Novel in situ preparation of crosslinked ethylene-vinyl alcohol copolymer foams with propylene carbonate

A novel in situ crosslinking and foaming process for ethylene-vinyl alcohol copolymers (EVOH) by propylene carbonate was investigated. The crosslinking process was believed to result from the ester-exchange reaction between propylene carbonate and EVOH, during which the 1, 2-propanediol by-product subsequently acts as the foaming agent for the crosslinked EVOH. The effects of propylene carbonate content, foaming condition, nucleating agent as well as plasticizer on the expansion ratio, morphology, and mechanical properties of the crosslinked EVOH foams were explored. Propylene carbonate not only acted as both crosslinking agent and foaming agent but also worked as plasticizer for the EVOH foams. The addition of nucleating agent or plasticizer led to foams with higher cell density and smaller cell size. Gel content, crystallization behavior, and thermal stability of the crosslinked EVOH foams were determined. The results revealed that the gel content and decomposition temperature increased with increasing propylene carbonate content, while the melting point, crystallization temperature and crystallinity decreased.