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Technical Textiles

Published: 15th Dec 2015

Technical Textiles are defined as materials and products manufactured primarily for their technical and performance properties rather than their aesthetic or decorative characteristics.

Technical textiles are used in different forms in various industries like construction, transport, agriculture, medical, hygiene, and sporting. In industrial manufacturing operations technical textiles are used for filters, machine clothing, conveyor belts, and abrasive substrates. They are also incorporated into industrial products such as electrical components and cables, flexible seals and diaphragms, and acoustic and thermal insulation for other domestic appliances.

It is a large and growing sector that supports a vast array of other industries. The global growth rate of technical textiles is about 4% per year greater than the growth of home and apparel textiles, which are growing at a rate of 1% per year. Currently, technical textile materials are most widely used in filters, clothing, furniture, hygiene, medical and construction products.

Scope for technical textiles

Figure 1.1 summarises the principal materials, processes and products that are commonly regarded as falling within the scope of technical textiles manufacturing. However, there remain many grey areas. For example, the manufacture and processing of metallic wires into products such as cables, woven or knitted screens and meshes, and reinforcing carcasses for tyres are not generally regarded as lying within the scope of the textile industry. This is despite the fact that many of the techniques employed and the final products obtained are closely related to conventional textile fibre equivalents.

Within the composites industry, woven, knitted, braided, nonwoven and wound yarn reinforcements made from glass, carbon fibre and organic polymer materials such as aramids are all now widely accepted as being technical textile products. On the other hand, more loosely structured reinforcing materials such as chopped strand mats, milled glass and pulped organic fibres are often excluded. The nonwovens industry has developed from several different technology directions, including paper manufacturing. The current definition of a nonwoven promulgated, for example, under the International Standards Organization (ISO) standard ISO 90923 acknowledges a number of borderline areas, including wet-laid products and extruded meshes and nets. Likewise, distinctions between textile fibres and filaments slit or fibrillated films, monofilaments and extruded plastics inevitably boil down to some fairly arbitrary and artificial criteria. Diameter or width is often used as the defining characteristic, irrespective of the technologies used or the end-uses served. Many of the definitions and categories embodied within existing industry statistics reflect historical divisions of the main manufacturing sectors rather than a functional or market-based view of the products involved.

Technical textile categories

Technical textiles can be divided into many categories, depending on their end use. The following sections detail the 12 application areas specified by Tech Textile.

Protech

The main target of the technical protective fabrics is to improve worker safety in the workplace. A technical protective fabric can save a worker's life and that's why they are used in the manufacture personal protective equipment. Demand for these fabrics is growing around the world thanks to the sensibilisation of society, requiring increased safety at work. There are some organisations around the world such as ASTM and ISO that describe the requirements and regulations that fabrics considered as technical protective fabrics must fulfil. The aim of a technical protective fabric isn't fashion; they are designed to have extra protective values against certain hazards.

Agrotech

Textiles used in agriculture are termed as agro textiles. They are used for crop protection and fertilisation. The essential properties required are strength, elongation, stiffness, bio-degradation, resistance to sunlight and resistance to toxic environment. All these properties help with the growth and harvesting of crops and other foodstuffs. There is a growing interest in using materials that gradually degrade.

Some of the examples of agro textiles are:

• Preventing erosion and paving the way for afforestation in greenhouse cover and fishing nets • Layer separation in fields, nets for plants, rootless plants and protecting grassy areas • Sun screens (since they have adjustable screening) and wind shields • Packing material and in bags for storing grass that has been mowed • Controlling stretch in knitted nets • Shade for basins • Anti-birds nets • Fabrics for sifting and separation, for the phases of enlargement of the larvae • Materials for ground and plant water management at times of scarcity and abundance of water

Buildtech

Textiles used in construction: concrete reinforcement, façade foundation systems, interior construction, insulations, proofing materials, air conditioning, noise prevention, visual protection, protection against the sun, and building safety. An interesting application is the use of textile membranes for roof construction. This area is also referred to as textile architecture. PVC coated high tenacity polyester (PES), Teflon coated glass fibre fabrics and silicone coated PES are used for their low creep properties. Splendid examples of such construction are found in football stadia, airports and hotels.

