Study On Structure And Properties Of Polypropylene Alloy

In the paper, different polypropylene/ metallocene-ethylene propylene elastomer (PP/m-EPE) blend compositions were prepared in XXS-30 mixer under five kinds of temperature (180°C ,190°C,200°C,210°C,220°C) and five kinds of rotating speed (16rpm,32rpm,48rpm,64rpm,80rpm). Phase structure and morphology evolution of PP/m-EPE blends were studied. The diameter was defined to describe the dynamic evolution rule using scanning electronic microscope (SEM) graphs. The distribution of diameter of dispersed phase is proved to comply with the normal-log distribution based on the graph-estimation theory and the parameterσwas calculated to describe the distribution width of diameter. Results showed that the change mainly occurs in the initial stage of the mixing. In the late stage, the change levels off due to the dynamic equilibrium between the breakup and coalescence of particles. The size of particles of dispersed phase is influenced by the rotating speed and the temperature, and there exist an optimal rotating speed and an optimal temperature at which the phase structure was more exquisite. Size of particles increases as the volume fraction of the dispersed phase rises.From the dynamic strain sweep test, it is known that critical shear strain (γc) of m-EPE is 30%. The curves of dynamic time sweep test indicate that the structure of m-EPE destroyed by the cumulating shear strain is repairable. The master curves of m-EPE with relatively largeωranges were obtained from the curves of dynamicωsweep based on time-temperature principal. It is found that the WLF equation and Arrhenius equation can be applied to simulate the curves of shift factors~temperature, and the fluid activation energy of m-EPE can be obtained. The curves of logG'vs. logG"shows that the master curves are upturned in the highωbecause of the micro-phase separation structure. Studies on the linear viscoelastic behavior of PP/m-EPE blends were carried out. The complex viscosity of m-EPE approaches a constant at the lowω, exhibiting a behavior of Newtonian fluid; while for PP no Newtonian plateau appears in theωobserved. For the blends, curves of G'~ωand G"~ωare located between those of virgin PP and m-EPE, and the G'and G"of blends decrease with the content of m-EPE increasing. The positive-negative deviation is observed in the curves of G',G"andη*(ω) vs. composition of blends. The curves of logG'vs. logG"of blends depend on the composition of blends.A mathematic model is obtained to describe the change of size of particles acting as the dispersed phase. This equation is used to study the blends of polystyrene/ polypropylene and blends of polypropylene/ethylene-octene copolymer. The parameters of the model are related to the kinds of blends, composition and process condition.