Relationships between crosslinking behaviour and morphological development in PLA/ENR blends using maleic anhydride as a coupling and TPV agent

Maleic anhydride (MA) can function as both a grafting agent and a thermoplastic vulcanizate (TPV) agent or crosslinker in thermoplastic elastomer (TPE) blends of polylactic acid (PLA) and epoxidized natural rubber (ENR), depending on the degree of crosslinking. To validate the claim, a set of formulations with MA ranges from 0 to 2.0 phr was added to the PLA/ENR blend at different matrix blend ratios and compounding sequences. To distinguish the types of networks responsible for altering the blend’s phase and melt flow behaviour, various tests including mechanical, rheological, viscoelasicity validation, visual imaging, thermal analysis and spectroscopy testing of X-ray diffraction analysis (XRD) and Fourier transform infrared (FTIR) were conducted. The results revealed that, without the presence of MA, the blends behave as typical thermoplastic elastomers (TPEs). Meanwhile, the addition of MA enhances the tensile properties and modifies the blend microstructure, indicating the presence of a coupling effect in the PLA/ENR blend. With further inclusion of more MA inside the blends, the rise in crosslinking degree transforms the blend into a thermoplastic vulcanizate (TPV) compound. Interestingly, in the molten state, the TPV blends exhibit dilatant flow behaviour, which is in contrast with the shear-thinning flow pattern of PLA.