High performance and high tech textile products: manufacturing technologies and final applications

Paper by Antonio Piccolini, Rovetex, presented at the 5th International Istanbul Textile Conference (2005). The original slides are available as a PDF.

The textile industry is constantly searching for innovation, above all for new products for technical applications. Within technical textiles, high performance and high tech textiles are a class of products of remarkable importance: they bring good added value to the whole textile chain, and their market grows larger and more important every day.

At the same time, developing and manufacturing these products is more expensive and more complex, across the whole textile process, than processing conventional technical textiles. The final applications also demand a different approach: the requirements are very strict and no mistake is allowed.

It is not easy to summarise such a large and diverse family of products in a few pages. This paper explains the main differences between high performance and high tech technical textiles, focusing on:

• the intrinsic chemical and physical characteristics of the raw materials;
• the basic concepts of how these products must be processed in spinning, weaving and finishing;
• the requirements of the final applications, with examples from body protection and industrial end uses.

Defining high performance and high tech textiles

Whether a textile product is “high performance” or “high tech” is not rigidly defined. For the purposes of this paper, the two terms are used as follows.

High performance textile products

A high performance textile product is one that has one or more characteristics giving it an advantage in one or more end uses, compared with the standard product used for the same end use. For example:

• a fabric for curtains or upholstery whose measured LOI (Limiting Oxygen Index) gives it a permanent flame retardant characteristic;
• a fabric for liquid filtration with better resistance to hydrolysis than similar products on the market (polypropylene performs better than polyester here);
• a textile for clothing, bed linen or bath towels that also has antibacterial properties.

High tech textile products

A high tech textile product is one that meets one or more genuinely technical requirements and is designed and engineered for a specific technical end use. For example:

• an industrial textile designed as composite reinforcement for the aircraft or car industry, which must work under stress for the whole life of the final product without any loss of performance;
• a body protection textile (personal protective equipment) that must protect the human body for a defined minimum time at a defined temperature, such as Formula 1 drivers’ suits: more than 15 seconds at a temperature above 340°C;
• a hot gas filter textile that must work continuously at high temperature, above 270°C, under alkali or acid attack, for its whole design life, such as filter bags for power stations working above 300°C for a life of not less than one year.

The Limiting Oxygen Index is one of the key measures that separates these products. Conventional fibres such as cotton, viscose, polyamide and polyester sit at the low end of the LOI scale, while flame retardant and high tech fibres such as FR viscose, aramid, polyamide-imide, polyimide and PBI reach considerably higher values.

High performance and high tech textiles by end use

It is not possible to catalogue every high performance and high tech textile product in a short paper. The most important ones, from a market development point of view, are summarised below.

High performance textile products

Product group	Typical applications	Raw materials
Industrial textiles	High tenacity textiles for belts, sails, medium-level composite reinforcement	Commodity raw materials such as polyester (PES), polyamide (PA) and polypropylene (PP)
Flame retardant textiles	Curtains, upholstery, mattresses	Modified standard polymers such as FR polyester and modacrylic, and blends of FR fibres or yarns with cotton, wool or viscose
Antibacterial textiles	Bed linen, bath towels, curtains, upholstery, mattresses	Bioactive fibres
UV protective textiles	Sun tents, clothing
IR absorbing textiles	Soldiers’ uniforms
Filtration textiles	Liquid filtration, low-temperature gas filtration

High tech textile products

Industrial textiles. These include textiles for belts, sails, top-level composite reinforcement, fire and high temperature protection and hot gas filtration. They must meet very demanding basic requirements. In hot gas filtration, for example:

• LOI equal to or greater than that of a flame retardant fibre;
• thermo-mechanical resistance of not less than 60% after heat treatment at 260°C for 48 hours, or alternatively not less than 90% at 200°C for 48 hours;
• degradation temperature above 370°C;
• melting temperature above 285°C, without softening.

Protective clothing textiles. Textiles for personal protective equipment must protect the human body in risk situations, mostly against multiple risks at once: fire and heat, cuts, chemicals, electricity, ballistic threats and electromagnetic fields. Examples include EU firefighters’ uniforms, Formula 1 drivers’ suits and uniforms for the petroleum industry.

The main protection functions for these textiles are:

• fire and heat protection;
• electrostatic protection;
• chemical protection;
• antibacterial protection;
• electromagnetic protection;
• together with the degree of comfort for the wearer.

