Strong Interface via Weak Interactions: Ultratough and Malleable Polylactic acid/Polyhydroxybutyrate Biocomposites

Bio-based and biodegradable polymer composites, most notably poly(l-lactic acid) (PLLA) and poly(3-hydroxybutyrate) (PHB), represent a promising solution to replace conventional petroleum-based plastics. However, the brittleness and low miscibility of PLLA and PHB remain two major obstacles to practical applications. In this work, first PLLA/PHB blends are reported by melt mixing with a rigid component, poly(methyl methacrylate) (PMMA). Driven by favorable entropy, PMMA forms an interfacial nanolayer, which transforms the morphology of resultant blends. The ternary blends show 55-fold increase in elongation, 50-fold in toughness, and metal-like malleability (≈180° bending and twisting), while retaining its high stiffness (3.4 GPa) and strength (≈50 MPa). The mechanical improvement arises from numerous craze fibrils and shear deformation of the matrix, induced by the incorporated PMMA. Furthermore, this generic strategy can be applied to design other mechanically robust biocomposites for advanced green devices.