Study On Preparation And Properties Of In-Situ-Compatibilized PP/POE Blends

In order to overcome the disadvantage of low-temperature impact strength of polypropylene(PP)and to meet the end-requirements for the automobile bumpers,the objective of the present dissertation was to improve the mechanical properties of PP via in situ compatibilization method.The metallocene polyolef in elastomers ploy (ethylene-1-octene),was used as toughening rubber and dicumyl peroxide(DCP)/ Trimethylolpropane triacrylate(TMPTA)was used as co-during systems.PP/POE blends were prepared in an internal mixer at 175℃,and their mechanical properties, morphology,crystallization kinetics,and rheological behaviors were investigated by differential scanning calorimetry(DSC),polarized optical microscopy,scanning electron microscopy and capillary rheometer,respectively.The results of the mechanical properties demonstrated that the impact strength of PP/POE blends was improved significantly by in situ compatibilization method,the maximum value of the room-temperature and low-temperature impact strength for the in situ compatibilized PP/POE blends was reached to 52.03KJ/m~2 and 37.29KJ/m~2, and was 11.74 times and 16.28 times of that of pure PP,respectively.SEM photographs of PP/POE blends indicated the POE seperatation phase became smaller and dispersed much unifrormly within PP matrix with the increasing of DCP concentration.The impact-fractured surface displayed distinguished interfaces for the PP/POE blends while a coarser breakage surface interface was observed for the compatibilized PP/POE blends.The analysis of isothermal crystallization behavior indicated that the Avrami equation described well the isothermal crystallization of PP and its blends.The POE served as nucleating agent and increased the nucleating rate of the blends.The mode of the nucleation and growth of PP and its blends might be a mixture of may be two-dimensional and three dimensional growth with thermal nucleation.The equilibrium melting point and the folding surface free energy of compatibilized PP/POE blends were higher than that of pure PP.The investigation of non-isothermal crystallization showed that Ozawa equation was not suitable to describe the non-isothermal crystallization process,while the modified Avrami and Mo equations took great advantages over treating the non-isothermal crystallization kinetics.Although the incorporation of POE into PP increased the crystallization nucleating rate of PP in the blends,it didn't change the mechanism of nucleation and the growth of PP crystallites.The data calculated from the Hoffman-Lauritzen theory and its deduction revealed that the addition of POE decreased the absolute values of effective activation energy and the effective activation energy of non-isothermal crystallization.The results of POM(Polarized Optical Microscopy)showed that the domain of PP spherulites decreased while the numbers of PP spherulites increased in the compatiblized PP/POE blends.The experimental results of rheological behaviors revealed that both PP and its blends are pseudo-plasticity fluid and exhibited shear-thinning behavior.The shear stress of the compatiilized PP/POE blends decreased gradually with the increasing of DCP concentration in the case of the same shear stress,indicating that the incorporation of DCP reduced the domains of the POE separation phase.The apparent viscosity of the compatibilized PP/POE blends was lower than that of the simple PP/POE blends,it was implied that the melt viscosity of the compatibilized blends was less temperature-sensitive than that of the simply blends.On the other hand,the apperant viscous activation energy tended to reduce with the increasing shear rate, inferring that the high processing temperature can improve the processability in the case of low shear rate.