Processing and characterization of solid and foamed injection-molded polylactide with talc

Polylactide (PLA) suffers from poor processability due to its low melt strength and slow crystallization kinetics and it is thus very challenging to achieve uniformly distributed fine-celled PLA foams with high void fractions in injection molding process. In this work, the low-pressure structural foam molding of linear PLA with a relatively high void fraction of ∼30% was conducted and by fine tuning the talc content and the foaming and processing parameters, a relatively uniform fine-celled structure with improved cell size and cell density was successfully produced. The effects of twin-screw compounding and the addition of talc on the foaming behavior, structural uniformity, crystallinity, and mechanical properties of the solid and foamed PLA samples were investigated. The results showed that the addition of 5 wt.% talc significantly improved the foaming properties such as cell density, cell size, structural uniformity, and consequently improved the mechanical properties of foams. The twin-screw compounding before injection molding did not significantly change the foaming behavior, but adversely affected the mechanical properties of the solid and foamed PLA samples due to mechanical and thermal degradation. The changes in the mechanical properties were discussed in terms of the crystallinity, talc toughening effect, and foam quality.