Injection moulding of PC/LCP in-situ composite

Blends of thermotropic liquid crystalline polymers (LCP) and thermoplastic polymers have received considerable attention during recent years, because of the attractive signatures of these blends: low melt viscosity and self-reinforcement. Self-reinforcement is caused by the extension of the spherical LCP domains by extensional flow or shear flow into oriented fibrils that are embedded in the matrix of essentially thermoplastic polymer. The common processing routes for LCP/ thermoplastic blends are extrusion drawing and injection moulding. However, with the traditional open-looped control injection moulding process, the processing parameters are not closely monitor and controlled. Also due to lacking of knowledge of complicated flow properties inside the mould cavity, the effects of processing conditions on the mechanical and morphological properties of PC/ LCP blends is limited. The objectives of the present work are to study the effects of injection temperature and injection speed on mechanical and morphological properties of PC/LCP blend (Vectra A950 15wt% and PC 85wt%) and to investigate the flow properties inside the mould cavity by means of C-MOLD simulation. Injection moulded specimens of different thickness are prepared by a closed-loop controlled injection moulding machine because of its superior control performance over traditional open-looped control injection moulding machine. Viscosity measurement indicated that PC/ LCP behave both Newtonian (<100s -1) and shear thinning (>100s -1) phenomenon. The Cross-WLF viscosity model is found matched with experimental measurements of both the Newtonian and shear thinning regimes of our PC/LCP blend, the Cross-WLF model is capable of extending the viscosity predication to a higher shear rate and higher temperature which are normally encountered in injection moulding. C-MOLD simulation reveals that under the same injection speed, the wall shear stress and frozen layer fraction decreases with increasing injection temperature. Moreover, under the same injection temperature, the shear rate and wall shear stress increase with increasing injection speed. In addition, shear heating effect is found more serious in thinner specimens. Tensile tests of PC/ LCP blend indicated that tensile strength, tensile modulus and strain at peak load depend on injection temperature and injection speed. The impact strength of the PC/ LCP blend was found also injection temperature and injection speed dependent. The variation in mechanical strength might due to fibre orientation, fibre fibrillation and skin layer thickness of the specimens