**1. Introduction**

178 Woven Fabrics

Varshney, R.K., Kothari, V.K., Dhamija, S. (2010). A study on thermophysiological comfort

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properties of fabrics in relation to constituent fibre fineness and cross-sectional shapes. *The Journal of The Textile Institute*; Vol. 101, No.6, pp.495-505, ISSN 0040-

> We are surrounded by textile fabrics every second of our daily life. Being produced in enormous amounts, these products were considered simple mechanical constructions for a long time. During the last few decades aspects of functional products and smart textiles directed more scientific attention towards a more profound understanding of the relations between fabric structure and performance properties.

> The overall properties of a textile fabric structure are determined by a series of constructive parameters built in at different levels of material design. For example the wetting behaviour and the final water uptake of a fabric will be determined by:


As a result an enormous variability of designs can be chosen for a certain application. The best performance of a product will be achieved by appropriate choice of the right technical design parameters for a certain application.

Fig. 1. Classification of textile fibres.

Alkali Treatments of Woven Lyocell Fabrics 181

The main raw material from which regenerated cellulosic fibres are manufactured is purified wood pulp; mainly produced from wood and linters, but also from annual plants. For its conversion into textile fibres, it must be dissolved in a suitable solvent from which it can be regenerated as continuous filaments after the solution has been extruded through a fine orifice. At present, the following three methods are mostly used: the viscose process; the

Most of the world's man-made cellulose fibres are produced via the viscose process; these fibres are called 'rayons' because of the basic fibre-forming process, which involves cellulose regeneration from a cellulose xanthate, a chemical derivative of cellulose and carbon disulfide. The viscose process is characterized by high versatility, which is the result of various modifications that can be made at different stages of the process. The degree of polymerization of cellulose used, additives to modify the viscose solution, coagulation (controlled by coagulation bath additives, exerting an effect on the orientation and alignment of the cellulose molecules in the direction of the fibre axis), and stretching applied during fibre processing, can lead to a huge range of rayon forms and properties. These variations and their consequences on the end products are given in details in Morton and

With regard to the macrostructure of viscose fibres, regenerated cellulosics are different in their morphology to cotton as they have no lumen and are non-fibrillar (Fig. 2), which is

Lyocell is the generic name of a new generation of regenerated cellulosic fibres made by a solvent spinning process. The development of this fibre was driven by the desire for an environmentally friendly process to produce cellulosic fibres with an improved performance profile and cost compared to viscose rayon, utilizing renewable resources as

This cellulosic fibre is derived from wood pulp (typically eucalyptus) produced from sustainably managed forests; the wood pulp (good quality, DP = 400-1000) is mixed at 70-90 °C with approximately 80% (v/v) *N*-methylmorpholine-*N*-oxide (NMMO) solution in water with a small quantity of degradation inhibitor. NMMO is capable of physically dissolving cellulose without any derivatisation, complexation or special activation, and it is able to

Fig. 2. Scanning electron microscope (SEM) micrographs of viscose fibres.

break the inter- and intra-molecular hydrogen-bonds of cellulose.

lyocell process; and the cuprammonium process.

directly due to the manufacturing process.

Hearle (1993).

raw materials.

Textile fibres can be divided into two main categories, natural and man-made, as it is depicted in Fig. 1; in addition, there is another category which lies in between, and shares some features of both categories – it is termed 'regenerated fibres' and includes regenerated cellulosic fibres, which are typically wood pulp converted into continuous filaments by dissolving the wood in suitable solvents from which they can be regenerated.

Cellulose fibres exhibit a unique position among the textile fibres, due to their hydrophilicity and their ability to change their dimension by swelling. Swelling occurs in water, polar solvents and in particular in aqueous alkali hydroxide solutions, which are widely applied in textile finishing processes of cotton and regenerated cellulose fibres. Due to their high swelling capability regenerated cellulose fibres are highly sensitive during the alkaline treatment, thus a careful selection of alkalisation conditions for such fabrics is required. This particular behavior of cellulose to swell extensively in alkaline solutions results in a different performance in comparison to synthetic fibres. Herein, the chapter is dedicated to detailed discussion of the fibre behavior and the resulting effects/impacts onto regenerated man-made fabrics, for example lyocell fabric, during alkalisation.
