Use of stereocomplex crystallites for fully-biobased microcellular low-density poly(lactic acid) foams for green packaging

Abstract Success in the typical extrusion foaming process is always achieved by adding inorganic/organic fillers, which inevitably sacrifice poly(lactic acid) (PLA)’s green nature. Herein, we successfully fabricated well-defined cell structures of fully bio-based PLA foams using a series of asymmetric biodegradable poly( l -lactide) (PLLA) and poly( d -lactide) (PDLA) blends with small amounts of PDLA. We obtained large-scale PLLA/PDLA blends using a continuous melt compounding technique. The crystallization kinetics in the presence of dissolved carbon dioxide (CO 2 ) under high pressures was investigated by using regular and high-pressure DSC. The PLA’s crystallization rates were notably accelerated due to the significant synergy of the dissolved CO 2 and the reserved SC crystallites. The continuous extrusion process, which could be easily scaled-up to industry, was used to fabricate the PLLA/PDLA blended foams. Using the neat PLLA foam, we successfully demonstrated how to make fully bio-based PLA foams with three orders of magnitude increased cell density, an enhanced expansion ratio over ten-fold, and increased crystallinity by 15%. Such a high cell density, a high expansion ratio and a high crystallinity are unprecedented in the continuous processing of fully green PLA foams. They possess great potential for use as a sustainable product in thermoformed food packaging applications.