Preparation of toughened thermal insulating polylactic acid/thermoplastic polyester elastomer (TPEE) microcellular foam using in situ fibrillation and multi-hydrazide nucleating agent self-assembly

Traditional foamed plastics can no longer meet the requirements of modern industries. High-performance biodegradable thermal-insulation materials are required for the food transportation and packaging industry. In this study, we introduced the synergistic self-assembly effect of nanoelastic (TPEE) fibers and TMC-300 (sebacic acid diphenyl hydrazide) through an in situ fibrosis to control the crystal morphology and phase structure. This effect improves the melt viscoelasticity of branched polylactic acid (CBPLA) and improves the foaming performance of PLA. The sea-island structure of PLA composites was transformed into an imperfect bi-continuous structure and its toughness was improved without the loss of PLA stiffness. Further, the toughness of the CBPLA/TMC/TPEE composite was improved by 76%, the thermal stability was significantly improved, and there was no effect on the tensile strength. CBPLA/TMC/TPEE microcellular foams were successfully prepared using supercritical CO2 in an intermittent high-pressure foaming autoclave with average cell diameter of 4 μm. The cell density of CBPLA foam was increased by 3 orders of magnitude compared to that of pure PLA foam, average cell diameter successfully reduce from 34 μm to 4 μm. The thermal conductivity of air in the micron-sized cells was reduced significantly, and therefore, the microcellular foam showed excellent thermal insulation performance with a thermal conductivity as low as 25.2 mW/mK. The TPEE/TMC elastic self-assembled fiber network dispersed on the cell wall cooperatively supported the PLA cell wall, which significantly improved the compressive resistance of PLA foams; the compression rebound rate of the foam was approximately 34%. The results indicate that CBPLA/TMC/TPEE microcellular foam materials are potential candidates for high-performance thermal applications because of their excellent thermal stability, toughness, and thermal insulation performance.