Applications of statistical tools in various processing stages of textile production


Fiber Production

Measures of central tendency like process average gives an idea about average staple length of fibre produced in a continuous or batch wise process. Coefficient of variation (CV) of the process signifies about the process control. On the other hand, analysis of time series is helpful in estimating the future production based on the past records. Measures of dispersion such as standard deviation and CV are useful in comparing the performance of two or more fibre-producing units or processes. Significance tests can also be applied to investigate whether significant difference exists between the batches for means or standard
deviations. Analysis of variance can be applied for studying the effect of parameters of fibre production and methods of polymer dissolving.

Textile Testing of Fiber Yarn and Fabrics

Results analysis in textile testing without the applications of statistical tools will be meaningless. In other words every experiment in textile testing include the use of statistical tools like average calculation, computation of SD, CV and application of tests of significance (t-test, z-test and f-test) or analysis of variance (one way, two way or design of experiments). Populations can be very well studied by normal or binomial or Poisson’s distributions. Random sampling errors are used in studying about the population mean and SD at 95% and 99% level of confidence. Application geometric mean for finding out the overall flexural rigidity or Go has an important role in fabric selection for garment manufacture.

A special mention is made in determination of fibre length by bear sorter where all the measures of central tendency and dispersion (mean length, modal length quartile deviation, etc., in the form of frequency distribution) are computed to understand about the cotton sample under consideration for testing its potential in yarn manufacture. On the other hand ball sledge sorter uses weight distribution from which mean and SD are computed. In the case of cotton fibres, the development of cell wall thickening commonly referred as “Maturity” concept can be very well determined using normal distribution and confidence intervals. Several properties are tested for different packages produced from the same material or from the same frame by applying significance tests. Effect of instruments and variables for different types of samples can be
very well studied by using ANOVA. All the fabric properties tested on a single instrument or different instrument can be understood by using design of experiments. In one of the research applications, which include the testing of low stress mechanical properties for nearly 1000 fabrics are studied by ‘Principle Bi component analysis or Bi plot’. Measures of dispersion like coefficient of variation and percentage mean deviation are very much used in evenness measurement.

Yarn Production

There are several stages involved in the cotton yarn production. When fibres are mixed and processed through blow room, within and between lap variations are studied by computing mean, SD and CV lap rejection, and production control are studied by p and x charts. Average measure is used to find the hank of silver in carding, draw frame, combing and average hank of roving in roving frame and average count at ring frame. Generally the spinning mill use ‘average count’ as the count specification if it is producing 4–5 counts. On the other hand the weaving section uses ‘resultant count’ which is nothing but the harmonic mean of the counts produced. Control charts are extensively used in each and every process of yarn production (for example, the process control with respect to thin places, neps, etc.). Application of probability distributions like Poisson, Weibull and binomial for various problems in spinning is found very much advantageous to understand the end breakage concept. In ring spinning section several ring bobbins are collected and tested for CSP and difference between the bobbins and within the bobbins is studied using ‘range’ method. In cone winding section the process control can be checked either by using control chart for averages or chart for number defectives.

Fabric Production

Design of experiments such as latin square design or randomized block design can be used to identify the effect of different size ingredients on wrap breakages on different looms in fabric formation. Most of the suiting fabric constructions involve the use of double yarn which is nothing but the harmonic mean of different counts. Poisson’s and normal distribution can be applied for loom shed for warp breakages. Using statistical techniques the interference loss can also be studied in loom shed. Various weaving parameters such as loom speed, reed and pick can be correlated with corresponding fabric properties and are interpreted in terms of loom parameters. Control charts are used to study the control of process/product quality in fabric production also. For example, selection of defective cones in a pirn winding from a lot (fixed population) or in a production shift n p and p charts are used. The width of the cloth and its control can be understood by x and defectives per unit length and their control is understood by c charts. The testing process includes determination of average tensile strength (and single thread strength also) and the corresponding CV%.

Chemical processing and Garment Production

The scope of statistics is unlimited. For example the effect of n number washes (identical conditions) on m fabrics on a particular fabric property can be easily found by either tests of significance or analysis of variance. Similarly the effect of different detergents on fabric types can be investigated by two-way analysis of variance. Similarly different types of fabrics and the effect of sewing conditions can be studied by ANOVA.
In garment production the control of measurements and its distribution can be well understood by control and polar charts.

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OLEFIN FIBERS


Olefin fibers, also called polyolefin fibers, are defined as manufactured fibers in which the fiber-forming substance is a synthetic  polymer of at least 85 wt% ethylene, propylene, or other olefin units (1). Several olefin polymers are capable of forming fibers, but only polypropylene [9003-07-0] (PP) and, to a much lesser extent, polyethylene [9002-88-4] (PE) are of practical importance. Olefin polymers are hydrophobic and resistant to most solvents. These properties impart resistance to staining but cause the polymers to be essentially undyeable in an unmodified form.

The first commercial application of olefin fibers was for automobile seat covers in the late 1940s. These fibers, made from low density polyethylene (LDPE) by melt extrusion, were not very successful. They lacked dimensional stability, abrasion resistance, resilience, and light stability. The success of olefin fibers began when high density polyethylene (HDPE) was introduced in the late 1950s. Yarns made from this highly crystalline, linear polyethylene have higher tenacity than yarns made from the less crystalline. Markets were developed for HDPE fiber in marine rope where water resistance and buoyancy are important. However, the fibers also possess a low melting point, lack resilience, and have poor light stability. These traits caused the polyethylene fibers to have limited applications.

Isotactic polypropylene, based on the stereospecific polymerization catalysts discovered by Ziegler and Natta,was introduced commercially in the United States in 1957. Commercial polypropylene fibers followed in 1961. The first market of significance, contract carpet, was based on a three-ply, crimper-textured yarn. It competed favorably against wool and rayon–wool blends because of its lighter  weight, longer wear, and lower cost. In the mid-1960s, the discovery of improved light stabilizers led to the development of outdoor carpeting based on polypropylene.

In 1967, woven carpet backing based on a film warp and fine-filament fill was produced. In the early 1970s, a bulked-continuous-filament (BCF) yarn was introduced for woven, texturized upholstery. In the mid-1970s, further improvement in light stabilization of polypropylene led to a staple product for automotive interiors and nonwoven velours for floor and wall carpet tiles. In the early 1980s, polypropylene was introduced as a fine-filament staple for thermal bonded nonwovens.

The growth of polyolefin fibers continues. Advances in olefin polymerization provide a wide range of polymer properties to the fiber producer. Inroads into new markets are being made through improvements in stabilization, and new and improved methods of extrusion and production, including multicomponent extrusion and spunbonded and meltblown nonwovens.

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Olefin Fibers

Innovations in fibres and textile materials for sportswear


Fibre developments

The evolution of fibre developments has gone through the phases of conventional fibres, highly functional fibres and high-performance fibres. Polyester is the single most common fibre used for sportswear and active wear. Other fibres suitable for active wear are polyamide, polypropylene, acrylics and elastanes. Wool and cotton fibres are still finding applications in leisurewear. Synthetic fibres can either be modified during manufacture, e.g. by producing hollow fibres and fibres with irregular cross-section, or be optimally blended with natural fibres to improve their thermo-physiological and sensory properties. Synthetic fibres with improved UV resistance and having anti-microbial properties are also commercially available for use in sportswear.

Improved fibre spinning techniques in melt spinning, wet spinning, dry spinning as well as new techniques such as gel spinning, bi-component spinning and microfibre spinning, have all made it possible to produce fibres, yarns and fabrics with unique performance characteristics suitable for use in sportswear and sports goods. New technologies for producing microfibres have also contributed towards production of high-tech sportswear.

By using the conjugate spinning technique, many different types of sophisticated fibres with various functions have been commercially produced  which has resulted in fabrics having improved mechanical, physical, chemical and biological functions. The technique of producing sheath/core melt spun conjugate fibres has been commercially exploited for producing added-value fibres. Unitika produced the first heat-degenerating conjugate fibre with a core containing zirconium carbide (ZrC). Since ZrC absorbs sunlight (visible and near-infrared radiation) and emits far-infrared radiation, one feels warmer when one puts on a jacket made from such fibres. Other types of heat-generating fibres contain ceramic micro-particles.

