Influence of long-chain branching on the rheological behavior of polyethylene in shear and extensional flow

Abstract

In this work, a study of the influence of molecular structure on the viscoelastic behavior of melts of commercial polyethylene (PE) copolymers, particularly in extensional flows, will be performed. To enable this study to be performed, a series of four very low-density polyethylenes (VLDPEs) (film and blow molding grades) with different parameters of molecular weight (M W ), molecular weight distribution (MWD), and degree of long-chain branching (LCB) will be used. Experiments in shear flow (steady state and oscillatory regime) are complemented with experiments in uniaxial extension (constant strain rate and stress relaxation after a step strain). It will be shown that a qualitative correlation exists between both types of experiments; the stress relaxation experiments being particularly sensitive to the different molecular features of the polymers. In addition, the failure behavior in extension was also investigated and the results indicate that, within experimental error, the Hencky strain to failure is sensitive to the type of molecular structure but the corresponding tensile stress is not. POLYM. ENG. SCI., 45:984 -997, 2005.

A Comprehensive Review on Controlled Synthesis of Long‐Chain Branched Polyolefins: Part 3, Characterization of Long‐Chain Branched Polymers

“…[128] However, it has also been found that the PDI has a similar effect on the phase angle δ as the LCB does. [129,130] A unique inflection point or bump (more or less developed) between the minimum and the 90° plateau can be found in long-chain branched polymers. This point shifts to the region having larger |G*| and lower δ in the figure with the increase of LCBD.…”

“…Münstedt et al provided excellent work on this topic [152,156,157] among other works. [128,130,158,159] However, the strain hardening in extension can also be a result of very small amount of high-molecular-weight materials in linear polymers. [160,161] The technique is not very sensitive to LCBD either.…”

Time dependent effects on the rupture of molten linear polymers in extension

“…The LLDPEs differ essentially in terms of degree of long chain branching (LCB) with LLDPE-C being the sample with the highest degree of LCB [29].…”

Methods of long chain branching detection in PE by triple‐detector gel permeation chromatography

“…1,2 For example, in LDPE extrusion coating process, LCB structure can improve neck-in properties. 1,2 For example, in LDPE extrusion coating process, LCB structure can improve neck-in properties.…”

“…To support the polymer design development, a well-defined characterization technique for LCB is required. (1). [6][7][8][9][10] The quantification of LCB of polymer by GPC with triple detectors is commonly based on a LCB frequency (LCBf) calculation with the assumption of the Zimm-Stockmayer (ZS) random branching model.…”