Study On Structure And Properties Of Shape Memory Materials Based On TPV

Heat-triggered shape memory polymer(HSMP)based on ethylene-vinyl acetate copolymer(EVA)was prepared,and its mechanical behavior,orientation structure,crystallization behavior and shape memory behavior were studied systematically.The HSMP based on EVA/nitrile-butadiene rubber(NBR)thermoplastic vulcanizate(TPV)was prepared by dynamic vulcanization,and its mechanical properties,microstructure,shape memory properties and viscoelastic behavior were studied systematically.HSMP based on zinc methacrylate(ZDMA)in-situ compatibilized EVA/NBR TPV was prepared by dynamic vulcanization,and the influence of ZDMA incorporation on the mechanical properties and microstructure of the EVA/NBR TPV were systematically studied;moreover,the effect of deformation temperature,recovery temperature,rubber/plastic ratio,ZDMA content and the degree of deformation on the shape memory properties of TPV was also investigated.The relationship between the shape memory effect(SME)and the viscoelastic behavior of the TPV system was discussed,and the shape memory effect mechanism of the TPV-based HSMP was proposed;moreover,a method and mechanism to tune the shape memory properties of thermoplastic elastomer(TPE)based HSMPs was proposed.EVA/waste nitrile-butadiene rubber powder(WNBRP)blends were prepared by melt-compounding,while chlorinated polyethylene(CM)was used as a compatibilizer.The compression Mullins effect and reversibility of EVA/CM/WNBRP blends were investigated systematically.The main results were shown as below:(1)The EVA-based HSMP material was prepared,and its structure and shape memory properties were studied systematically.The studies on the mechanical properties of EVA indicated that the EVA exhibited excellent mechanical properties and could be described as TPE.FE-SEM studies showed that there were obvious orientation microstructures on the longitudinal tensile surface of EVA samples.DSC results demonstrated that the stretching deformation for the EVA samples promoted the formation of crystals,and there was a more perfect melting peak in the DSC curve of theshape-recovered sample.The results of shape memory property tests showed that the EVA sample could exhibit excellent shape recovery ability and faster shape recovery speed(shape recovery time <30 s)in the tensile,spiral and crimp modes.The EVA sample can obtain good shape fixing ratio(>95 %)and excellent shape recovery ratio(>95 %)when the deformation temperature was set close to the melting temperature of EVA;moreover,the time required to reach the maximum shape recovery ratio could be significantly shorten by increasing the shape recovery temperature and heat transfer efficiency.A formation mechanism of SME for EVA was proposed.The microcrystalline region in the EVA could play a role similar to physical cross-linking points to restrain the amorphous region,and the microcrystalline structure and the branched molecular chain entanglement jointly constituted the elastic network of EVA,which brought the EVA a permanent shape.(2)The HSMP based on EVA/NBR TPV was prepared,and its structure and shape memory properties were studied systematically.The studies on the mechanical properties showed that,with increasing EVA content in the EVA/NBR dynamic vulcanization system,the elongation at break,tensile strength and tear strength of the EVA/NBR system increased significantly,and the series of EVA/NBR dynamic vulcanization systems can be described as TPE.The FE-SEM observation results showed that the irregular NBR vulcanizate particles were evenly dispersed in the etched surface of the TPV sample,and the TPV exhibited a typical sea-island structure;moreover,the distinct striped microstructure could be clearly observed on the longitudinal tensile surface.The shape memory properties test results showed that when the deformation temperature was set close to the melting temperature of the EVA phase,the EVA/NBR(weight ratio=80/20)TPV specimen exhibited high shape recovery ratio(>95 %)and shape recovery ratio(>95 %);moreover,the EVA/NBR(weight ratio=80/20)TPV specimen could also fulfill shape recovery in the tensile,spiral and crimp modes(shape recovery time <30 s).DMA test results in temperature scan mode showed that with increasing the EVA content in the EVA/NBR TPVs,the tan ? value decreased while the E' value increased.Combining with the shape memory properties test results,the higher the EVA content,the stronger shape fixing ability of the TPV.A SME mechanism of EVA/NBR TPV was deduced.In this mechanism,the SME of TPV was considered to be related to deformation temperature,and TPV specimen would exhibit excellent SME when the deformation temperature was set close to the melting temperature of the EVA.(3)The HSMP based on ZDMA in-situ compatibilized EVA/NBR TPV was prepared,and its structure and shape memory properties were studied systematically.The studies on mechanical properties showed that the in-situ compatibilization of ZDMA significantly improved the mechanical properties of EVA/NBR TPV.The torque-time curve showed that the incorporation of ZDMA accelerated the cross-linking speed of NBR phase and increased the cross-linking density of NBR phase.The FE-SEM observation results showed that the incorporation of ZDMA greatly enlarged the interface area between EVA and NBR phase by refining the size of NBR particles;moreover,the incorporation of ZDMA improved the toughness of TPV,which made the orientation microstructure on the longitudinal tensile surface of TPV more obvious.Shape memory properties test results showed that EVA/ZDMA/NBR TPV samples could exhibit good SME and very short shape recovery time(~20 s)in the stretch,fold,spiral and curl modes.The shape fixity ability and shape recovery ability of EVA/NBR/ZDMA TPV were determined by the EVA matrix phase and the cross-linked NBR phase,respectively.The incorporation of ZDMA significantly improved the shape memory properties of EVA/NBR TPV;moreover,the TPV samples still exhibited excellent SME even under high strain.The DSC results showed that with increasing NBR phase content in the TPVs,the melting peak of EVA gradually decreased while the melting region became wider,indicating that the crystallization of EVA phase was interfered by NBR phase and the ZDMA-compatibilized interface.DMA results and stress relaxation behavior studies showed that higher storage modulus and lower stress relaxation ratio contributed to higher shape fixity and shape recovery for the EVA/NBR/ZDMA TPV,respectively.A SME mechanism of ZDMA-compatibilized EVA/NBR TPV was proposed.In this mechanism,the ZDMA enhanced the interfacial interaction and increased the interfacial thickness between the EVA and NBR phases by reacting with NBR and EVA at the interface,which contributed to the delivery of force at the interface;moreover,the incorporation of ZDMA increased the strength of NBR particles,with higher elastic force stored in shape fixing stage and further provided a strong force to drive the shape recovery.The regulation mechanism of shape memory properties of TPE-based HSMP was summarized and found that the regulation of shape memory properties can be achieved by introducing a new elastic phase or compatibilizing the interface between two phase.(4)The EVA/WNBRP blends were prepared by melt-compounding,and the interface compatibilization was carried out in which CM was used as a compatibilizer.The compression Mullins effect and its reversible recovery behavior of the blend system were studied systematically.The stress softening phenomenon,that also called Mullins effect,was observed obviously in the EVA/WNBRP and EVA/CM/WNBRP blends,which was weakened with the incorporation of CM;moreover,increasing the heat treatment temperature or introducing the compatibilizer CM would also enhance the reversible recovery ability of the Mullins effect of the EVA/WNBRP blends to some extent,and the recovery ability was the best when the heat treatment temperature was 100 ?.