High-performance fibres

Today, a wide range of high-performance fibres is commercially available for technical and industrial applications. These types of fibres are used in sports protective wear/equipment developed for impact protection and in textile reinforcement in sports products for different applications. Among the speciality fibres already established are the following:

Aramid fibres:

± p-aramid fibre to provide high strength and ballistics
± m-aramid fibre to provide flame and heat resistance.

Ultra-high tenacity polyethylene fibres (UHMWPE).

Gel spun, ultra-high molecular weight polyethylene fibres with extremely high specific strength and modulus, high chemical resistance and high abrasion resistance.

Polyphenylene sulphide fibres (PPS).

Crystalline thermoplastic fibre with mechanical properties similar to regular polyester fibre. Excellent heat and chemical resistance.

Polyetheretherketone fibres (PEEK).

Crystalline thermoplastic fibre with high resistance to heat and to a wide range of chemicals.

· Novoloid (cured phenol-aldehyde) fibres.

High flame resistance, non-melting with high resistance to acid, solvents, steam, chemicals and fuels. Good moisture regain and soft hand.

· PBO (p-phenylene-2,6-benzobisoxazole) fibres.

The strength and modulus of this fibre exceed those of any known fibres.

Highly functional fabrics

There has been a strong growth in the development and use of highly functional materials in sportswear and outdoor leisure clothing. The performance requirements of many such products demand the balance of widely different properties of drape, thermal insulation, barrier to liquids, antistatic, stretch, physiological comfort, etc. The research in this field over the past decade has led to the commercial development of a variety of new products for highly functional end-uses. By designing new processes for fabric preparation and finishing, and as a result of advances in technologies for the production and application of suitable polymeric membranes and surface finishes, it is now possible to combine the consumer requirements of aesthetics, design and function in sportswear for different end-use applications. The fabrics for active wear and sportswear are also specially constructed both in terms of the geometry, packing density and structure of the constituent fibres in yarns and in terms of the construction of the fabric in order to achieve the necessary dissipation of heat and moisture at high metabolic rates. Many smart double-knitted or double- woven fabrics have been developed for sportswear in such a way that their inner face, close to human skin, has optimal moisture wicking and sensory properties whereas the outer face of the fabric has optimal moisture dissipation behaviour.

In addition to the innovations in highly functional man-made fibre-based fabrics, advances have also been made in cotton and wool fabrics for sportswear. An example is the development of `Sportwool’ weatherproof technology, where the constituent fibre, yarn and fabric properties and the fabric finishes of `Sportwool’ are supposed to create a drier and cooler microclimate.

Since the introduction of Gore-Tex fabric in 1976, a variety of lightweight breathable highly functional fabrics have been developed worldwide. Highly functional fabrics are generally characterized as being waterproof/moisture permeable, sweat-absorbing and with high thermal insulation at low thickness values. These fabrics are now extensively used in making sportswear and sports shoes. One can say that these products are basically complex materials with diverse functions. In many of these products the requirements of comfort and fashion have successfully been integrated with segmentation in uses.

Important developments are envisaged in making multifunctional coated or laminated fabrics for different applications. For example, some new innovative functional textiles for protective clothing were recently introduced by W. Gore and Associates. Gore-Tex Airlock is a functional textile which was developed by Gore for the special needs of firefighters. The concept of this product is to eliminate the conventional, bulky, thermal insulation layer and substitute it by a protective air cushion. Dots consisting of foamed silicone are discontinuously applied to a fibre substrate and anchored within the microporous Gore-Tex membrane. They measure only a few millimetres in height, creating a defined air cushion between the adjacent flame-retardant face fabric and the inner lining. This laminated fabric is characterized by thermal insulation, breathability, perspiration transport, absorption and quick-dry properties.

Biomimetics and textiles

The structure and functions of natural biological materials are precise and well defined. The imitation of living systems, `biomimetics’, could make it possible in future to replicate the molecular design and morphology of natural biological materials since their structure and functions are related. Already in many laboratories around the world, R&D work is going on in the field of biomimetic chemistry and fabric formation. A typical example is the development of water- and soil-repellent fabrics produced by imitating the surface structure of a lotus leaf. Water rolls like mercury from the lotus leaf, whose surface is micro-
scopically rough and covered with a wax-like substance with low surface tension. When water is dropped on to the surface of a lotus leaf, air is trapped in the dents and forms a boundary with water.

Intelligent textiles

There have been some interesting developments taking place regarding intelligent textiles and interactive materials with great market potential in the sportswear sector. These materials readily interact with human/environmental conditions thereby creating changes in the material properties. For example, the phase-change materials and shape-memory polymers embedded in fabric layers will be able to interact with a human body and produce thermoregulatory control by affecting the microclimate between the clothing and the human skin. In addition to the two dimensions of functionality and aesthetics, if `intelligence’ can be embedded or integrated into clothing as a third dimension, it would lead to the realization of protective and safety clothing as a personalized wearable information infrastructure.

Reference: “Textiles in sports” by R.Shishoo

Cloth Finishing


Cloth Finishing

( Originally Published Early 1900’s )

Importance of cloth finishing.-Cloth finishing is one of the chief arts in the textile industry. The appearance of the goods is often of first concern, and the appearance of any fabric is largely due to the methods of finishing.

BLEACHING

Bleaching is one of the most usual and important among the finishing processes. It has for its object the whitening or decolorizing of the textile fiber to which it is applied. Fibers, as they come from the plant, from the back of the sheep, or from the cocoon, are usually somewhat colored or stained. Some of them, like tussah silk or Egyptian cotton, are highly colored. This natural coloring of the fiber may be undesirable in many fabrics; hence, bleaching is employed to clear the fiber of this color. Again, most fibers accumulate stains of various kinds during the early processes of manufacture as, for example, in the spinning and weaving. This discoloration cannot be entirely removed by simple washing; hence, the bleaching process is applied to clear the fabric. In like manner, when the calicoes or other prints come from the printers, the white background between the colored figures may be soiled, spotted, or otherwise discolored; again, a light bleach is applied, but not enough appreciably to injure the color in the figures.

Bleaching agents.-There are two classes of bleaching substances, oxygen and sulphurous acid. Under certain conditions oxygen destroys the coloring matters entirely. Sulphurous acid probably does no more than change the color to white, leaving the coloring substances still in the textile. An object once bleached white by oxygen is not likely to turn yellow or to change back to its original color; whereas textiles bleached in sulphurous acid quite frequently do change back again after a time, especially when in contact with certain chemicals such as alkalies or soaps.

Grassing.-The oldest bleaching method is that of “grassing,” still used to a certain extent in Europe for bleaching linens. The linen fabrics are laid on the grass or ground for weeks. The oxygen of the air and that given off by green plants slowly attacks and destroys the little yellow color particles in the flax fiber. Slowly the linen becomes whiter and whiter until finally it is fully bleached. The particular value of the grass bleach over all others is its slowness. This guarantees permanence. Furthermore, the “grassing” process is not likely to be carried on a bit further than necessary. The oxygen which attacks the coloring matter may ultimately attack the cellulose in the fiber and does do so in chemical bleacheries unless the fabric is removed at the proper time. A few moments’ delay, therefore, in a chemical bleachery means great damage to the cloth; whereas a few days either one way or the other in grass bleaching makes practically no difference. Cotton also was at one time bleached in this manner, but the more rapid chemical oxygen bleachers have entirely superseded grass bleaching for this textile.

