| Poly(lactide)(PLA) is regarded as one of the most competitive renewable bio-based polymers because of its excellent biodegradability, good biocompatibility,high mechanical strength and easy processability. However, PLA exhibits natural brittleness with a notched impact strength of only 2.7 kJ·m-2 and poor ductility with an elongation yield at break of 3.5%.These inherent drawbacks of PLA restrict its use in the development and application in the plastic field. Therefore, the development of PLA blends with super toughness has an important theoretical and practical significant.In this paper, core-shell copolymer, modified natural rubber and biological elastomer were used to prepare supertoughened PLA blends through reactive melt blending. The influence of different toughening agent on the mechanical properties of PLA was studies. Meanwhile, the interfacial compatibilization and phase morphology of PLA with different toughening agents was studied using Fourier Transform Infrared Spectroscopy(FT-IR), thermal analysis, and scanning electron microscope(SEM) measurements. And toughening mechanisms of supertoughened PLA blends were further explored. The main results are as follows:(1) Poly(butadiene-g-styrene-glycidyl methacrylate)(PB-g-St-GMA) core-shell copolymer was prepared via emulsion polymerization with polybutadiene(PB) as seed emulsion, styrene(St) and glycidyl methacrylate(GMA) as grafting monomer. It was demonstrated that the target synthetic product was spindle-type core-shell structure using FT-IR and TEM measurements. The influence of reaction time, concentration of initiator and emulsifier on polymerization yield and product particle size were systematically studied. The results showed that the polymerization yield reaches at 93.5% when the concentration of initiator was 0.5%, concentration of emulsifier was 0.5% and the reaction time was 4h.(2) The influence of PB-g-St-GMA and poly(acrylonitrile-butadiene-styrene)(ABS) core-shell copolymer on the mechanical properties and crystallization behavior of PLA blends was studied. When the content of PB-St-GMA was 10wt%,the elongation at break was 10.1%,which was about 2 times higher than that of pure PLA.The results showed that the ductility of PLA blend was improved with a small amount of ABS. When the content of ABS was 6 wt%, the elongation at break and of PLA/ABS blend was 118%, which was about 23 times higher than that of pure PLA, and impact strength of PLA/ABS was increased by 1 time. It was demonstrated that the interfacial compatibilization of PLA and ABS was improved by polarity interaction between ester of PLA and PBSN shell of ABS. Meanwhile, a small amount of ABS core shell particles as heterogeneous nucleating agent enhanced the crystallization rate of PLA matrix.(3) The modified Nature rubber-g-GMA(NR-g-GMA) was prepared through reactive melting blending via free radical polymerization using GMA as modified agent. And a supertoughened PLA thermoplastic elastomer was obtained using PLA and NR-g-GMA through reactive melt blending. The results showed that notched impact strength and elongation at break reached up to 73.4 kJ·m-2 and 158.8%, which were about 26 times and 44 times higher than those of PLA, respectively,when the content of NR-g-GMA was 20 wt%. It was demonstrated that the epoxidation reaction between PLA and NR-g-GMA improved the interfacial adhesion of PLA matrix and NR-g-GMA dispersed phase. For supertoughened thermoplastic elasomer, the interfacial interaction between PLA matrix and NR-g-GMA phase was so strong that a large scale of shear-yielding for NR-g-GMA particles together with the PLA matrix was produced at the impact fractured surface, which could significantly improve impact strength of PLA blend.(4) Supertoughened PLA ternary blends were prepared by reactive melt blending using poly(butyleneadipate-co-terephthalate)(PBAT) and ethylene-acrylic ester-glycidyl methacrylate(E-AE-GMA) as modifiers. When the content of E-AE-GMA was 15wt%, the notched impact strength and elongation at break of PLA/10wt%PBAT ternary blend could reach up to 61.9 kJ·m-2 and 265.9%, which were about 21 times and 77 times higher than those of PLA, respectively. The phase morphology of supertoughed PLA ternary blends was systematically analyzed by SEM, DMA, and FT-IR measurements. The results indicated that the incorporation of E-AE-GMA in PLA/PBAT blends improved the interfacial adhesion and compatibility between PLA matrix and PBAT particles. E-AE-GMA phase played two important roles as reactive compatibilizer as well as toughing agent in the PLA/PBAT/E-AE-GMA ternary blends. The SEM results of PLA blends showed that co-continuous phase structure was formed with PLA matrix, because PBAT, and E-AE-GMA produced a large scale of shear-yielding at the impact fractured surface. The toughening mechanism of supertoughened PLA blend demonstrated the strong interfacial interaction between E-AE-GMA and PLA by reactive compatibilizing and a large scale of shear-yielding in E-AE-GMA and PBAT have synergistic effect on toughening of PLA. |
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