Rheological behavior, crystallization properties, and foaming performance of chain-extended poly (lactic acid) by functionalized epoxy

The inherently linear poly (lactic acid) suffers unsatisfying foaming behavior due to its low melt strength and poor crystallization properties. To overcome this drawback, a random terpolymer of ethylene, acrylic ester and glycidyl methacrylate (EGMA) was employed to improve the rheological behavior, crystallization properties, and foaming performance of poly (lactic acid) (PLA) through a chain extension reaction. The branched/micro-crosslinked structure formed by the chain extension reaction between EGMA and PLA effectively improved the dynamic rheological properties of PLA. As the content of EGMA increased from 0 wt% to 20 wt%, the crystal nucleation and crystal growth rate of various PLA samples have been significantly accelerated, resulting in a larger number and smaller size of spherulites, and the crystallinity of various PLA samples increased from 7.9% to 38.54%. The cell size of various PLA foams decreased from 53.5 to 22.0 μm and the cell density increased from 3.5 × 106 cells per cm3 to 2.5 × 107 cells per cm3, meanwhile, the cellular morphology of PLA foam was obviously improved. Moreover, the actual weight loss of PLA foams reached 26.1%, which is higher than the theoretical weight loss.