Page 39 - Basic Principles of Textile Coloration

28 FIBRES AND TEXTILES: PROPERTIES AND PROCESSING

The vast majority of carpets are made by simultaneously needle-punching a row
of thousands of nylon multi-filaments into a polypropylene backing material in a
process called tufting. The backing then advances slightly and another row of tufts
is inserted. Application of a latex adhesive to the rear of the backing anchors the
tufts in place. Carpet manufacture also consumes lesser amounts of polyester,
wool, polypropylene and acrylic fibres. Like fabrics, carpets can be assembled from
coloured yarns, dyed using both continuous and batch processes, or even printed.

Non-woven fabrics are formed of a mass of disoriented fibres pressed together
and held by their natural adhesion, by tangling them using a needle-punch, with
the help of an adhesive, or by heat welding of synthetic fibres, which soften when
hot. They often have poor strength but are equally resistant in all directions. Their
major applications are for industrial and engineering textiles, and for disposable
materials such as sanitary products. Non-woven fabrics are less likely to be dyed
than woven or knitted materials but manufacture from pre-dyed fibres is simple if
colour is required.

A multitude of different textile fabrics are manufactured, each type with its own
characteristic structure and uses. The machinery used for handling these
materials, particularly during wet processing, is dictated by the strength and weight
of the fabric and its ease of deformation. In addition to weight and strength, the
other major attributes of a fabric are flexibility, elasticity, handle, water
absorbency, resistance to the conditions met during use, and good dyeability.
Many fabrics have a different appearance on the two sides, which becomes even
more evident on dyeing. The face of the fabric is usually the one presented during
use. Carpets and pile fabrics are extreme examples of this.

Fabrics come in a wide range of widths, superficial weights (g m–2), and air
permeabilities, the latter two properties depending on the thread or loop spacing
and the degree of twist of the yarns. Heavier fabrics provide better draping
characteristics. The properties of a fabric depend on its construction and upon
those of the component fibres. For example, fabrics made from viscose filaments
are often weak and very absorbent whereas those made from polyester filament are
strong and do not absorb water. Fabric properties can thus be modified by using
combinations of fibres. Fibres are blended for aesthetic and special effects, for
economy and to give fabrics of superior performance in use. For the production of
yarns containing different fibres, blending takes place during the opening, carding
or drafting operations. Alternatively, yarns of different fibres can be combined
during fabric production. Of all fibre blends, those of cotton and polyester staple in
particular have become the most important in the modern market. The polyester