Preparation and properties of biodegradable polymeric blends from poly(propylene carbonate) and poly(ethylene-co-vinyl alcohol).

Biodegradable blends of poly(propylene carbonate)/ethylene-vinyl alcohol copolymers (PPC/EVOH) were melt prepared. The mechanical strength, crystallization and melting behavior, morphologies, and thermal properties of these blends were fully investigated using tensile tester, modulated differential scanning calorimetry, scanning electron microscopy, and thermogravimetric analysis, respectively. The results indicated that the thermal stability of blends could be enhanced by increasing EVOH content. No change was observed for the tensile strength when EVOH content was lower than 30 wt %. The tensile strength, however, increased obviously with increasing EVOH content when EVOH content was higher than 30 wt %. The crystallization behavior of the PPC/EVOH blends was studied accordingly. The degradability test showed that the weight loss of PPC/EVOH blends increased with increasing EVOH content because of the strong moisture sorption of EVOH. Morphology observation indicated that the PPC/EVOH blends exhibited a two-phase microstructure. The blends with EVOH contents ranging from 40 to 60 wt % showed the best comprehensive properties as biodegradable thermoplastic for many applications.

Biodegradability and thermal stability of poly(propylene carbonate)/starch composites.

Poly(propylene carbonate)/starch (PPC/starch) composites with different starch contents were prepared by melt compounding. The biodegradability of the composites was studied by soil burial for a period of 6 months. FTIR study, thermal analysis and morphology observation indicated clearly the changes of the buried specimens. The weight loss curves and the molecular weight changes of the specimens revealed a three-stage biodegradation, corresponding to the propagation of microorganisms, the degradation of starch and the degradation of PPC. The experimental results showed that the addition of starch accelerated the degradation of PPC. Specimens with higher starch content exhibited greater weight loss in the second stage and smaller weight loss in the third stage.