SYNOPSISThe effect of viscosity ratio and processing conditions on LCP/PP blend morphology was studied. The viscosity ratio ( vLcp/vpp) was varied from 0.1 to 3.6 by using five different polypropylene grades as the matrix and two LCPs as the dispersed phase (20 wt % ). The most spontaneous fiber formation was achieved when the viscosity ratio was between 0.5 and 1. In addition to shear forces, elongational forces are important in achieving a highly fibrillar structure and significant mechanical reinforcement. The lubricating effect induced by the low viscosity of LCP was most pronounced for the blends exhibiting a fibrillar morphology. The morphologies of blends produced by different mixing equipment differed only slightly. The greatest variation in the mixing efficiency was found for blends whose components had totally dissimilar melt viscosities. The slight differences in morphology due to melt blending in dissimilar equipment were decreased after injection molding, whereas the differences in morphology due to dissimilar viscosity ratios were still evident in the injection molded blends. Thus, the viscosity ratio a t processing in the actual processing conditions is of great importance. 0 1994 John Wiley & Sons, Inc. I NTROD UCTl ONThrough blending of thermotropic main-chain liquid crystalline polymers ( LCPs) with thermoplastics, the highly oriented fiber structure and good properties of LCPs can be transferred to the more flexible matrix polymer. The usual benefits sought in blending are mechanical reinforcement and improved thermal and dimensional stability achieved through creation of composite-like microstructure. In addition, because of its relatively low melt viscosity a small amount of LCP renders some thermoplastics easier to Since the two polymers are immiscible, the blends of LCPs and polypropylene (PP) consist of two separate phases. The dispersed LCP phase exists as small spheres or fibers within the PP matrix and a skin/core morphology is created. The LCP phases are more oriented in the skin region and less oriented in spherical form in the core.* To whom correspondence should be addressed. The primary factors determining the size, shape, and distribution of the LCP domains in the matrix are the LCP content, processing conditions, and rheological characteristics of the blend components, in particular the viscosity r a t i~.~.~ The morphology is also affected by the interfacial adhesion between the components, which may be modified by the addition of suitable compatibilizers.6 The effects of shear stress, viscosity ratio, and interfacial tension are related to each other by the Weber Besides the above, additional drawing greatly enhances the fibrillation and orientation of the LCP phases, resulting in improved strength and stiffness in the fiber d i r e~t i o n .~~~~'~ The effect of viscosity ratio on the morphology of immiscible polymer blends has been studied by several researchers. Min et al." found for polyethylenelpolystyrene ( P E / P S ) blends that when the dispersed phase had a lower visco...

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SYNOPSISThis article concerns the functionalization of polypropylene (PP) with oxazoline functionality by melt free radical grafting along with a low degree of degradation of PP in a batch mixer. A low volatile oxazoline, ricinoloxazoline maleinate (OXA), was used as the monomer. The grafting yield of OXA ranged from about 0.5 phr up to 1.5 phr (grams per 100 grams of PP) when its initial concentration and that of the peroxide ranged from 1.5 to 6.0 phr and 0.1 to 0.7 phr, respectively. The corresponding conversion of OXA to grafted OXA ranged from about 15 to 50%. Addition of styrene (St) as the comonomer did not enhance the grafting yield of OXA but markedly reduced the PP degradation. Also, little homoand/or copolymers of OXA and/or St were found in the grafting system. This agrees with our finding that OXA and St did not copolymerize easily. The potential of using an OXA modified PP (PP-g-OXA) as the compatibilizer precursor in PP/PBT blends was examined as well. The presence of PP-g-OXA reduced the particle size of the dispersed phase (PBT) along with improved cohesion between the PP and PBT phases. This is consistent with a model kinetic study, which showed that the reaction between oxazoline and carboxylic functionalities was very fast.

The effect of the screw configuration of a closely intermeshing co‐rotating twin‐screw extruder on residence time and mixing efficiency was studied for an uncompatibilized immiscible PA6/PP (80:20) bend. Alternative screw configurations were investigated systematically. The residence time distribution (RTD) was found to be a poor indicator of the total mixing efficiency, whereas the mixing intensity function yielded considerably better information. High shear stress, sufficient residence time, and high fill ratio in the melting section of the screw were the most important factors in achieving good dispersion of the minor phase. The evolution of morphology along the screw axis depended strongly on the screw configuration. The downstream flow characteristics after the screw end determined the final morphology of the blend.