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Irradiation of Plastics: Damage and Gas Evolution

Published online by Cambridge University Press:  29 November 2013

D. Evans  and
M.A. Crook
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Extract

There have been many studies (see for instance Reference 1) directed at quantifying the effects of ionizing radiation on polymers. Mainly these studies have focused on assessing the degradation of mechanical properties. In addition to changes in mechanical properties, a mixture of gases results from the irradiation of polymeric compounds. The amount of gas produced is related to the total absorbed dose while the type of gas is independent of dose and is related only to polymer structure. For many polymers, hydrogen is the major component in the gaseous mixture but polyesters and anhydride-cured epoxide resins are a notable exception.

Some problems associated with radiation damage may be further complicated when the irradiation temperature is in the cryogenic range. When materials are irradiated at low temperatures (<150 K), the release of volatile degradation products is delayed and occurs—possibly very rapidly and exceeding normal diffusion rates—only when the polymer is warmed. The rapid release of gaseous degradation products could occur as a result of warming a superconducting magnet that has been resin bonded and irradiated at low temperatures during operation. Radiation damage-related problems may be summarized as follows: (1) changes in short-term mechanical properties, (2) production of gases and low-molecular-weight species, and (3) longer term and geometrical effects (unknown) of trapped gases on electrical and mechanical properties.

This article considers mechanisms of radiation-induced damage and relates the chemical structure of the polymer to the rate of damage accumulation. Changes in electrical properties measured on irradiated polymers are generally small, and mechanical damage is generally more significant than changes in electrical characteristics. However all such reports are a result of electrical measurements on thin films and do not consider the effects of trapped gases on long-term electrical properties in bulk specimens.

Type
Materials Performance in a Radiation Environment
Information
MRS Bulletin , Volume 22 , Issue 4 , April 1997 , pp. 36 - 40
Copyright
Copyright © Materials Research Society 1997

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References

1.Simon, N.J., A Review of Irradiation Effects on Organic—Matrix Insulation (U.S. Department of Commerce, National Institute of Standards and Technology, Boulder, CO, NISTIR 3999, June 1993).Google Scholar
2.Dole, M., ed., The Radiation Chemistry of Macromolecules, vol. 1 (Academic Press, 1972).Google Scholar
3.Lee, H. and Neville, K., Handbook of Epoxy Resins (McGraw-Hill Book Company, New York, 1982).Google Scholar
4.Morgan, J.T. and Stapleton, G.B., Gas Evolution From Plastics Materials by High Energy Radiation (Rutherford Laboratory Internal Report RL-74-021, 1974).Google Scholar
5.Evans, D. and Morgan, J.T., “A Review of the Effects of Ionizing Radiation on Plastics Materials at Low Temperatures,” Adv. Cry. Eng. (Matls.) 28 (Plenum Publishing Corporation, New York, 1982).Google Scholar