Clothtech

Technical textiles for clothing applications. Especially in the finishing process, where fabric is treated under pressure and high temperature, the technical textile supports the fabric for smooth processing. This is usually a blend of PES, modal, viscose, and nylon. The technical textile products covered under Clothtech are: shoe laces, interlinings, zip fasteners, elastic narrow fabrics (tapes), Velcro, labels, umbrella cloth, and sewing threads.

Geotech

Geo textiles are used in the reinforcement of embankments or in constructional work. These textiles are permeable and used with soils as they have the ability to separate, filter, protect and drain. Application areas include civil engineering, earth and road construction, dam engineering, soil sealing and drainage systems. The fabric used must have good strength, durability, low moisture absorption and thickness. Mostly nonwoven and woven fabrics are used in it. Synthetic fibres like glass, polypropylene and acrylic are used to prevent cracking of the concrete, plastic and other building materials. Polypropylene and PES are used in geo textiles and dry/liquid filtration due to their compatibility.

Hometech

Textiles used in a domestic environment include interior decorations and furniture, carpeting, protection against the sun, cushion materials, fireproofing, floor and wall coverings, and textile reinforced structures/fittings.

In the contract market such as for large area buildings, ships and busses, fire retardant materials are used. Fire retardant properties are obtained either through the use of inherent fire retardant fibres such as modacryl or through the application of a coating with fire retardant additives, e.g. bromide of phosphorus compounds.

Indutech

Industrial textiles are used for chemical and electrical applications and textiles related to mechanical engineering. Applications include silk-screen printing, filtration, plasma screens, propulsion technology, lifting/conveying equipment, sound proofing elements, melting processes, roller covers, grinding technology, insulations, seals, and fuel cells. With advanced Indutech products like nonwoven nanofibre filtration, innovations are now filling the micro-filtration performance gap that had existed in the past, offering benefits such as enhanced air quality, reduced energy cost, and longer service life.

Medtech

Medical textiles include all the medical fabrics that are used in health and hygiene applications in both consumer and medical markets. They are generally used in bandages and sutures that are used for stitching wounds. Sutures and wound dressings use fibres like silk as well as synthetic fibres. Hollow synthetic fibres are used with nanoparticles for delivery of drugs to any specific part of the body. Cotton, silk, PES, and polyamide fabrics are also used in medical applications. Meditech products include surgical sutures, contact lenses and surgical dressings.

Mobiltech

These textiles are used in the construction of automobiles, railways, ships, aircraft and spacecraft. Examples are Truck covers (PVC coated PES fabrics), car trunk coverings, lashing belts for cargo tie downs, seat covers (knitted materials), seat belts, non-wovens for cabin air filtration airbags, parachutes, and inflatable boats. These textiles are used in automobiles, ships and aircrafts. Many coated and reinforced textiles are used in materials for engines such as air ducts, timing belts, air filters, and non-wovens for engine sound isolation. A number of materials are also used in the interiors of cars. The most obvious are seat covers, safety belts and airbags, but one can also find textile sealants. Nylon gives strength and its high bursting strength makes it ideal for car airbags. Carbon composites are mostly used in the manufacture of aeroplane parts, while carbon fibre is used for making high end tyres. High tensile PES is used for making hot air balloons.

Ecotech

New applications for textiles in environmental protection applications include: floor sealants, erosion protection, air cleaning, prevention of water pollution, water cleaning, waste treatment/recycling, depositing area construction, product extraction, domestic water sewerage plant. The primary segment in this is landfill waste management, which refers to the use of geosynthetic products to secure landfills against leakage of municipal or hazardous waste. Other areas include secondary protection in chemical/oil industries such as ground covers and the like around process tanks for secondary containment should the tanks leak. A modern engineering landfill has the following components: a basal lining system to prevent the contamination of soil and ground water by pollutants; a capping system to seal the waste when the capacity of the landfill is exhausted; an impervious sealing layer that prevents the entry of pollutants in the ground; a leachate collection system for the collection and transmission of leachates to a collection pit; and a secondary leachate collection/leak detection system.

Sporttech

Sports textiles, also known as Sporttex, are used mainly for making sports wear including sports shoes and other sports accessories. Increasing interest in active sports and outdoor leisure activities such as flying, sailing, climbing and cycling has led to immense growth in the consumption of textile materials in manufacturing sporting and related goods and equipment. Synthetic fibres and coatings have largely replaced traditional cotton fabrics and other natural fibres in the making of sport textiles.