Chemical bleaching.-The principal chemicals used in oxygen bleaching are chloride of lime, hydrogen peroxide, sodium peroxide, and potassium permanganate. All these substances are heavily charged with oxygen. In the bleaching process, this oxygen is set free, and this free oxygen attacks the coloring matters in unbleached goods. The bleaching powder of commerce is chloride of lime, the principal bleaching substance used for cotton and for all other vegetable fibers excepting jute. It is, however, entirely unsuitable for wool and silk. Hydrogen peroxide is the best bleaching substance of all. It may be used on any sort of fiber, for it attacks nothing but the coloring matter. It is frequently used in removing stains and also in bleaching hair. But for general textile bleaching purposes it is too expensive, and is hard to keep in concentrated form for even a short time. It is used extensively, however, in bleaching wool mousselines that are to be printed. Hydrogen peroxide produces a much better result than sulphurous acid, the common bleaching substance for wool. When cheaper means of producing peroxide are discovered, this chemical is bound to take front rank among the bleaching agents. Potassium permanganate is another oxygen-loaded chemical that is sometimes used in bleaching woolens. Sodium peroxide is a compound somewhat cheaper to produce than hydrogen peroxide, and contains a large amount of live, active oxygen. It is a rather new bleaching agent, but is already used to a certain extent on wool and silk, especially tussah silk.

Sulphur bleach.-Sulphurous acid bleach is applied in the form of either a gas or a liquid. The gas is produced by burning sulphur in the air. The fumes that arise from burning sulphur are sulphurous acid gas. The liquid is produced by saturating water with this gas. Sulphur bleach is used mainly for animal fibers (wool and silk) and jute. The most common method employs the gas rather than the liquid. Rooms called sulphur chambers are built out of brick especially for this purpose. The fabric or yarn is brought into this chamber and hung up damp in loose folds while sulphur is burned in pots on the floor. The rising fumes saturate the damp textiles, the dampness materially assisting, and the fibers gradually whiten. In large wool bleacheries the cloth is run through the sulphur chamber on rollers, bleaching on the way. The process is inexpensive and results in a beautiful white. Its tendency to make wool harsh is corrected by washing in soap and water. When the wool is mixed with cotton there is danger of the cotton’s being destroyed by the acid. The sulphur bleach is ordinarily used for wool and silk.

Chloride of lime.-In cotton bleaching, chloride of lime is the most common chemical used. Cotton is generally bleached in the piece or fabric form. The usual exceptions are sewing cotton, absorbent cotton, and jeweler’s cotton. The last two are bleached in the state of loose fibers. When the cotton comes from the looms it is still in the natural color, although somewhat altered by the sizing in the warp and by the dirt; grease, and dust accumulated in the machinery. The cloth is now said to be “in the gray.” It is, however, more of a dirty yellow than gray, and presents a soft, flabby, fuzzy, unattractive appearance. It is now ready for the bleaching process.

The bleaching process.-The cloth is first run through a washing machine to remove as much of the discoloration and dirt as possible. Next, most fabrics are either sheared or singed; that is, they are run through machines which either cut off or burn off the fuzziness that is always found on cloth direct from the loom. The shearing process is performed by a machine that works on the same principle as a lawn mower, cutting all loose ends and fibers very close to the body of the cloth. The singeing is done by very quickly passing the cloth over a line of gas jets, or over a red-hot plate, where the heat burns off the fuzz but has no time to burn the fabric itself. Recently, singeing has been successfully performed by electricity. Cloth is sometimes singed on both sides, sometimes on only one. The shearing and singeing processes leave the cloth apparently smooth.

As a rule, cotton cloths are then bleached. There are four common methods, or “bleachers” as they are called: “madder bleach,” “Turkey red bleach,” “market bleach,” and “rapid bleach.” Of these the madder bleach is the most thorough. The others differ from the madder bleach mainly in degree of thoroughness. Goods to be dyed in deep colors need less whitening; hence, they are given, for example, the Turkey red bleach. Goods to be dyed black need almost no bleaching; for these the rapid bleach is sufficient. The market bleach is really the rapid bleach with the addition of blueing and other substances to cover up defects in the process.

The bleaching industry.-Cotton bleaching is often conducted as a separate industry. In England this is quite the rule. The cloth is sent from the weaving concerns to the bleacheries to be bleached on commission or at so much a yard. Sometimes the products of the loom are purchased by converters who hire others to do all the finishing processes, including bleaching. Occasionally bleachers buy the cloth in the gray, bleach it, and again market it. In this country bleaching and dyeing works are usually associated, and both are frequently under the same management as the cotton mills. This joining together or integration of related industries is typical of American business organization, not only in the textile industries, but also in many other great businesses, such as steel production and meat packing.

How the bleacheries handle cotton goods.-Piece goods arrive at the bleacheries in bolts or rolls of an average length of fifty yards. Each of these is stamped with the owner’s name, the length of the bolt, and other necessary particulars. The ends of several hundred rolls are first stitched together to form one long sheet sometimes as much as twenty-five miles long.

Moistening and bowking.-When all is ready, the cloth is moistened, run through a six-to eight-inch ring to rumple it and form it into the shape of a rope, and in this form if is laid away in coils for several hours in bins to soften the sizing in the warp. Next, the cloth is turned into a covered tank called a kier, in which is a weak solution of caustic soda or milk of lime. The liquid is kept moving through the tank by means of pumps. Here the cloth is stirred for about eight or ten hours, a process which removes all fats and wax found in the cloth, such, for example, as the natu ral wax found around the cotton fibers. All of this must be thoroughly removed before bleaching if the cloth is to be made snow white. The mixture in the “kier” is called the “lime boil,” and this particular part of the process is called “bowking.” The process concludes with a thorough washing in pure, fresh water.

Brown sour.-The next step, known variously as the “brown sour,” “gray sour,” or “lime sour,” follows the washing. The cloth is passed into tanks of water containing sulphuric or hydrochloric acid, sometimes both. This souring process counteracts the action of any caustic soda or lime that may remain in the cotton fiber from the previous treatment. Here a knowledge of the chemistry of bleaching is absolutely essential. The proportion of acid in the “brown sour” must be just sufficient to destroy the alkali in the fiber. If not strong enough, the alkali will not all be destroyed and will continue to cause trouble throughout the entire life of the cloth. If too much acid is used, then not only will the alkali be destroyed, but the cotton fiber will be endangered as well. Much of the poor cotton cloth in the market owes its lack of strength to poor bleaching methods. Linen is more sensitive to these chemical changes than cotton; hence the difficulty of getting good chemically bleached linens. The acid or souring bath is followed by a washing in pure water.

Lye boil.-In the full madder bleach the cloth after the acid bath is usually passed into a second alkali bath containing hot lye and resin soap. This is called the “lye boil.” After three hours of boiling under pressure, with the alkali liquor forced through every part of the cloth by means of pumps, all of the fats and acids in the fiber have been ex tracted and changed into soapsuds. The invariable washing in pure water follows.

Chemicking.-The cloth is now ready to be transferred into the real bleaching bath, the chloride of lime solution, or “chemick,” as bleachers name it. Through this bath the cloth is passed back and forth, the liquid being forced through every part of it. After one or two hours this part of the process is completed. The cloth is removed and passed between heavy wooden rollers, which press out the excess of the chloride of lime solution. The cloth is then coiled or piled in bins so as to be exposed to the air. It is here that the real bleaching takes place. The chloride of lime absorbed in the fiber has a strong affinity for air and for water. Both are attracted, and in the chemical processes that follow a certain amount of oxygen is crowded out of the air and water, and this free, active oxygen attacks the coloring matters and destroys them. Now again the proportions must be scrupulously adjusted so that not too much or too little oxygen is produced. Too much would result in an oxidation or destruction not only of the color particles, but also of the cotton fiber itself.

White souring.-The chemicking or bleaching is followed by washing in pure water and afterward by treatment in a weak acid bath known as the “white sour.” In this bath all action of the chloride of lime is stopped. Then follows another most careful washing in water to remove every particle of acid, whereupon the bleaching process is ended. The cloth is opened up flat, spread out, beaten, stretched or tentered, and dried over hot rollers. It is now ready for dyeing, for printing, for mercerizing, or, if to remain in the white, for the final finishing processes of sizing and calendering. Dyeing, printing, and mercerizing have already been described; hence, we need only give our attention to the final finishing processes.

