Technical Textiles:

Technical Textiles:

A technical textile is a textile that has been developed to meet the exacting specified high-performance requirements of a particular end-use other than conventional clothing and furnishings. In many cases, specially developed technical yarns are employed to support and reinforce the fabric properties .

Technical Textiles

Markets for Technical Textiles:
According to Professor S. Anand of Bolton Institute, England, technical textiles account for approximately 21 per cent of all textiles. The main markets are: traditional industrial fabrics, for example, canvas, tents, etc. (43%); transportation and automotive (23%); leisure (12%); geotextiles (10%); medical textiles (10%); and protective apparel (2%). Two-thirds of automotive materials go into ‘interior trim’ for seat covers, roof and door liners, and carpets, where woven fabrics still dominate. Other uses include tyres, air bags and filters. Although non-woven and woven fabrics account for the majority of technical textiles, warp knitted and, to a lesser extent, weft knitted structures have captured some special end-use markets.These are particularly where certain properties such as drapability, mouldability, knitting to shape, open-work, extensibility, strength, lightness of weight and cost are at a premium and can be tailored to requirements.

End-uses for Technical Textiles:
Possible specific applications for technical textiles are as follows:

1. Geotextiles – Drainage, filter, and membrane material, road and tunnel reinforcement,erosion protection.
2. Tarpaulins, coverings – Air-inflated structures, tarpaulins, roof coverings, temperature-resistant sails, back-lit advertising signs.
3. Safety textiles – Heat and flame-resistant protective clothing for civil and military purposes, fluorescent safety clothing, inflatable life rafts, bullet-proof vests, helmets, sun protection blinds, radiation protection, parachutes, oil trap mats.(Bullet-proof vest fabric can be knitted on a Karl Mayer E 18 raschel machine with a magazine weft insertion and three guide bars. The front bar is threaded with 80 dtex polyester guide bars and laps 1–0/2–3. The other two bars ‘interweave’ with the front bar using the evasion technique 00/11/00/22 and 00/22/00/11 (Chapter 27).These, together with the weft insertion mechanism, are threaded with 840 dtex aramid.
4. Industrial Textiles – Filter fabrics, conveyor belts, adhesive tapes.
5. Medical Textiles – Plasters, tapes, gauze, artificial arteries, bandages, dialysisfilters, elastic net bandages, blankets and covers. (Small-diameter, single cylinder machines are ideal for weft knitting tubular stretch bandages from cotton yarn with inlaid elastic yarn .
6. Composites – Composites for buildings, aerospace, automobiles, boats.
7. Active Sportswear – Clothing and equipment.
8. Nets – Fabrics for construction, agriculture, for safety, weather and pest protection, blinds, fences, storage nets, sacks, fish nets .

Textile Fibers and Classification of 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:

• Natural fibers

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.

Preparatory Process of Cellulosic Fiber

1. Describe scouring of cotton:

• Other natural fibers such as cotton and silk contain impurities that are easier to remove than those that occur in wool, though it is still necessary to scour them to ensure uniform bleaching, dyeing and finishing as well as to enhance their wettability and absorbency. 

• Cotton may contain from 4-12% by weight impurities in the form of the waxes , proteins, pectins, ash and miscellaneous substances such as pigments, hemicelluloses and reducing sugars. The hydrophobic nature of the waxes makes their removal difficult relative to the removal of other impurities. 

• Effective removal of impurities in cotton, particularly waxes, is achieved by boiling in 3-6 % sodium hydroxide or less frequently in dilute solutions of calcium hydroxide (lime) or sodium carbonate (soda ash). 

• The proper choice of textile auxiliaries in the alkaline bath is essential for good scouring. These include sequestering or chelating agents such as ethylenediaminetetraacetic acid (EDTA) to solublize insoluble inorganic substances present in hard water and surfactants such as the anionic sodium lauryl sulfate that serves as a detergent, dispersing agent, and emulsifying agent to remove unsaponified waxes. 

• Synthetic fibers are scoured with milder formulations such as soap or detergents containing comparatively small amounts of alkali. Cotton/synthetic fiber blends (such as cotton/polyester) require alkaline concentrations and conditions intermediate between those of all cotton and all synthetics for effective scouring. 

• Techniques and machinery for scouring different fiber types and fabrics have evolved from batch processes utilizing various types of open and pressure kiers to continuous processes in which fabrics are passed through roller steamers under pressure. Continuous scouring processes are similar to those used to continuously bleach fabrics.

A. Open or pressure kiers are stainless steel containers that circulate the alkali at elevated temperatures from 100 degrees C at atmospheric pressure to over 130 degrees C at reduced pressure.

• The alkaline solution is injected or introduced from the bottom of the kier and air removed by displacement by steam.
• After scouring for sufficient time, the fabric is rinsed by continually introducing hot water to dilute the alkali in the bath.

