Color formation in irradiated polymers

Discoloration is a problem in the radiation processing of polymers (such as radiation sterilization), and also in emerging applications in which optical-property materials are used in radiation environments (such as scintillation detectors). We have completed a survey of 17 different types of optical polymers, in which it is found that these materials form both permanent and annealable color centers, but in very different magnitudes and ratios. Optical absorption spectra of irradiated polymers both immediately after irradiation and following different time periods of annealing are provided. Also provided are tables showing rank ordering of the relative resistance of different polymer types to induced discoloration. It is found that the extent of radiation-induced discoloration of polymers has little or no dependence on whether the macromolecule is aromatic or aliphatic, and shows no correlation with the relative extent of radiation-induced mechanical property change. Examples of the influence of stabilizer additives on the extent of discoloration are discussed.