty, grayish-black ash powder. It is self-extinguishing, i.e., it burns itself out. • Tencel : Same as Rayon • Wool, and other Protein Fibers: Burns with an orange sputtery color, but does not melt. It shrinks from the flame. It has a strong odor of burning hair or feathers. The residue is a black, hollow irregular bead that can be easily crushed into a gritty black powder. It is self-extinguishing, i.e., it burns itself out.
Most synthetic fibers both burn and melt, and also tend to shrink away from the flame. Synthetics burn with an acrid, chemical or vinegar-like odor and leave a plastic bead.
Other identifying characteristics include: • Acetate: Flames and burns quickly; has an odor similar to burning paper and hot vinegar. Its residue is a hard, dark, solid bead. If you suspect a fabric is acetate, double-check by placing a scrap of it in a small amount of fingernail polish remover-if you’re correct, the fabric will dissolve • Acrylic: Flames and burns rapidly with hot, sputtering flame and a black smoke. Has an acrid, fishy odor. The residue is a hard irregularly-shaped black bead. • Nylon: It will shrink from the flame and burn slowly. Has an odor likened to celery. Its residue is initially a hard, cream-colored bead that becomes darker gray. • Olefin/Polyolefin: Has a chemical type odor. The residue id a hard, tancolored bead. The flames creates black smoke. • Polyester: It will shrink from the flame and burn slowly giving off black smoke. Has a somewhat sweet chemical odor. The residue is initially a hard cream-colored bead that becomes darker tan. • Spandex: It burns and melts, but does not shrink from the flame. It has a chemical type odor. Its residue is a soft, sticky black ash.
Gin equipment is designed to remove foreign matter, moisture, and cottonseed from raw seed cotton. Two types of gins are in common use—the saw gin and the roller gin. Saw gins are normally used for Upland cottons, whereas roller gins are used for the ELS (Pima) cottons. In a saw gin, the cotton enters the saw gin stand through a huller front and the saws grasp the seed cotton and draw it through widely spaced ribs. The ginning action is caused by a set of saws rotating between a second set of narrowly spaced ginning ribs. The saw teeth pass between the ribs pulling the fiber through at the ginning point. The space is too narrow for the seed to pass and so the fiber is pulled from the seed. A roller gin consists of a ginning roll (covered with a compound cotton and rubber material), a stationary knife held against the roll, and a rotary knife. The rotating roll pulls the fiber under the stationary knife. The seeds cannot pass under the stationary knife and is separated from the fiber. The rotary knife then pushes the ginned seed away from the ginning point allowing room for more seed cotton to be ginned.
Fig. 1. A modern gin stand that separates fiber from cottonseed.
Typical types of gin equipment are cylinder cleaners, stick machines, and lint cleaners for cleaning; hot air driers for removing moisture; gin stands for separating the fiber from the cottonseed; and the bale press for packaging the lint . The gin stand (Fig. 1) is actually the only item of equipment required to gin cotton, the other equipment is for trash removal and drying. About 636 kg of seed cotton is required to produce a bale (∼227 kg; 500 lb) of lint cotton from spindle-harvested cotton. The remainder consists of about 354-kg seed and 55-kg trash and moisture. Typical gins contain one to four individual gin stands, each rated at 6–15 bales/h. However, a few gins contain as many as eight gin stands and produce up to 100 bales/h. The greatest number [30,498] of gins existed in the United States in 1902. The majority were on plantations, and they processed 10.6 million bales (2.3 × 109 kg) of cotton (43). Since then the number of gins has declined, and the average number of bales processed per gin has increased. In 2000, a total of ∼1018 active gins handled a crop of 16,742,000 bales (∼3.65 × 109 kg) for an average of 16,446 bales (3.58 × 106 kg) per gin plant. The number of bales produced in the United States varies substantially from year to year, which places a severe financial burden on the ginning industry.
Mechanical harvesting systems were made possible by the invention of saw type lint-cleaning systems in the early 1950s. Lint cleaners enabled gins to remove from the cotton the additional trash that resulted from mechanical harvesting. The mechanical systems reduced the harvesting period from 4–5 months to ∼6–8 weeks of intensive operation. Severe congestion problems at the gin were eased with the storage of seed cotton in 8- to 15-bale, freestanding modules. Modules avoided the massive need for wheeled trailers during the compressed harvest season. Storage of seed cotton in modules increased rapidly from the 1970s onward, accounting for >90% of the crop in 2000. At present, the average U.S. cotton ginning capacity is ∼30 bales/h. A few gins process in excess of 100 bales/h.
Most of the U.S. gins are now operated as cooperatives or as corporations serving many cotton producers. Automatic devices do the work faster, more efficiently,and more economically than hand labor. High volume bulk seed cotton handling systems and hydraulic suction systems to remove cotton from modules, high volume trailers to get cotton into the gin, larger trailers and modules, increased processing rates for gin equipment, automatic controls, automated bale packaging and handling devices, and improved management have all increased efficiency.
After ginning, baled cotton is sampled so that grade and quality parameters can be determined (classification). The fiber quality/physical attributes affect the textile manufacturing efficiency and the quality of the finished product. Cotton bales are normally stored in warehouses in the form of highly compressed bales.The International Organization for Standardization (ISO) specifies that bale dimensions should be of length 140 cm (55 in.), width 53.3 cm (21 in.), height 70–90 cm (27.6–35.4 in.), and density of 360–450 kg/m 3 (22.4–28 lb/ft 3) . Bales of cotton produced in the United States meet these dimensional standards. Bales of cotton packaged in accordance with these dimensions (ISO 8115) are not considered a flammable solid by the International Maritime Organization and the U.S. Department of Transportation for transportation purposes for vessel and other types of shipment and are considered to present no measurable pest risk to the importing country. Baled cotton fiber is merchandized and shipped by the merchant to the textile
mill for manufacturing into products for the consumer. The seed is shipped directly for feeding to dairy cattle or to a cottonseed oil mill for crushing.
COTTON is defined as white fibrous substance covering seeds harvested from Cotton Plant.
SEED COTTON (called Kapas in India – Paruthi in Tamil)harvested from Cotton Plant.
LINT COTTON (RUIA in Hindi, PANJU in Tamil) is obtained by removing the seeds in a ginning machine.
LINT COTTON is spun into Yarn, which is woven or knitted into a Fabric. Researchers have found that cotton was grown more than 9000 years ago. However large scale cultivation commenced during middle of 17th Century AD.
Many varieties of Cotton are cultivated mainly from 3 important genetic species of Gossipium.
G. HIRSUTUM – 87% Grown in America, Africa, Asia, Australia Plant grows to a height of 2 Meters.
G. BARBADENSE– 8% Grown in America, Africa & Asia. Plant grows to a height of 2.5 Meters with yellow flowers, long fibers with good quality, fibers with long staple and fineness
There are four other species grown in very negligible quantities. Cotton harvested from the Plant by hand – picking or machine picking is ginned to remove seeds and the lint is pressed into Bales for delivery to Spinning Mills. Cotton is Roller Ginned (RG) or Saw Ginned (SG) depending varieties and ginning practices.
Cotton is cultivated in 75 Countries with an area of 32 Million Hectares. Cultivation period varies from 175 days to 225 days depending on variety. Cotton is harvested in two seasons, summer and winter seasons.
Saw ginned cotton is more uniform and cleaner than Roller Ginned Cotton. But fibers quality is retained better quality in Roller Ginning than Saw Ginning which has high productivity.
Cotton Fiber is having a tubular structure in twisted form. Now. researchers have developed coloured cotton also. As on date, percentage of Cotton fiber use is more than synthetic fibers. But, its share is gradually reducing. Cotton is preferred for under garments due its comfort to body skin. Synthetics have more versatile uses and advantage for Industrial purposes.
PROPERTIES OF COTTON
No other material is quite like cotton. It is the most important of all natural fibres, accounting for half of all the fibres used by the world’s textile industry.
Cotton has many qualities that make it the best choice for countless uses:
Cotton fibres have a natural twist that makes them so suitable for spinning into a very strong yarn.
The ability of water to penetrate right to the core of the fibre makes it easy to remove dirt from the cotton garments, and creases are easily removed by ironing.
Cotton fabric is soft and comfortable to wear close to skin because of its good moisture absorption qualities.
Charges of static electricity do not build up readily on the clothes.
HISTORY OF COTTON
Nobody seems to know exactly when people first began to use cotton, but there is evidence that it was cultivated in India and Pakistan and in Mexico and Peru 5000 years ago. In these two widely separated parts of the world, cotton must have grown wild. Then people learned to cultivate cotton plants in their fields.
In Europe, wool was the only fiber used to make clothing. Then from the Far East came tales of plants that grew “wool”. Traders claimed that cotton was the wool of tiny animals called Scythian lambs, that grew on the stalks of a plant. The stalks, each with a lamb as its flower, were said to bend over so the small sheep could graze on the grass around the plant. These fantastic stories were shown to be untrue when Arabs brought the cotton plant to Spain in Middle Ages.
In the fourteenth century cotton was grown in Mediterranean countries and shipped from there to mills in the Netherlands in western Europe for spinning and weaving. Until the mid eighteenth century, cotton was not manufactured in England, because the wool manufacturers there did not want it to compete with their own product. They had managed to pass a law in 1720 making the manufacture or sale of cotton cloth illegal. When the law was finally repealed in 1736, cotton mills grew in number. In the United States though, cotton mills could not be established, as the English would not allow any of the machinery to leave the country because they feared the colonies would compete with them. But a man named Samuel Slater, who had worked in a mill in England, was able to build an American cotton mill from memory in 1790.
GROWING THE COTTON
Cotton plant’s leaves resemble maple leaves and flowers look very much like pink mallow flowers that grow in swampy areas. They are relatives and belong in the same plant family.
Cotton is grown in about 80 countries, in a band that stretches around the world between latitudes 45 North to 30 South. For a good crop of cotton a long, sunny growing season with at least 160 frost-free days and ample water are required. Well drained, crumbly soils that can keep moisture well are the best. In most regions extra water must be supplied by irrigation. Because of it’s long growing season it is best to plant early but not before the sun has warmed the soil enough.
Seedlings appear about 5 days after planting the seeds. Weeds have to be removed because they compete with seedlings for water, light and minerals and also encourage pests and diseases. The first flower buds appear after 5-6 weeks, and in another 3-5 weeks these buds become flowers.
Each flower falls after only 3 days leaving behind a small seed pot, known as the boll. Children in cotton-growing areas in the South sometimes sing this song about the flowers:
First day white, next day red,
third day from my birth – I’m dead.
Each boll contains about 30 seeds, and up to 500 000 fibres of cotton. Each fibre grows its full length in 3 weeks and for the following 4-7 weeks each fiber gets thicker as layers of cellulose build up the cell walls. While this is happening the boll matures and in about 10 weeks after flowering it splits open. The raw cotton fibres burst out to dry in the sun. As they lose water and die, each fibre collapses into what looks like a twisted ribbon. Now is time for harvesting. Most cotton is hand-picked. This is the best method of obtaining fully grown cotton because unwanted material, called “trash”, like leaves and the remains of the boll are left behind. Also the cotton that is too young to harvest is left for a second and third picking. A crop can be picked over a period of two months as the bolls ripen. Countries that are wealthy and where the land is flat enough usually pick cotton with machines – cotton harvesters.
GLOBAL COTTON – VATIETIES – PLANTING AND HARVESTING PERIODS
COTTON AND YARN QUALITY CO-RELATION:
Instead of buying any cotton available at lowest price, spinning it to produce yarn of highest count possible and selling Yam at any market in random, it is advisable to locate a good market where Yarn can be sold at highest price and select a Cotton which has characteristics to spin Yarn of desired specifications for that market.
ESSENTIAL CHARACTERISTICS of cotton quality and characteristics of Yarn quality of Yarn are given from detailed experimental investigations. Some of the important conclusions which help to find co-relation between Yarn quality and Cotton quality are given below
STAPLE LENGTH: If the length of fiber is longer, it can be spun into finer counts of Yarn which can fetch higher prices. It also gives stronger Yarn.
STRENGTH : Stronger fibers give stronger Yarns. Further, processing speeds can be higher so that higher productivity can be achieved with less end-breakages.
FIBER FINENESS: Finer Fibers produce finer count of Yarn and it also helps to produce stronger Yarns.
FIBER MATURITY : Mature fibers give better evenness of Yarn. There will be less end – breakages . Better dyes’ absorbency is additional benefit.
UNIFORMITY RATIO: If the ratio is higher. Yam is more even and there is reduced end-breakages.
ELONGATION :A better value of elongation will help to reduce end-breakages in spinning and hence higher productivity with low wastage of raw material.
NON-LINT CONTENT: Low percentage of Trash will reduce the process waste in Blow Room and cards. There will be less chances of Yarn defects.
SUGAR CONTENT: Higher Sugar Content will .create stickiness of fiber and create processing problem of licking in the machines.
