(199l) A Study on Extent of Chain Crosslink on HDT Improvement of Poly (lactic acid)

The low heat deflection temperature (HDT) of poly(lactic acid) (PLA), at approximately 55^oC, has greatly limited its use in many fields of work especially in the high temperature applications. It was anticipated that the molecular structure of PLA greatly influenced the HDT values. Therefore, samples of crosslinked PLA with different crosslinking density were prepared by reactive extrusion in the presence of triallyl isocyanurate (TAIC) and luperox 101 to observed the impact of changes to the molecular structure on the HDT of PLA. The gel contents, rheological properties, crystallinity, HDT and dynamic mechanical (DMA) properties of the crosslinked PLA were determined in this study. The results found that the HDT of the crosslinked PLA remained unchanged around 55 ^oC, even when the sample was highly crosslinked. The DMA studies suggested that the glass transition of the crosslinked chains were the same as the linear PLA. It was then inferred that the chain segment movement had not been limited by the crosslinking, and thus the final HDT of the amorphous PLA was not improved. Finally, we increase the crystallinity of the crosslinked samples, finding that the HDT was improved at a critical crystallinity value. The research concluded that the improvement of the HDT of PLA can only be achieved by limited the movement of the PLA chain segments, rather than the chain coil, which can be a guide in our future work on improving the HDT of PLA.

Acknowledgment: This research is financially supported by the Ontario Research Fund, Research Excellence Program; Round-7 (ORF-RE07) from the Ontario Ministry of Research, Innovation and Science (MRIS) (Project # 052644 and 052665); the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA)/University of Guelph Gryphon’s LAAIR Program (Project # 298636); Agriculture and Agri-Food Canada (AAFC) and Competitive Green Technologies through AgriInnovation Program project (Project # 052882 and 051910); and the Natural Sciences and Engineering Research Council (NSERC), Canada Discovery Grants (Project # 401111 and 400320).