The rheology of liquid crystal polymer blends.

The present studies are concerned with the observation and explanation of the interaction between liquid crystal and isotropic polymers. An investigation of the rheological behaviour has been carried out on blends containing small additions of a main chain thermotropic liquid crystal polymers using capillary rheometry. Samples of these blends were moulded and tested using a Hounsfield tensometer and a Houndsfield swinging arm impact rig. The addition of a small amount of liquid crystal polymer was found to have a major effect upon both the rheological and morphological properties of the base material. This indicates the liquid crystal polymer can be used as a processing aid. A reduction of viscosity was noticed in all of the tests carried out and is attributed to the change in morphology induced by the addition of liquid crystal polymer. It would be of great benefit to the polymer processor if an understanding of the mechanisms involved could be highlighted. It is felt that the large interfacial area created between the binodal and spinodal has a bearing on the viscosity reduction. The morphology was different for material in the centre and the skin regions. The characteristic skin/core morphology was seen in all samples produced above a critical amount of liquid crystal polymer and temperature. The interaction between the liquid crystal polymer and the base material was explained using a model which predicted the velocity profiles given the shear rate, consistency constant and shear thinning index of the blends. The interface position is important because on one side of the interface the material is subject to elongational forces and compressive forces on the other. The elongational forces extend the LCP domains inducing an imposed morphology on the isotropic matrix. This could be seen in extruded and injection moulded samples, in the form of highly orientated surface skin layers. The orientation in the skin layers improved the barrier properties of the resultant blends, by allowing molecules in the surface layers to pack more closely together.