Abstract
The method of reduced variables or superposition is applied to investigate the first normal stress difference ( N 1)-temperature dependence over the shear rate (γ) range 10–1000 s −1 for polystyrene (PS) and high-impact polystyrene (HIPS) melts, at temperatures of 180 C and above. These conditions are similar to those for industrial polymer processing. For PS, the first normal stress differences are obtained using Tanner's equation, leading to good agreement with values obtained by other authors and methods. For HIPS we have not found data in the literature for N 1 at shear rates above 10s −1. In our case N 1 was obtained by measurements of entrance pressure losses. Correlations, based on master curves, are found for first normal stress difference in terms of shear rate and temperature. All samples follow the power law equation N 1 = k γ ̇ m , with values of m ranging from 0.50 to 0.64.
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