Foaming of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Foams with Double Melting Peaks
摘要
Due to environmental concerns and the oil crisis, biodegradable polymer foams have garnered increasing attention. Among all biodegradable materials, Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(HB-co-HV)) distinguishes itself with the advantage of being biodegradable in all natural environments. However, preparing P(HB-co-HV) foam with a fine cellular structure remains challenging. Herein, P(HB-co-HV) foams with a double melting peak structure were developed. P(HB-co-HV) samples were first heated briefly near the melting temperature to melt most of the crystals, followed by saturation and foaming at a lower temperature (foaming temperature). P(HB-co-HV) foams with cell sizes of 7.1–30.0 µm and relative densities ranging from 0.3 to 0.9 were prepared, and the foaming temperature window was as wide as 16 °C. The effect of heat treatment temperature and foaming temperature on the crystallization and cell structure was investigated through DSC and SEM. It was found that the high-melting temperature crystals generated during the saturation step significantly improved the cell structure of P(HB-co-HV), since these crystals can enhance the heterogeneous cell nucleation and hinder the cell growth during foaming. The low-melting temperature crystals were formed during foaming. In situ WAXD analysis during heating showed that the high- and low-melting peaks corresponded to HV-unit-excluded and HV-unit-included PHB crystals, respectively.