Microcellular processing of polylactide–hyperbranched polyester–nanoclay composites

The effects of addition of hyperbranched polyesters (HBPs) and nanoclay on the material properties of both solid and microcellular polylactide (PLA) produced via a conventional and microcellular injection-molding process, respectively, were investigated. The effects of two different types of HBPs (i.e., Boltorn H2004® and Boltorn H20®) at the same loading level (i.e., 12%), and the same type of HBP at different loading levels (i.e., Boltorn H2004® at 6 and 12%), as well as the simultaneous addition of 12% Boltorn H2004® and 2% Cloisite®30B nanoclay (i.e., HBP–nanoclay) on the thermal and mechanical properties (both static and dynamic), and the cell morphology of the microcellular components were noted. The addition of HBPs and/or HBP with nanoclay decreased the average cell size, and increased the cell density. The stress–strain plots of all the solid and microcellular PLA-H2004 blends showed considerable strain softening and cold drawing, indicating a ductile fracture mode. Among the two HBPs, samples with Boltorn H2004® showed higher strain-at-break and specific toughness compared to Boltorn H20®. Moreover, the sample with Boltorn H2004® and nanoclay exhibited the highest strain-at-break (626% for solid and 406% for microcellular) and specific toughness (405% for solid and 334% for microcellular). Finally, the specific toughness, strain-at-break, and specific strength of microcellular samples were found to be lower than their solid counterparts.