Research On Molding Process Of Silane Crosslinked PP/POE(EPDM) Blends

Silane crosslinked polypropylene/polyolefin elastomer(PP/POE)blends and polypropylene/ethylene propylene terpolymer(PP/EPDM)blends are widely used in many aspects of production and life due to their excellent impact toughness.However,there are many kinds of polypropylene,and huge differences in the internal composition between each type.How to choose a suitable matrix for silane cross-linking modification has became an urgent problem to be solved in the actual production and processing.Silane cross-linking blends based on PP can be used to make large-scale plastic sheets,and have been widely used in practical production.But the traditional equipment and methods for producing large-scale plastic sheets are backward,which seriously affects the performance and service life of products.In this work,silane crosslinked PP/POE(EPDM)blends were prepared using block impact resistant copolymer polypropylene(PP-B)and homopolymer polypropylene(PP-H)as matrix.The structure,properties and morphology of the blends were studied by various testing and characterization methods.In the non-isothermal crystallization kinetic study of silane crosslinked PP/EPDM blends,it was found that EPDM and branched or crosslinked gel particles could play a heterogeneous nucleation role,which significantly increased the initial crystallization temperature and crystallization peak temperature of PP.The performance differences of silane crosslinked PP/POE blends were compared.It was found that silane crosslinked PP/POE blends were more suitable for practical production.Finally,the integrated extrusion-injection molding technology of large plastic sheet based on silane cross-linked PP/POE blends was studied,and the optimum extrusion and pressing parameters of silane cross-linked PP/POE blends were obtained.The main research work is as follows:(1)Silane crosslinked PP/POE(EPDM)blends were prepared by using block impact resistant copolymer polypropylene(PP-B)and homopolymer polypropylene(PP-H)as matrix resins.Infrared spectroscopy(FTIR)test showed that vinyl trimethoxy silane(VTMS)was successfully grafted onto silane crosslinked PP/POE(EPDM)blends.Differential scanning calorimetry(DSC)analysis showed that the addition of POE or EPDM and the formation of silane cross-linking structure reduced the crystallinity of PP,but improved the thermal stability.The impact strength of PP-B was much higher than that of PP-H,but after crosslinking with POE and EPDM silane,the impact strength of PP-B was lower than that of PP-H.The ethylene in PP-B was also silane crosslinked,resulting in excessive silane crosslinking structure,which has a negative effect on the impact resistance of PP-B.Scanning electron microscope(SEM)photos showed that the cross-section of silane-crosslinked PP-B/POE(EPDM)blends treated with n-heptane etching was smaller and the interface was rougher than that of silane-crosslinked PP-H/POE(EPDM).Above results showed that the cross-linking degree of silane-crosslinked materials based on PP-B was higher than PP-H.The crystallinity and rheological properties of silane crosslinked PP-H/POE(EPDM)blends were similar to those of silane crosslinked PP-B/POE(EPDM),but PP-B/POE(EPDM)had better mechanical properties and thermal stability.(2)The crystallization behavior and non-isothermal crystallization kinetics of silane crosslinked PP/EPDM blends were studied by DSC.The results showed that EPDM and branched or crosslinked gel particles could play heterogeneous nucleation,and increased the initial crystallization temperature and crystallization peak temperature of PP.When PP was blended with EPDM,the crystallization rate of PP phase increased to a certain extent,while the formation of silane cross-linking structure played a negative role in the crystallization rate of PP phase.The Avrami and Mo models could describe the non-isothermal crystallization kinetics of the samples well.The values of folding surface free energy(σe)and molecular chain folding work(q)were ranked as follows:PP>simple PP/EPDM blends>silane crosslinked PP/EPDM blends.Kissinger and Vyazovkin methods were used to evaluate the non-isothermal crystallization activation energy of the samples.The results showed that silane crosslinked PP/EPDM blends had the lowest crystallization activation energy(AE)value,which indicated that silane crosslinked PP/EPDM blends were the easiest to crystallize.Based on previous studies,the non-isothermal crystallization process of silane crosslinked PP/POE blends was compared,and it was found that the non-isothermal crystallization behavior of silane crosslinked PP/POE blends was similar to that of silane crosslinked PP/POE blends.(3)The formulation of silane crosslinked PP/POE blends was fixed,the extrusion and die-pressing process of large thick plate of silane crosslinked PP/POE blends were studied.The optimum extrusion process parameters in the study range were:feeding speed 190rpm,extrusion processing temperature 210℃.The optimum molding conditions in the study range were:molding temperature 100℃,molding time 5min,molding pressure 15MPa.Based on those parameters above,the rheological properties of samples,the half-life and decomposition rate of DCP were studied under different extrusion conditions.The gel content of silane crosslinked PP/POE blends at different extrusion temperatures was found to have some corresponding relationship,which provided a reference for the silane crosslinking blending material in the setting of extrusion parameters.Combined with extrusion and die-pressing parameters,the integrated extrusion-injection process parameters of large-scale silane-crosslinked PP/POE blends with thickness of 10mm were obtained.At the same time,the set of integrated extrusion-injection system for large-scale plastic sheets was designed,which improved production efficiency and product quality.