Relaxation effects of slip in shear flow of linear molten polymers |
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Authors: | Igor B Kazatchkov Savvas G Hatzikiriakos |
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Institution: | (1) Schulich School of Engineering, University of Calgary, Calgary, AB, Canada;(2) Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, BC, Canada; |
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Abstract: | The transient shear response of a linear molten polymer (linear low-density polyethylene) in the nonlinear domain was studied
using a true shear (sliding plate) rheometer with different gap spacings to detect slip effects. It was found that nonlinear
viscoelasticity is further complicated by wall slip phenomena. Experimental evidence suggested that static slip models coupled
with Wagner’s constitutive equation cannot adequately describe the experimental data at large and fast shear deformations.
A new dynamic slip model involving multiple slip relaxation times is proposed in this paper, together with a method to assess
the model parameters. Significant improvement in predicting the stress response is demonstrated by several examples of start-up
of steady shear and large-amplitude oscillatory tests of a linear low-density polyethylene. |
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