Phase Structure's Evolution And Properties Of Metallocene Polyethyulene/Metallocene Ethulene-Propylene Elastomer Blends

In the paper, different metallocene polyethylene/metallocene catalyst ethylene- propylene copolymers (mPE/mEP) blend compositions were prepared in mixer under different kinds of temperature and different kinds of rotating speed. Online-sampling-microscope was employed to study the morphology development of mPE/mEP blending system during the process of dispersion and coalescence. The image analysis was used and 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. Besides, effect of mixing time, blends composition, mixing temperature and rotor speed on each structure parameter was also investigated. The 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, so the size and the shape keep relatively stable. The size of particles of dispersed phase is influenced by the rotating speed and the temperature, and there exists an optimal rotating speed and an optimal temperature at which the phase structure was more exquisite. During the quiescent coalescence, larger particles were formed by merge with adjacent particles, particle diameter and their distribution increase with the coalescence time, the morphology of particles always maintain spherical or elliptical shape. During the shear-induced coalescence, the particle diameter increases distinctly and attains to a quasi-stable situation, larger particles and smaller particles all exist in the same time during the whole coalescence process.Besides the structure and morphology of mPE/mEP blends, the rheological property, dynamic mechanical property and tensile property were also studied using rheometer, dynamic mechanical analyzer and tensile testing machine, respectively. The results of dynamic frequency scanning curves show that mPE presents Newton fluid behavior in low-frequency and high temperature conditions. The blends show shear thinning characteristic in the whole frequency range, theη*(ω) and G〞curves of blends are located between the two corresponding curves of pure components, increased along with the increase of mPE contents. The results of dynamic mechanical property indicate that mEP shows higher storage modulus than mPE in low temperature, storage modulus of the blends ranged between the pure components, increased with the increase of mEP contents. The blends showed a glass transition temperature, which indicates good compatibility. Moreover, the dynamic mechanical property of mPE/mEP was calculated by Kerner theoretical model, the results show that Kerner theoretical model has good applicability of blends. Tensile testing showed that Young modulus increased and elongation at break decreased with the increase of mPE contents. Tensile strength showed complex trend of change, which is related to micro-phase structure of blends.