MOISTURE CONTENT : If Moisture Content is more than standard value of 8.5%, there will be more invisable loss. If moisture is less than 8.5%, then there will be tendency for brittleness of fiber resulting in frequent Yarn breakages.
FEEL : If the feel of the Cotton is smooth, it will be produce more smooth yarn which has potential for weaving better fabric.
CLASS : Cotton having better grade in classing will produce less process waste and Yarn will have better appearance.
GREY VALUE: Rd. of calorimeter is higher it means it can reflect light better and Yam will give better appearance.
YELLOWNESS : When value of yellowness is more, the grade becomes lower and lower grades produce weaker & inferior yarns.
NEPPINESS : Neppiness may be due to entanglement of fibers in ginning process or immature fibers. Entangled fibers can be sorted out by careful processing But, Neps due to immature fiber will stay on in the end product and cause the level of Yarndefects to go higher.
An analysis can be made of Yarn properties which can be directly attributed to cotton quality.
1. YARN COUNT: Higher Count of Yarn .can be produced by longer, finer and stronger fibers.
2. C.V. of COUNT: Higher Fiber Uniformity and lower level of short fiber percentage will be beneficial to keep C.V.(Co-efficient of Variation) at lowest.
3. TENSILE STRENGTH : This is directly related to fiber strength. Longer Length of fiber will also help to produce stronger yarns.
4. C.V. OF STRENGTH : is directly related CV of fiber strength.
5. ELONGATION : Yam elongation will be beneficial for weaving efficiently. Fiber with better elongation have positive co-relation with Yarn elongation.
6. C.V. OF ELONGATION: C.V. of Yarn Elongation can be low when C.V. of fiber elongation is also low.
7. MARS VARIATION : This property directly related to fiber maturity and fiber uniformity.
8. HAIRINESS : is due to faster processing speeds and high level of very short fibers,
9. DYEING QUALITY : will defend on Evenness of Yarn and marketing of cotton fibers.
10. BRIGHTNESS : Yarn will give brighter appearance if cotton grade is higher.
COTTON QUALITY SPECIFICATIONS:
The most important fiber quality is Fiber Length
Less than 24
Coarse Below 20
Medium Count 20s-34s
Fine Count 34s – 60s
Superfine Count 80s – 140s
Spinning Count does not depend on staple length only. It also depends on fineness and processing machinery.
Length is measured by hand stapling or Fibrograph for 2.5% Span Length
2.5%SL (Spun Length) means at least 2.5% of total fibers have length exceeding this value.
50% SL means at least 50% of total fibers have length exceeding this value.
Length Uniformity is Calculated by 50SL x 100 / 2.5 SL
Significance of UR (Uniformity Radio) is given below:
UR% Classification 50-55
Very Good 45-50 Good 40-45
Poor Below 30 Unusable
M= 50% SL
UHM SL – Average value of length of Longest of 50% of Fibers
UI Uniformity Index
Interpretation of Uniformity Index
Now Uniformity is measured by HVI
Fiber Strength, next important quality is tested using Pressley instrument and the value is given in Thousands of Pounds per Square inch. (1000 psi) For better accuracy, Stelometer is used and results are given in grams / Tex.
Lately, strength is measured in HVI (High Value Instrument) and result is given in terms of grams/tex.
Interpretation of Strength value is given below
Strength is essential for stronger yarns and higher processing speeds.
Fiber Fineness Fiber Fineness and maturity are tested in a conjunction using Micronaire Instrument.
Finer Fibers give stronger yarns but amenable for more neppiness of Yarn due to lower maturity.
Micronaire values vary from 2.6 to 7.5 in various varieties.
FINENESS AND MATURITY
Usually Micronaire value is referred to evaluate fineness of Cotton and its suitability for spinning particular count of Yarn. As the value is a combined result of fineness and maturity of Cotton fiber, it cannot be interpreted, property for ascertaining its spinning Value. This value should be taken in conjunction with standard value of Calibrated Cotton value.
The following table will explain that micronaire value goes up along with maturity but declines with thickness of fiber. An Egyptian variety of Cotton, three samples of High maturity. Low maturity and Medium maturity were taken and tested. Test results are given below,
Here, Micronaire Value of 4.3 is higher than 3.9 of low maturity cotton Another Greek Cotton was tested and results are give below
Micronaire Value of 3.8 is higher than 3.2 of low maturity cotton. Another American Cotton was tested and results are as follows
Hence, it is essential to know what Micronaire value is good for each variety of Cotton.
1.00 and above
0.95 – 1.0
0.85 – 0.95
0.80 – 0.85
Less than 0.80
Cotton grade is determined by evaluating colour, leaf and ginning preparation. Higher grade cottons provide better yarn appearance and reduced process waste.
Colour is determined by using Nickerson-Hunter Calorimeter. This gives values Rd (Light or Dark) and +b (Yellowness).
AMERICAN UPLAND COTTONS ARE CLASSIFIED
ACCORDING TO GRADES AS GIVEN BELOW
STRICT LOW MIDDLING
STRICT GOOD ORDINARY
Similar grading is done for Light Spotted, Spotted, Tinged and Yellow Stained Cottons. PIMA cottons are graded I to 9
HOW TO BUY COTTON?
COTTON BUYING is the most important function that will contribute to optimum profit of a Spinning Mill.
EVALUATION of cotton quality is generally based more on experience rather than scientific testing of characteristics only.
TIMING of purchase depends on comprehensive knowledge about various factors which affect the prices.
CHOOSING the supplier for reliability of delivery schedules and ability to supply cotton within the prescribed range of various parameters which define the quality of Cotton.
BARGINING for lowest price depends on the buyer’s reputation for prompt payment and accept delivery without dispute irrespective of price fluctuations.
ORGANISING the logistics for transportation of goods and payment for value of goods will improve the benefits arising out of the transaction.
PROFIT depends on producting high quality Yarn to fetch high prices. Influence of quality of raw material is very important in producing quality Yarn. But, quality of yam is a compound effect of quality of raw material, skills of work-force, performance of machines,- process know-how of Technicians and management expertise.
A good spinner is one who produces reasonably priced yarn of acceptable quality from reasonably priced fiber. Buying a high quality, high priced cotton does not necessarily result in high quality Yarn or high profits.
GUIDELINES FOR COTTON CONTRACTS:
Buyer and seller should clearly reach correct understanding on the following factors.
1. Country of Origin, Area of Growth, Variety, Crop year
2. Quality – Based on sample or
Description of grade as per ASTM standard or sample
For grade only and specifying range of staple length,
Range of Micronaire, range of Pressley value, uniformity,
Percentage of short fiber, percentage of non-lint content,
Tolerable level of stickiness
3. Percentage of Sampling at destination
4. Procedure for settling disputes on quality or fulfillment of contract obligations.
5. Responsibility regarding contamination or stickiness.
6. Price in terms of currency, Weight and place of delivery.
7. Shipment periods
8. Certified shipment weights or landing Weights
9. Tolerances for Weights and Specifications
10. Port of Shipment and port of destination, partial shipments allowed or not, transshipment allowed or not, shipments in containers or Break-bulk carriers
11. Specifications regarding age of vessels used for shipment, freight payment in advance or on delivery
15. Terms of Letter of. Credit regarding bank .negotiation, reimbursement and special conditions, if any
Choose Correct Supplier or Agent:
Apart from ensuring correct terms of Contract, Buyer should ensure that purchase is made from Reliable Supplier or through a Reliable Agent. Some suppliers evade supplies under some pretext if the market goes up. Otherwise, they supply inferior quality Either way buyer suffers.
By establishing long term relationship will reliable Suppliers, Buyers can have satisfaction of getting correct quality, timely deliveries and fair prices.
It is good to establish long term relationship with a few Agents who represent reputed Trading Companies in various Cotton Exporting Countries. They usually give reliable market information on quality, prices and market trends so that buyer can take intelligent decision. As cotton is not a manufactured Commodity, it is good to buy from dependable suppliers, who will ensure supply of correct quality with a variation within acceptable limits at correct price and also deliver on due date.
In a market with varying market demand situation. Buyers should decide which counts of Yarn to spin. Buyer can call for samples suitable for spinning Yarn counts programmed for production. Many spinners plan to do under-spinning. For Example, cotton suitable for 44s is used for spinning 40s. Some spinners do over-spinning. They buy cotton suitable for 40s and spin 44s count. But, is advisable to spin optimum count to ensure quality and also keep cost of raw material at minimum level as for as possible. Some spinners also buy 2 or more varieties and blend them for optimum spinning. For’ this purpose, a good knowledge to evaluate cotton quality and co-relate with yarn properties of required specifications. Cotton buyer should develop expertise in assessing cotton quality. Machine tests must be done only to confirm manual evaluation.
TAKING RIGHT OPTION:
It is not advisable just to look at price quoted by supplier. Correct costing should be done to work out actual cost when the cotton arrives at Mills. Further lowest price does not always mean highest profit for buying. Profitability may be affected by anyone or more of the following factors.
If the trash is higher, more waste will be produced reducing the Yarn out- turn and hence profit.
If the uniformity is less, end – breakages will be more reducing productivity and profitability.
If grade is poor or more immature fibers are found in cotton, the yarn appearance will be affected and Yarn will fetch lesser price in the market.
If the transit period for transport of cotton is longer, then also profitability will be reduced due blocking of funds for a longer period and increased cost of Interest.
Rate of Sales Tax varies from State to State. This must be taken in to account.
Hence, thorough costing should be worked out before deciding on the quoted pnce onlv
The margin of profit in spinning cotton should be calculated before deciding on The various options available depending on market conditions should be studied.
The factors to be considered for taking options are as follows.
Count for which demand is good in market
Prices for various counts for which demand exists.
Cost of manufacturing various counts.
Adequacy of machinery for the selected count.
Various varieties of cotton available for spinning the selected count.
Profit margin for each count using different varieties.
Price quoted by different Agents for same variety of selected cotton.
Reliability of supplier for quality and timely delivery.
Apart from the price quoted by the seller, other incidental costs must be taken into consideration before buying.
a) Duration for goods to reach Buyer’s godown from the seller’s Warehouse. If the duration is longer, buyer will incur higher interest charges.
b) Cost of Transportation and taxes.
Resolution of differences
If any discrepancy arises in the quality, weight and delivery periods, sellers should be willing to resolve the differences amicably and quickly. In case the matter is referred to Arbitrator, the award of the Arbitrator must be immediately enforced.
Bench Marks for Easy Reference
It is better if quality bench marks are established for different varieties so that buying decisions are easy for buyers Following standards have been found to be appropriate for Strict Middling Grade Cotton of staple 1.3/32″.
Staple Length ( 2.5% Spun Length) – Minimum 1.08″ or 27.4 mm
Micronaire : Minimum 3.8, Maximum-4.6 Variation within bulk sample should not be more than _ 0.1
Colour : Rd not less than 75 not more than 10
Nep Content: Less than 150 per gram
Strength : More than 30 grams/tex
Length Uniformity Ratio: Not less than 85%
Elongation : More than 8%
Short Fiber Content: Less than 5%
Seed Count Fragments : Less than 15 per grams
Commercial Bench marks can be given as follows:
Easy Availability throughout year
Uniform Classing and Grading system
Even- running Cotton in all Characteristics
Reliable deliveries òr Respect for sanctity of contract.
The need for quality evaluation is for following purposes
a) To get optimum quality at lowest price.
b) To decide whether cotton bought will can be processed to spin Yarn of desired specifications.
c) To check the quality of sample cotton with quality of delivered cotton.
d) To decide about correct machine settings and speeds for processing the cotton
e) To estimate profitability of purchase decisions.
Knowing the cotton properties is only half the battle for profits. It needs expertise to know how to get best of its value.
Currently popular instrument called HVI gives ready information on various parameters to make correct purchase decisions.
If may not be possible to get all the desired qualities in one variety or one lot of Cotton. In such case, an intelligent decision to select best combination of different varieties or lots to get desired Yam quality is necessary to get optimum yarn quality at optimum cost.
If correct evaluation is made, profits are large. Hence, evaluation of quality is essential for optimum profit making and also make the customers happy with supply of correct quality of Yarn.
Expert classers can manage to achieve reasonable level of correct evaluation. Now, with availability of better instruments, it is better to check qualities to make sure that desired quality of cotton is procured. These details should give cotton buyer reasonable guidance to make correct evaluation of cotton quality and ensure its suitability for producing required quality of yarn.
