Improving the heat deflection temperature of poly(lactic acid) foams by annealing

Abstract Poly(lactic acid) is a promising biopolymer but due to its low heat deflection temperature, the usage of PLA-based products is limited. In the case of bulk products, annealing is an effective way to increase the heat deflection temperature. Our aim was to improve the heat deflection temperature of poly(lactic acid) foams by annealing. In this study, we showed that D-lactide content affects the crystallinity of foam structures in the same way it affects the crystallinity of bulk PLA. Lower D-lactide content resulted in a higher degree of crystallinity. Annealing proved to be an effective way to induce cold crystallization. The heat deflection temperatures were calculated with the use of DMA, which produced more accurate results than the HDT device. Outstanding heat deflection temperature results were achieved (from 54°C to 131°C) with the use of annealing of chemically foamed PLA foams (1.4% D-lactide content) containing a nucleating agent. The excellent results can be explained with increased crystallinity, which exceeded 40%. Also, no signs of thermal degradation were found after successful annealing.