The effect of the addition of various stearate esters on the crystalline structure and the toughness was studied concerning the molecular weight and the concentration of each modifier. The toughness was increased with the decrease of the molecular weight of stearate ester at the content of the 0.5wt%. The volume expansion of blended i-PP as an index of nucleated void density showed the largest value in the case of butyle stearate. This result indicated that the toughening improved with the decrease of butyle stearate content. From these results, it was concluded that the toughness improvement is mainly caused by the increase of the crase strength by craze strength by the addition of butyle stearate into i-PP.

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Dispersive mixing performance of special rotor segments, commercially named VCMT (various clearance mixing technology) in an intermeshing co-rotating twin-screw extruder has been studied using a numerical analysis method. Characteristics of residence time distribution of fluid have also been studied. In this study, the barrel was assumed to be fully filled with isothermal molten polymer and the properties of polypropylene were applied in the computation. Commercial computational software "POLYFLOW" was used and the particle tracking method was adopted for evaluation. As the evaluation index of dispersive mixing performance, maximum 1st principal stress was selected. The results were compared with those of two kinds of kneading disk (KD) segments. From the results, it is found that VCMT has better dispersive mixing and uniformity of residence time than KDs. Furthermore, for investigation of mixing mechanism, the observation of trajectories of characteristic particle groups in peak region of two dimensional probability distribution was proposed. One dimension was residence time and the other was the maximum 1st principal stress. We also suggested the relationships between mixing performance and the shape of mixing segments by focusing on maximum stress points of characteristic particle groups and flow fields around the point.

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