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

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.

Soy Fibers


Soybean protein fiber is a new type of textile material. It has been praised by industry expert as the Healthy and Comfortable Fiber of 21 Century.

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Properties of this fiber are excellent. It has many merits of natural fiber and chemical fiber: thinness, lightness, high strength (tenacity), good resistance to acid and alkali, excellent moisture-absorption and wet-transference etc.

It can be used to produce knitting fabric or weaving fabric which are suitable for underskirt and garment.

Wood Fibres


Lumber from eco-friendly managed forests in the Americas are processed through an electrolysis process which separates the Wood fiber from oil and sugar. The result is
100% pure and natural Wood Fiber which contain no additive and chemicals.

FEATURES OF WOOD-FIBERimage

Because Wood Fiber is an all natural material, Wood Fiber products contain many of the natural characteristics of Wood in nature.

SMOOTH AS SILK These silky Fibers are the finest we have seen in a long time. It looks and feels like silk but washes and wears like cotton!

STATIC-FREE Wood-Fiber products are static free because it is 100% pure fiber and contains no chemical impurities.

ECO-FRIENDLY/ DETERGENT FREE Made entirely from the wood of sustainably harvested forests

Wood-Fiber is an eco-friendly alternative to the cotton industry. Using a process that continuously recycles 99.6% of the bleach-free solvent and the water used to make this fiber makes this product Eco-friendly and Nature Loving.

Wood Fiber are so silky smooth that dusts just falls off its surface. Detergent is not required and not recommended to clean it. Just gently rinse/ machine wash and tumble dry. Easiest cleaning instructions ever.image

ALLERGEN-FREE & DERMATOLOGICAL FRIENDLY Did you know that your bedding/towels may behosting millions of dust mites/allergen? If you suffer from burning eyes, a runny nose, and morning headaches you may have these tiny creatures and the allergen in their feces invading your bathroom. The allergen thrives in warm moist environments such as mattresses, pillows, face/bath towels and causes allergic reactions when inhaled. What is an Allergic ? An Allergy is your body’s reaction to certain substances. Different people have different tolerance towards the allergens. For allergic people only a small amount of allergens can cause the various symptoms above.Wood fiber products are 100% pure fibers without the sugar or oil. As a result bacterias do not multiply in Wood Fiber products. Together with the fact that Wood Fiber is all natural it is dermatologically friendly and suitable for allergy prone people.

SMELL-FREE Wood Fiber products are Smell resistant because it is resistant to smell causing bacterias.

HIGHLY ABSORBANT Wood-Fiber absorbs moisture, water, sweat and oil better than cotton. Products made from Wood Fiber such as socks are extremely breathable and does not trap moisture in the feet. This prevents many foot related diseases
and smell.

Lyocell Fibers


Since 1998 the Lyocell process has been used in Austria and the special feature of this process is the solution of the pulp which is in an organic solvent (NMMO =  methylmorpholine- N-oxide), instead of CS2/NaOH, which has the effect of eliminating the odorous and noxious emission of sulphurous gases. The properties of the products from this Lyocell process are different to the standard viscose fibre, and therefore this process should not be regarded as an environmentally compatible alternative to the viscose process.

The core part of the Lyocell process is the direct dissolution of cellulose through NMMO (Nmethyl-morpholine-n-oxide). The solvent, which is 100 % biodegradable, is able to dissolve cellulose physically without any chemical pretreatment. Therefore, the chopped pulp is mixed with NMMO. Water is removed from the socalled ‘premix’ to form a solution, which is then filtrated and spun through spinnerets into an aqueous NMMO solution to make the filaments.

The wet filaments are cut and the staples run through several after-treatment sections. After washing out residual NMMO, spin finish is applied and the fibre is dried and packed.
Through a multistage cleaning process, more than 99.6 % of the solvent can be recovered. Also the water that is regained during the evaporation step is recycled back into the washing section of the fibre line. This leads to a low specific water demand and overall low environmental emission figures.
Generally, the process includes the following steps:
• dissolving
• spinning
• precipitating
• washing
• finishing
• drying

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Figure shows a simplified diagram of the Lyocell process.

The Burn Test to Identify Textile Fibers


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.

Synthetic Fibers

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.

 

PROCESS PARAMETER IN BLOW ROOM


With all harvesting methods, however, the cotton seed, together with the fibres, always gets into the ginning plant where it is broken up into trash and seed-coat fragments. This means that ginned cotton is always contaminated with trash and dust particles and that an intensive cleaning is only possible in the spinning mill.

