Physical properties of irradiated polymers

Irradiation often produces changes in the visible or UV absorption spectra of polymers. These changes depend, in most cases, on the temperature of irradiation, post-irradiation treatment and the presence of additives. The new absorption bands are, in most cases, due to the formation of conjugated double bonds or trapped ions and radicals. The discolouration of polymer samples has sometimes been used in dosimetry. 

Electrical conductivity strongly increases in many polymers during irradiation. This induced conductivity in polymeric insulating materials is often the cause of operational failure of electrical devices in intense radiation fields. 

For crystalline polymers that crosslink, a decrease in crystallinity is observed by X-ray diffraction at high irradiation doses and is accompanied by a decrease in specific volume the melting behaviour of these polymers is thus strongly affected by irradiation. 

The mechanical properties of most polymers are modified by irradiation. They usually deteriorate in polymers undergoing predominant chain scission. In crosslinked polymers, the mechanical properties strongly depend on the temperature at which the measurements are performed and improvements are often obtained, especially above the melting point. Crosslinked polyethylene, for instance, is a rubbery solid above its crystalline melting point instead of being a viscous liquid if not irradiated. At room temperature, the elastic modulus and tensile strength are often increased by irradiation. Results on individual polymers will be discussed in section 5. 

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