Evaluate the nonlinear viscoelasticity of polyolefin melts using the Larson model

Abstract

Nonlinear rheological properties of polyolefins have long been studied and predicted by using the Larson model with the damping function generally obtained from the stress relaxation measurements. In this study, we investigate the nonlinear rheological properties of high density polyethylene (HDPE) and polypropylene (PP) using the Larson model with damping functions obtained from either the dynamic frequency sweep or the stress relaxation test. Experimental measurements and their corresponding model predictions for the rheological parameters were then compared to evaluate the applicability of the Larson model to the nonlinear rheology, and the following conclusions could be achieved. The steady shear viscosity could be satisfactorily described by the Larson model with the damping functions obtained from the two different methods, except at shear rates higher than 103 s−1. The predicted first normal stresses also account for the measured data, except for those using the stress relaxation data showing a little deviation for the PP sample. In addition, the predictions for elongation viscosity are also in good agreement with the experimental results within the short range of elongation rate achieved in this work. POLYM. ENG. SCI., 54:2354–2361, 2014. © 2013 Society of Plastics Engineers

Mechanical reprocessing of polyolefin waste: A review

“…Extensive research has been carried out in this stage, especially in terms of collection and sorting techniques, such as flotation , optical sorting, density separation , electrical separation , etc. In the second stage, the recycled plastic pellets, powder or flakes are molten and reprocessed into final products by resin molding techniques , including extrusion molding , injection molding , blow molding , vacuum molding , inflation molding , melt spinning , etc.…”