Bio-based triblock copolymers from natural rubber and poly(lactic acid): Synthesis and application in polymer blending

•New bio-based PLA-NR-PLA triblock copolymers were synthesized from poly(lactic acid) and natural rubber.•New ester linkages between PLA and HTNR were observed in the 1H NMR spectrum.•PLA and HTNR block were investigated by DSC and TGA.•PLA-NR-PLA triblock copolymers acted as a toughening agent for PLA and a compatibilizer of PLA/NR blends.

This work involved the development of a synthetic method to produce a novel bio-based triblock copolymer (PLA-NR-PLA) that consisted of poly(lactic acid) and natural rubber. The 1H NMR analysis showed the presence of new ester linkages that resulted from a reaction between the carboxyl end-groups of the PLA prepolymer and the hydroxyl end-groups of the HTNR, together with the characteristics of the PLA endblock and the HTNR midblock. The Mn of PLA-NR-PLA as determined from the GPC agreed with that from the calculation. The DSC and TGA results also substantiated the formation of a block copolymer. PLA-NR-PLA acted as a toughening agent for PLA and as a compatibilizer in the PLA/NR blend. The PLA-NR-PLA was as good as a toughening agent as NR although the PLA-NR-PLA had a much lower molecular weight than the NR. The compatibilization effect was more dominant in the blend containing 10% rubber than in the blend that contained >10% rubber. The compatibilization effect was also observed in the morphology of the blend as a reduction in the rubber particle diameter. PLA-NR-PLA not only increased the impact strength of the blends, but also increased the elongation at break.

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