Improved flexibility of thermally stable poly-lactic acid (PLA)

The objective of this research was to determine the optimum solvent mixture ratio to improve flexibility while maintaining the thermal expansion stability of PLA film. PLA films were produced from mixed solvent solutions of (M: methylene chloride) and (A: acetonitrile) and 10% plasticizer using the solvent-casting technique. The ratio of solvents used were 70% methylene chloride with 30% acetonitrile (73MA10), 60% methylene chloride with 40% acetonitrile (64MA10) and 50% methylene chloride with 50% acetonitrile (55MA10). The single solvent solution was 100% methylene chloride (100M10). Thermal stability was enhanced by the addition of acetonitrile. Thermal stability of 55MA10 was 0.6219 μm/°C as compared to 15.63μm/̊C for 100M10. Increased concentration of acetonitrile also improved crystal formation as seen by the peak intensity of WAXD. Films that had more crystallinity (64MA10, 55MA10), had less thermal expansion stability and brittle behavior. In contrast, 73MA10 having less crystallinity, had the best flexibility at 49.36% elongation while having similar thermal behavior as the more crystalline films. This work shows that PLA film produced by solvent casting from solvent mixture compared to a traditional single solvent will have better thermal and mechanical performance.