Techniques for improving one or more aesthetic and functional properties of textiles encompass several major approaches that are far more comprehensive and diverse than employing only conventional textile finishing methods. Such improvement can be achieved by three major approaches: (a) dimensional stabilization, (b) surface modification and (c) physicochemical and chemical techniques. Dimensional stabilization of fabrics is usually achieved during processing by various mechanical and/or thermal techniques. Modification of the surface of fibers in fabrics by a variety of techniques (chemical, physical, exposure to high energy sources) changes the appearance, aesthetics and surface characteristics of fabrics. Physicochemical and chemical methods include coating, exposure to high energy sources, microencapsulation and application of chemical finishes and polymers to improve one or more textile properties for specific end uses. 4.2 DIMENSIONAL STABILIZATION BY MECHANICAL AND THERMAL METHODS 4.2.1 Mechanisms of stabilization The purpose of dimensional stabilization is to set the fibers and yarns in various fabric constructions so that the textile will not shrink or alter its dimensions during use and/or refurbishing. Dimensional stabilization of fibers and of fabrics has been accomplished by a basic knowledge of the effects that heat and mechanical forces have on textile structures during processing. Such stabilization occurs by application of techniques such as tenter frame control, heat and/or steam setting and compressive shrinkage. All fibers in fabrics are subject to the constraints imposed I sensitive to: temperature, (strong dipole; hydrogen bonds). >■ moisture, stress 3. Crystallization. J 4. Chemical crosslinks. 5. Impregnation with matrix. Mechanisms that are important for obtaining set within fibers during processing include chain stiffness, intermolecular hydrogen bonding and crystallinity. The energy change between fibers (6E b ), derived from frictional resistance, is always positive. The relationship of 6E b to the frictional resistance is given by the equation: 5E b = (μΝ).|χ ι> |, where μ is the coefficient of friction, N is the normal load between fibers 195 and |x b | is the relative fiber displacement. If the normal load for a system is known (as in the forces at crossover points for woven or for knitted fabrics), then the displacement in the textile structure may be measured or predicted (ref. 1). Hydrogen bonding is perhaps the most important type of bond between and within fibers that influences setting and stabilization. Cellulosics (hydroxyl groups) and polyamides and wool (amide groups) have strong hydrogen bonding networks. However, these types of bonds may be broken or disrupted at elevated temperatures with hot water or with steam. Thus, desetting or relaxation of these types of fibers may occur in the presence of sufficient moisture near the boiling point of water. Conversely, setting occurs when these fibers or fabrics derived from them are dried to remove water, and new hydrogen bonds ...
