| Replacement of petroleum-based plastics with biodegradable polylactic acid(PLA)-based materials is an effective way to reduce the consumption of petroleum resources,alleviate the energy crisis,reasonably prevent and control plastic pollution,and promote the development of a green and circular economy.However,the poor toughness of PLA limits its further application.Flexible biodegradable polyesters are usually used to improve the toughness of PLA,and in view of the poor compatibility between PLA and flexible polyesters,copolymers containing PLA molecular chains,functional polymers or low molecular weight additives are commonly used to regulate the interfacial compatibility between the phases,and how to regulate the interfacial compatibility between PLA and other phases is the priority of research to obtain high-performance PLA-based.In this paper,three epoxy functional oligomer with different structures were introduced into the PLA/polybutylene terephthalate adipate(PBAT)blend system.The effects of the molecular chain structure and interfacial reaction efficiency of the epoxy functional polymers on the microscopic molecular chain structure,condensed structure,interfacial morphology evolution,interfacial compatibility and properties of PLA and PLA/PBAT blend system were investigated.The effects of the synergistic interaction between highly reactive epoxy functional oligomer and carboxylated multi-walled carbon nanotubes(MWCNTs)on the interfacial phase structure and dielectric properties of PLA/PBAT composites were also investigated on this basis.The main work is as follows:(1)High-performance PLA/PBAT/binary oligomer(SG)blends were prepared by the melt blending method.The modulation of the interfacial phase structure and phase behaviour of PLA and PBAT by the reactive SG was investigated by DSC,DMA,SEM,rheological behaviour,mechanical properties and processing properties;the effects of SG on the microscopic molecular chain movement,evolution of interfacial phase morphology and macroscopic mechanical properties of PLA/PBAT blends were systematically investigated.It was found that the introduction of low content of SG has low interfacial reactivity,which tends to form short branched chains at the interface,promoting the untwisting of molecular chains and leading to a decrease in the viscosity of the material;the introduction of high content of SG(>1.0 wt%)has high interfacial reactivity,which can promote the entanglement of molecular chains by forming branched chains in the molecular chains of PLA or PBAT and improving the interaction between molecular chains,increasing the viscosity and modulus of the material.With the addition of 0.5 wt% SG,the material has excellent stiffness and toughness balance under the combined effect of plasticisation and reaction capacitation.(2)Furthermore,a high-strength and high-toughness PLA/PBAT/CE blend was prepared with the introduction of a highly reactive multifunctional zwitterion(CE)into the PLA/PBAT(80/20)blend system by melt blending.The effects of CE on the interfacial phase morphology evolution,microscopic molecular chain movement and properties of PLA/PBAT blends were systematically investigated by DSC,DMA,SEM,rheological behaviour,mechanical properties and processing properties.It was found that CE has high interfacial reactivity and can promote the entanglement of PLA and PBAT molecular chains by building a three-dimensional network of micro-crosslinks at the interface between PLA and PBAT phases,which enhances the interaction between molecular chains and improves interfacial compatibility.At the same time,the morphology of the PLA and PBAT phases was modified from “island structure” to“bicontinuous phase structure”,which resulted in the material exhibiting solid-like characteristics.In particular,when 0.5 wt% of CE was added,the interfacial reaction between the two phases was the most efficient,and a more complete interfacial microcrosslinking network could be formed,which improved the ductility of the material,where the tensile strength of the material reached 49.1 MPa and the elongation at break increased to 366.3%.(3)The effect of functional zwitterion structure on the morphological evolution of the PLA/PBAT interface,ternary functional zwitterions(TE)with well-defined structures were designed and synthesized,and high-performance PLA/PBAT/TE blends were prepared by melt blending.The influence of the functional zwitterion structure on the interfacial reaction efficiency was investigated by DSC,DMA,SEM,rheological behaviour,mechanical properties and processing properties,and the effect of the functional zwitterion structure on the microstructure and properties of the PLA/PBAT blend system was systematically studied.It was found that the interfacial reaction efficiency of TE was slightly lower than that of CE,but significantly higher than that of SG.Moreover,TE can construct a more complete interfacial branching and microcrosslinking network at the phase interface,which can improve the inherent elasticity and melt strength of the material and promote the transformation of the material to solid-like properties.Meanwhile,the phase morphology of the PLA/PBAT blends is changed from“island” to “bicontinuous phase”.In particular,when 0.5 wt% of TE was introduced,the tensile strength and elongation at break of the blends were simultaneously increased,with the tensile strength reaching 49.3 MPa and the elongation at break increasing to 320.7%,providing an excellent stiffness and toughness balance.(4)Based on the previous study,PLA-based composites with high dielectricity and high toughness were prepared by introducing carboxylated MWCNTs into the PLA/PBAT/CE blending system.The effects of the synergistic interaction between the highly reactive CE and carboxylated MWCNTs on the interfacial phase behaviour and microscopic molecular chain motion of PLA/PBAT were investigated by DSC,DMA,SEM,TG,rheological behaviour,mechanical properties,dielectric properties and processing properties.And the modulation of CE on the position of MWCNTs in the matrix,which effect on the properties of the composites was investigated.It was found that the carboxyl groups in the MWCNTs could react with the epoxy groups in the CE molecular chains to regulate the migration of MWCNTs to the interface between PLA and PBAT,and by constructing a multidimensional cross-linked network with MWCNTs and CE as the core at the interface,the movement of PLA molecular chains was restricted and the entanglement ability of interfacial molecular chains was improved,which promoted the transition of PLA/PBAT composites to a bicontinuous phase structure.However,the high content of carboxylated MWCNTs tends to form a physical shielding effect which reduces the efficiency of the interfacial reaction of CE.At the same time,the introduction of CE can form a conductive network through the interaction of groups and a multi-level "micro-capacitance" structure between the adjacent MWCNTs and the polymer matrix,which improves the dielectric properties of the material.In particular,when 3.0 wt% of MWCNTs are introduced,the composite not only has high dielectric properties but also has excellent stiffness and toughness balance.Figure 32 table 25 reference 143... |
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