CLOTH DRESSING

Whether the cloth shall be made soft or stiff, dull or glossy, and so on, depends upon the finish applied and the materials used. Certain sizings fill up the spaces between the threads in the fabric, stiffen the fabric, and give it greater weight and body. Other sizing materials give stiffness without adding weight. Some give weight without stiffness. Some help to make the fabric glossy, others to give the cloth some special appearance in imitation of a different fiber. It would take a volume to give in detail an account of how these various effects are obtained. Such a description is not necessary here. A fair idea of the possibilities of cloth finishing can be obtained by a study of fabrics themselves, especially with the help of a small magnifying glass and with such tests as boiling and rubbing.

Dressing materials,-The materials used in cotton finishing or dressing include starches, glue, fats, casein, gelatin, gluten, minerals, and antiseptic substances. The starches give stiffness and weight; glue gives tenacity to the starches and other materials. Minerals, such as clay, are used to give weight. Fats give the qualities of softness and help make the fabric more elastic. Wax, stearin, and paraffin are frequently used to develop a high luster in the calendering or pressing processes. Antiseptic substances such as zinc chloride, salicylic acid, and zinc sulphate are added to prevent the starches and fats used in the dressing from molding or putrefying.

Starches.-The starchy substances commonly used include wheat flour, wheat starch, potato starch, rice starch, and cornstarch. Sometimes the starch is baked until brown before using. In this form it is called dextrin or British gum. Dextrin gives a softer dressing than any other starchy material. Wheat and corn starches produce the stiffest effects. Potato starch comes between the two extremes. Starch is sometimes treated for a couple of hours with caustic soda at about the freezing point. At the end of this time the excess of alkali is neutralized with acid. The result is a gum, called apparatine, which stiffens the cloth and does not wash out so easily as most other stiffening substances. Starch treated with acid produces glucose, and this is used largely as a weighting or loading material.

Fats.-Among the fats used are tallow, stearin, several different kinds of oils and waxes, and paraffin. These are sometimes added to the starches to reduce the stiffness of the fabrics. Glycerin and magnesium chloride are frequently added for the same reason. Fats may be added to waterproof the cloth, although waterproofing is usually accomplished by rubberizing; that is, by soaking the cloth in a solution of crude rubber or caoutchouc.

Minerals.-The minerals are added for various reasons. China clay increases the weight as do also salts of lime and baryta. Alum, acetate of lead, and sulphate of lead are sometimes used. Adding large proportions of borax, ammonium phosphate, salts of magnesia, and sodium tungstate makes the fabric fireproof.

How the dressing is applied.-The dressing material is usually applied as a liquid paste to the back of the cloth and then run over hot rolls or cylinders in order to dry the paste quickly. Sometimes it is applied lightly to the surface, sometimes it is pressed in deeply by means of rollers. When both sides are dressed, the fabric is passed into and through the dressing material. When the cloth is dry, the sizing or dressing process is complete. If merely a dull, hard finish is desired, nothing further is necessary except to stretch and smooth out the cloth, measure, bolt, and press it. But if any kind of polish is demanded, then the cloth must be calendered, pressed, mangled, or ironed.

CALENDERING

Calendering is accomplished by passing the cloth between large rolls, from two to six, under heavy pressure. In the rolls the dressing is smoothed out, and the hard, dull finish becomes soft and glossy in appearance. Heated rolls give a better gloss. When the rolls are made to turn over each other at different rates, there is a heavy friction or ironing effect on the cloth. For the highest glosses not only starch but also fats and waxes are used, and all are ironed into the cloth under heavy pressure and at as great heat as the cloth will stand. When calendered the fabrics are usually dampened first, just as clothes are dampened by the housewife before she irons them. The dampening in a cloth-finishing plant is done by a special machine that sprays the cloth very evenly as it passes through.

The beetle finish.-There are several special finishes possible through variations in the calendering process. Beetling is one of these methods. The cloth is passed into a machine over wooden rollers and beaten by wooden hammers operated by the machine. The beetle finish gives to cotton or linen an appearance almost like satin and is very beautiful.

Watered effects.-Moire or watered effects are produced by pressing some parts of the threads in a fabric down flat while leaving the other parts of the threads in their natural or round condition. The effect is usually that of an indistinct pattern. It is obtained in different ways, sometimes by running the cloth through the calender double, or again by running the single fabric between rollers especially engraved with moire designs. Only soft fabrics are suited to this finish; hence, no dressing except fats is used for moire goods.

Embossing.-Soft fabrics are sometimes stamped with patterns in the manner of embossing by means of engraved calender rolls. This process is called stamping.

Schreiner finish.-Another special finish, known as “Schreiner finish,” is applied in the calendering operation by passing the cloth between rolls covered with great numbers of finely engraved lines. The number often runs as high as six hundred to the inch. Under a pressure of 4,500 pounds these lines are pressed into the fabric. The result is that the round threads are pressed flat, but the lines break up the flat surfaces into little planes that reflect the light much better than an ordinary flat surface would. This peculiar light reflection gives the cloth the quality of a very high luster. Heating the rolls makes this luster more lasting. The effect is very beautiful. Mercerized cotton finished in the Schreiner finish rivals silk in appearance.

Most of the finishes spoken of so far, the result of dressing and calendering, are easily destroyed. Wear destroys any of them in time. Washing destroys most of them. But as long as they last they are highly important elements in the appearance of the fabrics.

OTHER FINISHING PROCESSES

Dressings applied to the various textiles.-Dressings are usually applied in much greater quantity to cotton than to any other textile. Linen comes second, and the principal dressing substance used in linens is starch. Glue, gelatin, dextrin, albumen, and water glass are applied under certain conditions and for certain effects in woolen goods. The common weighting materials added to woolens are short hairs or short wool fibers, sometimes called flocks. Flocks are the ends of fibers sheared off from the surface of wool or worsted cloth. Woolen cloths are padded or impregnated with these in the fulling mills, sometimes adding from one-fourth to three-fourths to the weight of the wool. Such finishing processes as beetling, mangling, moireing, and stamping are never applied to woolens. Silk usually has very little dressing applied to it in the finishing process, and that little generally consists of gelatin, gum arabic, or tragacanth. The other finishing processes are very much the same for silk as they are for cotton.

Lisle finish.-Several other finishes, or modifications of the finishes just described, are used in cotton goods when it is desired to show special effects. The lisle finish is given yarns that are to be used in the manufacture of hosiery and underwear. The true lisle finish is obtained by using combed, long-stapled, sea-island or Egyptian cotton. The yarns made from these fibers are rapidly but repeatedly run through gas flames until they are entirely free from any projecting fiber ends or fuzz. The result is a very smooth, glossy thread. Another kind of lisle finish is obtainable in a finished fabric, as, for example, in hosiery, by treating with a weak solution of sulphuric or hydrochloric acid and then drying before washing out the acid. The goods are afterward tumbled around in a machine that exposes them to the air and heats them to about 100 degrees Fahrenheit. After a time the loose ends and fuzzy fibers become brittle and break off in the tumbling given the goods. When the goods present the proper lisle finish, they are cooled off and washed in an alkaline bath which stops the action of the dry acid and neutralizes it. After thorough washing in clean water, they are dried and are ready for dyeing or any other finishing process. Sometimes the acids are added to the dye bath to cause more speedily the same effect in the appearance of the goods. Some dyes are regularly made up with the acid mixture.

Wool finishing.-The finishing processes for woolens and worsteds are much more laborious and complex than those employed for cottons. A greater variety of machinery is required, and there are more steps in the process. The finishing of wool goods is divided into two main parts: the first is called the “wet finishing,” which includes washing, soaping, steaming, carbonizing, and the use of liquids; the second is called “dry finishing” and includes napping, shearing, polishing, measuring, and putting up in rolls or bolts.

Preparation of wool fabrics.-Woolen or worsted cloth, as it comes from the weave rooms to the finishers, is first inspected for flaws, broken threads, and weak places, and wherever these are found, chalk marks are made to assist the burlers and menders in finding the places. To aid in the inspection, the cloth is generally “perched” or thrown over a roller and drawn down in single thickness by the inspector as fast as he can look it over. A good light is desirable. Inspectors with practice attain great proficiency in finding weak places or imperfections in the cloth. After the bad spots in the fabric are repaired the goods are tacked together; that is, the pieces are fastened together in pairs with the faces of the cloth turned towards each other. The tacking is simply a stitching along the edge, done either by hand or machine. The purpose of tacking is to protect the faces of the cloth from becoming damaged in any way by the heavy operations to follow or from becoming impregnated with any foreign substance difficult to remove, such as short hairs or flocks.

