Chemistry of Textile Materials

Chemistry of Textile Materials

The dyeing and printing processing of textile materials. Textile materials called fabrics or cloths are prepared by weaving or by knitting ... 9:08 AM

The dyeing and printing processing of textile materials. Textile materials called fabrics or cloths are prepared by weaving or by knitting with continuous strands of textile materials called threads or yarns. Yarns are prepared from short length materials called staple fibres or continuous materials called filaments . Fibrics called non-woven are prepared from fibres directly by special methods.

For successful chemical processing through knowledge of the chemical constitution, physiochemical structure and chemical properties of the textile materials is extremly essential. One may wonder at the many and varied properties of fibres, yarns and fabrics that have been produced , particularly since the advent of man made fibres. One may ask what makes a material suitable for use as a textile fibre. Why fibre properties like strength , elasticity, thermal properties, dyeability, resistance to chemicals vary so widely. To answer all these questions pne must closely examine the structure of textile fibres.

Textile Fibres:

Textile fibres are defined as units of matter characterised by flexibility, fineness and a high ratio of length to thickness. They should have sufficiant strength to resist breakage due to stress applied during manufacture and use. They should also processes enough thermal and chemical stability to withstand the environment to which the fibres are exposed. Moreover, an extensibility of 5-50% is required, depending on the end-use of the final product.

Until the introduction of man made fibres, one had to rely ob fibres from natural sources. Not all of these fibres were suitable for use as textile fibres because they lacked certain characteristics, for example many were not long,flexible or strong enough. Soil, feed and other climate and environmental conditions affect natural fibres. These result in non-uniform properties of natural fibres. Man-made fibres are not much influenced by these factors and greater control can be exercised over their production. However, even with greater control, slight variations in the production of man-made fibres can give rise to significant variation in dyeability, strength and some other properties.

Each individual fibre is made of millions of individual long molecular chains of discrete chemical structure. The morphology i.e. the arrangement and orientation of these molecules within the individual fibre as well as the gross cross-section and shape of the fibre influence the fibre properties. However, the basic physical and chemical properties largely depend on the chemical structure of the long molecular chains constituting the fibre. The total number of units that repeat themeselves in a chain vary from a few units to several hundreds and is termed as the degree of polymerisation for molecules within the fibre.

Cotton for example, has a DP of about 10000 and viscose rayon, a regenerated fibre, about 300-350. The DP of man-made fibre is determined by various factors during production of these fibres.

Fibre Structure: 

With the exception of a dew speciality fibres based on inorganic substances like glass, asbestos etc, fibres are a class of solid organic polymers that are distinguised from other polymers by their physical properties and by their characteristic geometric dimensions. A fibre is readily identifiable as a substance that is extremely long with respect to its width or diameter is flexible and has high anisotropic physical properties. However, fundamental difference between fibres and other solid substances is in their molecular structure , which in turn, decides the differences in their chemical and physical properties.

For a complete description of fibre structure, it is useful to consider three levels of molecular structure, each realting to certain aspects of fibre behaviour and properties. The organochemical structure defines the structure of the reoeating unit in the base polymer and the nature of polymeric link. This is directly related to chemical properties, dyeability, moisture absorption, swelling characteristics and indirectly to all physical properties. The macromolecular structure describes the family of polymer molecules in terms of chain length, chain length distribution, chain stiffness, molecular size and molecular shape. A supermolecular structure provides a description of the arrangements of the polymer chains, primarily in terms of factors like orientation crystallinity and fibrillar structure.

In general, all fibres that are useful in textile applications are semi crystalline, irresversibly oriented polymers. This means that the fibres have certain region in which the molecular chains are highly oriented, closely packed and near-perfectly arranged. These region are usually refered to as crystalline regions or crystallites. The degree of orientation and the degree of crystallinity are important quantities that strongly influance the physical properties of fibre . In other regions, the molecular chains are not well ordered, tending to a random-coil configuration and these are usally referred to as amorphous region. In the case of natural fibres, there are various identifiable aggregates of polymer chains, which are very pften reffered to as micelles, fibrils, microfibrils and also macrofibrils.

Polymer System:

The basic unit of the textile fibre is a molecular segment called monomer which is repeated a large number of times to form a long chain or a molecule called polymer. A polymer may also be formed from two or more different monomers. Such polymers are called copolymer. There is no definite regularity in the order of monomers, which make up a copolymer. Some fibres may contain additional monomers , which do not form part of the polymer chain and are incorporated to improve certain properties of the fibre such as dye affinity. Those are grafted onto the polymer chain as side group or branch. The homopolymers, copolymers and grafted polymers, which can be prepared from the three monomers.