Talc-thermoplastic compounds: particle orientation in flow and rheological properties

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We describe an investigation of the orientation of talc particles in flow and the rheological properties of talc-thermoplastic compounds. The orientation of talc particles in samples removed from rheometers was determined using a wide angle X-ray diffraction technique. Talc particles, being disc-like in shape, orient with the disc normals perpendicular to the flow direction in the sandwich, cone-plate, parallel plate, capillary, and elongational rheometer. The level of orientation of particles is represented in terms of orientation factors. A broad range of experimental studies of the shear, elongational, and oscillatory flow behavior on thermoplastic melts with high loadings of talc particles is presented. The rheological measurements include the steady state shear viscosity, transient shear viscosity, elongational viscosity, complex viscosity, storage modulus, and loss modulus. Generally, the viscosity increases with increasing particle loading and with decreasing particle size. At low deformation rates, the stresses build up in an unbounded manner. There are stresses below which there is no flow indicating the existence of yield values. The implication of yield values in anisotropic particle compounds is considered. The compound as studied is considered a liquid crystalline particle array. The implication of the measurements to rheological modelling is considered.