CHARACTERISTICS CO-RELATION TO YARN
1. Staple Length
2. Fiber Strength
Yarn strength, less Breakages
Finer Spinning Potential
Yarn Strength and even ness, better dyeing
5. Non-Lint.content (Trash)
6, Uniformity Ratio
Better productivity and Evenness
Less end Breakages
Spinning problem by lapping & Dyeing quality
11. Grey Value
14. Moisture Content
8.5% moisture content optimum for spinning at 65%
QUALITY TESTING INSTRUMENTS:
Fiber Bundle Strength
HV I Instrument
Length, Strength, Uniformity, Elongation, Micronaire, Color and Trash
Manipulation of fiber perimeter has a potential to impact the length, micronaire, and strength of cotton fibers. The perimeter of the fiber is regulated by biological mechanisms that control the expansion characteristic of the cell wall and establish cell diameter.
mprovements in fiber quality can take many different forms. Changes in length, strength, uniformity, and fineness In one recent analysis, fiber perimeter was shown to be the single quantitative trait of the fiber that affects all other traits . Fiber perimeter is the variable that has the greatest affect on fiber elongation and strength properties. While mature dead fibers have an elliptical morphology, living fibers have a cylindrical morphology during growth and development. Geometrically, perimeter is directly determined by diameter (perimeter = diameter × p). Thus, fiber diameter is the only variable that directly affects perimeter. For this reason, understanding the biological mechanisms that regulate fiber diameter is important for the long-term improvement of cotton.
A review of the literature indicates that many researchers believe diameter is established at fiber initiation and is maintained throughout the duration of fiber development . A few studies have examined, either directly or indirectly, changes in fiber diameter during development. Some studies indicate that diameter remains constant ; while others indicate that fiber diameter increases as the fiber develops.
The first three stages occur while the fiber is alive and actively growing. Fiber initiation involves the initial isodiametric expansion of the epidermal cell above the surface of the ovule. This stage may last only a day or so for each fiber. Because there are several waves of fiber initiation across the surface of the ovule , one may find fiber initials at any time during the first 5 or 6 d post anthesis. The elongation phase encompasses the major expansion growth phase of the fiber. Depending on genotype, this stage may last for several weeks post anthesis. During this stage of development the fiber deposits a thin, expandable primary cell wall composed of a variety of carbohydrate polymers . As the fiber approaches the end of elongation, the major phase of secondary wall synthesis starts. In cotton fiber, the secondary cell wall is composed almost exclusively of cellulose. During this stage, which lasts until the boll opens (50 to 60 d post anthesis), the cell wall becomes progressively thicker and the living protoplast decreases in volume. There is a significant overlap in the timing of the elongation and secondary wall synthesis stages. Thus, fibers are simultaneously elongating and depositing secondary cell wall.
The establishment of fiber diameter is a complex process that is governed, to a certain extent, by the overall mechanism by which fibers expand. The expansion of fiber cells is governed by the same related mechanisms occurring in other walled plant cells. Most cells exhibit diffuse cell growth, in which new wall and membrane materials are added throughout the surface area of the cell. Specialized, highly elongated cells, such as root hairs and pollen tubes, expand via tip synthesis where new wall and membrane materials are added only at a specific location that becomes the growing tip of the cell. While the growth mechanisms for cotton fiber have not been fully documented, recent evidence indicates that throughout the initiation and early elongation phases of development, cotton fiber expands primarily via diffuse growth . Later in fiber development, late in cell elongation, and well into secondary cell wall synthesis (35 d post anthesis), the organization of cellular organelles is consistent with continued diffuse growth . Many cells that expand via diffuse growth exhibit increases in both cell length and diameter; but cells that exhibit tip synthesis do not exhibit increases in cell diameter . If cotton fiber expands by diffuse growth, then it is reasonable to suggest that cell diameter might increase during the cell elongation phase of development.
Cell expansion is also regulated by the extensibility of the cell wall. For this reason, cell expansion most commonly occurs in cells that have only a primary cell wall . Primary cell walls contain low levels of cellulose. Production of the more rigid secondary cell wall usually signals the cessation of cell expansion. Secondary cell wall formation is often indicated by the development of wall birefringence.
Analyses of fiber diameter and cell wall birefringence show that fiber diameter significantly increased as fibers grew and developed secondary cell walls. Both cotton species and all the genotypes tested exhibited similar increases in diameter; however, the specific rates of change differed. Fibers continued to increase in diameter during the secondary wall synthesis stage of development, indicating that the synthesis of secondary cell wall does not coincide with the cessation of cell expansion.
The generally recommended machinery sequence at gins for spindle-picked cotton is rock and green-boll trap, feed control, tower drier, cylinder cleaner, stick machine, tower drier, cylinder cleaner, extractor feeder, gin stand, lint cleaner, lint cleaner, and press.
Cylinder cleaners use rotating spiked drums that open and clean the seedcotton by scrubbing it across a grid-rod or wire mesh screen that allows the trash to sift through. The stick machine utilizes the sling-off action of channel-type saw cylinders to extract foreign matter from the seedcotton by centrifugal force. In addition to feeding seedcotton to the gin stand, the extractor feeder cleans the cotton using the stick machine’s sling-off principle.
In some cases the extractor-feeder is a combination of a cylinder cleaner and an extractor. Sometimes an impact or revolving screen cleaner is used in addition to the second cylinder cleaner. In the impact cleaner, seedcotton is conveyed across a series of revolving, serrated disks instead of the grid-rod or wire mesh screen.
Lint cleaners at gins are mostly of the controlled-batt, saw type. In this cleaner a saw cylinder combs the fibers and extracts trash from the lint cotton by a combination of centrifugal force, scrubbing action between saw cylinder and grid bars, and gravity assisted by an air current
Seedcotton-type cleaners extract the large trash components from cotton. However, they have only a small influence on the cotton’s grade index, visible liint foreign-matter content, and fiber length distribution when compared with the lint cleaning effects. Also, the number of neps created by the entire seedcotton cleaning process is about the same as the increase caused by one saw-cylinder lint cleaner.
Most cotton gins today use one or two stages of saw-type lint cleaners. The use of too many stages of lint cleaning can reduce the market value of the bale, because the weight loss may offset any gain from grade improvement. Increasing the number of saw lint cleaners at gins, in addition to increasing the nep count and short-fiber content of the raw lint, causes problems at the spinning mill. These show up as more neps in the card web and reduced yarn strength and appearance .
Pima cotton, extra-long-staple cotton, is roller ginned to preserve its length and to minimize neps. To maintain the highest possible quality bale of pima cotton, mill-type lint cleaners were for a long time the predominant cleaner used by the roller-ginning industry. Today, various combinations of impacts, incline, and pneumatic cleaners are used in most roller-ginning plants to increase lint-cleaning capacity.
COTTON FIBER QUALITY:
Two simple words, fiber quality, mean quite different things to cotton growers and to cotton processors. No after-harvest mechanisms are available to either growers or processors that can improve intrinsic fiber quality.
Most cotton production research by physiologists and agronomists has been directed toward improving yields, so the few cultural-input strategies suggested for improving fiber quality during the production season are of limited validity. Thus, producers have limited alternatives in production practices that might result in fibers of acceptable quality and yield without increased production costs.
Fiber processors seek to acquire the highest quality cotton at the lowest price, and attempt to meet processing requirements by blending bales with different average fiber properties. Of course, bale averages for fiber properties do not describe the fiber-quality ranges that can occur within the bales or the resulting blends. Further, the natural variability among cotton fibers unpredictably reduces the processing success for blends made up of low-priced, lower-quality fibers and high-priced, higher-quality fibers.
Blends that fail to meet processing specifications show marked increases in processing disruptions and product defects that cut into the profits of the yarn and textile manufacturers. Mill owners do not have sufficient knowledge of the role classing-office fiber properties play in determining the outcome of cotton spinning and dyeing processes.
Even when a processor is able to make the connection between yarn and fabric defects and increased proportions of low-quality fibers, producers have no way of explaining why the rejected bales failed to meet processing specifications when the bale averages for important fiber properties fell within the acceptable ranges.
If, on the other hand, the causes of a processing defect are unknown, neither the producer nor the processor will be able to prevent or avoid that defect in the future. Any future research that is designed to predict, prevent, or avoid low-quality cotton fibers that cause processing defects in yarn and fabric must address the interface between cotton production and cotton processing.
Every bale of cotton produced in the USA crosses that interface via the USDA-AMS classing offices, which report bale averages of quantified fiber properties. Indeed, fiber-quality data reports from classing offices are designed as a common quantitative language that can be interpreted and understood by both producers and processors. But the meaning and utility of classing-office reports can vary, depending on the instrument used to evaluate.
Fiber maturity is a composite of factors, including inherent genetic fineness compared with the perimeter or cross section achieved under prevailing growing conditions and the relative fiber cell-wall thickness and the primary -to- secondary fiber cell-wall ratio, and the time elapsed between flowering and boll opening or harvest. While all the above traits are important to varying degrees in determining processing success, none of them appear in classing-office reports.
Micronaire, which is often treated as the fiber maturity measurement in classing-office data, provides an empirical composite of fiber cross section and relative wall thickening. But laydown blends that are based solely on bale-average micronaire will vary greatly in processing properties and outcomes.
Cotton physiologists who follow fiber development can discuss fiber chronological maturity in terms of days after floral anthesis. But, they must quantify the corresponding fiber physical maturity as micronaire readings for samples pooled across several plants, because valid micronaire determinations require at least 10 g of individualized fiber.
Some fiber properties, like length and single fiber strength, appear to be simple and easily understood terms. But the bale average length reported by the classing office does not describe the range or variability of fiber lengths that must be handled by the spinning equipment processing each individual fiber from the highly variable fiber population found in that bale.
Even when a processing problem can be linked directly to a substandard fiber property, surprisingly little is known about the causes of variability in fiber shape and maturity. For example:
Spinners can see the results of excessive variability in fiber length or strength when manifested as yarn breaks and production halts.Knitters and weavers can see the knots and slubs or holes that reduce the value of fabrics made from defective yarns that were spun from poor-quality fibre
Inspectors of dyed fabrics can see the unacceptable color streaks and specks associated with variations in fiber maturity and the relative dye-uptake success.
The grower, ginner, and buyer can see variations in color or trash content of ginned and baled cotton.
But there are no inspectors or instruments that can see or predict any of the above quality traits of fibers while they are developing in the boll. There is no definitive reference source, model, or database to which a producer can turn for information on how cultural inputs could be adapted to the prevailing growth conditions of soil fertility, water availability, and weather (temperature, for example) to produce higher quality fiber.
The scattered research publications that address fiber quality, usually in conjunction with yield improvement, are confusing because their measurement protocols are not standardized and results are not reported in terms that are meaningful to either producers or processors. Thus, physiological and agronomic studies of fiber quality frequently widen, rather than bridge, the communication gap between cotton producers and processors.
This overview assembles and assesses current literature citations regarding the quantitation of fiber quality and the manner in which irrigation, soil fertility, weather, and cotton genetic potential interact to modulate fiber quality. The ultimate goal is to provide access to the best answers currently available to the question of what causes the annual and regional fiber quality variations
From the physiologist’s perspective, the fiber quality of a specific cotton genotype is a composite of fiber shape and maturity properties that depend on complex interactions among the genetics and physiology of the plants producing the fibers and the growth environment prevailing during the cotton production season.
Fiber shape properties, particularly length and diameter, are largely dependent on genetics. Fiber maturity properties, which are dependent on deposition of photosynthate in the fiber cell wall, are more sensitive to changes in the growth environment. The effects of the growth environment on the genetic potential of a genotype modulate both shape and maturity properties to varying degrees.
Anatomically, a cotton fiber is a seed hair, a single hyperelongated cell arising from the protodermal cells of the outer integument layer of the seed coat. Like all living plant cells, developing cotton fibers respond individually to fluctuations in the macro- and microenvironments. Thus, the fibers on a single seed constitute continua of fiber length, shape, cell-wall thickness, and physical maturity .
Environmental variations within the plant canopy, among the individual plants, and within and among fields ensure that the fiber population in each boll, indeed on each seed, encompasses a broad range of fiber properties and that every bale of cotton contains a highly variable population of fibers.
Successful processing of cotton lint depends on appropriate management during and after harvest of those highly variable fiber properties that have been shown to affect finished-product quality and manufacturing efficiency . If fiber-blending strategies and subsequent spinning and dyeing processes are to be optimized for specific end-uses and profitability, production managers in textile mills need accurate and effective descriptive and predictive quantitative measures of both the means and the ranges of these highly variable fiber properties .
In the USA, the components of cotton fiber quality are usually defined as those properties reported for every bale by the classing offices of the USDA-AMS, which currently include length, length uniformity index, strength, micronaire, color as reflectance (Rd) and yellowness (+b), and trash content, all quantified by the High Volume Instrument (HVI) line. The classing offices also provide each bale with the more qualitative classers’ color and leaf grades and with estimates of preparation (degree of roughness of ginned lint) and content of extraneous matter.
The naturally wide variations in fiber quality, in combination with differences in end-use requirements, result in significant variability in the value of the cotton lint to the processor. Therefore, a system of premiums and discounts has been established to denote a specified base quality. In general, cotton fiber value increases as the bulk-averaged fibers increase in whiteness (+Rd), length, strength, and micronaire; and discounts are made for both low mike (micronaire less than 3.5) and high mike (micronaire more than 4.9).
