Non-isothermal crystallization kinetics of poly(3-hydroxybutyrate)/EVA 80 blends enhanced by NH4Cl as a nucleating agent

Abstract

The crystallization kinetics of poly(3-hydroxybutyrate) (PHB), PHB/NH4Cl composites, PHB/ethylene-vinyl acetate (EVA 80) blends and PHB/EVA 80/1 mass% NH4Cl blends were studied under non-isothermal conditions. The modified Avrami equation and the MO approach were found to successfully describe the non-isothermal crystallization process. It was found that the inverse half time of crystallization and the values of Avrami rate constant, K, of PHB increased with decreasing EVA 80 content, increasing cooling rate and the addition of NH4Cl. Moreover, the crystallization mechanism remains unchanged in spite of the EVA 80 content and the presence of NH4Cl. Furthermore, the effective energy barrier of the non-isothermal crystallization process, EX(t), was evaluated with the isoconversional methods of Friedman. The EX(t) values of PHB/NH4Cl composites are much lower than those of pure PHB. Moreover, EX(t) values of PHB in PHB/EVA 80/1 mass% NH4Cl increase with increasing EVA content. A large number of small PHB spherulites were observed by polarized optical microscopy in the presence of NH4Cl.