Low and high shear rate rheology of injection moulding grade liquid crystal polymersection moulding grade liquid crystal polymer

Liquid crystals (LCs) materials have the properties between those of a conventional liquid and those of a solid crystal. The rheology of liquid crystalline polymers (LCPs) is a topic of practical importance because of their unique properties. It has a particular kind of structural orientation at one or two dimensional level. Whenever a LCP is subjected to a shear field, there is a molecular reorientation process taking place resulting in the formation of a polydomain structure of randomly oriented nematic micro domains. Based on the microstructural evolution the shear behaviour, in most cases does not show a plateau region or a zero shear viscosity. It has been reported that accurate measurements of the shear rheological properties of (LCPs) is critical to allow appropriate prediction, as it flows under pressure in a typical injection moulding machine.. Rheological properties of four thermotropic LCPs were investigated from low to high shear rate regions. ARES and capillary rheometer were used for low shear rate and high shear rate respectively. The shear viscosities of four LCPs show almost three zone dependency. The complex viscosities of the four LCPs show a typical shear-thinning behaviour. LCPs also depict first negative normal stress difference because of the tumbling nature of rod like molecule. The effect of filler was investigated in terms of various rheological properties. The abnormal temperature dependence of the viscosities can be explained by the nematic-isotropic transition, in which the rod-like molecules lost part of their orientation ordering and became partially isotropic with increase in temperature.