Ideal fiber-quality specifications favored by processors traditionally have been summarized thusly: “as white as snow, as long as wool, as strong as steel, as fine as silk, and as cheap as hell.” These specifications are extremely difficult to incorporate into a breeding program or to set as goals for cotton producers. Fiber-classing technologies in use and being tested allow quantitation of fiber properties, improvement of standards for end-product quality, and, perhaps most importantly, creation of a fiber-quality language and system of fiber-quality measurements that can be meaningful and useful to producers and processors alike.
GENE AND ENVIRONMENTAL VARIABILITY:
Improvements in textile processing, particularly advances in spinning technology, have led to increased emphasis on breeding cotton for both improved yield and improved fiber properties Studies of gene action suggest that, within upland cotton genotypes there is little non-additive gene action in fiber length, strength, and fineness ; that is, genes determine those fiber properties. However, large interactions between combined annual environmental factors (primarily weather) and fiber strength suggest that environmental variability can prevent full realization of the fiber-quality potential of a cotton genotype.
More recently, statistical comparisons of the relative genetic and environmental influences upon fiber strength suggest that fiber strength is determined by a few major genes, rather than by variations in the growth environment . Indeed, spatial variations of single fertility factors in the edaphic environment were found to be unrelated to fiber strength and only weakly correlated with fiber length .
Genetic potential of a specific genotype is defined as the level of fiber yield or quality that could be attained under optimal growing conditions. The degree to which genetic potential is realized changes in response to environmental fluctuations such as application of water or fertilizer and the inevitable seasonal shifts such as temperature, day length, and insolation.
In addition to environment-related modulations of fiber quality at the crop and whole-plant levels, significant differences in fiber properties also can be traced to variations among the shapes and maturities of fibers on a single seed and, consequently, within a given boll.
EFFECT ON FIBER LENGTH:
Comparisons of the fiber-length arrays from different regions on a single seed have revealed that markedly different patterns in fiber length can be found in the micropylar, middle, and chalazal regions of a cotton seed – at either end and around the middle . Mean fiber lengths were shortest at the micropylar (upper, pointed end of the seed) . The most mature fibers and the fibers having the largest perimeters also were found in the micropylar region of the seed. After hand ginning, the percentage of short fibers less than 0.5 inch or 12.7 mm long on a cotton seed was extremely low.
It has been reported that, in ginned and baled cotton, the short fibers with small perimeters did not originate in the micropylar region of the seed . MEasurements of fibers from micropylar and chalazal regions of seeds revealed that the location of a seed within the boll was related to the magnitude of the differences in the properties of fibers from the micropylar and chalazal regions.
Significant variations in fiber maturity also can be related to the seed position (apical, medial, or due to the variability inherent in cotton fiber, there is no absolute value for fiber length within a genotype or within a test sample . Even on a single seed, fiber lengths vary significantly because the longer fibers occur at the chalazal (cup-shaped, lower) end of the seed and the shorter fibers are found at the micropylar (pointed) end. Coefficients of fiber-length variation, which also vary significantly from sample to sample, are on the order of 40% for upland cotton.
Variations in fiber length attributable to genotype and fiber location on the seed are modulated by factors in the micro- and macroenvironment . Environmental changes occurring around the time of floral anthesis may limit fiber initiation or retard the onset of fiber elongation. Suboptimal environmental conditions during the fiber elongation phase may decrease the rate of elongation or shorten the elongation period so that the genotypic potential for fiber length is not fully realized . Further, the results of environmental stresses and the corresponding physiological responses to the growth environment may become evident at a stage in fiber development that is offset in time from the occurrence of the stressful conditions.
Fiber lengths on individual seeds can be determined while the fibers are still attached to the seed , by hand stapling or by photoelectric measurement after ginning. Traditionally, staple lengths have been measured and reported to the nearest 32nd of an inch or to the nearest millimeter. The four upland staple classes are: short (<21 mm), medium (22-25 mm), medium-long (26-28 mm) and long (29-34 mm). Pimastaple length is classed as long (29-34 mm) and extra-long (>34 mm). Additionally, short fiber content is defined as the percentage of fiber less than 12.7 mm.
Cotton buyers and processors used the term staple length long before development of quantitative methods for measuring fiber properties. Consequently, staple length has never been formally defined in terms of a statistically valid length distribution.
In Fibrograph testing, fibers are randomly caught on combs, and the beard formed by the captured fibers is scanned photoelectrically from base to tip . The amount of light passing through the beard is a measure of the number of fibers that extend various distances from the combs. Data are recorded as span length (the distance spanned by a specific percentage of fibers in the test beard). Span lengths are usually reported as 2.5 and 50%. The 2.5% span length is the basis for machine settings at various stages during fiber processing.
The uniformity ratio is the ratio between the two span lengths expressed as a percentage of the longer length. The Fibrograph provides a relatively fast method for reproducibility in measuring the length and length uniformity of fiber samples. Fibrograph test data are used in research studies, in qualitative surveys such as those checking commercial staple-length classifications, and in assembling cotton bales into uniform lots.
Since 1980, USDA-AMS classing offices have relied almost entirely on high-volume instrumentation (HVI) for measuring fiber length and other fiber properties (Moore, 1996). The HVI length analyzer determines length parameters by photoelectrically scanning a test beard that is selected by a specimen loader and prepared by a comber/brusher attachment
The fibers in the test beard are assumed to be uniform in cross-section, but this is a false assumption because the cross section of each individual fiber in the beard varies significantly from tip to tip. The HVI fiber-length data are converted into the percentage of the total number of fibers present at each length value and into other length parameters, such as mean length, upper-half mean length, and length uniformity . This test method for determining cotton fiber length is considered acceptable for testing commercial shipments when the testing services use the same reference standard cotton samples.
All fiber-length methods discussed above require a minimum of 5 g of ginned fibers and were developed for rapid classing of relatively large, bulk fiber samples. For analyses of small fiber samples , fiber property measurements with an electron-optical particle-sizer, the Zellweger Uster AFIS-A2 have been found to be acceptably sensitive, rapid, and reproducible. The AFIS-A2 Length and Diameter module generates values for mean fiber length by weight and mean fiber length by number, fiber length histograms, and values for upper quartile length, and for short-fiber contents by weight and by number (the percentages of fibers shorter than 12.7 mm). The AFIS-A2 Length and Diameter module also quantifies mean fiber diameter by number .
Although short-fiber content is not currently included in official USDA-AMS classing office reports, short-fiber content is increasingly recognized as a fiber property comparable in importance to fiber fineness, strength, and length . The importance of short-fiber content in determining fiber-processing success, yarn properties, and fabric performance has led the post-harvest sector of the U.S. cotton industry to assign top priority to minimizing short-fiber content, whatever the causes .
The perceived importance of short-fiber content to processors has led to increased demands for development and approval of a standard short-fiber content measurement that would be added to classing office HVI systems . This accepted classing office-measurement would allow inclusion of short-fiber content in the cotton valuation system. Documentation of post-ginning short-fiber content at the bale level is expected to reduce the cost of textile processing and to increase the value of the raw fiber . However, modulation of short-fiber content before harvest cannot be accomplished until the causes of increased short-fiber content are better understood.
Fiber length is primarily a genetic trait, but short-fiber content is dependent upon genotype, growing conditions, and harvesting, ginning, and processing methods. Further, little is known about the levels or sources of pre-harvest short-fiber content .
It is essential that geneticists and physiologists understand the underlying concepts and the practical limitations of the methods for measuring fiber length and short-fiber content so that the strong genetic component in fiber length can be separated from environmental components introduced by excessive temperatures and water or nutrient deficiencies. Genetic improvement of fiber length is fruitless if the responses of the new genotypes to the growth environment prevent full realization of the enhanced genetic potential or if the fibers produced by the new genotypes break more easily during harvesting or processing. The reported effects of several environmental factors on fiber length and short-fiber content, which are assumed to be primarily genotype-dependent, are discussed in the subsections that follow. FIBER LENGTH AND TEMPERATURE:
Maximum cotton fiber lengths were reached when night temperatures were around 19 to 20 °C, depending on the genotype . Early-stage fiber elongation was highly temperature dependent; late fiber elongation was temperature independent . Fiber length (upper-half mean length) was negatively correlated with the difference between maximum and minimum temperature.
Modifications of fiber length by growth temperatures also have been observed in planting-date studies in which the later planting dates were associated with small increases in 2.5 and 50% span lengths . If the growing season is long enough and other inhibitory factors do not interfere with fiber development, early-season delays in fiber initiation and elongation may be counteracted by an extension of the elongation period .
Variations in fiber length and the elongation period also were associated with relative heat-unit accumulations. Regression analyses showed that genotypes that produced longer fibers were more responsive to heat-unit accumulation levels than were genotypes that produced shorter fibers . However, the earliness of the genotype was also a factor in the relationship between fiber length (and short-fiber content by weight) and accumulated heat units .
As temperature increased, the number of small motes per boll also increased. Fertilization efficiency, which was negatively correlated with small-mote frequency, also decreased. Although fiber length did not change significantly with increasing temperature, the percentage of short-fibers was lower when temperatures were higher. The apparent improvement in fiber length uniformity may be related to increased assimilate availability to the fibers because there were fewer seeds per boll. FIBER LENGTH AND WATER:
Cotton water relationships and irrigation traditionally have been studied with respect to yield . Fiber length was not affected unless the water deficit was great enough to lower the yield to 700 kg ha-1. Fiber elongation was inhibited when the midday water potential was -2.5 to -2.8 mPa. Occurrence of moisture deficits during the early flowering period did not alter fiber length. However, when drought occurred later in the flowering period, fiber length was decreased .
Severe water deficits during the fiber elongation stage reduce fiber length , apparently due simply to the direct mechanical and physiological processes of cell expansion. However, water availability and the duration and timing of flowering and boll set can result in complex physiological interactions between water deficits and fiber properties including length.
FIBRE LENGTH AND LIGHT:
Changes in the growth environment also alter canopy structure and the photon flux environment within the canopy. For example, loss of leaves and bolls from unfavorable weather (wind, hail), disease, or herbivory and compensatory regrowth can greatly affect both fiber yield and quality . The amount of light within the crop canopy is an important determinant of photosynthetic activity and, therefore, of the source-to-sink relationships that allocate photoassimilate within the canopy . Eaton and Ergle (1954) observed that reduced-light treatments increased fiber length. Shading during the first 7 d after floral anthesis resulted in a 2% increase in the 2.5% span length .
Shading (or prolonged periods of cloudy weather) and seasonal shifts in day length also modulate temperature, which modifies fiber properties, including length.
Commercial cotton genotypes are considered to be day-length neutral with respect to both flowering and fruiting . However, incorporation of day-length data in upland and pima fiber-quality models, based on accumulated heat units, increased the coefficients of determination for the length predictors from 30 to 54% for the upland model and from 44 to 57% for the pima model .
It was found that the light wavelengths reflected from red and green mulches increased fiber length, even though plants grown under those mulches received less reflected photosynthetic flux than did plants grown with white mulches. The longest fiber was harvested from plants that received the highest far red/red ratios.
FIBER LENGTH AND MINERAL NUTRITION:
Studies of the mineral nutrition of cotton and the related soil chemistry usually have emphasized increased yield and fruiting efficiency . More recently, the effects of nutrient stress on boll shedding have been examined . Also, several mineral-nutrition studies have been extended to include fiber quality .
Reports of fiber property trends following nutrient additions are often contradictory due to the interactive effects of genotype, climate, and soil conditions. Potassium added at the rate of 112 kg K ha-1yr-1 did not affect the 2.5% span length , when genotype was a significant factor in determining both 2.5 and 50% span lengths . Genotype was not a significant factor in Acala fiber length, but an additional 480 kg K ha-1yr-1 increased the mean fiber length . K ha-1yr-1 increased the length uniformity ratio and increased 50%, but not 2.5% span length. Genotype and the interaction, genotype-by-environment, determined the 2.5% span length.
As mentioned above, fiber length is assumed to be genotype-dependent, but growth-environment fluctuations – both those resulting from seasonal and annual variability in weather conditions and those induced by cultural practices and inputs – modulate the range and mean of the fiber length population at the test sample, bale, and crop levels.
Quantitation of fiber length is relatively straightforward and reproducible, and fiber length (along with micronaire) is one of the most likely fiber properties to be included when cotton production research is extended beyond yield determinations. Other fiber properties are less readily quantified, and the resulting data are not so easily understood or analyzed statistically. This is particularly true of fiber-breaking strength, which has become a crucial fiber property due to changes in spinning techniques.
The inherent breaking strength of individual cotton fibers is considered to be the most important factor in determining the strength of the yarn spun from those fibers . Recent developments in high-speed yarn spinning technology, specifically open-end rotor spinning systems, have shifted the fiber-quality requirements of the textile industry toward higher-strength fibers that can compensate for the decrease in yarn strength associated with open-end rotor spinning techniques.
