Prospects for Radiation Techniques in Dyeing and Finishing

Abstract

This paper evaluates the role, actual and potential, of high‐energy and low‐energy radiation in textile technology. Emphasis is placed on the cobalt‐60 source and the electron accelerator as high‐energy sources, and the glow discharge as a source of low‐energy radiation. The effect of high‐energy radiation on the structure and properties of fibres is reviewed. Two types of effect may be produced: crosslinking and degradation. The latter predominates with some polymers, whereas with others crosslinking of the polymer chains is the major effect. It is concluded that the direct effects of high‐energy radiation are of insufficient value to justify its application to textiles without some simultaneous or subsequent chemical treatment of the fibre. The free radicals produced by the radiation serve as reactive sites at which the graft copolymerisation of monomers may be initiated within the fibre structure. Three methods are available for the radiation grafting of unsaturated monomers on to fibrous substrates: the ‘simultaneous’ method, the ‘post‐irradiation’ method, and the ‘peroxide’ method. Most effort in this area has been devoted to the modification of synthetic‐polymer fibres to make them more readily dyeable. Several examples of this are described. To achieve good penetration of the graft copolymer into the fibre, it is necessary that the fibre should be sufficiently swollen to permit penetration by the monomer molecules. Experiments on the swelling of polyester fibres in relation to grafting are described. The use of radiation‐initiated grafting in the finishing of textiles is discussed next. The outstanding example of this, one that has achieved commercial exploitation, is the Deering Milliken Visa process for conferring durable‐press properties on cotton and cotton–polyester fabrics. Flame‐resistant cotton can also be produced by radiation‐grafting techniques. The modification of the surfaces of textile fibres, for example, to confer soil‐release and antistatic properties, is another potential application of radiation grafting in textile finishing. The deposition of coatings on solid surfaces by low‐energy gas‐discharge techniques has been the subject of many investigations. Recent work at the Shirley Institute, in collaboration with the Electricity Council Research Centre, has shown that several percent of vinyl monomers can be deposited on polyester fabric by means of the glow discharge. With hydrophilic monomers, the fabrics have improved antisoil and soil‐release properties. Terylene (ICI) fabrics treated in a glow discharge with acrylic acid can be dyed to solid colours with basic dyes. The paper concludes with a brief assessment of the economics of radiation processes in relation to their use in textile technology.