Evaluation of Thermally Induced Degradation of Branched Polypropylene by Using Rheology and Different Constitutive Equations

Abstract

Abstract:In this work, virgin as well as thermally degraded branched polypropylenes were investigated by using rotational and Sentmanat extensional rheometers, gel permeation chromatography and different constitutive equations. Based on the obtained experimental data and theoretical analysis, it has been found that even if both chain scission and branching takes place during thermal degradation of the tested polypropylene, the melt strength (quantified via the level of extensional strain hardening) can increase at short degradation times. It was found that constitutive equations such as Generalized Newtonian law, modified White-Metzner model, Yao and Extended Yao models have the capability to describe and interpret the measured steady-state rheological data of the virgin as well as thermally degraded branched polypropylenes. Specific attention has been paid to understanding molecular changes during thermal degradation of branched polypropylene by using physical parameters of utilized constitutive equations.

Effect of die exit stress state, Deborah number, uniaxial and planar extensional rheology on the neck-in phenomenon in polymeric flat film production

“…In the first step, deformation rate dependent 'steady state' uniaxial extensional viscosity data (taken from the transient viscosity data peaks for given deformation rates, [60] and [69])…”

Effect of molecular weight, branching and temperature on dynamics of polypropylene melts at very high shear rates

“…Recent studies on entangled linear polypropylene melts have shown a well-developed Newtonian regime occurs above 2 • 10 6 1/s, which is linearly dependant on molecular weight suggesting that polymer chains become fully disentangled in such a flow regime [11]. In order to understand the role of the chain branching and temperature on high shear rate dynamics of polypropylene melts, well characterized low molecular weight linear PP Borflow HL512FB (L-PP) [11] and high molecular weight branched PP Daploy WB180HMS (LCB-PP) [12], both produced by Borealis Polyolefine (Linz, Austria), have been used in this work. Polymer blends were prepared by adding 10, 20 and 30 wt% of LCB-PP to L-PP in a twin screw extruder.…”

Generalized Newtonian fluid constitutive equation for polymer liquids considering chain stretch and monomeric friction reduction for very fast flows modeling

“…In this work, we used GNF constitutive equation, which belongs to a new family of models [68][69][70][71][72][73],…”

“…The models handle the differences between highextensional-rate uniaxial, planar and biaxial extensional viscosities compared to others, more advanced constitutive equations (including the molecular-based Pom-Pom model), which unrealistically predict steady-state uniaxial and planar extensional viscosities virtually identical at high extensional strain rates [19,68,74]. These types of GNF models have been successfully tested for polymer melts with linear (mLLDPE [68,71], HDPE [68,69]) and differently branched structures (mLLDPE [68,69,71], mHDPE [68], LDPE [68][69][70]72]) including polymers with star type of the branching (LCB-PP [73]) using steadystate extensional viscosities measured at extensional strain rates typically up to about 10 s -1 , (i.e. at low Wi, where entanglements dominate the dynamics).…”