Study On Morphology Development And Corresponding Phase Evolution Dynamics In PP/PS Blends

Small angle light scattering (SALS) and online-sampling-microscope were employed to study the morphology development of polypropylene/polystyrene blending system during the process of dispersion and coalescence. Further, the corresponding mechanism and dynamics of morphology development, as well as the mechanical properties of final products were also investigated. For SEM micrographs, a method of digital analysis was applied to these micrographs to get corresponding structure parameters-particle diameter and their distribution and subsequently, relationship between particle diameter and their distribution with blend composition, blending time and content of compatibilizer was studied. Moreover, the SALS images were digitally analyzed by means of Debye-Bueche and Mie scattering theory to obtain corresponding structure parameters describing the morphology, e.g., correlation distance ac, integral constant Q and fractal dimension Dc as well as the relationship between these parameters with blend composition, blending time and content of the compatibilizer.The results shows that, during the phase dispersion, the main morphology development occurs in the initial stage of the mixing and approaches to a dynamic equibilium between particle breakup and coalescence in the late stage, leading to a stable and fine phase morphology. More interesting, further increase in blending time will lead to a rebound of particle size. The addition of compatibilizer will result in a decrease in particle diameter and the dependence of particle diameter on the content of compatibilizer obeys the Favis emulsification curve; during the quiescent coalescence, particle diameter and their distribution increase with the coalescence time or equivalently, the shear strain. Analysis regarding to the fractal character of particle diameter indicated that the quiescent coalescence may obeys a scaling law which is similar with that in spinodal decomposition. During the shear-induced coalescence, the particle diameter increases distinctly and attains to a quasi-stable situation, the dependence of particle diameter on the shear stain is affected by both blend composition and shear rate.The mechanism of morphology development was studied. The results shows that in the initial stage of the mixing, the breakup of particles complies with a crisp-break rule and consequently, the development dynamics can be described by the typical dispersion parameter in the crisp-break theory. Study concerning these dispersion parameters shows that the effect of rotor speed and mixing temperature on the dispersion parameter was different at different mixing stage.Regarding the process of phase dispersion and coalescence as different living-death process, we deduced different dynamic equations of morphology development of phase dispersion and coalescence, respectively. The simulation results by these equations are accord to our experimental results, indicating these dynamic equation s are appropriate to describe the morphology development in some respects. Especially, examination of scaling character during the shear-induced coalescence indicated that there exists another scaling behavior during the shear-induced coalescence which is different from that in spinodal decomposition.Investigation with regard to the mechanical properties of blends shows that, the properties depend on the micro-structure of blends. For PP/PS incompatible blends, the dispersed phase often acts as inert stuff. Addition of compatibilizer can improve the mechanical properties of blends to great extent. The mechanical properties can be forecasted using corresponding micro-mechanical model among which the Mori-Tanaka is more effective.