Elastomers radiation resistance

Radiation In general, plastics are superior to elastomers in radiation resistance but are inferior to metals and ceramics. The materials that will respond satisfactorily in the range of I010 and 10n erg per gram include... 

In general, plastics are superior to elastomers in radiation resistance but are inferior to metals and ceramics. The materials that will respond satisfactorily in the range of 1010 and 1011 erg per gram are glass and asbestos-filled phenolics, certain epoxies, polyurethane, polystyrene, mineral-filled polyesters, silicone, and furane. The next group of plastics in order of radiation resistance includes polyethylene, melamine, urea formaldehyde, unfilled phenolic, and silicone resins. Those materials that have poor radiation resistance include methyl methacrylate, unfilled polyesters, cellulosics, polyamides, and fluorocarbons. 

In general, there is a paucity of information on the relationship between polymer structure and degradation kinetics. This becomes especially critical in multiphase polymers like heterophasic copolymers, thermoplastic elastomers and blends. This review should stimulate research in this important area, which could ultimately lead to polymers with better photo-thermal and radiation resistance as well as more effective stabilizers. 

Seguchi, T. Morita, Y. Radiation resistance of plastics and elastomer, Polymer Handbook, 1998, VI 583. 

T. Seguchi, T. Sasuga, K. Yoshida, H. Yagyu and Y. Yamamoto, EIM 82-114 (1982) (in Japanese) T. Seguchi and Y. Morita, Radiation resistance of plastics and elastomers , in Polymer Handbook, VI-583, John Wiley and Sons, New York (1999)... 

They have made contributions on fluoropolymers especially on high-temperature and low-temperature adhesives and elastomers. One interesting copolymer is ethylene and tetrafluoroethylene (1 1), which is emulsion polymerized in the presence of a persulfate catalyst. This copolymer, unlike PTPE, is radiation-resistant. Another fluoropolymer project is the copolymerization between tetrafluoroethylene and hexafluoropropene. One high-... 

Polyurethanes Properties vary from those of an elastomer to those of hard, rigid cross-linked polymers with mechanical properties showing no reduction after an exposure to 1000 Mrad. (General radiation resistance excellent.)... 

It is generally considered that polyurethane elastomers are resistant to the effects of damage by high-energy radiation. As dosage increases then... 

Fig. 13.12. Relative radiation resistance of polyurethanes to other elastomers and materials. (Source P. Wright A. P. C. Gumming, Solid Polyurethane Elastomers. Maclaren Sons, London, 1969).

Often low-heat-resistant resins show the greatest radiation resistance. Some otherwise excellent plastics are known to be rather strongly affected by high-energy radiations. These are polyvinylidene chloride, polymethylmethacrylate, polytetraflu-oroethylene, butyl rubber, etc. Fig. R.1 shows relative radiation resistance data for some of the more commonly used plastics and elastomers. 

High molecular weight polydlmethylsiloxane with 3,000 to 10,000 repeat units containing less than 1% of vinyl functionality are the basis of most heat cured high consistency elastomers. Phenyl groups are added to inhibit crystallization at low temperature and Improve radiation resistances. 

The data on radiation resistance -have been compiled mainly for practical polymer materials that have been classified into four groups thermoplastics, elastomers, all aromatic polymers, and composite materials. The values of radiation resistance were determined by the change in mechanical properties. Radiation-induced degradation of polymer materials depends greatly on the irradiation conditions, as indicated in the tables hence, the reader is advised to use these data with caution, considering all the factors. 

Radiation resistance is characterizEd by the half-value-dose of significant changes in mechanical properties. For elastomers and thermoplastics, with large ultimate elongation by tensile test, the resistanee is eharaeterized by 100%... 

The properties can be affected differently, therefore more than one relevant property should be considered. In most cases, the properties used to characterize radiation resistance are the elongation at break for elastomers and flexible plastics, and the flexural strength for rigid plastics and composite materials. However, the elongation at break sometimes increases with elastomers deterioration, but in that case, the strength decreases greatly. 

The undesirable properties of thermoplastic polyurethane elastomer, i.e., softening at high temperatures and flow under pressure, which limit their use at elevated temperamres have been reduced by cross-linking with EB radiation. The cross-linked polyurethane shows good mechanical properties and also displays good resistance to aggressive chemicals, e.g., brake fluid [432 35]. 

---