Structure And Properties Of Functional EMA/NBR TPV And Coordination Crosslinking NBR

In this research,ethylene-methyl acrylate(EMA)/nitrile rubber(NBR)thermoplastic vulcanizates(TPV)were prepared via dynamic vulcanization.The micro-morphology,Mullins effect under tearing mode and shape memory behavior under compression mode were investigated,and their mechanism was proposed.The metal coordination crosslinking NBR/copper sulfate(CuSO₄)/tetramethylthiuram disulfide(TMTD)vulcanizates with synergistic effect was prepared by blending and hot vulcanization.The synergistic mechanism between TMTD and CuSO₄ in the metal coordination reaction was elaborated,and the effects of TMTD dosages on its coordination crosslinking behavior,segment mobility of coordination crosslinking products,mechanical properties,micro-morphology,crosslinking density and Mullins effect under compression mode of vulcanizates were investigated systematically.The energy loss behavior and the reversible recovery behavior of Mullins effect under cyclic uniaxial compression were investigated,and the coordination crosslinking network structure of NBR/CuSO₄was destroyed by mechanical shearing at room temperature to realize green regeneration.The effects of mechanical shearing on the cure curves,glass transition temperature(T_g)and swelling behavior of NBR were investigated,and the application of green recycled rubber was explored.(1)The micro-morphology of EMA/NBR TPV showed a typical"sea-island"microstructure and the cryogenically fractured surface of EMA/NBR TPV after compression showed the orientation structure which was perpendicular to the compression direction.Dynamic thermomechanical analysis(DMA)results showed the excellent compatibility between EMA phase and NBR phase.Differential scanning calorimetry(DSC)demonstrated that the melting temperature of EMA/NBR TPV was about 98?.EMA/NBR TPV had obvious Mullins effect under tearing mode,and the maximum tearing strength,instantaneous residual deformation,internal consumption and tan?gradually increased with the increase of strain,but the stress softening factor gradually decreases with the increase of strain.The Mullins effect of EMA/NBR TPV could be restored to a certain extent after proper heat treatment.EMA/NBR TPV had the best recovery ability when the heat treatment temperature was 100?.The increasing dosages of EMA would increase the shape fixation rate and decrease the shape recovery rate of EMA/NBR TPV.The shape fixation ra`tio and shape recovery ratio of EMA/NBR TPV were 97.89%and 95.25%respectively when the fixation temperature and recovery temperature were 95?and 100?,respectively.(2)The results of cure curves of the NBR/CuSO₄ and NBR/CuSO₄/TMTD system and mechanical properties of vulcanizates showed that the torque,tensile strength,tearing strength and hardness of the vulcanizates were increased significantly and the elongation at break decreased accordingly with the increase of CuSO₄,TMTD dosages or appropriate increase of the curing temperature.The incorporation of TMTD in NBR/CuSO₄ strengthened the crosslinking network and weakened the Mullins effect of NBR vulcanizates,and the weakening effect was more significant with the increase of TMTD dosages.The results of Fourier transform infrared spectroscopy(FTIR),DSC,X-ray photoelectron spectroscopy(XPS),Field emission scanning electron microscope(FE-SEM)and swelling behavior showed that the crosslinking network of vulcanizates was formed by the reaction of copper ion(Cu²⁺)and nitrile(-CN)after heating.The crosslinking density of vulcanizates was increased significantly with the incorporation of TMTD into NBR/CuSO₄,resulting in the increae of glass transition temperature(T_g).These were due to the combination of highly active free radicals produced by the pyrolysis of TMTD and Cu²⁺and formed[Cu(Sn CNMe2)]^·2+complex which had stronger reaction activity and higher binding energy compared with Cu²⁺and reacted with-CN easily.The XPS test results further demonstrated the synergistic effect of TMTD and CuSO₄ in crosslinking with-CN.The results of XPS further demonstrated that TMTD and CuSO₄ had a synergistic effect in coordination crosslinking with-CN.The experimental results of cyclic uniaxial compression and reversible recovery showed that the Mullins effect of NBR/CuSO₄ and NBR/CuSO₄/TMTD vulcanizates could be recovered to a certain extent after heat treatment at appropriate temperature,and the compression Mullins effect recovery of vulcanizates was best when the heat treatment temperature was 150?.(3)The green regeneration test results of NBR/CuSO₄ vulcanizates showed that the samples had lower torque,T_g and crosslinking density under the strong mechanical shearing action of rubber open mixer at room temperature,indicating that the shearing action at room temperature could successfully destroy the coordination crosslinking action of NBR/CuSO₄ vulcanizates.The NBR vulcanizates with excellent performance could be obtained again by reheating the green recycled NBR.The tensile strength,tear strength and hardness of vulcanizates could be significantly improved,permanent set and elongation at break decreased accordingly when the heating time was 30 min and the heating temperature was 180?.(4)EMA/NBR/CuSO₄ blending TPV based on coordination crosslinking was successfully prepared via dynamic vulcanization,and EMA/green recycled NBR TPV was prepared by using NBR material after mechanical shearing.With the same preparation conditions,the mechanical properties of coordination crosslinking EMA/NBR/CuSO₄ TPV increased with the increase of CuSO₄ dosages gradually.Morever,TPV prepared by EMA/green recycled NBR had better mechanical properties than that prepared by NBR/CuSO₄ compounds and EMA with the same rubber/plastic content ratio and CuSO₄ dosages in the system,which might provide a new way for the reuse of metal ion coordination crosslinking rubber.The results of shape memory behavior of EMA/NBR/CuSO₄ TPV showd that the coordination crosslinking EMA/NBR/CuSO₄ TPV possessed well shape memory performance under compression mode.The shape fixation ratio decreased and the shape recovery ratio increased gradually with the increase of CuSO₄ dosages.EMA/green recycled coordination crosslinking NBR vulcanizates TPV(50/50/10)possessed similar shape memory performance to EMA/NBR/CuSO₄ TPV(50/50/20).The shape fixation ratio and shape recovery ratio of EMA/NBR/CuSO₄ TPV were 85.50%and 88.30%respectively.