Critical Stress and Recoverable Shear for Polymer Melt Fracture

Abstract

<p>The dependence of the critical shear stress and the critical recoverable shear strain on molecular weight has been studied . Polystyrene of narrow and broad molecular weight distribution, low and high density polyethylene and polypropylene were the polymers used in this study. The behaviour of the melts at the onset of instabiIity was explained by using Graessley's correlation between "true" and Rouse shear compliance in Hooke's law. It was found that the critical stress increases linearly as the weight average molecular weight decreases, increases slightly with temperature and is nearly independent of the distribution of molecular weights . The critical recoverable shear, calculated using Tanner's dieswell theory was found proportional to the factor M₂M₂₊₁/M_w², the proportionality factor being about 2.5 for linear polymers.</p>