Nep content increases drastically with mechanical harvesting, ginning and subsequent cleaning process. The reduction of the trash content which is necessary for improving cotton grade and apperance unfortunately results in a higher nep content level.

The basic purpose of  Blow room is to supply

  • small fibre tufts
  • clean fibre tufts
  • homogeneously blended tufts if more than one variety of fibre is used

to carding machine  without increasing  fibre rupture, fibre neps , broken seed particles and without removing more  good fibres.

The above is achieved by the following processes in the blowroom

  1. Pre opening
  2. pre cleaning
  3. mixing or blending
  4. fine opening
  5. dedusting

CLEANING EFFICIENCY:

Cleaning efficiency of the machine is the ratio of the trash removed  by the machine to that of  total trash fed to the machine, expressed as percentage

Cleaning efficiency % =(( trash in feed % – trash in del %) x 100) / (trash in feed%)

Following are the basic parameters  to be considered in Blowroom process.

  • no of opening machines
  • type of beater
  • type of beating
  • Beater speed
  • setting between feed roller and beater
  • production rate of individual machine
  • production rate of the entire line
  • thickness of the feed web
  • density of the feed web
  • fibre micronaire
  • size of the flocks in the feed
  • type of clothing  of the beater
  • point density of clothing
  • type of grid and grid settings
  • air flow through the grid
  • position of the machine in the sequence
  • amount of trash in the material
  • type of trash in the material
  • temp and relative humidity in the blow room department

PREOPENING:

Effective preopening results in smaller tuft sizes, thus creating a large surface area for easy  and efficient removal of trash particles by the fine openers.

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Fig:-BO-c bale opener

If MBO (Rieter) or  BO-c ( Trutzschler) type of machine is used as a first machine

  • the tuft size in the mixing should be as small as possible. Normally it should be less than 10 grams
  • since this machine does not take care of long term blending, mixing should be done properly to maintain the homogenous blending
  • the inclined lattice speed and the setting between inclined lattice and clearer roller decides the production of the machine
  • the setting between inclined lattice and clearer roller decides the quality of the tuft
  • if  the setting is too close, the tuft size will be small, but the neps in the cotton will be increased due to  repeated action of the  inclined lattice pins on cotton.
  • the clearance should be decided  first to confirm the quality, then inclined lattice speed can be decided according to the   production required
  • the setting of inclined lattice depends upon the fibre density, fibre micronaire and the tuft size fed. If smaller tuft is fed to the feeding conveyor, the fibre tufts will not be recycled many times, hence the neps will be less.
  • if the machine is with beater, it is advisable to use only disc type beater. Saw tooth and Pinned beaters should not be used in this machine, because the fibre  damage at this stage will be very high and heavier trash particles will be broken in to small pieces.
  • the beater  speed  should be around 500 to 800 rpm depending upon the rawmaterial. Coarser the fibre,  higher the speed
  • the setting between feed roller to beater should be around 4 to 7 mm
  • this machine is not meant to remove trash ,  hence the fibre loss should also be less
  • trash removal in this machine will result in breaking the seeds, which is very difficult to remove
  • It is easier to remove the bigger trash than the smaller trash, therefore enough care should be taken to avoid breaking the trash particles
  • this machine is  just to open the tufts into small sizes so that cleaning becomes easier in the next machines.
  • the fibre tuft size from this  machine should be  preferably around 100 to 200 milligrams.
  • If tuft size is  small, removing trash particles becomes easier , because of large surface area

Unifloc11

Fig:- Unifloc11

If Uniflco11(Rieter) or Blendomat BDT 019(Trutzschler) is used as a first machine

  • It helps to maintain the homogeneity of the long term blending
  • cotton is opened gently without recyling as it is done in manual bale openers
  • with the latest automatic bale opening machines,  the tuft size can be as small as 50 to 100 grams without  rupturing the fibres
  • the opening roller speed should be around 1500 to 1800 rpm.
  • the depth of penetration of the opening  should be as minimum as possible for better quality
  • It is better to use this machine with one mixing or maximum two mixing at  the same.
  • If the production per feeding machine is less than 150 kgs, then four mixings can be recommended
  • production rate of this machine depends upon the no of mixings working at the same time
  • production rate depends  upon opening roller depth, traverse speed and the fibre tuft density
  • in general , the machine parameters should be set in such a way that  maximum number of take-off points are available  per unit time.
  • with the latest machines (Rieter -Unifloc A11), around 60% of take-off points are more compared to earlier machines

