Enhancement of the crystallization and thermal stability of polyhydroxybutyrate by polymeric additives

The crystallization and thermal degradation of polyhydroxybutyrate (PHB) blended with a small amount of carboxyl-terminated butadiene acrylonitrile rubber (CTBN) and biocompatible polyvinylpyrrolidone (PVP) are analyzed by differential scanning calorimetry (DSC), dynamic thermogravimetric analysis (TG), gel permeation chromatography (GPC), polarized optical microscope (POM), and wide angle X-ray diffraction (WAXD). From results of DSC, TG, and GPC, it is shown that the presence of PVP or CTBN could affect the crystallization rate, crystallinity, melting temperature, and thermal stability of PHB. The changes of crystal sizes by the added CTBN and PVP are also confirmed by the POM and WAXD analyses. The addition of the 1 wt% PVP or CTBN into PHB can significantly increase the crystallization rate and thermal degradation temperature, and affect the degradation kinetics of PHB due to the steric hindrance effects of the added PVP and CTBN on retarding the degradation reaction. The best improvement of the thermal stability is obtained from the PVP-modified PHB. The method of using CTBN or PVP to improve the thermal stability of PHB is of great processing advantages in industry because it is functional with low purity PHB, henceforth, saves the cost of the purification process.