Enhancing the compatibility and performance of poly (lactic acid) and thermoplastic polyolefin elastomer blends through a dual compatibilization strategy.

Application of biodegradable polylactic acid (PLA) is limited by its poor toughness. This research focuses on modifying PLA using thermoplastic elastomers (TPO), primarily due to their dual advantages of enhancing performance and reducing application costs. Two thermoplastic polyolefin elastomers (TPO) (NS06, Versify2300) were blended to prepare a superior elastomer TPO(NV) (NS06:Versify2300 = 80:20). This improved TPO(NV) was then used as a toughening agent to enhance the toughness of polylactic acid (PLA). To enhance the compatibility between PLA and TPO(NV), TPO(NV)-g-(GMA-co-St) graft copolymer and dibutyl itaconate (DBI) were introduced into the PLA/TPO(NV) blend system. The effects of different compatibilizers on the compatibility, crystallization behavior, rheological properties, mechanical properties, and microstructure of the PLA/TPO(NV) blends were systematically studied. The results indicated that glycidyl methacrylate (GMA) and styrene (St) were successfully grafted onto the TPO(NV) molecular chains. The epoxy groups in GMA within the graft copolymer could react with the end groups of the PLA resin, while the double bonds in DBI could react with the main chains of either PLA or TPO(NV) elastomer. This effectively connected the PLA and TPO(NV) molecular chains, collectively enhancing the compatibility between TPO(NV) elastomer and PLA. The non-isothermal crystallization ability of TPO(NV) decreased after blending with PLA, and this effect was further amplified with the introduction of the TPO(NV)-g-(GMA-co-St) graft copolymer or DBI. However, the plasticizing effect of DBI increased the mobility of the polymer molecular chains, thereby enhancing the crystallization ability. Therefore, when DBI was used alone to enhance the compatibility of PLA/TPO(NV) blends, the crystallinity of the blend did not change significantly. In contrast, when the TPO(NV)-g-(GMA-co-St) graft copolymer was used alone or in combination with DBI, the crystallinity of the blend decreased significantly. Mechanical property tests indicated that the addition of either the TPO(NV)-g-(GMA-co-St) graft copolymer or DBI improved the compatibility of PLA/TPO(NV) blends, thereby enhancing their mechanical properties. However, the combined addition of both the TPO(NV)-g-(GMA-co-St) graft copolymer and DBI resulted in a more pronounced effect. The notched impact strength and elongation at break reached optimal values, which were 1.9 times and 10.4 times those of the PLA/TPO(NV) blend, respectively. At this point, the fracture surface of the blend exhibited significant plastic flow, indicating characteristics of ductile fracture.