Effect of viscosity ratio and processing conditions on the morphology of blends of liquid crystalline polymer and polypropylene

Abstract

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...

In-situ composite based on polypropylene and nylon6

“…It was found that fiber spinning is particularly advantageous because the elongational force field in the spinning process is more effective for producing the fibrillar morphology than is the shear force field. A PP/ Nylon6 in-situ composite obtained with a spinning process has been reported in some articles [8][9] ; under spinning conditions both PP and Nylon6 can form fibers in the composite. In the present study, it was reported that PP/ Nylon6 insitu composites containing different concentration of PP and Nylon6 were obtained under an ordinary extrusion condition.…”

Characterization of a PE-g-LCP compatibilizer, prepared by reactive blending of acrylic acid grafted polyethylene (PE) and a semiflexible liquid crystalline polymer (LCP)

“…It has been shown that the compatibilizers consisting of a PP or PE backbone and maleic anhydride or acrylic acid grafts promote mainly specific polar interactions such a hydrogen bonds between the components [1][2][3][4][5][6][7][8] . The compatibilization mechanism of reactive compatibilizers containing epoxy groups is based on the reaction between the functional groups and the LCP end groups 9,10) .…”

Morphology and rheology of HDPE/LCP blends compatibilized by a novel PE-g-LCP copolymer

“…These studies have shown that maleic anhydride-grafted PP (PPMA) or acrylic acid-functionalized PP (PPAA) can improve the interfacial adhesion in PP/LCP blends, and an enhancement of the tensile modulus, tensile strength, and surface finish was observed. [1][2][3][4][5][6] For blends of PE with a semiflexible LCP, compatibilized with two samples of maleic anhydride-grafted PE (PEMA), 7,8 the enhancement of the mechanical properties was generally modest. Also, in this case, the enhancement of some of the blend properties was attributed to the promotion of specific polar interactions between the components.…”

“…Recent investigations [1][2][3][4][5][6][7][8] have dealt with the preparation and the characterization of blends of polypropylene (PP) or polyethylene (PE) with liquid crystalline polymers (LCPs) containing different commercially available compatibilizers. These studies have shown that maleic anhydride-grafted PP (PPMA) or acrylic acid-functionalized PP (PPAA) can improve the interfacial adhesion in PP/LCP blends, and an enhancement of the tensile modulus, tensile strength, and surface finish was observed.…”