Study On The Phase Morphology Evolution Of Polypropylene And Poly(Ethylene-co-1-octene) Blends During Twin-screw Extruder

Polypropylene (PP) and Poly(ethylene-1-octene) (POE) blends were prepared in an intermeshing co-rotating twin-screw extruder. The online-sampling-microscope and small angle light scattering (SALS) online analysis system self-made by our laboratory were applied to study the phase morphology of the blends during the whole extrusion process.Phase morphology of PP/POE blends which were on-line sampled was observed by scanning electron microscopy (SEM). A method of digital analysis was applied to the SEM images to get corresponding structure parameters- average particle diameter (dp) and average characteristic length (L_m) for characterizing the dispersed phase size; average particle distribution(σ_dp) and average characteristic length distribution (σ_Lm) and fractal dimension (D_L) got by the scaling function for characterizing homogeneity of the dispersed phase. The images obtained by SALS were digitally analyzed by means of Debye-Bueche scattering theory to get the corresponding structure parameters-correlation distance ac 2,average chord length(L₁ ), inhomogeneity distance (lc)and average gyration radius ( R_g1) for characterizing the dispersed phase size; integral invariant ( Q ) and fractal dimension(D_f )for characterizing homogeneity of the dispersed phase. The relationships between these structure parameters with the screw's axis, blend composition and screw speed were analyzed and discussed.The results obtained by SALS were in agreement with SEM, therefore, method of on-line analysis by SALS may be feasible to study the phase morphology of polymer blends during twin-screw extrusion.The phase morphology development of PP/POE blends during twin-screw extrusion coincided with development model of the phase morphology introduced in the initial stage by Elemans: The dispersed phase forms ribbon or sheet structures before the structures shears in nubs, which becomes into spherical droplets later.The dimension of the dispersed particles and the distribution of it decreased along the screw's axis (exception of special composition).To different composion, as content of the dispersed phase increased, the dimension of the dispersed particles and the distribution of it increased, so the dispersed particles became uneven. Moreover, screw speed and mixed temperature had definite influences on the phase morphology. With screw speed and mixed temperature increasing, the dimension of the dispersed particles decreased at frist and then increased, Uniformity of the dispersed phase improved and then reduced. there was an optimal screw speed and mixed temperature at which the phase structure was more exquisite.