On the Application of a Viscoplastic Elastic Model To Uniaxial Elongational Flow

Abstract

Uniaxial extension experimental data of several polymeric melt systems are compared with the predictions of a viscoplastic elastic model which was originally developed to be used in blown film process simulation. The systems include an extensively studied low density polyethylene melt (melt-1), two distinct polystyrene systems, and a series of blends of low density polyeth ylene and linear low density polyethylene. The systems cover a range of vari ables associated with the molecular characterization of the polymeric melts, i.e., the extent of branching, the molecular weight, and the molecular weight distribution. The prominent strain hardening behavior in the non-linear range is accounted for in the model by incorporation of the alignment strength as in troduced by Larson. Yield stress, hardening constant, and structure constant are the parameters of the model. The agreement of the predicted elongational viscosity and the measured values over the total strain history is quite good given the small number of adjustable parameters. The different behavior of the two polystyrene systems considered here can be correlated by a change in the structure constant. This may imply that the presence of a small concentration of the high molecular weight species could result in a similar effect as branch ing does in polyethylene.