Preparation and properties of the crosslinked poly(L-lactide) with high crystallinity and high gel content

Poly(L-lactide) (PLA) is the most important biobased polymer and is widely used in various fields. However, its application is still greatly limited by the distinct disadvantage such as poor thermal resistance. In this study, in order to improve the thermal properties, crosslinked PLA with high crystallinity (44 %) and high gel content (91 %) is prepared by the UV irradiation of its semicrystalline films by the loading of certain photoinitiators and curing agents. The structure and properties of the obtained films are systematically investigated with NMR, DSC, DMA, TG and WAXD. It is found that the crosslinking of the semicrystalline PLA film is more difficult than that of the amorphous in the absence of crosslinker. However, the combinations of 2phr photoinitiator such as 4,4′-dichloro benzophenone (DCB) and 2 phr crosslinker of 1,3,5-triallylisocyanurate (TAIC) can effectively trigger the crosslinking and high gel content up to 91 % can be achieved. Corresponding to the high density crosslinking, an increase of the glass transition temperature from 66.6 °C to 75.5 °C is observed for crystallized PLA, indicating an obvious improvement in thermal resistance. More interestingly, it is found that this crosslinked PLA with high crystallinity and high gel content still possesses high crystallizability.