Study On Structure And Properties Of PP/EPDM/NBR TPV By Core-shell Dynamic Vulcanization

Polypropylene/ethylene propylene diene monomer(PP/EPDM)thermoplastic vulcanizate(TPV)has the advantages of excellent weather resistance,corrosion resistance,good processability and low price.However the pure PP/EPDM TPV has some shortcomings,such as poor heat resistance,poor oil resistance and insufficient mechanical strength,etc.In order to solve these problems,researchers have conducted a lot of study,including changing the crosslinking density of rubber phase,adding nanomaterials,mixing with other elastomers,improving compatibility and regulating processing technology,etc.Among them,improving the compatibility between plastic matrix and rubber has been a hot topic.When studying polyvinylidene fluoride/fluorone silicone rubber(PVDF/FKM/SR)system,our group proposed core-shell dynamic vulcanization,and successfully improved the compatibility between PVDF and SR,which provided a new idea for improving the compatibility of polymer blends.In this paper,PP/EPDM/nitrile rubber(NBR)TPV was prepared by core-shell dynamic vulcanization.The mechanical properties,morphology,crystallization,rheology,stress relaxation/softening and thermo-oxidative aging performances of PP/EPDM/NBR TPV with different rubber ratios were studied by adjusting the ratio of EPDM/NBR.The results show that rubber phase in all TPV is dispersed in the form of pellets in a continuous PP matrix,showing a typical “sea-island” structure.With the increase of NBR content,the tensile strength and tear strength of PP/EPDM/NBR TPV increase first and then decrease,the elongation at break gradually decreases,the 100% tensile strength and elastic modulus gradually increase.When EPDM content is the same as NBR in the TPV,the tensile strength,tear strength,100% elongation strength,and Young's modulus of the PP/EPDM/NBR(40/30/30)TPV are 12.57 MPa,81.20 k N/m,12.12 MPa and 138.93 MPa,respectively.Compared with P4E6,they increased by 17.37%,20.60%,32.75%,and 51.13%,respectively.With the increase of NBR content,the modulus of TPV increases,the crystallization peak temperature and melting point increase,and the stress relaxation rate decreases.Thermo-oxidative aging experiments show that in the PP/EPDM/NBR ternary system,the higher the EPDM-shell content,the better the TPV's heat-resistant oxygen aging resistance.On the basis of fixed rubber-plastic ratio and EPDM/NBR ratio in the TPV,the effects of different oil content on the mechanical properties,morphology,crystallization,resilience and compression set of PP/EPDM(40/60)TPV and PP/EPDM/NBR(40/30/30)TPV were studied.The results show that the increase of oil content has similar effects on the mechanical properties and compatibility of the two systems.With the oil content increasing,the tensile strength and hardness gradually decrease,the elongation at break increases first and then decreases,the resilience becomes smaller and smaller,the compression set increases gradually,and the compatibility becomes better and then worsens.In addition,the oil resistance and shape memory behavior of PP/EPDM/NBR TPV with different rubber ratios were also studied.Oil resistance results demonstrate that the higher the NBR content,the better the dimensional stability and performance stability corresponding to TPV,which shows that NBR can effectively improve the oil resistance of PP/EPDM TPV.Studies on shape memory behavior show that in the PP/EPDM/NBR ternary system,the higher the EPDM-shell content,the higher the shape fixation and recovery ratios,and the faster the recovery rate.