B. In semi continuous process where the fabric is scoured in rope or open width form

• A device called a saturator serves as scouring bath. The fabric is then rapidly preheated by steam and passed into a J-box storage, chamber or alternatively, the fabric is directly heated in the storage chamber
• After storage in the J-box the fabric is then washed with hot water to remove alkali and impurities

C. Continuous processes that rebatch the fabric or utilize roller steamers under pressure, reduce the dwell time of the fabric considerably and allow for higher proceeding speeds.

D. Solvent scouring of cotton and cotton/polyester blends has been employed, with trichloroethylene frequently used as the scouring solvent.

• However, only waxes are removed by this method and some form of aqueous alkaline scouring is still required.
• When the only impurities in fabrics are oils incorporated to assist in knitting or weaving, trichlorotrifluoroethane is claimed to be very advantageous in solvent scouring.

2. Process and effects of mercerization of cotton:

• Mercerization is one of the most important finishing processes of cotton with a strong caustic alkaline solution in order to improve the lustre, hand and other properties. 

• It imports gloss to the fiber, increases its hygroscopicity, strength and improves its dye affinity. 

• Mercerizing improves the reactions with a variety of chemicals and elongation of the fibers and also improves the stability of form. Mercerizing process consists in treatment of cellulosic materials with concentrated solutions of caustic soda at a temperature of 15 to 18°C. 

• Mercerized cellulose is hydrated cellulose, i.e., a product which from the chemical point of view is identical to the original cellulose, but differing from it in physical properties. This method was patented in 1850 by the English calico printer John Mercer and hence forth this process has been called as mercerization.

Cellulose Mercerizing Process:
Stages at which cellulose mercerization is possible are- On greige goods, After desizing, After desizing and scouring, After bleaching, After dyeing Usually sodium hydroxide concentration varies from 20% - 30%.

The process, done in a continuous way, involves four subsequent steps:

1. Impregnation of the material in relaxed state, cold caustic solution of required strength and wettability.
2. Stretching while the material is still impregnated in the caustic solution.
3. Washing off the caustic soda from the material while keeping the material still in the stretch state.
4. Neutralizing with acids and rinsing.

Physio-chemical changes during mercerization:
Under the action of concentrated alkaline solutions chemical, physico-chemical and structural modifications of cellulose take place. Native cellulose (Cellulose I) forms alkali cellulose I with concentrated sodium hydroxide. On washing and neutralization cellulose II is formed.

As a result of the penetration of the alkali into the lattice, internal hydrogen bonds are broken and in Cellulose II the number of available hydroxyl groups (-OH) is increased by around 25%. The treatment with alkali and subsequent washing may be performed so that the fabric or yarn may either freely contract or they may be held under tension. In both cases the mercerized cotton has an increased affinity for both reactive and direct cotton dyes, water and an increased strength. Cotton yarn or fabric mercerized without tension contracts, but if held under tension it retains its original dimensions and the lustre is increased. Major changes during Mercerization can be divided into three levels.

Effects of Mercerization

1. Mercerization increases fibre lustre:
C1oncentrated solutions of caustic soda cause considerable swelling of cotton fibre. The changes in cellulose physical properties are being irreversible. When the fibre swells, its volume undergoes considerable changes; at maximum water absorption, the cross section of cotton fibre is increased by 40 to 50% with inconsiderable increase in length (about 1 to 2%). Swelling of fibre changes its cross section from squashed circular pipe shape to an oval shaped.

Lustre of a fibre is due to the regular reflection of light incident on the fibre surface, which depends on the cross-section of the fibre. If the fibres are placed under a tension or stretched position in the swollen state and then washed to reduce the caustic concentration below a particular limit, then there is an increase in the lustre of the fibre.

1. Before mercerizing
2-5. Swelling stage with 18% sodium hydroxide
6. Washing stage after mercerization
7. Final stage

The main factors influencing the factors of selling are temperature of treatment, the concentration of the alkali in the solution and additions made to the solution.

2. Mercerization increases tensile strength:
When cotton fibre, yarn or cloth is mercerized, its strength increased by 10-50%. The tensile strength increase depends on various factors, such as temperature of impregnation, concentration of alkali in impregnating bath, construction of yarn etc. Lower the temperature of mercerization, greater is the tensile strength (breaking load of the yarn). Increase of alkali concentration up to 520 Tw, tensile strength increased gradually and further increase of alkali concentration decrease the tensile strength. For long staple fibre yarn, greater the twist, greater is the tensile strength of mercerized material.

