Nonlinear Viscoelasticity of Silicone Carbide Whisker-Filled Liquid Crystalline Polymer Melts

Abstract

Dynamic viscoelasticity of melts of semi-aromatic liquid crystalline polymer (LCP) and its silicone carbide (SiC) whisker-filled compounds was measured to analyze quantitatively their nonlinear viscoelastic properties by Fourier expansion of the shear stress wave. For LCP the tertiary terms, G'3 and G″3, are considerably smaller than their primary terms, G'1 and G″1, i.e. their viscoelasticity is almost linear. Viscoelastic behaviour of the silicone carbide whisker-filled LCP system was compared with that of the carbon fiber (CF)- and glass fiber (GF)-filled LCP systems presented in [18]. The CF/LCP system shows a dependence of the oscillatory angle upon its G'i and G″i, making both accordingly decrease with increasing i from 1 to 3 and 5. The G'3 and G″3 values of the polymer system, compared to its G'1 and G″1 counterparts, are sufficiently large not to be negligible, suggesting that the system's viscoelasticity is nonlinear. Furthermore, the SiC whisker-filled LCP system was examined for the dependence of the ratios G'i/G'1 and G″i/G″1 (i = 3, 5), and Gi/G1 (i = 3, 5, 7) as indicators of the degree of viscoelastic nonlinearity upon angular frequency. The results did not show any significant difference between G'3/G'1 and G'5/G'1 values, or between G″3/G″1 and G″5/G″1 values. The ratio Gi/G1 (i = 3, 5, 7), representing the nonlinearity of viscoelasticity of the system, however, is higher with an increase in the oscillatory angle.