Fulling.-The next step is the fulling. All kinds of clearfinished worsted dress goods for ladies and practically all wool cloths for men’s wear except worsteds are fulled. This is the most characteristic process in the wool industry; no other textile goes through any process like it. The wool fibers, it will be recalled, are jointed and have scales that cause the fibers to cling together readily. This, we have learned, is called the felting quality. By beating a mass of wool fibers, a very hard, compact mass can be obtained, because the fibers creep into closer and closer contact with each other, holding fast because of the scales. Fulling makes use of this principle. Wool cloth is shrunken and made heavier and closer in structure and consequently stronger. Fulled cloth may also take many more kinds of finish than unfulled fabrics. The fulling process is performed in machines that apply pressure, moisture, and heat to the goods. The cloths are soaked in hot, soapy water, pressed, rolled, and tumbled; as a result, the woolen fabrics contract and become closer in texture throughout.

Flocking.-Short wool fibers or flocks are frequently felted into wool fabrics in the fulling operation. A layer of these short fibers is spread over the back of the cloth and matted down by moistening. In the fulling operation these fibers sink into the fabric and therefore help to give the fabric weight and closeness. That this process is not always well done is evidenced by the fact that the flocks in the backs of suitings often wear loose, drop down, and collect at the bottom of garments, especially at points where the lining and the suiting are sewed together. Flocks must from most standpoints be considered as an adulteration of wool although their presence really helps some fabrics, such as kerseys. All crevices are filled up and the fabric is made solid. If the felting has been done well, the flocks perform a good service in the cloth, but otherwise the flocks come out easily and are a decided nuisance to the wearer of the goods. Flocks made from wool waste such as shoddy, mungo, and extract, when applied on shoddy wool cloth are bound to come out. But flocks cut from new wool, when applied to new wool cloth, produce an excellent effect if not too largely used. Adding 25 per cent in weight to the cloth by flocking is not unreasonable, but doubling the weight of the original fabric would be unjustifiable adulteration. Flocking adds little if any to the strength of the cloth.

Speck dyeing.-After fulling, the cloth is washed very carefully, and is usually given a light dye to cover up spots or imperfections due to foreign matter that could not be taken out before. If not so dyed, all the little specks in the cloth have to be removed by hand, a process called speck dyeing or burr dyeing.

Carbonizing.-Carbonizing is usually performed before the wool is spun into yarn, but in some cases not until the cloth is woven. In this case it takes the place of speck dyeing. The process is the same for cloth as for loose wool. The vegetable matter is destroyed by soaking the cloth in weak acids and then heating in an oven.

Napping.-After washing, stretching, and drying, most goods are ready to receive the finish. In most cases this first involves raising a nap or fuzz evenly all over the surface, and for this purpose machines have been invented. The oldest of such machines use teasel or thistle burrs, whereas the later napping machines use little wire hooks. Some claim that the teasel burr has certain qualities for raising the wool nap that cannot be produced in any steel wire or spring hook or barb. The principle, however, is the same in all inventions for this purpose. The gigs or napping machines all stretch the cloth and then cause it to pass over many fine little hooks of teasel burrs or of steel wire which draw out a multitude of little ends of wool fiber all over the surface of the cloth. In some cases, the napping or gigging is performed on wet cloth; in others, the cloth is dry. Dry napping is in fact now the more common, although the wet methods are still employed for certain cloths and finishes.

The finish of wool cloth depends upon the degree o f napping and upon the variety of fiber. Meltons require only a little napping; kerseys, beavers, and doeskins, a very thorough one. Cloths that must wear exceedingly well must be napped as little as possible, since the process reduces the strength of the fabric. Cassimeres are given several kinds of finish, Saxony finish, for example, or velour finish. Other fabrics are each given their characteristic finish by slightly varying the amount of nap, or the treatment of the nap after it has been raised. Among such fabrics are cheviots, kerseys, meltons, beavers, chinchillas, outing flannels, doeskins, reversibles, thibets, satinets, blankets, and others.

Lustering.-After napping, such fabrics as kerseys, beavers, broadcloths, thibets, venetians, tricots, plushes, uniform cloths, and all worsteds, require another special operation known as steam lustering. Steam is forced through the cloth for about five minutes, followed by cold water. The steam brings out the luster which the cold water sets or fixes.

Stretching and clipping.-The dry finishing processes begin with stretching (or tentering) and then drying the cloth. Special machines accomplish this as well as all the other processes. The cloth now passes through a shearing machine which brushes the nap in the direction desired, afterward clipping it evenly over all the surfaces. The clippers operate like the revolving blades of a lawn mower. Goods that have not been napped are generally singed in much the same manner as cotton fabrics. Next, the sheared fabrics are brushed, and perhaps polished by means of pumice cloth or sandpaper, to make the cloth smooth and lustrous.

Final steps.-Finally the goods are pressed and thereby given a finished appearance. This is usually performed by means of heavy presses, either with dry heat or with steam. The most common present-day method of pressing cloth is by running it between heavy rollers heated by steam. Care must be taken not to get the rolls too hot or the wool will be damaged. The cloth is next inspected again, run through a measuring machine, doubled, rolled, and wrapped in paper, and packed into cases ready for the clothing manufacturer or the dry goods jobber and the retail store.

Worsted finishing.-Worsteds are not generally fulled as are woolens. After burling, worsteds are usually singed and then crabbed. The crabbing process sets the weave so that in the later operations it will not be obliterated. It consists in running the cloth tightly stretched over rollers through a trough containing hot water. After an hour or two of this the cloth is scoured and rinsed and then closely sheared. There are several varieties of worsted, each of which requires its own special finish or after-treatment. Innovations are constantly introduced to alter the appearance a little in one way or another. Among these are the fancy or yarn-dyed worsteds, serges, worsted dress goods, and worsted cheviots.

Production of Poly Ethylene Terephthalate


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PET is a polymer that possesses great importance in the contemporary world of plastics. Being a thermoplastic i.e. recyclable polymer made it the number one choice for numerous applications which satisfies the world need for a greener and more ecological alternative to commonly used plastics such as polyethylene and others.

Nowadays, Two PET grades dominate the global market fiber-grade PET and bottle-grade PET. They differ mainly in the end product properties such as optical appearance and production technologies where these properties can be controlled by molecular weight, intrinsic viscosity, and additives specific to each process or application. Other uses include film production and specialty nylons [17].

The scope of this report will focus on bottle-grade PET because of its high demand especially in the Egyptian market. The report discusses the historical development of PET, its importance, properties and material handling considerations.

Ever since its discovery in the beginning of 20th century several companies were interested n providing production technologies to supply the increasing need for large amounts of PET. Technologies and their current licensors are discussed in detail with their flow sheets, chemistry and specific properties.

The report splits the PET production processes into two main parts; monomer preparation and polymerization. Each of the technologies uses different raw materials, solvents, catalysts and reaction conditions with their advantages and disadvantages. After the detailed market study which has put into account both global and local markets’ considerations, a thorough evaluation study is constructed in the report to evaluate each technology according to standard evaluation techniques displayed in the evaluation section.

The carefully studied numbers and statistics in the market section led us to suggest a suitable capacity for the PET production plant based on many factors listed in the same place. The summation of the work done in this project is shown in the recommendation part where a justified process is selected to produce PET and TPA in Egypt. Further desired information about the report as a whole and any given part is attached to this report in the form of an appendix where much more detailed data can be found.

To download please click the following link.

PET-Production-Technical-Report

Dyeable Polypropylene Fiber


The ability to dye polypropylene fibers using conventional disperse dyes makes the fibers more attractive for apparel end-uses.

