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Fibre applications in technical textiles
V K Kothari
The driving force for important fibre developments, especially in the past
two decades has been the ever increasing applications for fibrous material in
non-conventional sectors such as protective clothing, medical devices and health
care products, automotive components, building material, geotextiles, agricultural
devices, sport and leisurewear, filter media, environmental protection. These
applications put strong demands on good performance properties such as strength/modulus,
durability and dimensional stability and on functions such as flame-retardance,
hydrophilicity; hydrophobicity; biocompatibility etc.
Technical textiles are generally recognised to be one of the most dynamic and
promising areas for the future of the textile industry. Advanes in polymers,
fibres, yarns, chemical technology and fabric/web forming technologies have
spearheaded the material development for technical textiles. The environmental
loading of oil-based polymers has also influenced the development of new fibres.
Technical textiles are likely to grow by 3.9 per cent per annum by weight and
by 3.7 per cent by value between years 2000 and 2005.
Technology and market trends
A technical textile product can exist and be used in various forms of fibrous
structures from simple filament to a complex end product. Textiles for technical
applications are used in fibre form (in filters, waddings, and upholstery fibrefill),
yarn form (industrial sewing threads, ropes, cord, twine, etc) and in fabric
form. A wide range of processes is employed in the manufacture of technical
textiles. Apart from the use of plaiting and knotting for the manufacture of
ropes and nets, weaving was, for many years, the pre-eminent technology employed
in the manufacture of ‘industrial’ textiles.
In terms of the total weight of textiles produced, weaving still plays a leading
role and developments such as three-dimensional and crimpless weaving have opened
up many new product and end-use possibilities. However, the historical progress
of technical textiles has seen the advance of alternative textile forming technologies,
most prominently the broad family of nonwoven techniques but also warp and weft
knitting, stitchbonding and modem braiding methods. The use of loose fibres
with sophisticated cross-sectional profiles for insulation, protection and fibrefill
applications is another important growth area. Fibres, yarns and textiles of
all types also provide the starting point for a diverse and fast expanding range
of composite reinforcement and forming technologies.
Weaving is still the most widely used technique of fabric formation, especially
where fabric strength is critical, but is increasingly being challenged by other
technologies. For example, weft insert warp knitting allows reinforcing yarns
to be laid into a knitted structure without significant deformation and at various
angles. This allows fabrics to be engineered with very precise geometries and
mechanical characteristics, suitable for reinforcing complex structures ranging
from geotextiles and nets to rigid engineering composites.
Fibre developments
The evolution of fibre developments has gone through the phases of conventional
fibres, high-functional fibres and high-performance fibres. As the result of
these developments it is possible now to produce advanced fibrous materials
for many non-conventional applications. One of the main driving forces of technical
textiles in recent years has been the development of new materials as well as
of more specialised forms of existing materials. The aramid fibres, pioneered
by DuPont of the USA and later Akzo of the Netherlands were the beginning of
a revolution in which textile manufacturers and end-users came to appreciate
the enormous potential of materials with the strength of steel and superior
temperature resistance to almost all other organic materials. At first, these
fibres were prohibitively expensive but as new applications were developed and
more manufacturing capacity installed, prices fell sharply. Now at least half
a dozen fibre producers worldwide offer their own versions of aramids and their
versatility and usefulness is accelerating.
Improved fibre spinning techniques in melt spinning, wet spinning, dry spinning
and new techniques such as gel spinning, bicomponent spinning, microfibre spinning,
have made it possible to produce fibres with characteristics more suitable for
use in technical textiles. It is now possible to produce manmade fibres with
highly sophisticated non-circular cross sections, blends of filaments in a yarn
having ‘differential shrinkage’”, splitting of bicomponent filaments,
surface treatments to produce nice required morphology and topography. The bicomponent
fibre technology is mainly used to produce microfibres, binder fibres, self-crimpable
fibres, electro-conductive fibres and heterofil yarns. The three main types
of bicomponent fibres are core-sheath, side-by-side and islands-on-sea.
Today a wide range of high performance fibres such as aramids, HPPE, PPS, PBI
is commercially available for technical and industrial applications. Recently,
some new fibres such as PEN, PBO and PTFE have also been introduced in the market.
The development of polyolefin (mostly polypropylene but also some polyethylene)
fibres as well as tape and film yarns in the 1960s was another milestone in
the development of technical textiles. The low cost and easy processability
of this fibre, combined with its low density and good abrasion and moisture-resistant
properties have allowed its rapid introduction into a range of applications
such as sacks, bags and packaging, carpet backings and furniture linings as
well as ropes and netting. Many of these markets were directly taken over from
jute and similar fibres but newer end-uses have also been developed, including
artificial sports surfaces.
Properties of the polyolefins such as their poor temperature resistance and
complete hydrophobicity have been turned to advantage in nonwovens. Initially
used in conjunction with viscose to permit thermal bonding, polypropylene has
now benefited from a growing appreciation of the important role that moisture
wicking (as opposed to absorption) can play in hygiene applications such as
coverstock for diapers (nappies).
High performance fibres
First and foremost are aramids, both the highly temperature-resistant meta-aramids
(widely used in protective clothing and similar applications) and the high strength
and modulus para-aramids (used in a host of applications ranging from bullet-proof
vests to reinforcement of tyres, hoses, friction materials, ropes and advanced
composites. World demand for p-aramids is estimated to be almost 40,000 tonnes
per annum in 2000, while for m-aramids, consumption was around 17,000-18,000
tonnes.
Early success of the aramids was a welcome contrast to the development of carbon
fibres, which have been commercially available since the 1960s, but largely
constrained by their high material and processing costs to selected high value
markets particularly aerospace applications.
The author is with Department of Textile Technology, Indian Institute of Technology,
Hauz Khas, New Delhi-110016, India
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