Tensile properties of microcellular poly(lactic acid) foams blown by compressed CO2

In this study, microcellular poly(lactic acid) foams with various crystallinities, cell morphologies, and densities were prepared using CO2 as the physical blowing agent. The evolution of crystallinity developments of four types of poly(lactic acid) samples during the saturation, foaming, and annealing processes was investigated. Crystallization of about 20% was reached in poly(lactic acid) samples after CO2 saturation, a high crystallinity of about 38.2% could be achieved for the foamed poly(lactic acid) that has the highest crystallization ability. Poly(lactic acid) samples had low elongation at break of 3.6–15.1%. After foaming, however, poly(lactic acid) foam presented a significant increase in the elongation at break up to 15.1 times compared with that of the unfoamed counterpart. On the other hand, microcellular foaming endowed poly(lactic acid) foams with a maximum increase in specific tensile strength of 53.1%. The influences of crystallinity, foam density, and cell morphology on the tensile properties of poly(lactic acid) foams were investigated.