To evaluate fabrics against these functions, a wide set of properties has to be measured:

• Thermal: degradation temperature, glass transition temperature, softening temperature, melting temperature, thermal conductivity, thermo-mechanical resistance, LOI.
• Electrical: dielectric constant, dielectric dissipation factor, resistivity.
• Biological: bioactive performance, micro-organism resistance.
• Comfort (“skin model”): water absorption and release index, drying time, moisture resistivity, liquid sweat absorption, surface friction, surface hairiness, flexural rigidity.
• Chemical: resistance to acids, alkalis and solvents.

Three of these terms need a precise definition:

• Thermo-mechanical resistance: the percentage of the initial mechanical strength at ambient temperature that remains after treatment for a given time at a constant temperature in air, or after treatment up to a given temperature in air.
• Degradation temperature: the characteristic temperature at which noticeable weight loss begins.
• Melting temperature: the characteristic temperature at which the crystalline phase of a semi-crystalline polymer changes from solid to liquid.

Evaluating woven fabrics for protective equipment

The paper presented an example evaluation of woven fabrics for protective equipment according to EU and UN norms. The fabrics were assessed for composition, burning behaviour, behaviour with liquids, mechanical characteristics, electromagnetic behaviour and comfort.

The evaluated fabrics were mostly made of man-made fibres (classified according to the BISFA 2000 fibre classification), with two samples containing significant percentages of natural fibres: wool in one and cotton in the other.

Although these fabrics are intended entirely for body protection, their environmental impact was also evaluated, for the moment at the end of their life when they must be destroyed by burning in a standard incinerator. Toxic gas emissions during burning were checked against ATS 1000.001 (the Airbus smoke and toxicity test) and IMO Resolution MSC.61(67), Annex 1, Part 2, “Smoke and toxicity test”.

Technical fibres and raw materials

With few exceptions, high performance and high tech textiles are made and engineered from high performance and high tech fibres, almost exclusively man-made. The most important ones, from a technical application and market point of view, are described below.

Flame retardant fibres

Flame retardant fibres are produced from three families of base polymers:

Family	Standard fibre (LOI)	Flame retardant version (LOI)	Trade names
Modified natural polymers	Viscose CV (20)	FR viscose (26–28)	Lenzing FR, Visil
Modified synthetic polymers	Polyester PET/PES (19–21)	FR polyester (28–30)	Trevira CS, Securelle
Modified synthetic polymers	Acrylic PAN (19–21)	FR modacrylic MAC (28–34)	Kanekaron, Protex
Intrinsically flame retardant polymers		Chlorofibre CLF (38–46)	Rhovyl

Bioactive (antibacterial) fibres

Bioactive fibres come from two families of base polymers:

• Modified natural polymers: cellulose, as bioactive modal (Modal Fresh).
• Modified synthetic polymers: bioactive polyester (Trevira Bioactive) and bioactive acrylic (Amicor, Amicor Plus).

High tech and high performance fibres

Organic fibres are produced only from engineered synthetic polymers. The most important on the market are:

Fibre	Polymer	LOI	Trade names
Para-aramid PPTA	Polyparaphenylene terephthalamide	27–29	Kevlar, Twaron
Para-aramid copolymer PPTAC	Polyparaphenylene/3,4’-oxydiphenylene terephthalamide	25	Technora
Meta-aramid PMIA	Polymetaphenylene isophthalamide	29–32	Nomex, Teijinconex
PAI	Polyamide-imide	32	Kermel
PIC	Copolyimide	36	P84
Fluoropolymer PTFE	Polytetrafluoroethylene	above 90	Teflon, Profilen
Melamine MF	Melamine formaldehyde resin	32	Basofil
Phenolic PHE	Phenol-aldehyde resin	30–34	Kynol
PBI	Polybenzimidazole	41	Celanese PBI
PBO	Poly-phenylene-2,6-benzobisoxazole	68	Zylon
PPS	Polyphenylene sulphide	34	Procon, Torcon

Inorganic fibres include carbon fibre (more than 99.9% carbon), metallic fibres (100% stainless steel, 100% silver or 100% copper), glass, boron, silicon carbide and silica.

These materials have very different mechanical and chemical characteristics:

• Density ranges from 1.2 for phenolic fibre to 2.1 for PTFE.
• Electrical resistivity ranges from 0.8–3 ohm·cm for carbon fibre up to around 10^19 ohm·cm for PTFE.
• Breaking tenacity ranges from low levels, 24 cN/tex for PBI, to very high levels, 220 cN/tex for para-aramid.
• Elongation at break ranges from below 10% for oxidised polyacrylonitrile to above 100% for chlorofibre.

