| Abstract: | A careful characterization and rheological study of low density polyethylene (LDPE) reveals that long-chain branching (LCB) plays a decisive role. At constant molecular weight (M?w) higher LCB reduces the Newtonian viscosity ηo and the shear sensitivity, increases the activation energy Eo, and finally delays transition to pseudoplastic flow to higher shear rates and the onset of melt fracture to higher shear stresses (τd). The flow parameters ηo, \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma _{cr} $\end{document} cr, τd, and the derived flow relaxation times are uniquely correlatable by means of a modified molecular weight (gM?w) incorporating the LCB effect. High density polyethylene are less shear sensitive than their low-density counterparts, have a lower activation energy, fracture at higher shear stress levels and cannot be regarded as branchless LDPE's. |
