Study on Heat Resistance of PLA Based Biodegradable Injection Molded Components

Abstract

With the increasingly serious problem of white pollution, biodegradable substitutes that can replace the existing plastic materials are in urgent need. In the present work, thermal shock experiments were carried out to investigate the heat resistance of injection molded F6510 products under specific humidity/temperature conditions. Specifically, two groups of experiments were designed at a constant humidity of 90%. For single-point temperature (SPT) experiments, the testing temperature was varied from 30°C to 75 °C with an interval of 5/10 °C, and for the thermal cycle (TC) experiments, samples underwent 60 °C -(-20 °C)-60 °C thermal cycles. The SPT experiments showed that samples began to deform at 45 °C, with 0.05mm increase in length, and 0.02mm decrease in both width and height, and the shape variation increases with enhanced temperature. Meanwhile, TC experiment samples showed obvious shrinkage during the nine-day testing period, with a maximal size variation of 0.44mm for the length. In addition, DSC results showed a higher crystallinity degree for the inner layer of samples. This is due to the slower cooling rate of the inner layer, facilitating polymer molecular chain migration and thus the crystal nucleus growing, which was supported by Moldex3D simulation analyses. Double melting peaks appeared in the heating stage of DSC test, indicating the formation of both α and α’ crystal forms, which has been verified by both thermal shock experiments and DSC tests. The findings of this work indicate that the crystallinity, crystal form, and thus the products’ heat resistance of F6510 can be improved by reasonably controlling injection molding parameters such as the mold temperature and cooling time.