The products where the textile industry has the opportunity to grow are high tech and high performance textiles made with high tech and high performance fibres.

EU market for high tech staple fibres

The EU market for high tech staple fibres, for spinning and direct uses, grew steadily between 1990 and 2004 (tonnes):

Fibre	1990	1993	1996	1999	2002	2004
Nomex	1,300	1,600	3,000	3,200	4,000	4,000
Kermel	500	600	600	700	850	900
P84	250	300	350	380	500	500
Twaron	600	800	800	950	1,200	1,200
Conex	120	130	150	300	530	650
Technora	0	0	50	100	220	250
Total	2,770	3,430	4,950	5,630	7,300	7,500

Manufacturing technologies in the textile cycle

High performance fibres, such as flame retardant or bioactive fibres, are used to make spun yarns both pure and in intimate blends with other fibres, including non-flame-retardant fibres. Combining different yarns (flame retardant, high tech and standard) on the loom is also possible. Because high performance fibres are not very different from the standard fibres they were developed from, they normally need no preliminary studies or special trials to set up the textile chain.

For high tech fibres, the situation is completely different.

High tech fibres are very often used in intimate blends with each other and with conductive fibres, either 100% stainless steel (Bekinox) or metal-coated organic synthetic fibres (R.Stat, X-Static and others). They are also used to make core yarns with a metallic or pure carbon filament core.

Manufacturing processes must be stable, repeatable and cost-effective. These fibres are very expensive: some, such as PBI and PBO, exceed 200 €/kg, and even a “normal” high performance fibre such as aramid or PPS costs no less than 25–30 €/kg. No mistakes are acceptable anywhere in the textile process, and waste should be close to zero.

Yarn manufacturing starts either from polymer extruded as continuous filament (followed by twisting, texturising and yarn dyeing) or from staple fibre (optionally fibre dyed), which is spun on the cotton ring, cotton compact, cotton open-end, worsted or woollen system, then twisted and yarn dyed.

Spinning high tech staple fibres

Until a few years ago, high tech staple fibre yarns were made almost only with cotton ring spinning; the other spinning systems were marginal. This has changed: the volume of yarn made on the long staple worsted system is growing, mainly in the EU, where it has reached 30% of the market. The main advantage of long staple spinning is better tenacity than short staple. Staple yarns produced by stretch-breaking, starting from tow or continuous filaments, are an interesting niche, but only a niche.

Key requirements for spinning these fibres:

• Climate control. The spinning mill needs perfect temperature and humidity conditions, with a really efficient air conditioning plant able to maintain different conditions in carding, drawing, spinning and twisting. Most of these products, especially blends of different fibres, need at a standard temperature of 25°C more than 12 g of water per kg of air in carding, and 10 g or less per kg of air in spinning. Refrigeration plants are essential, even in non-warm climates, to dry the air efficiently.
• Feed-stop devices. Every thread break on the ring frame inevitably causes fibres to lap onto the drafting rollers, so ring frames must be equipped with feed-stop devices.
• Low fibre-to-metal friction. The whole spinning process must be adapted to reduce friction between fibre and metal. Most high tech fibres have high longitudinal tenacity but very poor resistance to tangential abrasion.
• Gentle settings. Spinning plans and machine settings for spinning and winding must avoid any stress on the fibres, taking into account the physical and mechanical characteristics of every fibre component in the yarn.

Beyond the normal yarn quality parameters (regularity, cleaning, breaking tenacity, elongation at break, thin places, thick places, neps, hairiness), quality control must include parameters not usually used for conventional yarns:

• yarn shrinkage in hot water, steam and hot air;
• yarn modulus at 5%, 10% and 20% elongation;
• microscopic inspection of fibre abrasion;
• control of the micro-fly content of the yarn.

Many high tech yarns contain conductive fibres, and some standard quality control instruments, used both during spinning and in the laboratory, do not work at all with them, for example the Uster evenness tester and capacitive yarn clearers. Each mill has to develop internal tests with alternative instruments, such as optical devices, and correlate the results with the data usually given in yarn quality standards.

Yarn twisting

Most high performance fibres, such as FR polyester, and all high tech fibres are very sensitive to tangential friction. Twisting of these yarns must therefore be done only on double-twist frames, without a balloon control ring, to avoid any friction between the fibres and a metal ring. Twisted yarns, from both staple fibres and continuous filaments, normally need heat setting with steam under vacuum at temperatures above 100°C.