Compared with conventional ring spinning, open-end rotor-spun yarn production capacity is five times greater and, consequently, more economical. Rotor-spun yarn is more even than the ring-spun, but is 15 to 20% weaker than ring-spun yarn of the same thickness. Thus, mills using open-end rotor and friction spinning have given improved fiber strength highest priority. Length and length uniformity, followed by fiber strength and fineness, remain the most important fiber properties in determining ring-spun yarn strength.
Historically, two instruments have been used to measure fiber tensile strength, the Pressley apparatus and the Stelometer . In both of these flat-bundle methods, a bundle of fibers is combed parallel and secured between two clamps. A force to try to separate the clamps is applied and gradually increased until the fiber bundle breaks. Fiber tensile strength is calculated from the ratio of the breaking load to bundle mass. Due to the natural lack of homogeneity within a population of cotton fibers, bundle fiber selection, bundle construction and, therefore, bundle mass measurements, are subject to considerable experimental error .
Fiber strength, that is, the force required to break a fiber, varies along the length of the fiber, as does fiber fineness measured as perimeter, diameter, or cross section Further, the inherent variability within and among cotton fibers ensures that two fiber bundles of the same weight will not contain the same number of fibers. Also, the within-sample variability guarantees that the clamps of the strength testing apparatus will not grasp the various fibers in the bundle at precisely equivalent positions along the lengths. Thus, a normalizing length-weight factor is included in bundle strength calculations.
In the textile literature, fiber strength is reported as breaking tenacity or grams of breaking load per tex, where tex is the fiber linear density in grams per kilometer . Both Pressley and stelometer breaking tenacities are reported as 1/8 in. gauge tests, the 1/8 in. (or 3.2 mm) referring to the distance between the two Pressley clamps. Flat-bundle measurements of fiber strength are considered satisfactory for acceptance testing and for research studies of the influence of genotype, environment, and processing on fiber (bundle) strength and elongation.
The relationships between fiber strength and elongation and processing success also have been examined using flat-bundle strength testing methods . However cotton fiber testing today requires that procedures be rapid, reproducible, automated, and without significant operator bias. Consequently, the HVI systems used for length measurements in USDA-AMS classing offices are also used to measure the breaking strength of the same fiber bundles (beards) formed during length measurement.
Originally, HVI strength tests were calibrated against the 1/8-in. gauge Pressley measurement, but the bundle-strengths of reference cottons are now established by Stelometer tests that also provide bundle elongation-percent data. Fiber bundle elongation is measured directly from the displacement of the jaws during the bundle-breaking process, and the fiber bundle strength and elongation data usually are reported together (ASTM, 1994, D 4604-86). The HVI bundle-strength measurements are reported in grams-force tex-1 and can range from 30 and above (very strong) to 20 or below (very weak). In agronomic papers, fiber strengths are normally reported as kN m kg-1, where one Newton equals 9.81 kg-force .
The HVI bundle-strength and elongation-percent testing methods are satisfactory for acceptance testing and research studies when 3.0 to 3.3 g of blended fibers are available and the relative humidity of the testing room is adequately controlled. A 1% increase in relative humidity and the accompanying increase in fiber moisture content will increase the strength value by 0.2 to 0.3 g tex-1, depending on the fiber genotype and maturity.
Further, classing-office HVI measurements of fiber strength do not adequately describe the variations of fiber strength along the length of the individual fibers or within the test bundle. Thus, predictions of yarn strength based on HVI bundle-strength data can be inadequate and misleading . The problem of fiber-strength variability is being addressed by improved HVI calibration methods and by computer simulations of bundle-break tests in which the simulations are based on large single-fiber strength databases of more than 20 000 single fiber long-elongation curves obtained with MANTIS .
Fiber Strength, Environment, and Genotype:
Reports of stelometer measurements of fiber bundle strength are relatively rare in the refereed agronomic literature. Consequently, the interactions of environment and genotype in determining fiber strength are not as well documented as the corresponding interactions that modulate fiber length. Growth environment, and genotype response to that environment, play a part in determining fiber strength and strength variability .
Early studies showed fiber strength to be significantly and positively correlated with maximum or mean growth temperature, maximum minus minimum growth temperature, and potential insolation . Increased strength was correlated with a decrease in precipitation. Minimum temperature did not affect fiber strength. All environmental variables were interrelated, and a close general association between fiber strength and environment was interpreted as indicating that fiber strength is more responsive to the growth environment than are fiber length and fineness. Other investigators reported that fiber strength was correlated with genotype only.
Square removal did not affect either fiber elongation or fiber strength . Shading, leaf-pruning, and partial fruit removal decreased fiber strength . Selective square removal had no effect on fiber strength in bolls at the first, second, or third position on a fruiting branch . Fiber strength was slightly greater in bolls from the first 4 to 6 wk of flowering, compared with fibers from bolls produced by flowers opening during the last 2 wk of the flowering period .
In that study, fiber strength was positively correlated with heat unit accumulation during boll development, but genotype, competition among bolls, assimilatory capacity, and variations in light environment also helped determine fiber strength. Early defoliation, at 20% open bolls, increased fiber strength and length, but the yield loss due to earlier defoliation offset any potential improvement in fiber quality .
Of the fiber properties reported by USDA-AMS classing offices for use by the textile industry, fiber maturity is probably the least well-defined and most misunderstood. The term, fiber maturity, used in cotton marketing and processing is not an estimate of the time elapsed between floral anthesis and fiber harvest . However, such chronological maturity can be a useful concept in studies that follow fiber development and maturation with time . On the physiological and the physical bases, fiber maturity is generally accepted to be the degree (amount) of fiber cell-wall thickening relative to the diameter or fineness of the fiber .
Classically, a mature fiber is a fiber in which two times the cell wall thickness equals or exceeds the diameter of the fiber cell lumen, the space enclosed by the fiber cell walls . However, this simple definition of fiber maturity is complicated by the fact that the cross section of a cotton fiber is never a perfect circle; the fiber diameter is primarily a genetic characteristic.
Further, both the fiber diameter and the cell-wall thickness vary significantly along the length of the fiber. Thus, attempting to differentiate, on the basis of wall thickness, between naturally thin-walled or genetically fine fibers and truly immature fibers with thin walls greatly complicates maturity comparisons among and within genotypes.
Within a single fiber sample examined by image analysis, cell-wall thickness ranged from 3.4 to 4.9 µm when lumen diameters ranged from 2.4 to 5.2 µm . Based on the cited definition of a mature fiber having a cell-wall thickness two times the lumen diameter, 90% of the 40 fibers in that sample were mature, assuming that here had been no fiber-selection bias in the measurements.
Unfortunately, none of the available methods for quantifying cell-wall thickness is sufficiently rapid and reproducible to be used by agronomists, the classing offices, or fiber processors. Fiber diameter can be quantified, but diameter data are of limited use in determining fiber maturity without estimates of the relationship between lumen width and wall thickness. Instead, processors have attempted to relate fiber fineness to processing outcome. Estimating Fiber Fineness:
Fiber fineness has long been recognized as an important factor in yarn strength and uniformity, properties that depend largely on the average number of fibers in the yarn cross section. Spinning larger numbers of finer fibers together results in stronger, more uniform yarns than if they had been made up of fewer, thicker fibers . However, direct determinations of biological fineness in terms of fiber or lumen diameter and cell-wall thickness are precluded by the high costs in both time and labor, the noncircular cross sections of dry cotton fibers, and the high degree of variation in fiber fineness.
Advances in image analysis have improved determinations of fiber biological fineness and maturity , but fiber image analyses remain too slow and limited with respect to sample size for inclusion in the HVI-based cotton-classing process.
Originally, the textile industry adopted gravimetric fiber fineness or linear density as an indicator of the fiber-spinning properties that depend on fiber fineness and maturity combined . This gravimetric fineness testing method was discontinued in 1989, but the textile linear density unit of tex persists. Tex is measured as grams per kilometer of fiber or yarn, and fiber fineness is usually expressed as millitex or micrograms per meter . Earlier, direct measurements of fiber fineness (either biological or gravimetric) subsequently were replaced by indirect fineness measurements based on the resistance of a bundle of fibers to airflow.
The first indirect test method approved by ASTM for measurement of fiber maturity, lineardensity, and maturity index was the causticaire method. In that test, the resistance of a plug of cotton to airflow was measured before and after a cell-wall swelling treatment with an 18% (4.5 M) solution of NaOH (ASTM, 1991, D 2480-82). The ratio between the rate of airflow through an untreated and then treated fiber plug was taken as indication of the degree of fiber wall development. The airflow reading for the treated sample was squared and corrected for maturity to serve as an indirect estimate of linear density. Causticaire method results were found to be highly variable among laboratories, and the method never was recommended for acceptance testing before it was discontinued in 1992.
The arealometer was the first dual-compression airflow instrument for estimating both fiber fineness and fiber maturity from airflow rates through untreated raw cotton (ASTM, 1976, D 1449-58; Lord and Heap, 1988). The arealometer provides an indirect measurement of the specific surface area of loose cotton fibers, that is, the external area of fibers per unit volume (approximately 200-mg samples in four to five replicates). Empirical formulae were developed for calculating the approximate maturity ratio and the average perimeter, wall thickness, and weight per inch from the specific surface area data. The precision and accuracy of arealometer determinations were sensitive to variations in sample preparation, to repeated sample handling, and to previous mechanical treatment of the fibers, e.g., conditions during harvesting, blending, and opening. The arealometer was never approved for acceptance testing, and the ASTM method was withdrawn in 1977 without replacement.
The variations in biological fineness and relative maturity of cotton fibers that were described earlier cause the porous plugs used in air-compression measurements to respond differently to compression and, consequently, to airflow . The IIC-Shirley Fineness/Maturity Tester (Shirley FMT), a dual-compression instrument, was developed to compensate for this plug-variation effect (ASTM, 1994, D 3818-92). The Shirley FMT is considered suitable for research, but is not used for acceptance testing due to low precision and accuracy. Instead, micronaire has become the standard estimate of both fineness and maturity in the USDA-AMS classing offices.
Fiber Maturity and Environment:
Whatever the direct or indirect method used for estimating fiber maturity, the fiber property being as sayed remains the thickness of the cell wall. The primary cell wall and cuticle (together »0.1 µm thick) make up about 2.4% of the total wall thickness ( »4.1 µm of the cotton fiber thickness at harvest) . The rest of the fiber cell wall (»98%) is the cellulosic secondary wall, which thickens significantly as polymerized photosynthate is deposited during fiber maturation. Therefore, any environmental factor that affects photosynthetic C fixation and cellulose synthesis will also modulate cotton fiber wall thickening and, consequently, fiber physiological maturation
Fiber Maturity and Temperature and Planting Date:
The dilution, on a weight basis, of the chemically complex primary cell wall by secondary-wall cellulose has been followed with X-ray fluorescence spectroscopy. This technique determines the decrease, with time, in the relative weight ratio of the Ca associated with the pectin-rich primary wall . Growth-environment differences between the two years of the studies cited significantly altered maturation rates, which were quantified as rate of Ca weight-dilution, of both upland and pima genotypes. The rates of secondary wall deposition in both upland and pima genotypes were closely correlated with growth temperature; that is, heat-unit accumulation .
Micronaire (micronAFIS) also was found to increase linearly with time for upland and pima genotypes . The rates of micronaire increase were correlated with heat-unit accumulations . Rates of increase in fiber cross-sectional area were less linear than the corresponding micronaire-increase rates, and rates of upland and pima fiber cell-wall thickening were linear and without significant genotypic effect .
Environmental modulation of fiber maturity (micronaire) by temperature was most often identified in planting- and flowering-date studies . The effects of planting date on micronaire, Shirley FMT fiber maturity ratio, and fiber fineness (in millitex) were highly significant in a South African study (Greef and Human, 1983). Although genotypic differences were detected among the three years of that study, delayed planting generally resulted in lower micronaire. The effect on fiber maturity of late planting was repeated in the Shirley FMT maturity ratio and fiber fineness data.
Planting date significantly modified degree of thickening, immature fiber fraction, cross-sectional area, and micronaire (micronAFIS) of four upland genotypes that also were grown in South Carolina . In general, micronaire decreased with later planting, but early planting also reduced micronaire of Deltapine 5490, a long-season genotype, in a year when temperatures were suboptimal during the early part of the season.
Harvest dates in this study also were staggered so that the length of the growing season was held constant within each year. Therefore, season-length should not have been an important factor in the relationships found between planting date and fiber maturity. Fiber Maturity and Source-Sink Manipulation:
Variations in fiber maturity were linked with source-sink modulations related to flowering date , and seed position within the bolls . However, manipulation of source-sink relationships by early-season square (floral bud) removal had no consistently significant effect on upland cotton micronaire in one study . However, selective square removal at the first, second, and third fruiting sites along the branches increased micronaire, compared with controls from which no squares had been removed beyond natural square shedding . The increases in micronaire after selective square removals were associated with increased fiber wall thickness, but not with increased strength of elongation percent. Early-season square removal did not affect fiber perimeter or wall thickness (measured by arealometer) . Partial defruiting increased micronaire and had no consistent effect on upland fiber perimeter in bolls from August flowers.
