Post-curing effect on the chemical structure and its relationship with heat resistance and thermal-mechanical properties of crosslinked PVC foams

Abstract

Crosslinked polyvinyl chloride (PVC) foams were post-cured in 65 °C water for 5, 10, and 15 days. The effects of post-curing time were investigated regarding the chemical structure of semi-interpenetrating polymer networks (SIPNs) and its relationship with heat resistance and thermal-mechanical performances, and selected properties, such as cellular morphology, apparent density, compressive and flexural behaviors of the resulting PVC foams. The post-cured PVC foam with 5 days was specifically beneficial to the compressive and flexural properties as well as storage modulus, because this process promoted the crosslinking reaction and led to increasing polyimide proportion in the matrix. A longer post-curing time (10 days) would improve the chain interactions and limit the initial dehydrochlorination of PVC macromolecules, due to the increased H-bonded polyurea and polyamide groups in the SIPNs. The post-cured foam with 10 days increased the degradation temperature from 198.3 °C to 236.5 °C, with a 5% weight loss, and the glass transition temperature (Tg) from 73.4 °C to 91.6 °C. With the formation of a large amount of free urea groups, severe irreversible damage to the cellular microstructure was observed after 15 days of post curing, resulting in deteriorations in heat resistance, mechanical and thermal-mechanical properties of foams.