Preparation And Properties Of Silane Crosslinked PP/EPDM(POE) Blends

Polypropylene/ethylene propylene diene monomer(PP/EPDM)blends and PP/polyolefin elastomer(PP/POE)blends are widely used in many aspects of production and life because of their excellent impact toughness.However,its relatively low thermal stability,low solvent resistance and stiffness limit the ranges of their applications.Crosslinking modification(peroxide crosslinking,silane crosslinking,radiation crosslinking)is one of the effective ways to overcome these disadvantages.Silane crosslinking modification technology with its relatively simple production technology,less equipment investment and easy to promote advantages have received widespread attention.In this work,silane crosslinked PP/EPDM and silane crosslinked PP/POE blends were prepared by one-step extrusion process using PP,EPDM and POE as matrix.The morphology,structure and properties of silane crosslinked PP/EPDM blends and silane crosslinked PP/POE blends were investigated by various tests and characterization methods.Meanwhile,we also discussed the correlation between the dynamic viscoelastic properties parameter and the best comprehensive properties of the blends,the relationships between the“gel point”and the blending ratio,which provides a new theoretical basis for the optimization of material properties and the improvement of processing technology.The main work is as follows:(1)In the system of silane crosslinked PP/EPDM,the influence of different PP and EPDM ratios on the performance of silane crosslinked PP/EPDM blends were studied.The two step crosslinking mechanism of PP/EPDM blends was verified Fourier Transform infrared spectroscopy(FTIR)analysis.Dynamic mechanical analysis(DMA)and scanning electron microscopy(SEM)analysis showed that the silane crosslinking reaction can improve the compatibility between PP and EPDM phases.When the EPDM content is 20%,the tensile strength and elongation at break of the silane crosslinked PP/EPDM blends reach the maximum at the same time,which is in certain correspondence with the"gel point"obtained from the dynamic rheological analysis,and the tensile properties of blends at"gel point"was discussed in detail.(2)In the system of silane crosslinked PP/EPDM(70/30),the effects of vinyl trimethoxy silane(VTMS)and dicumyl peroxide(DCP)contents on the properties of silane crosslinked PP/EPDM blends were investigated in detail.The results showed that with the increase of VTMS and DCP content,the degree of crosslinking and thermal stability of silane crosslinked PP/EPDM blends increased,while the crystallinity decreased.Dynamic rheological analysis showed that with the increase of cross-linking degree,the elasticity of the silane crosslinked PP/EPDM blends gradually increased and the relaxation time became longer.When the contents of VTMS and DCP were between 0.25-0.5phr and 0-0.02phr,respectively,the silane crosslinked PP/EPDM blends showed a"liquid-solid"transition.Compared with PP/EPDM blends,the addition of appropriate amounts of VTMS and DCP can significantly improve the mechanical properties of the blends.(3)In the system of silane crosslinked PP/POE,the influence of different PP and POE ratios on the performance of silane crosslinked PP/POE blends were studied.The two step crosslinking mechanism of PP/POE blends was verified by FTIR analysis.SEM analysis confirmed the formation of a silane crosslinked network,which corresponds to the"second platform"in the low frequency region of the dynamic rheological curves,which is the main reason for increasing the solvent resistance of the blends.The tensile strength of the silane crosslinked PP/POE blends maintains relatively high levels and the toughness of the blends increases significantly due to the presence of the crosslinked network.When POE content is30%,the blends show good mechanical properties.The"gel point"obtained from the dynamic rheological analysis had some corresponding relationship with mechanical properties and solvent resistance.Meanwhile,the influence of different VTMS and DCP contents on the properties of silane crosslinked PP/POE blends were studied in detail when the ratio of PP/POE was 70/30,and that was compared with the properties of silane crosslinked PP/EPDM blends.(4)In the study of non-isothermal crystallization kinetics of silane crosslinked PP/POE blends,it was found that Jeziorny and Mo’s method can well describe the non-isothermal crystallization kinetics of samples,while the Ozawa’s method was not suitable.The nucleation parameters(K_g)and non-isothermal crystallization activation energy(ΔE)of the blends were calculated by Lauritzen-Hoffman equation and Kissinger’s method respectively.The results showed that with the increase of POE content,K_g andΔE did not show obvious changes,and the Kg andΔE of S73 are slightly lower than P73 because of the heterogeneous nucleation of the branched or crosslinked gel particles on the PP phase.The addition of POE and the formation of silane crosslinking structure did not change the crystalline form of the PP phase in the blends,but the size of PP spherulites was obviously reduced.