Raw materials

Technical textiles are manufactured from a variety of fibres/filaments based on the desired properties of the end product. The fibres/filaments used can be broadly classified as natural or manmade. Natural fibres are important raw materials for the technical textile industry. The natural fibres predominantly used in technical textiles include: cotton, jute, silk and coir. Manmade fibres (MMF) and manmade filament yarns (MMFY) account for around a 40% share of the total fibre consumption in the textile industry as a whole. These fibres form a key raw material for the technical textile industry because of their customisable properties. The key manmade fibres, filaments and polymers used as raw materials in technical textiles are: viscose, PES, nylon, acrylic/mod acrylic, polypropylene and the polymers like high density poly ethylene (HDPE), low density poly ethylene (LDPE), and poly vinyl chloride (PVC).

Heat and flame protective clothing

With industrialisation, worker safety has become an important issue. A growing segment of the industrial textiles industry, therefore, has been involved in a number of new developments in fibres, fabrics and protective clothing. For heat and flame protection, requirements range from clothing for situations in which the wearer may be subjected to occasional exposure to a moderate level of radiant heat as part of his/her normal working day, to clothing for prolonged protection where the wearer is subject to severe radiant and convective heat or to direct flame, such as the firefighter’s suit.

In the process of accomplishing flame protection, however, the garment may be so thermally insulative and impermeable to water vapour that the wearer may begin to suffer discomfort and heat stress. Body temperature may rise and the wearer may become wet with sweat. With this in mind, attempts have been made to develop thermal and flame protective garments that can be worn without any discomfort.

Ease of ignition, rate of burning and heat release rate are the important properties of textile materials that determine the extent of the fire hazard. Other factors that influence the thermal protection level include melting and shrinkage characteristics of synthetic fibre fabrics and emission of smoke and toxic gases during burning.

While selecting and designing flame protective clothing, the following points should be kept in mind:

• The thermal or burning behaviour of textile fibres • The influence of fabric structure and garment shape on the burning behaviour • Selection of non-toxic, smoke-free and flame-retardant additives or finishes • Design of the protective garment, depending on its usage, including comfort properties • The intensity of the ignition source • The oxygen supply.

Thermal behaviour of fibres

In protective clothing, it is desirable to have low propensity for ignition from a flaming source or, if the item does ignite, a slow fire spread with low heat output. In general, thermoplastic-fibre fabrics such as nylon, PES fibre and polypropylene fibres fulfil these requirements because they shrink away from flame and, if they burn, they do so with a small, slowly spreading flame and abate. For protective clothing, however, there are additional requirements, such as protection against heat by providing insulation, as well as high dimensional stability of the fabrics, so that upon exposure to the heat fluxes that are expected during the course of the wearer’s work, they will neither shrink nor melt, and if they then decompose, they form char. The above mentioned requirements cannot be met by thermoplastic fibres and so recourse must be made to one of the so-called high-performance fibres such as aramid fibre, flame-retardant cotton or wool, partially oxidised acrylic fibres and so on. It may also be noted that the aramid fibre, in spite of its high oxygen index and high thermal stability, has not been found suitable for preventing skin burns in molten-metal splashes because of their high thermal conductivity.

From the foregoing discussion, it may be noted that the mode of decomposition and the nature of the decomposition products (solid, liquid, and gaseous products) depend on the chemical nature of the fibre, and also on the type of finishes or coatings applied to the fabrics. If such decomposition products are of a flammable nature, the presence of atmospheric oxygen gives rise to ignition, with or without flames. When the heat involved is higher than that required for thermal decomposition, it can spread the ignition to cause the total destruction of the material. In addition to the fibre characteristics and fabric finish, several garment characteristics also influence thermal protection. For a given fabric thickness, the lower the density, the greater the thermal resistance. This applies to fibres such as cotton and wool, which produce an insulating char on heating. Hence, thicker fabrics made from cotton, wool and other non-melting fibres give good thermal protection, whereas the thicker thermoplastic-fibre fabrics produce more severe burns.

Conclusion

Technical textiles are used for many industrial applications. The prime use of technical textiles is for protective fabrics that are improving people’s safety in their workplaces. Protective technical fabrics provide protection from high temperatures, burns, electric arc flash discharge, molten metal impacts, metal sparks, and acidic environments such as petrochemical, gas plant and refineries. In future, technical textiles will dominate the safety sphere by providing protective garments for various hazards.

Published: 15th Dec 2015 in Health and Safety Middle East

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Jayandran Mohan
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