Anomalous Postprocessing Dimensional Change of Injection- Molded Products Composed of Poly(lactic acid) and Poly(vinyl alcohol)

The present study revealed that an injection-molded product comprising poly(lactic acid) (PLA) and poly(vinyl alcohol) (PVAL) exhibited an anomalous dimensional change, i.e., expansion in the flow direction, after postprocessing annealing (around 2.9% expansion by annealing at 80-100 degrees C for 3 h). Although the crystallization of the PLA during cooling was not accelerated by the addition of PVAL, the PLA showed transcrystallization from the dispersed PVAL droplets, which were deformed in the flow direction, during postprocessing annealing. Therefore, after annealing, the injection-molded products exhibited a high degree of molecular orientation, in contrast to the original unannealed products, which were not oriented. This anomalous behavior should be noted as a means of controlling dimensional change after processing.

Automated summary

The study found that an injection-molded product made from poly(lactic acid) (PLA) and poly(vinyl alcohol) (PVAL) exhibited expansion in the flow direction after postprocessing annealing. This was due to the transcrystallization of PLA from the deformed PVAL droplets during annealing. The injection-molded products showed a high degree of molecular orientation after annealing, unlike the unannealed products.