Preparation Of Polylactic Acid/Rubber/Inorganic Particle Thermoplastic Vulcanizates And Study On Their Structure And Properties

As one of the most effective methods to toughen polylactic acid(PLA),the introduction of rubber can improve the toughness of PLA,which is also accompanied by a sharp decrease in the tensile strength and modulus of PLA.Therefore,it is urgent to continuously improve the toughness of PLA-based materials while maintaining high tensile strength and modulus.At the same time,a high-performance material can no longer meet the special requirements of cutting-edge technologies in the fields of space,microelectronics,and medical treatment.In this case,smart materials that can respond the changes of external environment have attracted more and more attention,such as various sensitive materials,shape memory materials and self-healing materials.Therefore,this thesis hopes to regulate the dispersion of fillers in the rubber and plastic phases of thermoplastic vulcanizate(TPV),and utilize the rubber and fillers to synergistically toughen PLA and endow the PLA-based TPV with balanced stiffness-toughness.And then we explore the mechanism of shape memory and self-healing behavior of the TPV,providing new strategies and methods for the design of PLA-based TPV with high-performance and multi-functionalization.The specific research contents and main results are as follows:(1)PLA,epoxidized natural rubber(ENR)and silica(Si O₂)were utilized to fabricate PLA/ENR/Si O₂ TPV with balanced stiffness-toughness based on dynamic vulcanization,in which Si O₂ was regulated to selective distribute in the ENR phase by changing the feeding process.The phase morphology and mechanical properties of PLA/ENR/Si O₂ TPV were studied thoroughly.The addition of Si O₂ did not change the co-continuous structure of the PLA/ENR TPV.By regulating the distribution of Si O₂ in ENR phase,the reinforcement of the ENR phase can be achieved,thus the structural integrality and strength of continuous ENR network were improved,realizing the synergistic toughening of PLA.With the incorporation of 20 phr Si O₂,the impact strength of the TPV increased to 64.1 k J/m².Meanwhile,the tensile strength and modulus of TPV did not decreased significantly,demonstrating that the PLA/ENR/Si O₂ TPV exhibited balanced stiffness-toughness.(2)The ferroferric oxide(Fe₃O₄)was introduced into the PLA/ENR system to fabricate PLA/ENR/Fe₃O₄ TPV with different distribution of Fe₃O₄.The contact angle,swelling experiment,TEM and SEM and other test methods were carried out to study the effect of Fe₃O₄ on the structure,mechanical properties and thermally induced shape memory properties of the TPV.Fe₃O₄ was regulated to distributed int the ENR phase by premixing Fe₃O₄ with ENR,which helped to restrict the agglomeration and migration to the PLA phase,improving the mechanical properties of TPV.Meanwhile,the addition of Fe₃O₄ helped to improve the heat-triggered shape memory performance of TPV.(3)Based on the above research,we successfully realized the synergistic toughening of PLA by introducting Fe₃O₄ and ENR.The PLA/ENR/Fe₃O₄ TPV with balanced stiffness-toughness was successfully prepared,and the TPV showed excellent shape memory performance under different stimuli.With 30 phr Fe₃O₄,the notched impact strength of the TPV increased to 146.3 k J/m²,which was 8 times that of PLA/ENR TPV and 53 times that of pure PLA.However,the PLA/ENR/Fe₃O₄ TPV still maintained the similar tensile strength and Young's modulus like the PLA/ENR TPV,indicating that PLA/ENR/Fe₃O₄ TPV exhibited balanced stiffness-toughness.The continuous ENR network reinforced by Fe₃O₄ could maintain a relatively integrated structure and high mechanical strength during the shape memory cycles,showing a shape recovery ratio of more than 93%after multiple shape memory process.At the same time,the excellent magnetocaloric and photothermal effects of Fe₃O₄ endowed the TPV with remotely/locally triggered shape memory performance induced by alternating magnetic fields and near-infrared light.(4)Based on the study of shape memory-assisted self-healing materials with semi-interpenetrating structure,we explored the self-healing performance of PLA/ENR/Fe₃O₄TPV assisted by the shape memory effect.The TPV self-healing mechanism was proposed:the shape memory effect of TPV raelized the physical contact of the damaged surface;the“adsorption-desorption”reversible process of ENR-Fe₃O₄ bound rubber at high temperature endowed the continuous ENR phase with self-healing ability;ENR chains were grafted onto the PLA chains,and the grafted PLA chains were driven by ENR during its healing process,achieving the repair of the PLA phase.The disulfide bonds were introduced into PLA/ENR vulcanizate and PLA/ENR TPV to realize self-healing of rubber-plastic blending systems based on reversible covalent bonds.First,the disulfide bonds were introduced into PLA/ENR vulcanizate through solution blending,and the self-healing process of PLA/ENR vulcanizate was realized through the reversible process of disulfide bonds and assistance of the shape memory effect.Then,the disulfide bonds were introduced into PLA/ENR TPV through dynamic vulcanization and realized the self-healing of TPV.(5)The metal-ligand coordination interaction was introduced into the dynamic vulcanization process,and the coordination was utilized to induce the dynamic vulcanization of butadiene acrylonitrile rubber(NBR)to prepare the PLA/NBR TPV successfully.Copper sulfate(Cu SO₄)was continuously refined through the process of“dissolution-reaction-redissolution-reaction”under the action of shearing force and high temperature.Cu SO₄ was coordinated with NBR in the form of Cu²⁺and refined nanoparticles.Coordination was performed to realize the dynamic vulcanization of NBR,and the refined Cu SO₄ nanoparticles could reinforce the NBR,improving the mechanical properties and shape memory properties of the TPV.Meanwhilr,metal-ligand coordination-induced dynamic vulcanization showed good applicability in preparing different TPV systems.The coordination between ferric chloride and NBR was utilized to prepare acrylonitrile-styrene copolymer(SAN)/NBR TPV,which effectively improved the mechanical properties of SAN-based TPV.With the incorporation of 5 phr Fe Cl₃,the tensile strength and elongation at break increased to 13.4MPa and 112.2%.