PRECLEANING:

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Fig: Uniclean B12

Precleaning should be gentle. Since removing finer trash particles is difficult , seeds and bigger trash particles should not be broken. Finer trash particles require severe treatment in Fine openers. This will lead to fibre damage and more nep generation. Therefore, precleaning should be as gentle as possible and no compromise on this. If preopening and precleaning are done  properly,  consistency in trash removal by fine openers is assured. Dust removal should be started in this machine. Enough care should be taken remove dust  in this process.

Rieter’s Uniclean B11 and Trutzschler’s Axiflow or Maxiflow  are the machines which does this work

  • the fibre treatment in this machine is very gentle because  the fibres are not gripped by the feed roller during beating.  Fibre tufts treated by the pin beater when it is carried by air medium
  • all heavy trash particles fall down before it is broken
  • cleaning efficiency of this machine is very high in the blow room line
  • Mostly all heavy seeds( full seeds) fall in this machine without any problem
  • around 50 pascal suction pressure should be maintained in the waste chamber for better cleaning efficiency
  • beater speed, air velocity through the machine, grid bar setting and gap between grid bars will affect the cleaning efficiency
  • higher the cleaning efficiency,  higher the good fibre loss, higher the nep generaion and higher the fibre rupture
  • the optimum cleaning means maximum cleaning performance, minimum loss of good fibres, a high degree of fibre preservation and minimum nep generation
  • Rieter has a unique concept called “VARIOSET”. With this machine, selective trash removal is possible. Waste  amount can be changed in a range of 1:10.

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fig: from Rieter which shows , degree of cleaning, fibre loss, neps, fibre damage.

  • with normal machines like Monocylinder or axiflow, a lot of trials to be conducted to arrive at optimum beater speed, air velocity(fan speed), grid bar setting and grid bar gap.
  • in general the beater speed is around 750 and  minimum 50 Pascal suction pressure to be maintained in the suction chamber

BLENDING:

  • Barre or streakiness is due to uneven mixing of different cottons. Hence mixing technology is a decisive factor in spinning mill technology
  • bigger the differences of cotton parameters like fineness, color and staple length, the greater the importance of mixing
  • if the cotton has honeydew, the intensive mixing of the rawmaterial is a precondition  for an acceptable running behaviour  of the complete spinning mill

following  fig is given by trutzschler for different  mixing requirements

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standard               standar- plus              high                   high-end

  • Trutzschler’s tandem mixing concept is an  ultimate solution, if the mixing requirement is very high. This principle guarantees a maximum homogeneous of the mix

FIG.Tandem mixing concept from TRUTZSCHLER:

FINE CLEANING:

Fine cleaning is done with different types of machines. Some fine cleaners are with single opening rollers  and some are with multiple opening rollers.

  • If single roller cleaning  machines are used, depending upon the  amount and type of trash in the cotton, the number of fine cleaning points can be either one or two.
  • If the production  rate is lower than 250 kgs and the micronaire is less than 4.0, it is advisable to use single roller cleaning machines instead of multiple roller cleaning machine.
  • Saw tooth beaters can be used, if trash particles are more and the machine is not using suction and deflector blades. i.e beater and regular grid bar arrangements
  • Normal beater speeds with saw tooth beater depends upon the production rate,  fibre micronaire and trash content
TYPE OF COTTON COTTON MICRONAIRE PROUDCTION RATE kgs/hr BEATER SPEED rpm
more trash 3.5 to 4.0 200 to 300 kgs /hr 600 to 750
less trash 3.5 to 4.0 200 to 300 kgs/hr 600 to 750
more trash 4.0 to 4.5 200 to 300 kgs 700 to 850
less trash 4.0 to 4.5 350 to 500 kgs 1000 and above
  • the number of wire points depends on the production rate and trash.
  • setting between feed roller and beater depends on the production rate and micronaire.  The setting should be around 2 to 3 mm.  Wider setting always result  in higher rawmaterial faults, if carding does not take care.
  • closer the setting between beater and mote knives, higher the waste collected. It is advisable to keep around 3 mm.
  • If it is a Trutzschler blowroom line, it is better to use  CVT1 ( single opening roller machine) if  roller ginned cotton  is used.
  • CVT3  or CVT4 machines with 3 or 4 opening rollers can be used for saw ginned cotton.
  • The cleaning points in CVT1, CVT3, CVT4 etc consists of opening roller, deflector blades, mote knives and suction hood. Trash particles released due to centrifugal forces are  separated at the mote knives and continuously taken away by the  suction. This gives better cleaning