TW Special Report

Polypropylene fibers possess a number of attractive properties when compared to other fibers (See Table 1). Despite desirable properties, polypropylene fibers traditionally have suffered from a major drawback that has limited their adoption in textile apparel applications: In contrast to other fibers, conventional polypropylene fibers cannot be dyed. Instead, the color has to be imparted at the fiber extrusion step through mass coloration or solution dyeing. The process involves adding a relatively thermally stable pigment color during the melt spinning of the fiber. The pigments used are not usually miscible with polypropylene. Thus, the pigments are present as discrete particles in the fiber, and the color imparted becomes permanent in the fiber. While this has the benefit of very good colorfastness, there are two significant disadvantages. The first is that introducing new colors involves a relatively complex color-matching step. The second is the absence of greige goods to be dyed. This means that relatively large lots of fiber are made for every new color, and the time required to go from a new color concept to the final fabric or garment can be long.

There has been a long-standing interest in commercializing a dyeable polypropylene fiber. Ideally, it should have a dyeing profile similar to or compatible with large-volume fibers such as polyester, nylon or cotton, so that it is compatible with the dyeing and related processes that are already well-established. Furthermore, it should not change the essential benefits of polypropylene fibers presented in Table 1, especially its low density and its low surface energy. There have been several attempts to make dyeable polypropylene fibers, but they have not been successful because the resulting product did not meet these criteria.
FiberVisions has developed a revolutionary new polypropylene fiber, CoolVisions™ dyeable polypropylene fiber, that meets the needs of facile dyeing and polypropylene fiber characteristics by incorporating an additive within the polypropylene fiber. The fiber can be dyed using conventional disperse dyes in a manner similar to that used for polyester fibers. The fibers feature a wide array of inherent benefits and properties including:

  • light weight and comfort;
  • cottony softness;
  • easy care, easy wear;
  • moisture management;durability;
  • breathability;
  • thermal insulation; and
  • stain resistance.

FWfeaturechart

Lightweight And Comfortable

Polypropylene fibers are among the lightest in weight of all commercial fibers. The increased number of polypropylene fibers per kilogram of fabric offers added value compared to many other fibers, resulting in improved coverage for the same weight range or equal coverage in lighter-weight fabrics for comfortable garments. In addition, CoolVisions fibers are inherently softer than traditional polypropylene fibers, resulting in greater comfort, according to FiberVisions. This combination of attributes makes garments made from these new fibers inherently easy care, easy wear.

Moisture Management

According to FiberVisions, CoolVisions polypropylene fibers outperform all other dyeable fibers in low-moisture-absorption tests. In addition, garments made from polypropylene tend to have a high moisture-vapor-transmission rate. This is important in comfort, especially when one wants the skin to stay cool and dry. The mechanical properties of polypropylene fibers are not affected when the fabric is wet an inherent advantage compared to fibers like rayon, which can lose strength substantially.
As with traditional polypropylene, CoolVisions offers excellent chemical resistance and aqueous stain resistance. Bleach and other household cleaning chemicals do not affect the fibers, which also are not attacked by microbial organisms such as mold, mildew and bacteria.

windsurfers
Dyeable polypropylene fibers are suitable for apparel end-uses including sports applications.

Dyeing Characteristics

CoolVisions dyeable polypropylene fibers can be dyed using commonly available polyester high-energy disperse dyes and in standard high-pressure dyeing processes used for polyester fibers, but with lower dyeing temperatures possible. The color range and color-matching process are similar to those for polyester fibers.
The ability to dye fabrics results in many benefits over the use of fabrics made with traditional solution-dyed fibers, including value chain and styling benefits. Some of the value-chain benefits include the ability to store greige goods, match colors quickly, produce smaller lot volumes and serve niche or fashion-related color lines, respond rapidly to market demand, and offer a wider range of colors without greatly increasing inventory costs. There are added financial benefits from reduced working capital needs and shortened production times. Styling benefits include reduction in barré found in solution-dyed garments and the ability to print with dye inks rather than pigment inks. Dye-printed fabrics exhibit a softer hand and better colorfastness than pigment-printed fabrics. CoolVisions fibers also have been engineered to have an inherently soft hand and cotton touch not found in traditional polypropylene fibers.
As noted previously, CoolVisions fibers contain an additive that acts as a dye receptor. The additive is present in the fibers as small domains into which the disperse dyes dissolve during the dyeing process. At dyeing temperatures greater than the boiling point of water, the disperse dyes diffuse readily through the polypropylene fiber into the encapsulated domains of the additive. Under actual garment use conditions — which include much lower temperatures — the diffusion of the disperse dyes back out of the fiber is greatly diminished, resulting in good colorfastness. As with polyester fibers, high-energy disperse dyes should be used to obtain optimum colorfastness.
The approach of encapsulating the additive within the polypropylene fiber has many benefits. The surface of the fiber is essentially unchanged, resulting in excellent aqueous stain resistance and low water absorption. The polypropylene fiber also serves to protect the dyes from chemicals such as chlorine, resulting in excellent bleach fastness.
Since the ability to dye the polypropylene fiber is imparted by the incorporation of an additive, the level of the additive affects the depth of shade. This has a couple of benefits, according to FiberVisions: The additive level can be controlled quite well, resulting in reduced shade sensitivity to processing conditions. In addition, the level can be intentionally changed to produce fibers that dye to different depths, thereby offering an additional styling tool.
FiberVisions officially launched CoolVisions dyeable polypropylene fibers at the recent Outdoor Retailer Show in Salt Lake City. A number of partner companies are currently working with these fibers to develop new fabrics and apparel styles. Activities are underway to develop air-jet spun and filament-type products to broaden the range of styling tools.

September/October 2006

REEF:- TEXTILE WORLD

Health effects of Man-made fibers


Clara S. Ross, James E. Lockey

The industrial use of various types of man-made fibres has been increasing, particularly since restrictions were placed on the use of asbestos in view of its known health hazards. The potential for adverse health effects related to the production and use of man-made fibres is still being studied. This article will provide an overview of the general principles regarding the potential for toxicity related to such fibres, an overview of the various types of fibres in production (as listed in table 1) and an update regarding existing and ongoing studies of their potential health effects.

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Table 1    Synthetic fibres

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Toxicity Determinants

The primary factors related to potential for toxicity due to exposure to fibres are:

1. fibre dimension

2. fibre durability and

3. dose to the target organ.

Generally, fibres that are long and thin (but of a respirable size) and are durable have the greatest potential for causing adverse effects if delivered to the lungs in sufficient concentration. Fibre toxicity has been correlated in short-term animal inhalation studies with inflammation, cytotoxicity, altered macrocyte function and biopersistence. Carcinogenic potential is most likely related to cellular DNA damage via formation of oxygen-free radicals, formation of clastogenic factors, or missegregation of chromosomes in cells in mitosis-alone or in combination. Fibres of a respirable size are those less than 3.0 to 3.5 in diameter and less than 200 in length. According to the “Stanton hypothesis,” the carcinogenic potential of fibres (as determined by animal pleural implantation studies) is related to their dimension (the greatest risk is associated with fibres less than 0.25 in diameter and greater than 8 in length) and durability (Stanton et al. 1981). Naturally occurring mineral fibres, such as asbestos, exist in a polycrystalline structure that has the propensity to cleave along longitudinal planes, creating thinner fibres with higher length-to-width ratios, which have a greater potential for toxicity. The vast majority of man-made fibres are non-crystalline or amorphous and will fracture perpendicularly to their longitudinal plane into shorter fibres. This is an important difference between asbestos and non-asbestos fibrous silicates and man-made fibres. The durability of fibres deposited in the lung is dependent upon the lung’s ability to clear the fibres, as well as the fibres’ physical and chemical properties. The durability of man-made fibres can be altered in the production process, according to end-use requirements, through the addition of certain stabilizers such as . Because of this variability in the chemical constituents and size of man-made fibres, their potential toxicity has to be evaluated on a fibre-type by fibre-type basis.

Man-made Fibres

Aluminium oxide fibres

Crystalline aluminium oxide fibre toxicity has been suggested by a case report of pulmonary fibrosis in a worker employed in aluminium smelting for 19 years (Jederlinic et al. 1990). His chest radiograph revealed interstitial fibrosis. Analysis of the lung tissue by electron microscopy techniques demonstrated crystalline fibres per gram of dry lung tissue, or ten times more fibres than the number of asbestos fibres found in lung tissue from chrysotile asbestos miners with asbestosis. Further study is needed to determine the role of crystalline aluminium oxide fibres (figure 1) and pulmonary fibrosis.

