Thermal behavior and soil biodegradation for blends of poly(hydroxybutyrate)/ethylene vinyl acetate copolymer (EVA 60) with 1 mass% NH4Cl

Abstract

Poly(hydroxybutyrate) (PHB)/ethylene vinyl acetate copolymer (EVA 60) blends in the ratio from 90:10 to 30:70 by weight, where vinyl acetate content 60 mol%, and its composite with 1 mass% NH4Cl, were investigated by utilizing differential scanning calorimetry and polarizing optical microscopy. The experimental results showed that all investigated blend compositions exhibited two separate glass transition temperatures, corresponding to their components, suggesting immiscibility of PHB with EVA 60. The values of melt crystallization peak temperature and melting peak temperature of PHB in the blend and its composites were found to be almost composition independent, while the crystallinity percentage was slightly decreased with increasing the content of EVA 60 and increased in the presence of NH4Cl compared to pure PHB. The modified Avrami equation and the combination of Avrami and Ozawa methods were utilized to analyze the non-isothermal melt crystallization process successfully. Moreover, the presence of NH4Cl shortened the crystallization half-time and an increase in Avrami crystallization constant at various cooling rates. Polarized optical micrographs of PHB composites showed a large number of small, averaged sized spherulites compared with pure PHB. Additionally, a large number of small round no birefringence regions was appeared in the PHB/EVA 60 blend, which increased with increasing EVA 60 content, indicating a phase separation of PHB and EVA 60. The biodegradation for PHB composites in soil was tested via mass loss percentage and SEM. The results revealed that the biodegradability of PHB component in the blend was enhanced with an addition of NH4Cl and slightly decreased with increasing EVA 60 content. Such results make PHB/EVA60/1 mass%NH4Cl composites a promising candidate to substitute synthetic polymers derived from petroleum.