FIG: trash removal concept in CVT cleaners:

  • suction plays a major role in these machines. If suction  is not consistent , the performance will be affected badly.  Very high suction will result in more white fibre loss and less suction will result in low cleaning efficiency.
  • The minimum recommended pressure in the waste chamber (P2) is 700 Pascal’s. It can be upto 1000 Pascal’s.
  • material suction (P1) should be around 500 Pascal’s
  • Whenever the suction pressure is changed, the deflector blade settings should be  checked
  • Deflector blade setting can not be same for all the three rollers or four rollers. The setting for deflector blades in the panel looks like this 3, 12, 30 for 1st, 2nd and 3rd deflector blades.
  • The deflector blade setting should be done in such a way that  the setting should be opened till the fibres start slipping on the deflector blade.
  • wider the deflector blade setting, higher the waste. If the setting is too wide, white fibre loss will be very high.
  • for saw ginned cottons, the above concepts helps a lot because of constant suction concentrated directly at the moteknives, ensures much removal of dust from the cotton.

DEDUSTING:

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Fig: Dustex

Apart from opening cleaning of rawmaterial, dedusting is the very important process in blowroom process.

  • normally dedusting  starts with precleaning
  • it is always better to have a separate machine like DUSTEX of TRUTZSCHLER  for effective dedusting
  • dedusting keeps the atmospheric air clean
  • dedusting in machines like unimix , ERM of Rieter is  good
  • stationary dedusting condensers can be used for this purpose
  • in exhausts of  unimix , condensers , ERM etc, positive pressure of 100 pascal should be maintained. Exhaust fan speed and volume should be accordingly selected
  • DUSTEX should be installed before feeding to the cards, because better the fibre  opening better the dedusting
  • fine openers like ERM, CVT cleaners also help in dedusting
  • It is always better to feed the material through condenser for a feeding machine of cards.  Because condenser continuously removes the dust from a small quantity of fibres  and the material  fed to the feeding machine is opened to some extent.
  • Since material is not opened well in Unimix, the dedusting may not be very effective, even though  dedusting concept in Unimix is very good
  • for rotor spinning dedusting is very important. It is better to use a machine like DUSTEX  after the fine opener.

OTHERS:

  • setting between feed rollers is different for different types. It should be according to the standard specified by the manufacturer.  For Unimix it should be around 1 mm.
  • it is advisable to run the fans at optimum speeds.  Higher fan speeds will increase the material velocity and will create  turbulence  in the bends.This will result in curly fibres which will lead to entanglements.
  • If the feeding to cards  is not with CONTI -FEED, the efficiency of the feeding machine should be minimum 90 % and can not be more than 95%.
  • if the cards are fed by CONTI-FEED system,  the feed roller speed variation should not be more than 10%.  If the variation is more, then the variation in tuft size also will be more. Hence the quality will not be uniform
  • If two feeding machines feed to  10 cards and the no of cards can be changed according the requirement, then frequent changes will affect the tuft size which will affect the quality, if the line is fixed with CONTI-FEED.
  • if contifeed system is tuned properly and there are no machine stoppages, continuous material flow will  result in better opening and even feeding to the cards
  • If the production rate per line is high, the reserve chamber  for  the feeding machine should be big enough to avoid long term feed variations.
  • it is advisable to reduce the number of fans  in the line.
  • fan speeds, layout of machines should be selected in such a way that material choking in the pipe line, beater jamming etc will not happen.  This will lead to quality problems
  • all blowroom machines should work with maximum efficiency. The feed roller speeds  should be selected in such a way that  it works atleast 90% of the running time of the next machine.
  • blow room stoppages will always affect the sliver quality both in terms of linear density and  tuft size. Blow room stoppages  should be nil in a mill
  • heavy particles like metal particles, stones should be removed using heavy particle removers , double magnets etc, before they damage  the opening rollers and other machine parts.
  • Number of cleaning  points are decided based on  type of ginning (whether roller ginned or saw ginned), the amount of trash, and the number of trash particles and the type of trash particles.
  • machinery selection should be based on the type of cotton and production requirement. If the production requirement of a blowroom line is less than 200 kgs,  CVT-4 cleaner can not be  recommended, instead CVT-1 can be used.
  • Since blow room requires more space and power, it is better to make use of the maximum production capacity of the machines
  • material level in the storage chambers  should be full  and it should never be less than 1/4 th level.
  • grid bars should be inspected periodically, damaged grid bars  should be replaced.
  • grid bars in  the front rows can be replaced earlier
  • if the cotton is too sticky, the deposits on the machine parts  should be cleaned atleast once in a week, before it obstruct the movement of the fibre
  • fibre rupture should be checked for each opening point.  2.5 % span length should not drop by more than 3% . If the uniformity ratio drops by more than 3%, then  it  is considered that there is fibre rupture.
  • high fan speed, which will result in high velocity of air will increase neps in cotton
  • nep is increased in the blowroom process.  The increase should not be more than 100%.
  • the nep increase in each opening machine should be checked  with different beater speeds and settings, and the optimum  parameters  should be selected. But please remember that everything should be based on  yarn quality checking.  e.g. if nep increase in blow room is  more and the beater speed or feed roller setting is changed, the tuft size will become more. This may result in bad carding quality. Sometimes if the neps are slightly more and the  fibre is well opened, the neps can be removed by cards and combers and the yarn quality may be better.  Therefore all trials should be done upto yarn stage.
  • No of neps and trash particles  after different processes is given below.(an approximate value)
  • Blow room machinery lay out should be desined in such a way that there should be minimum number of bends, and there should not be sharp bends  to avoid fibre entanglements.
  • fibre travelling  surface should be smooth and clean
  • temperature should be around 30 degrees and the humidity is around 55 to 60%.

A best blowroom can be achieved by selecting the following machines:

1.RIETER UNIFLOC- A11 ( pre opening)

2.RIETER UNICLEAN B11 (  pre cleaning)

3.TRUTZSCHLER MPM 6 + MPM6 ( two mixers for blending)

4.TRUTZSCHLER CVT-1 ( for  roller ginned cotton) CVT-3 ( for saw ginned)

5.CONTAMINATION DETECTOR from either BARCO OR JOSSI

6.TRUTZSCHLER  DUSTEX-DX ( for dedusting)

7.TRUTZSCHLER CONTI-FEED and others

But enough care should be taken to synchronise the machines for better performance  , and to run the line without any electrical system breakdowns.

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MIXING(COTTON)


Once Valledupar's main economic produce; Cotton
Image via Wikipedia

Cotton is a hygroscopic material , hence it easily adopts to the atmospheric airconditions. Air temperature inside the mixing and blowroom area should be more than 25 degree centigrade and the relative humidity(RH%) should be around 45 to 60 %, because high moisture in the fibre leads to poor cleaning and dryness in the  fibre leads to fibre damages which ultimately reduces the spinnability of cotton.

Cotton is a natural fibre. The following properties vary very much between bales (between fibres) fibre micronaire fibre length fibre strength fibre color fibre maturity   Out of these , fibre micronaire, color, maturity and the origin of growth results in dye absorption variation.
There fore it is a good practice to check the maturity , color and micronaire of all the bales and to maintain the following to avoid dye pick up variation and barre in the finished fabric.

BALE MANAGEMENT :

Bale Management

In a particular lot

  • Micronaire range of the cotton bales   used should be same for all the mixings of a lot
  • Micronaire average of the cotton bales used should be same for all the mixings of a lot
  • Range of color of cotton bales used should be same for all the mixings of a lot
  • Average of color of cotton bales used should be same for all the mixings of a lot
  • Range of matutrity coefficient of cotton bales used should be same for all mixings of a lot
  • Average of maturity coefficient of cotton bales used should be same for all mixings of a lot

Please note, In practice people do not consider maturity coefficient since Micronaire variation and maturity variation are related to each other for a particular cotton.

It the cotton received is from different ginners, it is better to maintain the percentage of cotton from different ginners throught the lot, even though the type of cotton is same.

It is not advisable to mix the yarn made of out of two different shipments  of same cotton. For example , the first shipment of west african cotton is in january and the second shipment is in march, it is not advisable to mix the yarn made out of these two different shipments.  If there is no shadevariation after dyeing, then it can be mixed.