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Figure 1    Scanning electron micrograph (SEM) of aluminium oxide fibres

Courtesy of T. Hesterberg.

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This case report, however, suggests a potential for fibrization to take place when proper environmental conditions coexist, such as increased air flow across molten materials. Both phase-contrast light microscopy and electron microscopy with energy dispersion x-ray analysis should be used to identify potential airborne fibres in the work environment and in lung tissue samples in cases where there are clinical findings consistent with fibre-induced pneumoconiosis.

Carbon/Graphite Fibres

Carbonaceous pitch, rayon or polyacrylonitrile fibres heated to 1,200 form amorphous carbon fibres, and when heated above 2,200 form crystalline graphite fibres (figure 2). Resin binders can be added to increase the strength and to allow moulding and machining of the material. Generally, these fibres have a diameter of 7 to 10 , but variations in size occur due to the manufacturing process and mechanical manipulation. Carbon/graphite composites are used in the aircraft, automobile and sporting goods industries. Exposure to respirable-sized carbon/graphite particles can occur during the manufacturing process and with mechanical manipulation. Furthermore, small quantities of respirable-sized fibres can be produced when composites are heated to 900 to 1,100 . The existing knowledge regarding these fibres is inadequate to provide definite answers as to their potential for causing adverse health effects. Studies involving intratracheal injection of different graphite fibre composite dusts in rats produced heterogeneous results. Three of the dust samples tested produced minimal toxicity, and two of the samples produced consistent toxicity as manifested by cytotoxicity for alveolar macrophages and differences in the total number of cells recovered from the lung (Martin, Meyer and Luchtel 1989). Clastogenic effects have been observed in mutagenicity studies of pitch-based fibres, but not of polyacrylonitrile-based carbon fibres. A ten-year study of carbon fibre production workers, manufacturing fibres 8 to 10 mm in diameter, did not reveal any abnormalities (Jones, Jones and Lyle 1982). Until further studies are available, it is recommended that exposure to respirable-sized carbon/graphite fibres be 1 fibre/ml (f/ml) or lower, and that exposure to respirable-sized composite particulates be maintained below the current respirable dust standard for nuisance dust.

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Figure 2   SEM of carbon fibres

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Kevlar para-aramid fibres

Kevlar para-aramid fibres are approximately 12 in diameter and the curved ribbon-like fibrils on the surface of the fibres are less than 1 in width (figure 3). The fibrils partially peel off the fibres and interlock with other fibrils to form clumps which are non-respirable in size. The physical properties of Kevlar fibres include substantial heat resistance and tensile strength. They have many different uses, serving as a reinforcing agent in plastics, fabrics and rubber, and as an automobile brake friction material. The eight-hour time-weighted average (TWA) of fibril levels during manufacturing and end-use applications ranges from 0.01 to 0.4 f/ml (Merriman 1989). Very low levels of Kevlar aramid fibres are generated in dust when used in friction materials. The only available health effects data is from animal studies. Rat inhalation studies involving one- to two-year time periods and exposures to fibrils at 25, 100 and 400 f/ml revealed alveolar bronchiolarization which was dose-related. Slight fibrosis and alveolar duct fibrotic changes also were noted at the higher exposure levels. The fibrosis may have been related to overloading of pulmonary clearance mechanisms. A tumour type unique to rats, cystic keratinizing squamous cell tumour, developed in a few of the study animals (Lee et al. 1988). Short-term rat inhalation studies indicate that the fibrils have low durability in lung tissue and are rapidly cleared (Warheit et al. 1992). There are no studies available regarding the human health effects of exposure to Kevlar para-aramid fibre. However, in view of the evidence of decreased biopersistence and given the physical structure of Kevlar, the health risks should be minimal if exposures to fibrils are maintained at 0.5 f/ml or less, as is now the case in commercial applications.

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Figure 3    SEM of Kevlar para-aramid fibres

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Silicon carbide fibres and whiskers

Silicon carbide (carborundum) is a widely used abrasive and refractory material that is manufactured by combining silica and carbon at 2,400 . Silicon carbide fibres and whiskers-figure 4 (Harper et al. 1995)-can be generated as by-products of the manufacture of silicon carbide crystals or can be purposely produced as polycrystalline fibres or monocrystalline whiskers. The fibres generally are less than 1 to 2  in diameter and range from 3 to 30 in length. The whiskers average 0.5 in diameter and 10 in length. Incorporation of silicon carbide fibres and whiskers adds strength to products such as metal matrix composites, ceramics and ceramic components. Exposure to fibres and whiskers can occur during the production and manufacturing processes and potentially during the machining and finishing processes. For example, short-term exposure during handling of recycled materials has been shown to reach levels up to 5 f/ml. Machining of metal and ceramic matrix composites have resulted in eight-hour TWA exposure concentrations of 0.031 f/ml and up to 0.76 f/ml, respectively (Scansetti, Piolatto and Botta 1992; Bye 1985).

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Figure 4    SEMs of silicon carbide fibres (A) and whiskers (B)

A

B

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Existing data from animal and human studies indicate a definite fibrogenic and possible carcinogenic potential. In vitro mouse cell culture studies involving silicon carbide whiskers revealed cytotoxicity equal to or greater than that resulting from crocidolite asbestos (Johnson et al. 1992; Vaughan et al. 1991). Persistent adenomatous hyperplasia of rat lungs was demonstrated in a subacute inhalation study (Lapin et al. 1991). Sheep inhalation studies involving silicon carbide dust revealed that the particles were inert. However, exposure to silicon carbide fibres resulted in fibrosing alveolitis and increased fibroblast growth activity (Bйgin et al. 1989). Studies of lung tissue samples from silicon carbide manufacturing workers revealed silicotic nodules and ferruginous bodies and indicated that silicon carbide fibres are durable and can exist in high concentrations in lung parenchyma. Chest radiographs also have been consistent with nodular and irregular interstitial changes and pleural plaques.

Silicon carbide fibres and whiskers are respirable in size, durable, and have definite fibrogenic potential in lung tissue. A manufacturer of silicon carbide whiskers has set an internal standard at 0.2 f/ml as an eight-hour TWA (Beaumont 1991). This is a prudent recommendation based on currently available health information.

Man-made Vitreous Fibres

Man-made vitreous fibres (MMVFs) generally are classified as:

1. glass fibre (glass wool or fibreglass, continuous glass filament and special-purpose glass fibre)

2. mineral wool (rock wool and slag wool) and

3. ceramic fibre (ceramic textile fibre and refractory ceramic fibre).

The manufacturing process begins with melting raw materials with subsequent rapid cooling, resulting in the production of non-crystalline (or vitreous) fibres. Some manufacturing processes allow for large variations in terms of fibre size, the lower limit being 1 or less in diameter (figure 5). Stabilizers (such as , and ZnO) and modifiers (such as MgO,  , BaO, CaO, and ) can be added to alter the physical and chemical properties such as tensile strength, elasticity, durability and thermal non-transference.

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Figure 5    SEM of slag wool

Rock wool, glass fibres and refractory ceramic fibres are identical in appearance

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Glass fibre is manufactured from silicon dioxide and various concentrations of stabilizers and modifiers. Most glass wool is produced through use of a rotary process resulting in 3 to 15 average diameter discontinuous fibres with variations to 1 or less in diameter. The glass wool fibres are bound together, most commonly with phenolic formaldehyde resins, and then put through a heat-curing polymerization process. Other agents, including lubricants and wetting agents, may also be added, depending on the production process. The continuous glass filament production process results in less variation from the average fibre diameter in comparison to glass wool and special-purpose glass fibre. Continuous glass filament fibres range from 3 to 25 in diameter. Special-purpose glass fibre production involves a flame attenuation fibrization process that produces fibres with an average diameter of less than 3 .

Slag wool and rock wool production involves melting and fibrizing slag from metallic ore and igneous rock, respectively. The production process includes a dish shaped wheel and wheel centrifuge process. It produces 3.5 to 7 average diameter discontinuous fibres whose size may range well into the respirable range. Mineral wool can be manufactured with or without binder, depending on end-use applications.

