Structure And Properties Of Functional EAA/EVA Composite System And EAA/EVA/NBR Dynamic Vulcanization System

In this reserach,ethylene-acrylic acid copolymer（EAA）/ethylene-vinyl acetate copolymer（EVA）blends were prepared by simple melt compounding and dynamic vulcanization,respectively;and the prepared EAA/EVA/dicumyl peroxide（DCP）blends,EAA/EVA/nitrile butadiene rubber（NBR）dynamic vulcanization systems using sulfur（S）as rubber phase vulcanizing agent and EAA/EVA/NBR dynamic vulcanization systems using bis（tert-butylperoxy isopropyl）benzene（BIPB）peroxide as rubber phase vulcanizing agent were investigated systematically where the mechanical properties,microstructure and Mullins effect during tearing mode were charactered systematically.The research focuses on the triple shape memory behavior of the EAA/EVA/DCP blends,and the microstructure together with the thermo-mechanical properties were investigated.The relationship between the shape memory behavior and temperature was researched in depth;moreover,the shape memory mechanism was discussed.The non-isothermal crystallization kinetics of the EAA/EVA blends,EAA/EVA/DCP blends,EAA and EVA were also researched while the non-isothermal crystallization behavior was described by the Avrami and the Mo equations.And,a thermoplastic vulcanizate（TPV）consisting of ethylene-methyl acrylate copolymer（EMA）and NBR was prepared by dynamic vulcanization,and its microstructure,compression stress relaxation and reversible recovery behavior were investigated.The main conclusions are shown as below:（1）The Mullins effect and its reversible behavior of the EAA/EVA blend under tearing mode were researched.The results showed that the EAA/EVA blend exhibited the significant stress softening behavior during the uniaxial loading-unloading cycle and increasing the tearing strain could lead to the enhanced Mullins effect.Meanwhile,it was found that the reversible behavior of the Mullins effect under tearing mode was closely related to the heat treatment temperature;moreover,increasing the heat treatment temperature would significantly enhance the reversibility of the Mullins effect.（2）A simple strategy for designing a triple-shape memory polymer based on EAA/EVA/DCP blend was developed,which showed the low cost,recyclabilityand potential for large-scale production.Mechanical testing results showed that the EAA/EVA/DCP blend exhibited the excellent tensile strength and elongation at break.Differential scanning calorimetry（DSC）tests revealed that two distinct melting temperatures[the melting temperature of EAA in the blend(T_m-EAA)and the melting temperature of EVA in the blend(T_m-EVA)]and two distinct crystallization temperatures[the crystallization temperature of EAA in the blend(T_c-EAA)and the crystallization temperature of EVA in the blend(T_c-EVA)]could be found obviously for the EAA/EVA/DCP blend.Meanwhile,the shape memory property research indicated that the ideal first deformation temperature(T_d1),second deformation temperature(T_d2),first recovery temperature(T_r1),and second recovery temperature(T_r2)were 105,80,85,and110℃,respectively;while the first shape fixing ratio（SF₁）,second shape fixing ratio（SF₂）,first shape recovery ratio（SR₁）,and second shape recovery ratio（SR₂）was 90%,90%,100%,and 90%or so,respectively.In general,the results suggested that the EAA/EVA/DCP blend can be used to prepare the high-property and the shape-stable shape memory polymer.（3）The research aimed to investigate the effect of cooling rate on the non-isothermal crystallization behavior of pure EVA,pure EAA,EAA/EVA blends and EAA/EVA/DCP blends.The results showed that with increasing the cooling rate,the initial crystallization temperature（T₀）,crystallization peak temperature（T_p）and crystallization time(T_max)of the specimens were decreased obviously,and the crystallization enthalpy change（ΔH）also decreased.The initial crystallization temperature of EAA/EVA blends was higher than that of pure EVA and pure EAA,while it was decreased with the incorporation with DCP agent.The Jeziorny method and the Mo method were used to describe the crystallization process of the samples,and the analysis of the Avrami method showed that the higher cooling rates were beneficial to achieve the higher relative crystallinity and crystallization rates.（4）The influence of the different curing systems and the different NBR contents on the Mullins effect of dynamically vulcanized EAA/EVA/NBR blends under tear mode was researched.The results showed that the dynamically vulcanized EAA/EVA/NBR blends exhibited the obvious stress softening phenomenon in the uniaxial loading-unloading cycle.For the EAA/EVA/NBR dynamically vulcanized system using S as the rubber phase vulcanizing agent,increasing the NBR content led to the weak Mullins effect;however,for the EAA/EVA/NBR dynamically vulcanized system using BIPB as the rubber phase vulcanizing agent,increasing the NBR content resulted in the strong Mullins effect.The Mullins effect of the EAA/EVA/NBR dynamically vulcanized system using BIPB as the rubber phase vulcanizing agent was weaker than that of the EAA/EVA/NBR dynamically vulcanized system using S as the rubber phase vulcanizing agent when the NBR content was low in the EAA/EVA/NBR blends;increasing the NBR dosage,the Mullins effect of the EAA/EVA/NBR dynamically vulcanized system using BIPB as the rubber phase vulcanizing agent was stronger than that of the EAA/EVA/NBR dynamically vulcanized system using S as the rubber phase vulcanizing agent.（5）The compression stress relaxation curves of pure EMA,NBR static vulcanizate and EMA/NBR TPV were compared under different temperatures and strains.Parameters such as residual stress ratio,stress relaxation amount,compression permanent deformation and maximum stress recovery rate were calculated.The results showed that the compression stress relaxation of EMA/NBR TPV was mainly determined by the EMA continuous phase.The increase in the heat treatment temperature could significantly enhance the reversibility of TPV in compression stress relaxation,which reached its maximum at the melting point of EMA（90℃）.