Tensile properties of microcellular poly(lactic acid) foams blown by compressed CO 2

Abstract

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.