Physical properties of irradiated polymers

Polymers are irradiated for two reasons, namely, sterilisation and modification of the bulk or surface properties. Irradiation can be carried out with gamma rays from a cobalt-60 source or with accelerated electrons. On an industrial scale cobalt-60 is preferred for sterilisation whereas accelerators are mainly used to modify plastics and rubbers. Improvements in mechanical properties are brought about by crosslinking or grafting. Unfortunately, degradation often occurs. However, certain additives are able to influence the crosslinking/scission ratio in favour of the formation of crosslinks. Properties of interest which can be modified include environmental stress cracking, heat distortion temperature, high temperature modulus, tensile strength, shrinkability, abrasion resistance and volume resistivity. In most of the cases, elongation at break and impact strength are adversely affected by high-energy radiation. (author)