According to me, stack mixing is the best way of doing the mixing compared to using automatic bale openers which picks up the material from 40 to 70 bales depending on the length of the machine and bale size, provided  stack mixing is done perfectly. Improper stack mixing will lead to BARRE or SHADE VARIATION  problem.  Stack mixing with Bale opener takes care of short term blending and two mixers in series takes care of long term blending.

why?

  • Tuft sizes can be as low as 10 grams and it is the best way of opening the material(nep creation will be less, care has to be taken to reduce recyling in the inclined lattice)
  • contaminations can be removed before mixing is made
  • The raw material  gets   acclamatised to the required temp and R.H.%, since it is allowed to stay in the room for more than 24 hours and the fibre is opened , the fibre gets conditioned well.

Disadvantages:

  • more labour is required
  • more space is required
  • mixing may not be 100% homogeneous( can be overcome by installing double mixers)

If automatic bale opening machine is used the bales should be arranged as follows

let us assume that there are five different micronaires and five different colors in the mixing, 50 bales are used in the mxing. 5 to 10 groups should be made by grouping the bales in a mixing so that each group will have average micronaire and average color as that of the overall mixing. The position of a bale for micronaire and color should be fixed for the group and it should repeat in the same order for all the groups

It is always advisable to use a mixing with very low Micronaire range.Preferably .6 to 1.0 . Because

  • It is easy to optimise the process parameters in blow room and cards
  • drafting faults will be less
  • dyed cloth appearance will be better because of uniform dye pickup etc

It is advisable to use single cotton in a mixing , provided the length, strength micronaire ,maturity coefficient and trash content of the cotton will be suitable for producing the required counts.  Automatic bale opener is a must if more than two cottons are used in the mixing, to avoid BARRE or SHADE VARIATION problem.

It is better to avoid  using the following cottons

  • cottons with inseparable trash (very small size), even though the trash % is less
  • sticky cotton (with honey dew or sugar)
  • cotton with low maturity co-efficient

Stickiness of cotton consists of two major causes. Honeydew from Whiteflies and aphids and high level of natural plant sugars. The problems with the randomly distributed honey dew contamination often results in  costly production interruptions and requires immediate action often as severe as discontinuing the use of contaminated cottons.An effective way to control cotton   stickiness in processing is to blend sticky and non-sticky cotton.  Sticky cotton percentage should be less than 25%.

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FIBRE TESTING


IMPORTANCE OF RAWMATERIAL IN YARN MANUFACTURING:

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

  • fibre length
  • fineness
  • strength
  • maturity
  • Rigidity
  • fibre friction
  • structural features

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.

FIBRE LENGTH:
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

  • mean length
  • upper quartile
  • effective length
  • Modal length
  • 2.5% span length
  • 50% span length

Mean length:
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.

Effective length:
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.

Modal 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)

where,
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

  1. Co-efficient of variation of length (by weight or number)
  2. irregularity percentage
  3. Dispersion percentage and percentage of short fibres
  4. Uniformity ratio

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
  • Baer sorter
  • A.N. Stapling apparatus
  • Fibrograph

uniformity ration = (50% span length / 2.5% span length) x 100
uniformity index = (mean length / upper half mean length) x 100

SHORT FIBRES:
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
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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:
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.
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FIBRE FINENESS:
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
  • air-flow method
  • 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:

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

  1. Normal : rod like fibres with no convolution and no continuous lumen are classed as “normal”
  2. Dead : convoluted fibres with wall thickness one-fifth or less of the maximum ribbon width are classed as “Dead”
  3. 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
where,
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

  1. Mature : (Lumen width “L”)/(wall thickness”W”) is less than 1
  2. Half mature : (Lumen width “L”)/(wall thickness “W”) is less than 2 and more than 1
  3. 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”

Maturity Coefficient = (M + 0.6H + 0.4 I)/100 Where,

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.

FIBRE STRENGTH:
The different measures available for reporting fibre strength are

  1. breaking strength
  2. tensile strength and
  3. 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 factorsclip_image004

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.

 

FIBRE ELONGATION:
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.

FIBRE RIGIDITY:

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.

