Effect of long branches on the rheology of polypropylene

Abstract

In order to study the rheology of long chain branched polymers, branches have been added on linear polypropylene precursors in varying amounts using reactive modification with peroxydicarbonates. The branched polypropylene samples show distinct strain hardening, something absent from the linear melt; this considerably improves the melt strength of the modified polymer. The zero shear viscosity and the elasticity measured by the relaxation spectrum also increase with the number of branches per molecule. Two models are applied to describe strain hardening of the viscosity during the course of elongation. The model parameters were found to vary systematically with the degree of branching and, therefore, their values can be used as a measure of this. Consequently, fluidity, elasticity, strain hardening, and melt strength are all related to the degree of long chain branching.

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

“…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.…”

Long chain branching on linear polypropylene by solid state reactions

“…The best quantitative way to estimate the improvement of processing properties due to the addition of LCB on the linear chain is by directly measuring the strain hardening of the viscosity of the melt in uniaxial elongational flow, g þ E ð; _ Þ [30,31]. Indeed, in a series of peroxide-modified polypropylenes with increasing degree of long chain branches, Gotsis et al [30] showed that both the onset and the extent of strain hardening increased with B n .…”

“…Indeed, in a series of peroxide-modified polypropylenes with increasing degree of long chain branches, Gotsis et al [30] showed that both the onset and the extent of strain hardening increased with B n . The whole g þ E ðÞ curves could be described well by classical viscoelastic models that implemented a damping function with a parameter, b, which reflected the level of LCB in the fluid.…”

Using viscoelastic properties to quantitatively estimate the amount of modified poly(lactic acid) chains through reactive extrusion

“…The activation energy for viscous flow is affected by chain flexibility, intermolecular interactions, the concentration of polar groups, and side-chain branches. While the presence of LCB yields an increase in both the temperature dependence and E a , the thermorheological behavior becomes complex [Malmberg et al (2002); Lohse et al (2002); Gotsis et al (2004)]. That is, the sequence of the molecular relaxations is temperature dependent.…”