Research On Foam Injection Molding Of Polylactic Acid (PLA) With Chemical Foaming Agent

PLA is a biodegradable polyester, which is compostable in the environment with good biocompatibility, high tensile and bending strength as well. Foam injection molded products of PLA with light quality, complicated shape and high specific strength can be obtained, which can be applied widely in many fields such as biomedicine and daily necessities. But the melt strength of PLA is poor and the degree of crystallinity is low, which make foam injection molding of PLA quite difficult.In this paper, injection grade and extrusion grade of PLA were both chosen, and the melt strength and crystallinity nucleation were modified to overcome the drawbacks of PLA. The influence of melt strength modification, crystallinity nucleation modification, foaming agent system and injection molding parameters on foam injection molding of PLA were studied systematically. Then a kind of impact modifier was chosen to toughen the foamed products. The main conclusions in this paper are as belows:1. Chain extension improved the melt strength of PLA, making average cell size smaller and the mechanical properties improved. Three methods (Organic nucleation agent, inorganic nucleation agent and organic/inorganic nucleation agent) were applied successively to improve the crystallinity nucleation properties, and modified PLA was foam injection molded then.It found out that inorganic/organic nucleating agent had a better effect. Compared with extrution grade, foamed samples of injection grade PLA had better cell morphology and mechanical properties.2. Compared with single foaming agent, average cell size was samller under optimal content of modified foaming agent. The cell density was increased and mechanical properties were improved.3. The influence of injection process parameters (injection pressure, injection speed and temperature etc.) on the cell morphology and mechanical properties of foamed PLA was studied. The optimal process parameters were: injection pressure 95.6MPa, injection speed 100%, barrel temperature 200℃ and mold temperature 50℃.3. By toughen modification of impact modifier, foamed samples with good cell morphology and high toughness mechanical properties were prepared With optimal content 20wt% of impact modifier, the average cell size was 13.98μm, the cell density was 2.02×106/cm3, the elongation at break was 23.72%, the specific impact strength was 16.33kJ/(g·cm-3), but the specific tensile strength and specific bending strength were poor..