Thermal and Rheological Behavior of Binary Blends of Poly(hydroxybutyrate-co-hydroxyvalerate) and Poly(ethylene-co-vinyl acetate) with Different Vinyl Acetate Content

摘要

The aim of this study is to investigate the influence of vinyl acetate (VA) content on the thermal and rheological properties of poly(hydroxybutyrate-co-hydrox-yvalerate) (PHBV)/poly(ethylene-co-vinyl acetate) (EVA) blends. Binary blends of PHBV and EVA containing 65wt% (EVA65) and 90wt% (EVA90) VA were prepared by torque rheometry and their thermal properties were studied by differential scanning calorimetry (DSC). Rheograms of PHBV/EVA65 containing up to 40wt% EVA showed that the torque values decrease as a function of mixing time due to the thermo-mechanical degradation, which preferentially for PHBV is chain scission. The increase in the EVA65 concentration results in torque stability probably due to the balance between chain scission of the PHBV and chain branching of the EVA65. For PHBV/EVA90 blends, the torque values are stable indicating that the presence of EVA90 decreases the degradation process of the PHBV and hence increases the thermal stability of blends. DSC curves showed that the PHBV cold crystallization temperature (T_(cc)) increased and cold crystallization (ΔH_(cc)) and melting enthalpies (ΔHm) decreased with the increase in the EVA content, independently of VA content and blend morphology. DSC curves of PHBV/EVA65 showed two glass transition temper-atures and clear phase separations, in all studied formulations, typical of immiscible systems. In contrast to it, PHBV/EVA90 blends showed a single glass transition, suggesting total miscibility. Both findings were corroborated by scanning electron microscopy (SEM) analysis.