Rheological properties of HDPE and LDPE at the low-frequency range under supercritical CO2

Wan, Chengpeng; Sun, Gangwei; Liu, Tao; Esseghir, Mohamed; Zhao, Ling; Wang, Yuan

doi:10.1016/j.supflu.2016.12.016

Cited by 16 publications

(11 citation statements)

References 37 publications

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“…On the one hand, scCO 2 could reduce the interaction force between macromolecular segments; on the other hand, scCO 2 could also promote the mobility of polymer chains. Therefore, the shear viscosity of the PET/CO 2 solution must be lower than that of the pure PET melt [ 33 , 47 , 48 ]. It was necessary to investigate the sensitivity of shear viscosity to the bubble growth process.…”

Section: Resultsmentioning

confidence: 99%

Analysis of Bubble Growth in Supercritical CO2 Extrusion Foaming Polyethylene Terephthalate Process Based on Dynamic Flow Simulation

et al. 2021

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Bubble growth in the polymer extrusion foaming process occurs under a dynamic melt flow. For non-Newtonian fluids, this work successfully coupled the dynamic melt flow simulation with the bubble growth model to realize bubble growth predictions in an extrusion flow. The initial thermophysical properties and dynamic rheological property distribution at the cross section of the die exit were calculated based on the finite element method. It was found that dynamic rheological properties provided a necessary solution for predicting bubble growth during the supercritical CO2 polyethylene terephthalate (PET) extrusion foaming process. The introduction of initial melt stress could effectively inhibit the rapid growth of bubbles and reduce the stable size of bubbles. However, the initial melt stress was ignored in previous work involving bubble growth predictions because it was not available. The simulation results based on the above theoretical model were consistent with the evolution trends of cell morphology and agreed well with the actual experimental results.

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Section: Resultsmentioning

confidence: 99%

Analysis of Bubble Growth in Supercritical CO2 Extrusion Foaming Polyethylene Terephthalate Process Based on Dynamic Flow Simulation

et al. 2021

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“…In the complete melting stage, viscoelasticity was governed by molecular weight, which was consistent with the results of Zhai [ 8 ]. The shear thinning behaviors in the frequency range between 100 rad/s and 0.1 rad/s at 120 °C were shown in Figure 7 , which can be fitted by the cross model [ 27 ].

where

is the complex viscosity,

is the zero-shear viscosity,

is the characteristic relaxation time,

is the angular frequency, and

is the Cross index.…”

Section: Resultsmentioning

confidence: 99%

Insight into the Influence of Properties of Poly(Ethylene-co-octene) with Different Chain Structures on Their Cell Morphology and Dimensional Stability Foamed by Supercritical CO2

Chen

Yao

et al. 2021

Polymers

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Poly(ethylene-co-octene) (POE) elastomers with different copolymer compositions and molecular weight exhibit quite distinctive foaming behaviors and dimensional stability using supercritical carbon dioxide (CO2) as a blowing agent. As the octene content decreases from 16.54% to 4.48% with constant melting index of 1, both the melting point and crystallinity of POE increase, due to the increase in fraction of ethylene homo-polymerization segment. the foaming window of POE moves to a narrow higher temperature zone from 20–50 °C to 90–110 °C under 11 Mpa CO2 pressure, and CO2 solubility as well as CO2 desorption rate decrease, so that the average cell diameter becomes larger. POE foams with higher octene content have more serious shrinkage problem due to lower compression modulus, weaker crystal structure and higher CO2 permeability. As POE molecular weight increases at similar octene content, there is little effect on crystallization and CO2 diffusion behavior, the foaming window becomes wider and cell density increases, mainly owing to higher polymer melt strength, the volume shrinkage ratio of their foams is less than 20% because of similar higher polymer modulus. In addition, when the initiate expansion ratio is over 17 times, POE foams with longer and thinner cell wall structures are more prone to shrinkage and recovery during aging process, due to more bending deformation and less compression deformation.

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“…Here, the plasticizing effect of CO 2 on the melt rheology of PET is ignored. One reason is that the degree of viscosity reduction is very small . The most important reason is that melt fracture (cell rupture) always occurs in the later stages of expansion, at this time, only little CO 2 is present in the polymer melt and most of them have diffused into the bubble.…”

Section: Resultsmentioning

confidence: 99%

Prediction of foamability of polyethylene terephthalate using viscous and elastic parameters

et al. 2017

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Rheological behavior and foamability of polyethylene terephthalate (PET) with different molecular structures were investigated. The aim of this study was to find out the viscous and elastic parameters which can predict the foaming properties of PET.It is found that the foams of strain hardening PET have high expansion ratios and fine cell morphologies. This is correlated with the contribution of strain hardening to the improvement of melt strength and failure strain during elongational experiments.Basing on the fact that foamability of a material is governed by its strain hardening (a pure elastic behavior), a viscous parameter (complex viscosity), and an elastic parameter (loss tangent) obtained from dynamic shear rheology are well linked to the expansion ratios of foams. These two parameters formed an optimized viscoelastic window, which is suitable for foaming. This means the foamability of PET can be determined by viscous and elastic parameters without consideration of molecular constitution. K E Y W O R D Sfoams, polyesters, rheology, viscoelastic properties

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Rheological properties of HDPE and LDPE at the low-frequency range under supercritical CO2

Cited by 16 publications

References 37 publications

Analysis of Bubble Growth in Supercritical CO2 Extrusion Foaming Polyethylene Terephthalate Process Based on Dynamic Flow Simulation

Analysis of Bubble Growth in Supercritical CO2 Extrusion Foaming Polyethylene Terephthalate Process Based on Dynamic Flow Simulation

Insight into the Influence of Properties of Poly(Ethylene-co-octene) with Different Chain Structures on Their Cell Morphology and Dimensional Stability Foamed by Supercritical CO2

Prediction of foamability of polyethylene terephthalate using viscous and elastic parameters

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