Guiyan Zhao

Toughening polylactide with polyether-block-amide and thermoplastic starch acetate: Influence of starch esterification degree.

Native corn starch was esterified with acetic anhydride and plasticized with glycerol to give the thermoplastic starch acetate (TPSA). TPSA was blended with polylactide (PLA) and polyether-block-amide-graft-glycidyl methacrylate (PEBA-g-GMA) to obtain biodegradable PLA/PEBA-g-GMA/TPSA blends with high notched impact resistance and low cost. Compared with PLA/PEBA-g-GMA blends, as much as 9 wt% expensive PEBA-g-GMA elastomer could be substituted by the slightly acetylated thermoplastic starch while retaining high impact strength. The mechanical properties depended on the esterification degree of starch acetate. The impact strength, tensile strength and elongation at break increased to the peak value with increasing the esterification degree from 0 to 0.04, thereafter they decreased on further increasing the esterification degree. The morphological results showed that the TPSA particles were smaller and more uniform at the optimum esterification degree of 0.04, leading to the peak value of the mechanical properties.

Toughening poly(3-hydroxybutyrate) with propylene carbonate plasticized poly(propylene carbonate)

Abstract Poly(3-hydroxybutyrate) (PHB)/poly(propylene carbonate) (PPC) blends containing various amounts of plasticizer propylene carbonate (PC) were prepared, and the toughness of the blends as a function of temperature was studied. It was found that the brittle-ductile transition temperature (TBD) of PHB toughened by PPC decreased from 60°C to 10°C with the increase in PC content. As PC is the plasticizer of PPC, the mechanical properties, such as Young’s modulus of plasticized PPC with different PC contents, were also studied. Sequentially, the relationship between TBD and the ratio of the Young’s modulus (E1) of the PHB matrix to that of the plasticized PPC elastomer (E2) was investigated. It was found that the Young’s modulus of plasticized PPC should be considerably lower than that of the PHB matrix in order to obtain ’the tough PHB/plasticized PPC blends at a lower temperature. In contrast, the morphology of the dispersed particles also had an important influence on the toughness. When the plasticizer content was more than 20 wt.%, the PPC particles became more spherical and smaller. The toughness could be considerably improved accordingly.