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.