Block copolymers and melt blends of polylactide with Nodax microbial polyesters: preparation and mechanical properties.

Completely renewable resource-based, degradable composites of poly(l-lactide) and Nodax [poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)] were prepared by a melt blending procedure. oligoNodax-b-poly(l-lactide) diblock copolymers were synthesized and their use as compatibilizers in these melt blends was investigated. The block copolymers were prepared from microbially produced Nodax polyhydroxyalkanoate by a two-step transesterification and macroinitiator ring opening polymerization method. Addition of Nodax increased the notched Izod impact resistance of the binary blends compared to that of PLLA homopolymer (44+/-6 J m(-1) versus 22+/-2 J m(-1), respectively). Further addition of the oligoNodax-b-poly(l-lactide) block copolymers to form ternary blends resulted in composites with improved dispersion and decreased Nodax particle size, but no additional improvement in the notched Izod impact properties. Significant Nodax degradation during processing coupled with a high Nodax entanglement molecular weight, as well as crystallization and low impact resistance of the Nodax dispersed phase are implicated as major factors impeding further toughening.