TRASH CONTENT:
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

  1. spinning limit
  2. yarn strength
  3. yarn evenness
  4. yarn fullness
  5. drape of the fabric
  6. lustre
  7. handle
  8. productivity

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,

  1. loss of yarn strength
  2. neppiness
  3. high proportion of short fibres
  4. varying dyeability
  5. processing difficulties at the card and blowroom

Fibre length is one among the most important characteristics. It influnces

  1. spinning limit
  2. yarn strength
  3. handle of the product
  4. lustre of the product
  5. yarn hairiness
  6. productivity

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

  1. spinning limit
  2. yarn strength
  3. handle of the product
  4. lustre of the product
  5. yarn hairiness
  6. productivity

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
where,
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
  • pathogens
  • 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.

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Textile Fibers


Fibers -units of matter characterized by flexibility, fineness and high ratio of length to thickness. Other necessary attribute for textiles are adequate strength and resistance to conditions encountered during wears, as well as absence of undesirable colour, and finally the property of dye ability.

In generally, the steps in the manufacture of fabrics from raw material to finished goods are as follows:
· Fibre, which is either spun (or twisted) into yarn or else directly compressed into fabric.
· Yarn, which is woven, knitted, or otherwise made into fabric.
· Fabric, which by various dyeing and finishing processed becomes consumers goods.

  • Classification of textile fibers 

According to the nature and origin different textile fibers can be classified as follows:

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Natural fibers include those produced by plants, animals, and geological processes. They are biodegradable over time. They can be classified according to their origin:

  • Vegetable fibers are generally based on arrangements of cellulose, often with lignin: examples include cotton, hemp, jute, flax, ramie, and sisal.
  • Animal fibers consist largely of particular proteins. Instances are spider silk, sinew, catgut, wool and hair such as cashmere, mohair and angora, fur such as sheepskin, rabbit, mink, fox, beaver, etc.
  • Mineral fibers comprise asbestos. Asbestos is the only naturally occurring long mineral fiber. Short, fiber-like minerals include wollastinite, attapulgite and halloysite
  • Manmade fibers
Manmade fibers include those produced by reacting chemicals. They are non biodegradable. They can be classified according to their origin there are two sorts of man-made fibers: Organic and Inorganic.(a). Organic fibersSyntheticor man-made fibers generally come from synthetic materials such as petrochemicals.

  1.  Polymer fibers

Polymer fibers are a subset of man-made fibers, which are based on synthetic chemicals (often from petrochemical sources) rather than arising from natural materials by a purely physical process. Such fibers are made from:
o polyamide nylon,

o PET or PBT polyester

o phenol-formaldehyde (PF)

o polyvinyl alcohol fiber (PVOH)

o polyvinyl chloride fiber (PVC)

o polyolefins (PP and PE)

o acrylic polymers, pure polyacrylonitrile PAN fibers are used to make carbon fiber by roasting them in a low oxygen environment. Traditional acrylic fiber is used more often as a synthetic replacement for wool. Carbon fibers and PF fibers are noted as two resin-based fibers that are not thermoplastic, most others can be melted.

o Aromatic polyamids (aramids) such as Twaron, Kevlar and Nomex thermally degrade at high temperatures and do not melt. These fibers have strong bonding between polymer chains

o polyethylene (PE), eventually with extremely long chains / HMPE (e.g. Dyneema or Spectra).

o Elastomers can even be used, e.g. spandex although urethane fibers are starting to replace spandex technology.

o polyurethane fiber

o Co-extruded fibers have two distinct polymers forming the fiber, usually as a core-sheath or side-by-side. Coated fibers exist such
as nickel-coated to provide static elimination, silver-coated to provide anti-bacterial properties and aluminum-coated to provide RF deflection for radar chaff. Radar chaff is actually a spool of continuous glass tow that has been aluminum coated. An aircraft-mounted high speed cutter chops it up as it spews from a moving aircraft to confuse radar signals.
2. Regunrated fibers

Regunrated fibers are the fibers produced from natural cellulose, including rayon, modal, and the more recently developed Lyocell. Cellulose-based fibers are of two types, regenerated or pure cellulose such as from the cupro-ammonium process and modified or derivitized cellulose such as the cellulose acetates.

(b). Inorganic fibers

  • Mineral fibers

o Glass fiber, made from specific glass, and optical fiber, made from purified natural quartz, are also man-made fibers that come from natural raw materials.

o Metallic fibers can be drawn from ductile metals such as copper, gold or silver and extruded or deposited from more brittle ones, such as nickel, aluminum or iron.

o Carbon fibers are often based on carbonised polymers, but the end product is pure carbon.

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