Refractory ceramic fibre is manufactured through a wheel centrifuge or steam jet fibrization process using melted kaolin clay, alumina/silica, or alumina/silica/zirconia. Average fibre diameters range from 1 to 5 . When heated to temperatures above 1,000 , refractory ceramic fibres can undergo conversion to cristobalite (a crystalline silica).

MMVFs with different fibre diameters and chemical composition are used in over 35,000 applications. Glass wool is used in residential and commercial acoustical and thermal insulation applications, as well as in air handling systems. Continuous glass filament is used in fabrics and as reinforcing agents in plastics such as are employed in automobile parts. Special-purpose glass fibre is used in specialty applications, for instance in aircraft, that require high heat and acoustical insulation properties. Rock and slag wool without binder is used as blown insulation and in ceiling tiles. Rock and slag wool with a phenolic resin binder is used in insulation materials, such as insulation blankets and batts. Refractory ceramic fibre constitutes 1 to 2% of the worldwide production of MMVF. Refractory ceramic fibre is used in specialized high-temperature industrial applications, such as furnaces and kilns. Glass wool, continuous glass filament and mineral wool are manufactured in the greatest amounts.

MMVFs are thought to have less potential than naturally occurring fibrous silicates (such as asbestos) for producing adverse health effects because of their non-crystalline state and their propensity to fracture into shorter fibres. Existing data suggests that the most commonly utilized MMVF, glass wool, has the lowest risk of producing adverse health effects, followed by rock and slag wool, and then both special-purpose glass fibre with increased durability and refractory ceramic fibre. Special-purpose glass fibre and refractory ceramic fibre have the greatest potential for existing as respirable-sized fibres as they are generally less than 3 in diameter. Special-purpose glass fibre (with increased concentration of stabilizers such as ) and refractory ceramic fibre are also durable in physiologic fluids. Continuous glass filaments are non-respirable in size and therefore do not represent a potential pulmonary health risk.

Available health data is gathered from inhalation studies in animals and morbidity and mortality studies of workers involved with MMVF manufacturing. Inhalation studies involving exposure of rats to two commercial glass wool insulation materials averaging 1 in diameter and 20 in length revealed a mild pulmonary cellular response which partly reversed following discontinuation of exposure. Similar findings resulted from an animal inhalation study of a type of slag wool. Minimal fibrosis has been demonstrated with animal inhalation exposure to rock wool. Refractory ceramic fibre inhalation studies resulted in lung cancer, mesothelioma and pleural and pulmonary fibrosis in rats and in mesothelioma and pleural and pulmonary fibrosis in hamsters at a maximum tolerated dose of 250 f/ml. At 75 f/ml and 120 f/ml, one mesothelioma and minimal fibrosis was demonstrated in rats, and at 25 f/ml, there was a pulmonary cellular response (Bunn et al. 1993).

Skin, eye, and upper and lower respiratory tract irritation can occur and depends on exposure levels and job duties. Skin irritation has been the most common health effect noted and can cause up to 5% of new MMVF manufacturing plant workers to leave their employment within a few weeks. It is caused by mechanical trauma to the skin from fibres greater than 4 to 5 in diameter. It can be prevented with appropriate environmental control measures including avoiding direct skin contact with the fibres, wearing loose fitting, long-sleeved clothing, and washing work clothing separately. Upper and lower respiratory symptoms can occur in unusually dusty situations, particularly in MMVF product fabrication and end-use applications and in residential settings when MMVFs are not handled, installed or repaired correctly.

Studies of respiratory morbidity, as measured by symptoms, chest radiographs and pulmonary function tests among manufacturing plant workers generally have not found any adverse effects. However, an ongoing study of refractory ceramic fibre manufacturing plant workers has revealed an increased prevalence of pleural plaques (Lemasters et al. 1994). Studies in secondary production workers and end-users of MMVF are limited and have been hampered by the likelihood of the confounding factor of previous asbestos exposures.

Mortality studies of workers in glass fibre and mineral wool manufacturing plants are continuing in Europe and the United States. The data from the study in Europe revealed an overall increase in lung cancer mortality based upon national, but not local, mortality rates. There was an increasing trend of lung cancer in the glass and mineral wool cohorts with time since first employment but not with duration of employment. Using local mortality rates, there was an increase in lung cancer mortality for the earliest phase of mineral wool production (Simonato, Fletcher and Cherrie 1987; Boffetta et al. 1992). The data from the study in the United States demonstrated a statistically significant increased risk of respiratory cancer but failed to find an association between the development of cancer and various fibre exposure indices (Marsh et al. 1990). This is in accord with other case-control studies of slag wool and glass fibre manufacturing plant workers which have revealed an increased risk of lung cancer associated with cigarette smoking but not to the extent of MMVF exposure (Wong, Foliart and Trent 1991; Chiazze, Watkins and Fryar 1992). A mortality study of continuous glass filament manufacturing workers did not reveal an increased risk of mortality (Shannon et al. 1990). A mortality study involving refractory ceramic fibre workers is under way in the United States. Mortality studies of workers involved with product fabrication and end-users of MMVF are very limited.

In 1987, the International Agency for Research on Cancer (IARC) classified glass wool, rock wool, slag wool, and ceramic fibres as possible human carcinogens (group 2B). Ongoing animal studies and morbidity and mortality studies of workers involved with MMVF will help to further define any potential human health risk. Based on available data, the health risk from exposure to MMVF is substantially lower than what has been associated with asbestos exposure both from a morbidity and mortality perspective. The vast majority of the human studies, however, are from MMVF manufacturing facilities where exposure levels have generally been maintained below a 0.5 to 1 f/ml level over an eight-hour work day. The lack of morbidity and mortality data on secondary and end-users of MMVF makes it prudent to control respirable fibre exposure at or below these levels through environmental control measures, work practices, worker training and respiratory protection programmes. This is especially applicable with exposure to durable refractory ceramic and special purpose glass MMVF and any other type of respirable man-made fibre that is durable in biological media and that can therefore be deposited and retained in the pulmonary parenchyma.

Ref:-http://www.ilo.org/safework_bookshelf/english?content&nd=857170112

Needle Punching Technology


Abstract:

Needle punching is the oldest method of producing nonwoven products. The first needle punching loom in U.S. was made by James Hunter machine co. in 1948. Then in 1957, James Hunter produced the first high speed needle loom, the Hunter model 8 which is still used today.

The needle punching system is used to bond dry laid and spun laid webs. The needle punched fabrics are produced when barbed needles are pushed through a fibrous web forcing some fibers through the web, where they remain when the needles are withdrawn.If sufficient fibers are suitably displaced the web is converted into a fabric by the consolidating effect of these fibers plugs or tufts. This action occurs in needle punching occurs around 2000 times a minute.

Needle punched fabrics finds its applications as blankets, shoe linings, paper makers felts, coverings, heat and sound insulation, medical fabrics, filters and geotextiles.

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Essential Requirements of Fiber Forming Polymers


Both natural and man-made fibres are mainly composed of the compounds belonging to high polymers or macromolecules. Macromolecular structure is necessary for the production of materials of high mechanical strength and high melting point. The natural fibres are found to consist chain molecules of linear molecular type. Further, the chain molecules are oriented into the parallel bundles in the process of growth. Based on these investigations, it is assumed that polymers must satisfy the minimum requirements, if it is to serve as a fibre. These requirements are as mentioned follows:

· Flexibility

The polymer must be linear flexible macromolecule with a high degree of symmetry the effect of cross sectional diameter should be less than 15Å. The polymer should not contain any bulky side groups or chains.

· Molecular Mass

The polymer mass must have a comparatively high molecular mass. The average length of its molecular chain should be in order of 1000 Å or more.

· Configuration

The molecule must have the capacity to adopt an extended an extended configuration and state of mutual alignment.

· Crystallinity

A polymer should have at least a high degree of intermolecular cohesive power. This indicates that the molecular chains should have sufficient number of sites of attraction

· Orientation

A high degree of orientation of the molecules in the polymer is a pre-requisite for producing good tensile strength.