Modelling elongational and shear rheology of two LDPE melts

Abstract

V této praci byly analyzovány experimentální reologické data dvou tavenin LDPE pomocí MSF modelu. Bylo zjištěno, že pro kvantitativní modelování obou toků bylo nutné použít pouze tři nelineární viskoelastické materiálové parametry.

Experimental data of two low-density polyethylene (LDPE) melts at 200 degrees C for both shear flow (transient and steady shear viscosity as well as transient and steady first normal stress coefficient) and elongational flow (transient and steady-state elongational viscosity) as published by Pivokonsky et al. (J Non-Newtonian Fluid Mech 135: 58-67, 2006) were analysed using the molecular stress function model for broadly distributed, randomly branched molecular structures. For quantitative modelling of melt rheology in both types of flow and in a very wide range of deformation rates, only three nonlinear viscoelastic material parameters are needed: Whilst the rotational parameter, a(2), and the structural parameter, beta, are found to be equal for the two melts considered, the melts differ in the parameter f(max)(2) describing maximum stretch of the polymer chains.