Fiber Maturity and Water:
Generous water availability can delay fiber maturation (cellulose deposition) by stimulating competition for assimilates between early-season bolls and vegetative growth . Adequate water also can increase the maturity of fibers from mid-season flowers by supporting photosynthetic C fixation. In a year with insufficient rainfall, initiating irrigation when the first-set bolls were 20-d old increased micronaire, but irrigation initiation at first bloom had no effect on fiber maturity. Irrigation and water-conservation effects on fiber fineness (millitex) were inconsistent between years, but both added water and mulching tended to increase fiber fineness. Aberrations in cell-wall synthesis that were correlated with drought stress have been detected and characterized by glycoconjugate analysis .
An adequate water supply during the growing season allowed maturation of more bolls at upper and outer fruiting positions, but the mote counts tended to be higher in those extra bolls and the fibers within those bolls tended to be less mature . Rainfall and the associated reduction in insolation levels during the blooming period resulted in reduced fiber maturity . Irrigation method also modified micronaire levels and distributions among fruiting sites.
Early-season drought resulted in fibers of greater maturity and higher micronaire in bolls at branch positions 1 and 2 on the lower branches of rainfed plants. However, reduced insolation and heavy rain reduced micronaire and increased immature fiber fractions in bolls from flowers that opened during the prolonged rain incident. Soil water deficit as well as excess may reduce micronaire if the water stress is severe or prolonged . Fiber Maturity and Genetic Improvement:
Micronaire or maturity data now appear in most cotton improvement reports . In a five-parent half-diallel mating design, environment had no effect on HVI micronaire . However, a significant genotypic effect was found to be associated with differences between parents and the F1 generation and with differences among the F1 generation. The micronaire means for the parents were not significantly different, although HVI micronaire means were significantly different for the F1 generation as a group. The HVI was judged to be insufficiently sensitive for detection of the small difference in fiber maturity resulting from the crosses.
In another study, F2 hybrids had finer fibers (lower micronaire) than did the parents, but the improvements were deemed too small to be of commercial value. Unlike the effects of environment on the genetic components of other fiber properties, variance in micronaire due to the genotype-by-environment interaction can reach levels expected for genetic variance in length and strength . Significant interactions were found between genetic additive variance and environmental variability for micronaire, strength, and span length in a study of 64 F2 hybrids .
The strong environmental components in micronaire and fiber maturity limit the usefulness of these fiber properties in studies of genotypic differences in response to growth environment. Based on micronaire, fiber maturity, cell-wall thickness, fiber perimeter, or fiber fineness data, row spacing had either no or minimal effect on okra-leaf or normal-leaf genotypes . Early planting reduced micronaire, wall-thickness, and fiber fineness of the okra-leaf genotype in one year of that study. In another study of leaf pubescence, nectaried vs. no nectaries, and leaf shape, interactions with environment were significant but of much smaller magnitude than the interactions among traits .
Micronaire means for Bt transgenic lines were higher than the micronaire means of Coker 312 and MD51ne when those genotypes were grown in Arizona . In two years out of three, micronaire means of all genotypes in this study, including the controls, exceeded 4.9; in other words, were penalty grade. This apparent undesirable environmental effect on micronaire may have been caused by a change in fiber testing methods in the one year of the three for which micronaire readings were below the upper penalty limit. Genotypic differences in bulk micronaire may either be emphasized or minimized, depending on the measurement method used . GRADE:
In U.S. cotton classing, nonmandatory grade standards were first established in 1909, but compulsory upland grade standards were not set until 1915 . Official pima standards were first set in 1918. Grade is a composite assessment of three factors – color, leaf, and preparation . Color and trash (leaf and stem residues) can be quantified instrumentally, but traditional, manual cotton grade classification is still provided by USDA-AMS in addition to the instrumental HVI trash and color values. Thus, cotton grade reports are still made in terms of traditional color and leaf grades; for example, light spotted, tinged, strict low middling. Preparation:
There is no approved instrumental measure of preparation – the degree of roughness/smoothness of the ginned lint. Methods of harvesting, handling, and ginning the cotton fibers produce differences in roughness that are apparent during manual inspection; but no clear correlations have been found between degree of preparation and spinning success. The frequency of tangled knots or mats of fiber (neps) may be higher in high-prep lint, and both the growth and processing environments can modulate nep frequency . However, abnormal preparation occurs in less than 0.5% of the U.S. crop during harvesting and ginning.
Trash or Leaf Grade:
Even under ideal field conditions, cotton lint becomes contaminated with leaf residues and other trash . Although most foreign matter is removed by cleaning processes during ginning, total trash extraction is impractical and can lower the quality of ginned fiber. In HVI cotton classing, a video scanner measures trash in raw cotton, and the trash data are reported in terms of the total trash area and trash particle counts (ASTM, D 4604-86, D 4605-86). Trash content data may be used for acceptance testing. In 1993, classer’s grade was split into color grade and leaf grade . Other factors being equal, cotton fibers mixed with the smallest amount of foreign matter have the highest value. Therefore, recent research efforts have been directed toward the development of a computer vision system that measures detailed trash and color attributes of raw cotton .
The term leaf includes dried, broken plant foliage, bark, and stem particles and can be divided into two general categories: large-leaf and pin or pepper trash . Pepper trash significantly lowers the value of the cotton to the manufacturer, and is more difficult and expensive to remove than the larger pieces of trash.Other trash found in ginned cotton can include stems, burs, bark, whole seeds, seed fragments, motes (underdeveloped seeds), grass, sand, oil, and dust. The growth environment obviously affects the amount of wind-borne contaminants trapped among the fibers. Environmental factors that affect pollination and seed development determine the frequency of undersized seeds and motes.
Reductions in the frequencies of motes and small-leaf trash also have been correlated with semi-smooth and super-okra leaf traits . Environment (crop year), harvest system, genotype, and second order interactions between those factors all had significant effects on leaf grade . Delayed harvest resulted in lower-grade fiber. The presence of trash particles also may affect negatively the color grade.
Raw fiber stock color measurements are used in controlling the color of manufactured gray, bleached, or dyed yarns and fabrics . Of the three components of cotton grade, fiber color is most directly linked to growth environment. Color measurements also are correlated with overall fiber quality so that bright (reflective, high Rd), creamy-white fibers are more mature and of higher quality than the dull, gray or yellowish fibers associated with field weathering and generally lower fiber quality . Although upland cotton fibers are naturally white to creamy-white, pre-harvest exposure to weathering and microbial action can cause fibers to darken and to lose brightness.
Premature termination of fiber maturation by applications of growth regulators, frost, or drought characteristically increases the saturation of the yellow (+b) fiber-color component. Other conditions, including insect damage and foreign matter contamination, also modify fiber color.
The ultimate acceptance test for fiber color, as well as for finished yarns and fabrics, is the human eye. Therefore, instrumental color measurements must be correlated closely with visual judgment. In the HVI classing system, color is quantified as the degrees of reflectance (Rd) and yellowness (+b), two of the three tri-stimulus color scales of the Nickerson-Hunter colorimeter.
Fiber maturity has been associated with dye-uptake variability in finished yarn and fabric, but the color grades of raw fibers seldom have been linked to environmental factors or agronomic practices during production. Other Environmental Effects on Cotton Fiber Quality:
Although not yet included in the USDA-AMS cotton fiber classing system, cotton stickiness is becoming an increasingly important problem . Two major causes of cotton stickiness are insect honeydew from whiteflies and aphids and abnormally high levels of natural plant sugars, which are often related to premature crop termination by frost or drought. Insect honeydew contamination is randomly deposited on the lint in heavy droplets and has a devastating production-halting effect on fiber processing.
The cost of clearing and cleaning processing equipment halted by sticky cotton is so high that buyers have included honeydew free clauses in purchase contracts and have refused cotton from regions known to have insect-control problems. Rapid methods for instrumental detection of honeydew are under development for use in classing offices and mills .
FIBER QUALITY OR FIBER YIELD?
Like all agricultural commodities, the value of cotton lint responds to fluctuations in the supply-and-demand forces of the marketplace. In addition, pressure toward specific improvements in cotton fiber quality – for example, the higher fiber strength needed for today’s high-speed spinning – has been intensified as a result of technological advances in textile production and imposition of increasingly stringent quality standards for finished cotton products.
Changes in fiber-quality requirements and increases in economic competition on the domestic and international levels have resulted in fiber quality becoming a value determinant equal to fiber yield . Indeed, it is the quality, not the quantity, of fibers ginned from the cotton seeds that decides the end use and economic value of a cotton crop and, consequently, determines the profit returned to both the producers and processors.
Wide differences in cotton fiber quality and shifts in demand for particular fiber properties, based on end-use processing requirements, have resulted in the creation of a price schedule, specific to each crop year, that includes premiums and discounts for grade, staple length, micronaire, and strength . This price schedule is made possible by the development of rapid, quantitative methods for measuring those fiber properties considered most important for successful textile production . With the wide availability of fiber-quality data from HVI, predictive models for ginning, bale-mix selection, and fiber-processing success could be developed for textile mills .
Price-analysis systems based on HVI fiber-quality data also became feasible . Quantitation, predictive modeling, and statistical analyses of what had been subjective and qualitative fiber properties are now both practical and common in textile processing and marketing.
Field-production and breeding researchers, for various reasons, have failed to take full advantage of the fiber-quality quantitation methods developed for the textile industry. Most field and genetic improvement studies still focus on yield improvement while devoting little attention to fiber quality beyond obtaining bulk fiber length, strength, and micronaire averages for each treatment . Indeed, cotton crop simulation and mapping models of the effects of growth environment on cotton have been limited almost entirely to yield prediction and cultural-input management.
Plant physiological studies and textile-processing models suggest that bulk fiber-property averages at the bale, module, or crop level do not describe fiber quality with sufficient precision for use in a vertical integration of cotton production and processing. More importantly, bulk fiber-property means do not adequately and quantitatively describe the variation in the fiber populations or plant metabolic responses to environmental factors during the growing season. Such pooled or averaged descriptors cannot accurately predict how the highly variable fiber populations might perform during processing.
Meaningful descriptors of the effects of environment on cotton fiber quality await high-resolution examinations of the variabilities, induced and natural, in fiber-quality averages. Only then can the genetic and environmental sources of fiber-quality variability be quantified, predicted, and modulated to produce the high-quality cotton lint demanded by today’s textile industry and, ultimately, the consumer.
Increased understanding of the physiological responses to the environment that interactively determine cotton fiber quality is essential. Only with such knowledge can real progress be made toward producing high yields of cotton fibers that are white as snow, as strong as steel, as fine as silk, and as uniform as genotypic responses to the environment will allow.
Advanced Fibre Information System is based on the single fibre testing. There are two modules, one for testing the number of neps and the size of neps, while the other one is used for testing the length and the diameter. Both modules can be applied separately or together.
Among all physical properties of the cotton, fiber length varies the most within any one sample. There are two sources of variability;
1) Variability that comes from mixing cottons of various lengths
2) Variability that is biological in nature and exists within a sample of the same origin.
The same variety grown under different conditions, with lower or higher fertilizer doses, irrigation, or pest control, can produce various lengths. This is why fibre length is tested as an average of many fibres. Fibres also break during handling and processing thus, emphasizing the need for measurement of magnitude of the length variation. There are many different measurements of fibre length, including staple length, model length, mean length (aver-age length), 2.5% span length, effective length, upper quartile length, upper-half mean length, length uniformity index, length uniformity ratio, span length, short fibre contents and floating fibre length.
The AFIS test provides several length parameters deduced from individual fibre measurements. The main measurements include: the mean length, the length upper percentiles, the length CV%, and the Short Fibre Content (defined as the percentage of fibres less than 12.7 mm in length). Fibre length information is provided as a number or as weight-based data (by number/by weight). The length distribution by weight is determined by the weight-frequency of fibres in the different length categories, that is the proportion of the total weight of fibres in a given length category. The length distribution by number is given by the proportion of the total number of fibres in different length categories. The length parameters by weight and by number are computed from the two distributions accordingly. Once the AFIS machine determines the length distribution, the machine computes the length distribution by weight assuming that all fibres have the same fineness. Samples do not require any preparation and a result is obtained in 2-3 minutes. The results generally show a good correlation with other methods.
With the introduction of AFIS, it is possible to determine the average properties for a sample, and also the variation from the fibre to fibre. The information content in the AFIS is more. The spinning mill is dependent on the AFIS testing method, to achieve the optimum conditions with the available raw material and processing machinery. The AFIS-N module is dealt here and it is basically used for counting the number of neps and the size of neps. The testing time per sample is 3 minutes in AFIS-.N module.
