Rheological Properties and Fiber Dispersion and Orientation in Potassium Titanate Whisker Filled Polyoxymethylene Melts.

Dynamic viscoelastic properties, steady shear and biaxial extensional flow behaviors have been investigated for melts of potassium titanate whisker filled polyoxymethylene. A second plateau appears in the low frequency region of the storage modulus G', and the plateau value increases with whisker content. Addition of the whisker also increases the steady shear viscosity and the low strain rate asymptote of the biaxial extensional viscosity. The upturn of biaxial extensional viscosity from the low strain rate asymptote decreases by the addition of whisker due to suppression of polymer chain extension. Change in whisker dispersion and orientation in the melts was observed with scanning electron microscopy after quenching the samples in biaxial extensional flow. The degree of whisker orientation to the flow direction decreases with increasing strain rate in the range where the strain rate is much greater than the rate of whisker orientation and it is smaller than or comparable with the relaxation rate of the matrix chain. It is suggested that the matrix does not have enough power to orient the whisker in this range of strain rate.