Photo‐oxidation and photoprotection of the surface resin of a glass fiber–epoxy composite

Abstract

Abstract The rapid photo‐oxidation of the surface epoxy resin of a commercial seven‐ply laminate (Scotchply 1009‐26) is due principally to the epoxy novolac resin component. The photo‐oxidation rate of this resin is eight times that of the other component, a bisphenol A epoxy resin. This rate depends on the conditions of cure, and photo‐initiation occurs in part through aromatic carbonyl groups formed by oxidation of the methylene linkages of the novolac at the cure temperature (160–180°C). Inhibition of this thermal oxidation by vacuum cure or a chain‐terminating antioxidant increases the photostability. Photoprotection of thin resin sections by the UV stabilizer 2‐hydroxy‐4‐isooctoxybenzophenone and an epoxidized analog is assessed.