Environmentally-friendly, sustainable ScCO2-assisted fabrication of poly (lactic acid)/ramie fiber composite foams

In this study, green ramie fiber reinforced Poly (lactic acid) composite foam is prepared through a novel physical method based on one-step autoclave foaming and molding process, only using environmentally friendly CO2 as the foaming agent. The biodegradable ramie fiber not only remain the green nature of Poly (lactic acid), but also enhance the foaming performance, by virtue of the powerful ability in improving the melt strength and crystallization. The unique cavity structure inside the plant fiber can absorb large amount of CO2 and promote CO2 solubility in the composite by 32.9%. Melt bimodal peaks exist in the composite after the CO2 foaming treatment and the crystallinity levels up by 39.6% compared to pure Poly (lactic acid). The enhanced melt strength by ramie fiber reinforcement and the crystallinity by CO2 plasticizing effect jointly promotes the foaming process and cellular structures from collapsed and huge cells to idea regular and refined micropores. In addition, the different interfacial bonding abilities between matrix and fiber contribute to different cell structures around the fibers. The work provides a green method and an important guideline for the preparation of low-carbon and environmental-friendly lightweight polymer composite foams.