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Preparation And Performances Characterization Of IPP/HIPP/POE Ternary Blends

Posted on:2010-06-08Degree:MasterType:Thesis
Country:ChinaCandidate:H P WangFull Text:PDF
GTID:2121360275985415Subject:Materials science
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To overcome the disadvantage of brittleness and low notched impact strength polypropylene (PP), a novel iPP/HIPP/POE ternary blends were prepared via quadratic extrusion method on a twin-screw extruder. The metallocene polyolef elastomers ploy (ethylene-1-octene, POE) and copolymeric polypropylene were used as toughener and co-toughener, respectively. The mechanical properties, morphology, crystallization kinetics, and rheological behaviors were investigated in terms of impact/tensile strength, scanning electron microscopy, differential scanning calorimetry (DSC), polarized optical microscopy and capillary rheometer, respectively.(一) Mechanical properties and morphology of iPP/HIPP/POE ternary blends.Due to the various compositions between iPP and HIPP, the"brittle-ductile transition"occurred at low loading of POE for HIPP/POE blends while at high POE concentration ( 42.3-66.7 wt % relative to iPP matrix) for iPP/POE blends. Taking the above results and propylene homopolymer within HIPP into consideration, HIPP was expected to be used co-toughener of POE for improving synergically the toughness of iPP. The results demonstrated that the"brittle-ductile transition"occurred at low POE concentration (20-30 wt % relative to the total weight of polymer matrix) for iPP/HIPP/POE ternary blends in the case of HIPP/iPP≥40/60. The iPP(40)/HIPP(60)/POE(40) ternary blend displayed 47.9 KJ/m2 of toughness, and was increased by 17.4 times as that of iPP (2.6 KJ/m2). SEM photographs of iPP/HIPP/POE blends showed that a core-shell structure was formed in the case of low POE (or HIPP) loading level, in which the core was the separation phase containing LPE/EPR and the shell was POE. As the increasing POE (or HIPP) content, the separation phase containing LPE/EPR was difficult to be observed, and POE phase became smaller and dispersed much uniformly within PP matrix. The impact-fractured surface became coarser, indicating that the interfacial action was improved.(二) Investigation on the crystallization kinetics of iPP/HIPP/POE ternary blends. The analysis of isothermal crystallization behavior indicated that the Avrami equation described well the isothermal crystallization of PP and iPP/HIPP/POE blends. The POE sacted as the nucleating agent and increased the nucleating rate of PP. The mode of the nucleation and growth of PP and iPP/HIPP/POE blends might be a mixture of may be two-dimensional and three dimensional growth with thermal nucleation. The equilibrium melting point of the iPP/HIPP/POE blends determined from Hoffman-Weeks was lower than that of pure PP, indicating the addition of POE reduced the perfection o f PP crystals.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 and Co-PP increased the absolute values of effective activation energy and the effective activation energy of non-isothermal crystallization.The POM (Polarized Optical Microscopy) photographs showed that the domain of PP spherulites decreased while the numbers of PP spherulites after the incorporation of POE.(三) Investigation on the rheological behavior of iPP/HIPP/POE ternary blendsIt was determined that both PP and its blends were pseudo-plasticity fluid, as indicated by their non-Newton index lower than 1. All samples exhibited shear-thinning behavior. The shear stress of the iPP/HIPP/POE blends decreased gradually with the increasing of HIPP content in the case of the same shear stress, indicating that the incorporation of HIPP reduced the domains of the POE separation phase. The apparent viscosity of the iPP/HIPP/POE blends was lower than that of the PP, it was implied that the melt viscosity of the iPP/HIPP/POE blends was less temperature-sensitive than that of the PP. On the other hand, the apparent 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.
Keywords/Search Tags:Copolymeric polypropylene, Poly (ethylene-co-octane), Toughening, Structure morphology, Crystallization kinetics, Rheological behavior
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