Radiolysis of cured and uncured bisphenol A–epoxy resins
Polimery 2000, No 1, 1
A review with 28 references covering the resistance of cured and uncured bisphenol A–epoxy resins to ionizing radiation and the irradiation-effected changes in the physicochemical properties of the uncured resins in relation to molecular weight. Medium-M (900–1600, Table 2) resins irradiated with doses of 2 MJ/kg become infusible; low-M (500) resins require higher doses; higher-M (2000) resins do not crosslink even at 20 MJ/kg and their softening point remains unaffected. With the epoxy and the hydroxyl groups present in the resin in practically equal proportions, crosslinking proceeds easily. Low-M epoxies with a considerable excess of epoxy over hydroxyl groups, were crosslinked when irradiated with doses of 3 MJ/kg; the epoxy groups were isomerized and underwent destruction (eqns. 1–9). The resistance of epoxy materials to radiolysis is substantially related to the nature of curing agents and curing conditions. Arthydride- or aromatic amine-cured resins are most resistant to irradiation (1–10 MJ/kg); aliphatic amine-cured resins are least resistant (0.01–0.1 MJ/kg). Resistance to irradiation is directly related to thermal resistance. Dibutyl phthalate and other phthalate type diluents do not suppress the resistance of resins to irradiation. The dielectric properties of the electroinsulating laminates based on precondensed epoxy and novolak resins and glass fibers, remain unaffected upon absorption of 0.1 to 1 MJ/kg. Protective epoxy coatings made of compositions involving solvents or no solvents, resist doses of up to 0.1 MJ/kg. Solventless coatings exhibit good sorptive-desorptive properties toward radio-elements (cesium, strontium, plutonium, uranium).
Keywords: bisphenol A–epoxy resins, effect of ionizing radiation, crosslinking, mechanical and dielectric properties, sorption and desorption of radioactive elements, applications