In-situ cross-linking strategy for achieving excellent impact resistance and thermal insulation of closed-cell poly(lactic acid) (PLA)/poly (4-hydroxybutyrate) (P4HB) foams

Owing to inherent issues like interfacial stress concentration, open-cell, a low volume expansion ratio (VER) and cell density, the impact resistance and thermal insulation of supercritical foamed poly(lactic acid) (PLA) blend foams remain unsatisfactory. To overcome these challenges, an in-situ cross-linking strategy is employed to enhance the compatibility between PLA and poly(4-hydroxybutyrate) (P4HB), while improving the melt strength and crystallization behavior of the blends. The modified PLA/P4HB blend exhibits a blurred interfacial boundary with fewer stress concentrations. As a result, the specific impact strength increases from 9.76 to 26.17 kJ center dot m-2/ (g center dot cm-3) after foaming. The ambiguous interface and enhanced melt strength reduce the risk of cell wall rupture and collapse, while the increased crystallization provides additional nucleation sites. Consequently, the modified PLA/P4HB foam transitions from an open-cell to a closed-cell structure, achieving a VER of 35.4 and a cell density of 2.0 x 107cells/cm3, representing respective increases of 16.1-fold and 9.1-fold compared to unmodified PLA/P4HB foam. At this time, the thermal conductivity and thermal diffusivity of the PLA/P4HB foam reach 31.5 mW/m center dot K and 8.1 x 10-7m2/s, respectively. In conclusion, this strategy provides a method for producing PLA/P4HB foams with high impact resistance and thermal insulation, and addresses common issues associated with PLA-based blends foam.