Studies On Enr And Modified SiO₂ Or PEG Synergistic Toughening PLA Based On Dynamic Vulcanization

As a high-quality and sustainable biodegradable material,polylactic acid(PLA)has attracted catholic attention due to abundance in raw materials and excellent mechanical strength.However,the inherent high brittleness and poor impact resistance hinder its application and promotion,so PLA should be toughened.In this paper,rigid nanoparticle silica(SiO₂)or poly(ethylene glycol)(PEG)was used as the toughener of PLA in cooperation with epoxidized natural rubber(ENR),dicumyl peroxide(DCP)as the initiator via the dynamic vulcanization technology to prepare the PLA-based thermoplastic vulcanizate(TPV)with high toughness.Through a variety of testing methods,the structure and performance of PLA-based TPVs were studied in detail,and the synergistic effect between the toughening components and the mechanism of strengthening and/or toughening were also discussed.(1)Bio-based PLA/ENR TPVs with different DCP content were prepared of by dynamic vulcanization.Infrared spectroscopy(FT-IR)analysis shows that during the dynamic vulcanization process,DCP induced the cross-linking of rubber,and at the same time triggered the grafting reaction between PLA and ENR.The formation of grafted product reduced the interfacial tension between rubber and plastic,which would increase compatibility.Compared with PLA/ENR simple blend,the mechanical properties of TPV had been significantly improved.As the increasing amount of DCP,the tensile strength of TPV increases slightly,while the impact strength decreases slightly after increasing.Using 2phr of DCP made TPV reach the maximum impact strength of 34.1 k J/m²,which were 12.2-fold and 1.9-fold of pure PLA(2.8 k J/m²)and PLA/ENR simple blend(17.6 k J/m²)respectively.Scanning electron microscopy(SEM)results showed that the cross-linked ENR phase was distributed in the PLA matrix in a continuous network structure.This special co-continuous phase structure was significantly different from the traditional TPV"sea-island"structure.A proper amount of DCP was beneficial to improve the mechanical strength of ENR and keep the morphology of the rubber network more uniform and symmetrical.When impacted by external forces,the enhanced rubber phase and interface strength would effectively transfer and absorb external energy inside the material,the plastic deformation caused was the main manifestation of the high impact resistance of PLA/ENR TPV.Moreover,the smaller the Mooney viscosity of the rubber,the more conducive to the uniform distribution in the PLA matrix during melt blending,so that the TPV could obtain more stable tensile strength and higher impact strength.(2)Incorporated nano-SiO₂ modified with KH550 to prepared PLA/ENR/SiO₂/KH550TPV through dynamic vulcanization.The mechanical results showed that after SiO₂modification,the tensile strength and tear strength of ENR/SiO₂/KH550 vulcanizate were increased by up to 24%and 35%,respectively,while PLA/ENR/SiO₂/KH550 TPV exhibited a better balance of rigidity and toughness.Among them,the impact strength of could reach 23.7k J/m² at 0?,while maintaining the tensile strength above 42 MPa.The research results showed that the dispersion of modified SiO₂ was improved,and the agglomeration of nanoparticles in TPVs was reduced.SiO₂ was mainly selectively distributed in the continuous ENR phase,which helps to reduce the stress concentration inside the material.In addition,it was also beneficial to enhance the rubber and maintain the regular network of the rubber,thereby improving the efficiency of TPV dissipation and transfer of external energy.And a part of the SiO₂ migrated into the PLA matrix could accelerate the crystallization of PLA and slightly increase the crystallinity of PLA.In summary,comprehensive factors such as uniform rubber network morphology,rubber reinforcement,reduction of internal defects of the material,enhanced interface effect and increase of PLA crystallization finally endow PLA/ENR/SiO₂/KH550 TPV with an excellent balance of rigidity and toughness.(3)Incorporated plasticizer PEG to prepared PLA/PEG/ENR TPV via dynamic vulcanization.The interface contact angle,DSC and DMA results showed that PEG was mainly distributed in the PLA matrix for plasticization,which could greatly reduce the glass transition temperature(T_g)of PLA,increase the crystallization ability and the crystallinity of PLA.The compatibility of the two phases of rubber and plastic was improved.Mechanical tests showed that PEG could simultaneously increase the elongation at break and impact strength of TPV,making PLA/PEG/ENR TPV obtain good tensile toughness and impact toughness at higher PEG content,and the maximum values of 320.7%and 53.6 k J/m² were obtained at P-10,which were 19.6 times and 1.8 times that of P-0,respectively.SEM results suggested that when TPVs deformed due to external force,high content of PEG was more conducive to plastic flow of PLA matrix,thereby accelerating the slip and orientation of molecular chains.Therefore,by plasticizing the PLA matrix and improving the interface compatibility,high strain of TPV could be achieved,while the impact energy would also be effectively absorbed,so as to obtain excellent impact strength.