This system is quick, purpose oriented and reproducible counting of neps in raw material and at all process stages of short staple spinning mill. It is thus possible, based on forecasts supervisory measures and early warning information to practically eliminate subsequent complaints with respect to finished product. The lab personnel are freed from the time consuming, delicate and unpopular, proceeding of nep counting. Personnel turnover and job rotation no more affects the results of the nep counting. The personnel responsible for quality can now at least deal with the unpopular neps in a more purpose-oriented manner than ever before.
AFIS -Working principle:-
A fibre sample of approximately 500 mg is inserted between the feed roller and the feed plate of the AFIS-N instrument Opening rollers open the fibre assembly and separate off the fibres, neps, trash and dust. The trash particles and dust are suctioned off to extraction. On their way through the transportation and acceleration channels, the fibres and neps pass through the optical sensor, which determines the number and size of the neps.
The corresponding impulses are converted into electrical signals, which are then transmitted to a microcomputer for evaluation purposes. According to these analyses, a distinction is made between the single fibres and the neps. The statistical data are calculated and printed out through a printer. The measuring process can be controlled through a PC-keyboard and a screen.
Uster AFIS PRO- application report
Various HVI models available in market in present date are:-
· USTER® AFIS PRO 2
• Length and Maturity (L&M) Module to measure cotton fiber length and maturity, integrating results into the USTERÒ AFIS PRO 2.
• Trash (T) Module to measure the dust and trash content in cotton, integrating results into the USTERÒ AFIS PRO 2.
• USTERÒ AFIS AUTOJET (AJ) Module to measure up to 30 samples automatically, reducing idle operating time.
Raw material represents about 50 to 70% of the production cost of a short-staple yarn. This fact is sufficient to indicate the significance of the raw material for the yarn producer. It is not possible to use a problem-free raw material always, because cotton is a natural fibre and there are many properties which will affect the performance. If all the properties have to be good for the cotton, the raw material would be too expensive. To produce a good yarn with these difficulties, an intimate knowledge of the raw material and its behaviour in processing is a must.
Fibre characteristics must be classified according to a certain sequence of importance with respect to the end product and the spinning process. Moreover, such quantified characteristics must also be assessed with reference to the following
what is the ideal value?
what amount of variation is acceptable in the bale material?
what amount of variation is acceptable in the final blend
Such valuable experience, which allows one to determine the most suitable use for the raw material, can only be obtained by means of a long, intensified and direct association with the raw material, the spinning process and the end product.
Low cost yarn manufacture, fulfilling of all quality requirements and a controlled fibre feed with known fibre properties are necessary in order to compete on the world’s textile markets. Yarn production begins with the rawmaterial in bales, whereby success or failure is determined by the fibre quality, its price and availability. Successful yarn producers optimise profits by a process oriented selection and mixing of the rawmaterial, followed by optimization of the machine settings, production rates, operating elements, etc. Simultaneously, quality is ensured
by means of a closed loop control system, which requires the application of supervisory system at spinning and spinning preparation, as well as a means of selecting the most suitable bale mix.
BASIC FIBRE CHARACTERISTICS:
A textile fibre is a peculiar object. It has not truly fixed length, width, thickness, shape and cross-section. Growth of natural fibres or production factors of manmade fibres are responsible for this situation. An individual fibre, if examined carefully, will be seen to vary in cross-sectional area along it length. This may be the result of variations in growth rate, caused by dietary, metabolic, nutrient-supply, seasonal, weather, or other factors influencing the rate of cell development in natural fibres. Surface characteristics also play some part in increasing the variability of fibre shape. The scales of wool, the twisted arrangement of cotton, the nodes appearing at intervals along the cellulosic natural fibres etc.
Following are the basic characteristics of cotton fibre
STANDARD ATMOSPHERE FOR TESTING:
The atmosphere in which physical tests on textile materials are performed. It has a relative humidity of 65 + 2 per cent and a temperature of 20 + 2° C. In tropical and sub-tropical countries, an alternative standard atmosphere for testing with a relative humidity of 65 + 2 per cent and a temperature of 27 + 2° C
may be used.
The “length” of cotton fibres is a property of commercial value as the price is generally based on this character. To some extent it is true, as other factors being equal, longer cottons give better spinning performance than shorter ones. But the length of a cotton is an indefinite quantity, as the fibres, even in a small random bunch of a cotton, vary enormously in length. Following are the various measures of length in use in different countries
It is the estimated quantity which theoretically signifies the arithmetic mean of the length of all the fibres present in a small but representative sample of the cotton. This quantity can be an average according to either number or weight.
Upper quartile length:
It is that value of length for which 75% of all the observed values are lower, and 25% higher.
It is difficult to give a clear scientific definition. It may be defined as the upper quartile of a
numerical length distribution
eliminated by an arbitrary construction. The fibres eliminated are shorter than half the effective length.
It is the most frequently occurring length of the fibres in the sample and it is related to mean and median for skew distributions, as exhibited by fibre length, in the following way.
(Mode-Mean) = 3(Median-Mean)
Median is the particular value of length above and below which exactly 50% of the fibres lie.
2.5% Span length:
It is defined as the distance spanned by 2.5% of fibres in the specimen being tested when the fibres are parallelized and randomly distributed and where the initial starting point of the scanning in the test is considered 100%. This length is measured using “DIGITAL FIBROGRAPH”.
50% Span length:
It is defined as the distance spanned by 50% of fibres in the specimen being tested when the fibres are parallelized and randomly distributed and where the initial starting point of the scanning in the test is considered 100%. This length is measured using “DIGITAL FIBROGRAPH”.
The South India Textile Research Association (SITRA) gives the following empirical relationships to estimate the Effective Length and Mean Length from the Span Lengths.
Effective length = 1.013 x 2.5% Span length + 4.39
Mean length = 1.242 x 50% Span length + 9.78
FIBRE LENGTH VARIATION:
Even though, the long and short fibres both contribute towards the length irregularity of cotton, the short fibres are particularly responsible for increasing the waste losses, and cause unevenness and reduction in strength in the yarn spun. The relative proportions of short fibres are usually different in cottons having different mean lengths; they may even differ in two cottons having nearly the same mean fibre length, rendering one cotton more irregular than the other.It is therefore important that in addition to the fibre length of a cotton, the degree of irregularity of its length should also be known. Variability is denoted by any one of the following attributes
Co-efficient of variation of length (by weight or number)
Dispersion percentage and percentage of short fibres
Uniformity ratio is defined as the ratio of 50% span length to 2.5% span length expressed as a percentage. Several instruments and methods are available for determination of length. Following are some
Shirley comb sorter
A.N. Stapling apparatus
uniformity ration = (50% span length / 2.5% span length) x 100
uniformity index = (mean length / upper half mean length) x 100
The negative effects of the presence of a high proportion of short fibres is well known. A high percentage of short fibres is usually associated with,
– Increased yarn irregularity and ends down which reduce quality and increase processing costs
– Increased number of neps and slubs which is detrimental to the yarn appearance
– Higher fly liberation and machine contamination in spinning, weaving and knitting operations.
– Higher wastage in combing and other operations.
While the detrimental effects of short fibres have been well established, there is still considerable debate on what constitutes a ‘short fibre’. In the simplest way, short fibres are defined as those fibres which are less than 12 mm long. Initially, an estimate of the short fibres was made from the staple diagram obtained in the Baer Sorter method
Short fibre content = (UB/OB) x 100
While such a simple definition of short fibres is perhaps adequate for characterising raw cotton samples, it is too simple a definition to use with regard to the spinning process. The setting of all spinning machines is based on either the staple length of fibres or its equivalent which does not take into account the effect of short fibres. In this regard, the concept of ‘Floating Fibre Index’ defined by Hertel (1962) can be considered to be a better parameter to consider the effect of short fibres on spinning performance. Floating fibres are defined as those fibres which are not clamped by either pair of rollers in a drafting zone.
Floating Fibre Index (FFI) was defined as
FFI = ((2.5% span length/mean length)-1)x(100)
The proportion of short fibres has an extremely great impact on yarn quality and production. The proportion of short fibres has increased substantially in recent years due to mechanical picking and hard ginning. In most of the cases the absolute short fibre proportion is specified today as the percentage of fibres shorter than 12mm. Fibrograph is the most widely used instrument in the textile industry , some information regarding fibrograph is given below.
Fibrograph measurements provide a relatively fast method for determining the length uniformity of the fibres in a sample of cotton in a reproducible manner.
Results of fibrograph length test do not necessarily agree with those obtained by other methods for measuring lengths of cotton fibres because of the effect of fibre crimp and other factors.
Fibrograph tests are more objective than commercial staple length classifications and also provide additional information on fibre length uniformity of cotton fibres. The cotton quality information provided by these results is used in research studies and quality surveys, in checking commercial staple length classifications, in assembling bales of cotton into uniform lots, and for other purposes.
Fibrograph measurements are based on the assumptions that a fibre is caught on the comb in proportion to its length as compared to toal length of all fibres in the sample and that the point of catch for a fibre is at random along its length.
Fibre fineness is another important quality characteristic which plays a prominent part in determining the spinning value of cottons. If the same count of yarn is spun from two varieties of cotton, the yarn spun from the variety having finer fibres will have a larger number of fibres in its cross-section and hence it will be more even and strong than that spun from the sample with coarser fibres.
Fineness denotes the size of the cross-section dimensions of the fibre. AS the cross-sectional features of cotton fibres are irregular, direct determination of the area of croo-section is difficult and laborious. The Index of fineness which is more commonly used is the linear density or weight per unit length of the fibre. The unit in which this quantity is expressed varies in different parts of the world. The common unit used by many countries for cotton is micrograms per inch and the various air-flow instruments developed for measuring fibre fineness are calibrated in this unit.
Following are some methods of determining fibre fineness.
gravimetric or dimensional measurements
vibrating string method
Some of the above methods are applicable to single fibres while the majority of them deal with a mass of fibres. As there is considerable variation in the linear density from fibre to fibre, even amongst fibres of the same seed, single fibre methods are time-consuming and laborious as a large number of fibres have to be tested to get a fairly reliable average value.
It should be pointed out here that most of the fineness determinations are likely to be affected by fibre maturity, which is an another important characteristic of cotton fibres.
AIR-FLOW METHOD (MICRONAIRE INSTRUMENT):
The resistance offered to the flow of air through a plug of fibres is dependent upon the specific surface area of the fibres. Fineness tester have been evolved on this principle for determining fineness of cotton. The specific surface area which determines the flow of air through a cotton plug, is dependent not only upon the linear density of the fibres in the sample but also upon their maturity. Hence the micronaire readings have to be treated with caution particularly when testing samples varying widely in maturity.
In the micronaire instrument, a weighed quantity of 3.24 gms of well opened cotton sample is compressed into a cylindrical container of fixed dimensions. Compressed air is forced through the sample, at a definite pressure and the volume-rate of flow of air is measured by a rotometer type flowmeter. The sample for Micronaire test should be well opened cleaned and thoroughly mixed( by hand fluffing and opening method). Out of the various air-flow instruments, the Micronaire is robust in construction, easy to operate and presents little difficulty as regards its maintenance.
Fibre maturity is another important characteristic of cotton and is an index of the extent of
development of the fibres. As is the case with other fibre properties, the maturity of cotton fibres varies not only between fibres of different samples but also between fibres of the same seed. The causes for the differences observed in maturity, is due to variations in the degree of the secondary thickening or deposition of cellulose in a fibre.
A cotton fibre consists of a cuticle, a primary layer and secondary layers of cellulose surrounding the lumen or central canal. In the case of mature fibres, the secondary thickening is very high, and in some cases, the lumen is not visible. In the case of immature fibres, due to some physiological causes, the secondary deposition of cellulose has not taken sufficiently and in extreme cases the secondary thickening is practically absent, leaving a wide lumen throughout the fibre. Hence to a cotton breeder, the presence of excessive immature
fibres in a sample would indicate some defect in the plant growth. To a technologist, the presence of excessive percentage of immature fibres in a sample is undesirable as this causes excessive waste losses in processing lowering of the yarn appearance grade due to formation of neps, uneven dyeing, etc.
An immature fibre will show a lower weight per unit length than a mature fibre of the same cotton, as the former will have less deposition of cellulose inside the fibre. This analogy can be extended in some cases to fibres belonging to different samples of cotton also. Hence it is essential to measure the maturity of a cotton sample in addition to determining its fineness, to check whether the observed fineness is an inherent characteristic or is a result of the maturity.
DIFFERENT METHODS OF TESTING MATURITY:
MATURITY RATIO: The fibres after being swollen with 18% caustic soda are examined under the microscope with suitable magnification. The fibres are classified into different maturity groups depending upon the relative dimensions of wall-thickness and lumen. However the procedures followed in different countries for sampling and classification differ in certain respects. The swollen fibres are classed into three groups as follows
Normal : rod like fibres with no convolution and no continuous lumen are classed as “normal”
Dead : convoluted fibres with wall thickness one-fifth or less of the maximum ribbon width are classed as “Dead”
Thin-walled: The intermediate ones are classed as “thin-walled”
A combined index known as maturity ratio is used to express the results.
