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Characterizing long-chain branching in commercial HDPE samples via linear viscoelasticity and extensional rheology
Journal article   Peer reviewed

Characterizing long-chain branching in commercial HDPE samples via linear viscoelasticity and extensional rheology

Samantha L. Morelly and Nicolas J. Alvarez
Rheologica acta, v 59(11), pp 797-807
01 Nov 2020

Abstract

Mechanics Science & Technology Technology
It is well established that polymer chain architecture and the distribution of molecular weight play a key role in the flow behavior (processing) and performance of a given polymer material. Long-chain branching (LCB) in particular is known to strongly affect the processability and the material performance of polymers. Often branching is a result of the polymerization process and therefore must be quantified in every sample. We study four commercial high-density polyethylene (HDPE) samples with unknown degrees of polydispersity and LCB. We first use size-exclusion chromatography and linear shear rheology to identify differences in molecular weight, polydispersity, and LCB. Each material is then tested in constant rate and constant stress uniaxial extension using a filament stretching rheometer to quantify extensional viscosity and strain hardening. Correlations between nonlinear extensional rheology, LCB and polydispersity are discussed. We show that the combination of the van Gurp-Palmen plot and extensional rheology allows for a full characterization of the LCB fraction and their effect on extensional rheology.

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