3. Ecological impact and recovery of Sodium hydroxide: The main ecological impact in mercerizing is the high concentrated residual lye. Treating cotton materials with strong sodium hydroxide and washing it off gives a large volume of dilute NaOH solution, which cannot be discharged into the drain for economy and pollution points of view. By suitable means it is possible to recover/reuse 90-95% of NaOH used in mercerizing. The alkaline load of waste water is reduced drastically and acid required for waste water neutralisation is minimised. Wash liquor may be used for the preparation of sodium hypochlorite solution (for use in bleaching). NaOH from the impregnated fabric may be recovered by washing using counter-current principle and by using steam in a recuperator.

4. Compare the process of enzymatic and oxidative desizing.
Most earlier desizing utilized enzymes such as alpha and beta amylase at temperatures around 40-70 degrees C and pH values of 4.6-7.0 to remove starch sizes from cellulosics or by steeping the yarns in dilute solutions of acid.

Enzymatic desizing ·         It is effective ,though limited to the removal of natural polymers, such as starches and cellulose derivatives because an enzyme will only be active or affect a particular substrate ·         It consists of three main steps: application of the enzyme, digestion of the starch and removal of the digestion products. The common components of an enzymatic desizing bath are as follows: -          Amylase enzyme -          pH stabilizer -           Chelating agent -          Salt -          Surfactant, and -          Optical brightener  ·         Advantages -          No damage to the fibre -          No usage of aggressive chemicals -          Wide variety of application processes, and -          High biodegradability ·         Disadvantages -          Lower additional cleaning effect towards other impurities, no effect on certain starches (e.g. tapioca starch) and possible loss of effectiveness through enzyme poisons.

Oxidative desizing ·         It may be employed to remove both natural and synthetic polymers ·         Oxidative desizing can be effectede  by hydrogen peroxide, chlorites, hypochlorites, bromites, perborates or persulphates. ·         Two important oxidative desizing processes are:  the cold pad-batch process based on hydrogen peroxide with or without the addition of persulphate; and the oxidative pad-steam alkaline cracking process with hydrogen peroxide or persulphate.  ·         advantages -          Supplementary cleaning effect -          Effectiveness for tapioca starches -          No loss in effectiveness due to enzyme poisons. ·         disadvantages includes -          possibility of fibre attack, use of aggressive chemicals and less variety of application methods.

5. Give method of bleaching cotton with hydrogen peroxide (H2O2) in detail.

The bleaching bath is composed of hydrogen peroxide (35% or 50% by wt.) as the bleaching agent, an activator (usually alkali) and stabilizer

Hydrogen peroxide bleaching can be done by:

(1) Batch or Discontinuous process
e.g. Kier, Jigger, Winch.

(2) Continuous process.
e.g. J – box, Vaporloc

(3) Semi – continuous process
e.g. pad – roll.

1. Batch or Discontinuous process
A. kier boiling: –It consists essentially of circulating hot alkaline liquor through the cloth, which is commonly manipulated in ‘rope form’. The kier consists of a vertical cylindrical iron vessel with perforated false bottom in which cloth is laid down in a regular fashion either manually or by mechanical plaiting. It is frequently used and as able to carry out high pressure scoring. The sizes of kiers vary and in general are capable of holding from 500 lbs to 5 tons of cloth. In its simple form, steam is injected through a hole at the centre of the bottom of the kier and is able to pass up the tube thereby forcing liquor up with it. Kier boiling may be carried out either at atmospheric pressure in an open kier and under pressure. Temperature in kier is around 130 degrees C. cotton goods are normally treated as kier a period of time varying from 2-12 hours depending on the type of cloth and the effect which is required.

2. Continuous process: 
A. J-box - in this the cloth is impregnated by passage through a caustic soda solution (3-4%) in a saturator and then squeeze rolls so that the cloth retains its own weight of liquor. The cloth is then heated in steam and stored in J-box for one hour. J- box consists essentially of a stainless chute is piled at the bottom of the chute where it is able to reside for periods up to an hour. Temperature in J-box is 95 degrees C. successful scouring by continuous methods requires good and rapid wetting in order to obtain a good alkali penetration continuous alkaline treatment is convenient when used as preparation for a continuous peroxide bleaching process.

B. Vapor lock- it is a high temperature high pressure machine used for continuous scouring. In this, fabric is padded and passes through machine treated at very high temperature pH of the liquor is around 14 and fabrics are treated in it for 1-2 minutes.

Differentiate between alkaline and solvent scouring:

Alkaline scouring 1. It is carried out by using NaOH. For medium weighed fabric 4% and for heavy fabric 6% on the weight of fabric NaOH is used. 2. Anionic wetting agent is added to improve penetration of scouring liquor in hydrophobic fabric 3. Emulsifying agent is added to keep the impurities in suspension and secondly does not allow the impurities to redeposit on fabric.

Solvent scouring 1. Wax cannot be dissolved in water, therefore organic solvent (e.g. Per chloro ethylene) is used to dissolve wax. 2. Organic solvent is costy. 3. Do not remove proteins, pectins and minerals fabric should be completely dry