Maturity ratio = ((Normal – Dead)/200) + 0.70
N – % of Normal fibres
D – % of Dead fibres
MATURITY CO-EFFICIENT: Around 100 fibres from Baer sorter combs are spread across the glass slide(maturity slide) and the overlapping fibres are again separated with the help of a teasing needle. The free ends of the fibres are then held in the clamp on the second strip of the maturity slide which is adjustable to keep the fibres stretched to the desired extent. The fibres are then irrigated with 18% caustic soda solution and covered with a suitable slip. The slide is then placed on the microscope and examined. Fibres are classed into the following three categories
Mature : (Lumen width “L”)/(wall thickness”W”) is less than 1
Half mature : (Lumen width “L”)/(wall thickness “W”) is less than 2 and more than 1
Immature : (Lumen width “L”)/(wall thickness “W”) is more than 2
About four to eight slides are prepared from each sample and examined. The results are presented as percentage of mature, half-mature and immature fibres in a sample. The results are also expressed in terms of “Maturity Coefficient”
M is percentage of Mature fibres
H is percentage of Half mature fibres
I is percentage of Immature fibres
If maturity coefficient is
less than 0.7, it is called as immature cotton
between 0.7 to 0.9, it is called as medium mature cotton
above 0.9, it is called as mature cotton
AIR FLOW METHOD FOR MEASURING MATURITY:
There are other techniques for measuring maturity using Micronaire instrument. As the fineness value determined by the Micronaire is dependent both on the intrinsic fineness(perimeter of the fibre) and the maturity, it may be assumed that if the intrinsic fineness is constant then the Micronaire value is a measure of the maturity
DYEING METHODS: Mature and immature fibers differ in their behaviour towards various dyes. Certain dyes are preferentially taken up by the mature fibres while some dyes are preferentially absorbed by the immature fibres. Based on this observation, a differential dyeing technique was developed in the United States of America for estimating the maturity of cotton. In this technique, the sample is dyed in a bath containing a mixture of two dyes, namely Diphenyl Fast Red 5 BL and Chlorantine Fast Green BLL. The mature fibres take up the red dye preferentially, while the thin walled immature fibres take up the green dye. An estimate of the average of the sample can be visually assessed by the amount of red and green fibres.
The different measures available for reporting fibre strength are
tensile strength and
tenacity or intrinsic strength
Coarse cottons generally give higher values for fibre strength than finer ones. In order, to compare strength of two cottons differing in fineness, it is necessary to eliminate the effect of the difference in cross-sectional area by dividing the observed fibre strength by the fibre weight per unit length. The value so obtained is known as “INTRINSIC STRENGTH or TENACITY”. Tenacity is found to be better related to spinning than the breaking strength.
The strength characteristics can be determined either on individual fibres or on bundle of fibres.
SINGLE FIBRE STRENGTH:
The tenacity of fibre is dependent upon the following factors
chain length of molecules in the fibre orientation of molecules size of the crystallites distribution of the crystallites gauge length used the rate of loading type of instrument used and atmospheric conditions
The mean single fibre strength determined is expressed in units of “grams/tex”. As it is seen the the unit for tenacity has the dimension of length only, and hence this property is also expressed as the “BREAKING LENGTH”, which can be considered as the length of the specimen equivalent in weight to the breaking load. Since tex is the mass in grams of one kilometer of the specimen, the tenacity values expressed in grams/tex will correspond to the breaking length in kilometers.
BUNDLE FIBRE STRENGTH:
In practice, fibres are not used individually but in groups, such as in yarns or fabrics. Thus, bundles or groups of fibres come into play during the tensile break of yarns or fabrics. Further,the correlation between spinning performance and bundle strength is atleast as high as that between spinning performance and intrinsic strength determined by testing individual fibres. The testing of bundles of fibres takes less time and involves less strain than testing individual fibres. In view of these considerations, determination of breaking strength of fibre bundles has assumed greater importance than single fibre strength tests.
There are three types of elongation
Permanent elongation: the length which extended during loading did not recover during relaxation
Elastic elongation:The extensions through which the fibres does return
Breaking elongation:the maximum extension at which the yarn breaks i.e.permanent and elastic elongation together Elongation is specified as a percentage of the starting length. The elastic elongation is of deceisive importance, since textile products without elasticity would hardly be usable. They must be able to deforme, In order to withstand high loading, but they must also return to shatpe. The greater resistance to crease
for wool compared to cotton arises, from the difference in their elongation. For cotton it is 6 -10% and for wool it is aroun 25 – 45%. For normal textile goods, higher elongation are neither necessary nor desirable. They make processing in the spinning mill more difficult, especially in drawing operations.
The Torsional rigidity of a fibre may be defined as the torque or twisting force required to twist 1 cm length of the fibre through 360 degrees and is proportional to the product of the modulus of rigidity and square of the area of cross-section, the constant of proportionality being dependent upon the shape of the cross-section of the fibre. The torsional rigidity of cotton has therefore been found to be very much dependent upon the gravimetric fineness of the fibres. As the rigidity of fibres is sensitive to the relative humidity of the surrounding atmosphere, it is essential that the tests are carried out in a conditional room where the relative
humidity is kept constant.
THE SLENDERNESS RATIO:
Fibre stiffness plays a significant role mainly when rolling, revolving, twisting movements are involved. A fibre which is too stiff has difficulty adapting to the movements. It is difficult to get bound into the yarn, which results in higher hairiness. Fibres which are not stiff enough have too little springiness. They do not return to shape after deformation. They have no longitudinal resistance. In most cases this leads to formation of neps. Fibre stiffness is dependent upon fibre substance and also upon the relationship between fibre length and fibre fineness. Fibres having the same structure will be stiffer, the shorter they are. The slenderness ratio can serve as a measure of stiffness,
slender ratio = fibre length /fibre diameter
Since the fibres must wind as they are bound-in during yarn formation in the ring spinning machine, the slenderness ratio also determines to some extent where the fibres will finish up.fine and/or long fibres in the middle coarse and/or short fibres at the yarn periphery.
In addition to useable fibres, cotton stock contains foreign matter of various kinds. This foreign material can lead to extreme disturbances during processing. Trash affects yarn and fabric quality. Cottons with two different trash contents should not be mixed together, as it will lead to processing difficulties. Optimising process parameters will be of great difficulty under this situation, therefore it is a must to know the amount of trash and the type of trash before deciding the mixing.
SHIRLEY TRASH ANLAYSER:
A popular trash measuring device is the Shirley Analyser, which separates trash and foreign matter from lint by mechanical methods. The result is an expression of trash as a percentage of the combined weight of trash and lint of a sample. This instrument is used
to give the exact value of waste figures and also the proportion of clean cotton and trash in the material
to select the proper processing sequence based upon the trash content
to assess the cleaning efficiency of each machine
to determine the loss of good fibre in the sequence of opening and cleaning.
Stricter sliver quality requirements led to the gradual evolution of opening and cleaning machinery leading to a situation where blow room and carding machinery were designed to remove exclusively certain specific types of trash particles. This necessitated the segregation of the trash in the cotton sample to different grades determined by their size. This was achieved in the instruments like the Trash Separator and the Micro Dust Trash Analyser which could be considered as modified versions of the Shirley Analyser.
The high volume instruments introduced the concept of optical methods of trash measurement which utilised video scanning trash-meters to identify areas darker than normal on a cotton sample surface. Here, the trash content was expressed as the percentage area covered by the trash particles. However in such methods, comparability with the conventional method could not be established in view of the non-uniform distribution of trash in a given cotton sample and the relatively smaller sample size to determine such a parameter. Consequently, it is yet to establish any significant name in the industry.
RAW MATERIAL AS A FACTOR AFFECTING SPINNING:
Fineness determines how many fibres are present in the cross-section of a yarn of particular linear density. 30 to 50 fibres are needed minimum to produce a yarn fibre fineness influences
drape of the fabric
productivity is influenced by the end breakage rate and twist per inch required in the yarn
Immature fibres(unripe fibres) have neither adequate strength nor adequate longitudinal siffness. They therefore lead to the following,
loss of yarn strength
high proportion of short fibres
processing difficulties at the card and blowroom
Fibre length is one among the most important characteristics. It influnces
handle of the product
lustre of the product
It can be assumed that fibres of under 4 – 5 mm will be lost in processing(as waste and fly). fibres upto about 12 – 15 mm do not contribute to strength but only to fullness of the yarn. But fibres above these lengths produce the other positive characteristics in the yarn.
The proportion of short fibres has extremely great influence on the following parameters
handle of the product
lustre of the product
A large proportion of short fibre leads to strong fly contamination, strain on personnel, on the machines, on the work room and on the air-conditioning, and also to extreme drafting difficulties.
A uniform yarn would have the same no of fibres in the cross-section, at all points along it. If the fibres themeselves have variations within themselves, then the yarn will be more irregular.
If 2.5% span length of the fibre increases, the yarn strength also icreases due to the fact that
there is a greater contribution by the fibre strength for the yarn strength in the case of longer fibres.
Neps are small entanglements or knots of fibres. There are two types of neps. They are 1.fibre neps and 2.seed-coat neps.In general fibre neps predominate, the core of the nep consists of unripe and dead fibres. Thus it is clear that there is a relationship between neppiness and maturity index. Neppiness is also dependent on the fibre fineness, because fine fibres have less longitudinal stiffness than coarser fibres.
Nature produces countless fibres, most of which are not usable for textiles because of inadequate strength.
The minimum strength for a textile fibre is approximately 6gms/tex ( about 6 kn breaking length).
Since blending of the fibres into the yarn is achieved mainly by twisting, and can exploit 30 to 70% of the strength of the material, a lower limit of about 3 gms/tex is finally obtained for the yarn strength, which varies linearly with the fibre strength.
Low micronaire value of cotton results in higher yarn tenacity.In coarser counts the influence of micronaire to increase yarn tenacity is not as significant as fine count.
Fibre strength is moisture dependent. i.e. It depends strongly upon the climatic conditions and upon the time of exposure. Strength of cotton,linen etc. increases with increasing moisture content.
The most important property inflencing yarn elongation is fibre elongation.Fibre strength ranks seconds in importance as a contributor to yarn elongation. Fibre fineness influences yarn elongation only after fibre elongation and strength. Other characters such as span length, uniformity ratio, maturity etc, do not contribute significantly to the yarn elongation.Yarn elongation increases with increasing twist. Coarser yarn has higher elongation than finer yarn. Yarn elongation decreases with increasing spinning tension. Yarn elongation is also influenced
by traveller weight and high variation in twist insertion.
For ring yarns the number of thin places increases, as the trash content and uniformity ratio increased For rotor yarns 50%span length and bundle strength has an influence on thin places.
Thick places in ringyarn is mainly affected by 50%span length, trash content and shor fibre content.
The following expression helps to obtain the yarn CSP achievable at optimum twist multiplier with the available fibre properties.
Lea CSP for Karded count = 280 x SQRT(FQI) + 700 – 13C
Lea CSP for combed count = (280 x SQRT(FQI) + 700 – 13C)x(1+W)/100
FQI = LSM/F
L = 50% span length(mm)
S = bundle strength (g/tex)
M = Maturity ratio measured by shirly FMT
F = Fibre fineness (micrograms/inch)
C = yarn count
W = comber waste%
Higher FQI values are associated with higher yarn strength in the case of carded counts but in combed count such a relationship is not noticed due to the effect of combing
Higher 2.5 % span length, uniformity ratio, maturity ratio and lower trash content results in lower imperfection. FQI does not show any significant influence on the imperfection.
The unevenness of carded hosiery yarn does not show any significant relationships with any of the fibre properties except the micronaire value. As the micronaire value increases, U% also increases. Increase in FQI however shows a reduction in U%.
Honey-dew is the best known sticky substance on cotton fibres. This is a secretion of the cotton louse. There are other types of sticky substances also. They are given below.
honey dew – secretions
fungus and bacteria – decomposition products
vegetable substances – sugars from plant juices, leaf nectar, over production of wax,
fats, oils – seed oil from ginning
synthetic substances – defoliants, insecticides, fertilizers, oil from harvesting machines
In the great majority of cases, the substance is one of a group of sugars of the most variable composition, primarily but not exclusively, fructose, glucose, saccharose, melezitose, as found, for example on sudan cotton. These saccharides are mostly, but not always, prodced by insects or the plants themselves, depending upon the influence on the plants prior to plucking. Whether or not a fibre will stick depends, not only on the quantity of the sticky coating and it composition, but also on the degree of saturation as a solution. Sugars are broken down by fermentation and by microorganisms during storage of the cotton. This occurs more quickly the higher the moisture content. During spinning of sticky cotton, the R.H.% of the air in the production are should be held as low as possible.