Correlation of low density polyethylene rheological measurements, with optical and processing properties

Abstract

AbstractThe processing properties of low density polyethylene melts, such as drawdown and neck‐in, and the final product properties, such as film haze and gloss, have been successfully correlated with rheological functions and the level of longchain branching. The rheological functions employed are the entrance pressure drop ΔPo and the swell ratio So, determined at a specified shear stress using aft‐orifice with a length/ diameter (L/D) ratio of zero. The calculation of shear stress requires additional measurements using adie with a finite L/D e.g. 20. The rheological functions ΔPo, and So are governed by the level of high molecular weight species and/or the level of long‐chain branching(LCB). If determined at a constant shear stress, in order to eliminate the effect of viscosity, they are a relative measure of elasticity. Higher ΔP0 and So indicate a higher level of LCB and correlate with poorer optical properties and drawdown in films.