Effect of poly(butylenes succinate) on the microcellular foaming of polylactide using supercritical carbon dioxide

Microcellular Polylactide (PLA) and PLA/poly(butylenes succinate) (PBS) foams were prepared by batch foaming process with supercritical carbon dioxide. The introduced PBS phase was immiscible with the PLA matrix and separated as domains. The study of CO2 solubility in PLA and PLA/PBS blends indicated the addition of PBS decreased the gas solubility due to the poor affinity of CO2 for PBS. The crystallization behavior of PLA was enhanced by small amount of PBS with lower cold crystallization temperature and higher crystallinity. However, separated PBS droplets led to less perfect and small crystallites, which showed greatly effect for the PLA foaming process. The investigation on the foaming conditions dependence indicated the PLA/PBS blends required higher temperature and longer time for the cell growth, which were nucleated around the interface between PLA and PBS. With less CO2 content in the PLA or PLA/PBS blends after different desorption time, the final cell morphology exhibited more uniform size distribution with bigger average cell size and smaller cell density. Different from the well closed-cell structure for neat PLA foam. the PLA/PBS foam presented open cell structure due to the cell nucleation around the PLA/PBS interface and the lower melt strength of PBS phase.