Filament yarns

Continuous filaments are produced entirely by a few fibre producers and, from a market point of view, are limited to aramid fibres. They need no modification in the yarn cycle, except in a few cases such as combining high tenacity filaments (para-aramid, PBO, PTFE) with conductive metallic or carbon filaments.

The use of continuous filaments is limited in volume, both for cost reasons and because blending different high tech fibres to optimise the final product is not possible with filaments. With current technology it is practically impossible to texturise high performance filaments, even those made from thermoplastic polymers such as PPS; only flat filaments are available on the market.

Yarn dyeing

High performance yarns made from modified standard polymers (FR polyester, FR viscose, bioactive polyester, bioactive acrylic) dye in much the same way as the original “parent” fibre.

High tech fibres, on the other hand, are not dyeable or are very difficult to dye:

• When needed, aramid fibres are dope dyed during extrusion. Fastness of dope-dyed fibres is at top level on both the grey and blue scales.
• Some types of meta-aramid can be package dyed with basic cationic dyes at high temperature (above 130°C), using a high percentage (more than 20%) of carriers such as benzyl alcohol in the dye bath. Fastness is very poor.
• In the fairly common case of yarns blending flame retardant and high tech fibres, the high tech fibre is generally dope dyed, while the flame retardant fibre is normally dyed on cones.

Fabric manufacturing: warping and weaving

Warping. Warping tensions must be perfectly uniform. High performance fabrics often have very high density, in many cases over 3,000 g/m², and under these conditions an imperfect warp cannot be processed on the loom. When conductive yarns are used, warping machines with electrical contacts must be avoided. Sizes and oils that are not fully water soluble, or not compatible with the final end use of the article, must be avoided altogether.

Weaving. Any type of loom can be used, provided it has the right characteristics for the type of fabric to be produced: very light or very heavy, from spun yarns, continuous filaments or both. Fabrics made with very stiff or slippery yarns need to be woven on rapier looms with positive rapier insertion. In weaving too, any electrical contact must be eliminated when conductive yarns are used.

Knitting

Warp knitting. Beams are needed only for warp knitting. Only continuous filaments are used, mainly flame retardant fibres such as FR polyester. There are also some meta-aramid and para-aramid continuous filament fabrics, mainly used as backing for coating, but the quantities produced are marginal.

Circular knitting. Single jersey and interlock fabrics for protective underwear are mainly produced from aramid spun yarns, pure or blended with FR viscose. Any type of knitting machine can be used. In the fairly common case of fabrics made from single yarns, it is often necessary to use yarns with opposite twist (S and Z) to give the finished fabric stability. When conductive yarns are used, any electrical contact must be avoided.

Finishing and piece dyeing

In finishing and piece dyeing, high performance fabrics made from modified standard polymers (FR polyester, FR viscose, bioactive polyester, bioactive acrylic) follow a cycle similar to that of the parent fibre.

Until a few years ago, high tech fabrics were almost only fibre dyed. Today, many fabrics based on meta-aramid and its blends with FR fibres are piece dyed under pressure on modified beam dyeing machines. Fastness is not top level, but in many cases it is sufficient for non-critical end uses.

Finishing, however, is very important to meet the requirements of many final products:

• Desizing and scouring must be carried out perfectly. Small traces of size or oil on the fabric can compromise the performance of the final product.
• Heat setting is normally carried out under extreme conditions of temperature and treatment time.
• Functional finishes. Some high tech fibres keep their primary characteristics, such as fire protection and heat resistance, even when the fabric receives special finishes such as anti-crease, water-repellent or antibacterial treatments. In these cases, finishing products compatible with the characteristics of the fibres must be selected.

Conclusions

Over the past ten years, high performance and high tech textiles have evolved constantly, both in new products introduced to the market and in volume.

High performance products were developed along the “traditional textile route”: existing products were modified step by step, optimising their characteristics by adding flame retardant or bioactive components to established polymers.

High tech textile products, by contrast, required a major research and development effort. Today their market, growing on average by 5% per year in both volume and turnover, is the only one that gives the EU textile industry really good added value and return on investment.

New products are now being developed with computer simulation models, using a limited number of highly effective initial parameters. In the intermediate calculations leading to the final simulation, every fibre, yarn and fabric parameter must automatically feed new parameters into the database of the final product model.

Developing new high tech textile products certainly requires substantial investment, not only in hardware, new plants and machines, but also in training people. Textile university research centres could play an important role in this sector, provided they have the practical tools and the funding to carry out these studies.