Rheological Properties Related to Extrusion of Polyolefins

Mitsoulis, Evan; Hatzikiriakos, Savvas G.

doi:10.3390/polym13040489

Cited by 12 publications

(11 citation statements)

References 77 publications

(141 reference statements)

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“…Applying the Cox–Merz rule, as the frequency was replaced by the shear rate, the values of viscosities at shear rates at 100 s −1 tended to lie below 10,000 Pa s [ 84 ]. As the data points for this frequency were measured at the beginning, the loss of PEG was minimal and the values confirmed the processibility of these blends in an extruder at 200 °C [ 82 , 85 , 86 , 87 , 88 , 89 ]. Figure 8 b shows the influence of temperature on the viscosity of blend E3_PEG200_20.…”

Section: Resultsmentioning

confidence: 59%

Open-Celled Foams from Polyethersulfone/Poly(Ethylene Glycol) Blends Using Foam Extrusion

et al. 2022

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Polyethersulfone (PESU), as both a pristine polymer and a component of a blend, can be used to obtain highly porous foams through batch foaming. However, batch foaming is limited to a small scale and is a slow process. In our study, we used foam extrusion due to its capacity for large-scale continuous production and deployed carbon dioxide (CO2) and water as physical foaming agents. PESU is a high-temperature thermoplastic polymer that requires processing temperatures of at least 320 °C. To lower the processing temperature and obtain foams with higher porosity, we produced PESU/poly(ethylene glycol) (PEG) blends using material penetration. In this way, without the use of organic solvents or a compounding extruder, a partially miscible PESU/PEG blend was prepared. The thermal and rheological properties of homopolymers and blends were characterized and the CO2 sorption performance of selected blends was evaluated. By using these blends, we were able to significantly reduce the processing temperature required for the extrusion foaming process by approximately 100 °C without changing the duration of processing. This is a significant advancement that makes this process more energy-efficient and sustainable. Additionally, the effects of blend composition, nozzle temperature and foaming agent type were investigated, and we found that higher concentrations of PEG, lower nozzle temperatures, and a combination of CO2 and water as the foaming agent delivered high porosity. The optimum blend process settings provided foams with a porosity of approximately 51% and an average foam cell diameter of 5 µm, which is the lowest yet reported for extruded polymer foams according to the literature.

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Section: Resultsmentioning

confidence: 59%

Open-Celled Foams from Polyethersulfone/Poly(Ethylene Glycol) Blends Using Foam Extrusion

et al. 2022

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“…We began the nonisothermal capillary flow simulations with the viscous Cross-WLF model for the orifice die depicted in Figure 1 a (

), based on the shear viscosities with and without temperature correction. It is known that the contraction flow has an elongational character along the centerline [ 35 , 37 , 46 ] and that a purely viscous model has a much lower elongational viscosity than a viscoelastic model, therefore it is not surprising to see that the viscous Cross-WLF model severely underpredicted the entrance pressure drop

[ 35 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 ]. This is illustrated for GPPS in Figure 6 a, where

were measured using the 0.2-mm-long orifice die.…”

Section: Resultsmentioning

confidence: 99%

Retrieving Equivalent Shear Viscosity for Molten Polymers from 3-D Nonisothermal Capillary Flow Simulation

Wen¹,

Wang²,

Cyue³

et al. 2021

Polymers

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For highly viscous polymer melts, considerable fluid temperature rises produced by viscous heating can be a disturbing factor in viscosity measurements. By scrutinizing the experimental and simulated capillary pressure losses for polymeric liquids, we demonstrate the importance of applying a viscous heating correction to the shear viscosity, so as to correct for large errors introduced by the undesirable temperature rises. Specifically, on the basis of a theoretical derivation and 3-D nonisothermal flow simulation, an approach is developed for retrieving the equivalent shear viscosity in capillary rheometry, and we show that the shear viscosity can be evaluated by using the average fluid temperature at the wall, instead of the bulk temperature, as previously assumed. With the help of a viscous Cross model in analyzing the shear-dominated capillary flow, it is possible to extract the viscous heating contribution to capillary pressure loss, and the general validity of the methodology is assessed using the experiments on a series of thermoplastic melts, including polymers of amorphous, crystalline, and filler-reinforced types. The predictions of the viscous model based on the equivalent viscosity are found to be in good to excellent agreement with experimental pressure drops. For all the materials studied, a near material-independent scaling relation between the dimensionless temperature rise (Θ) and the Nahme number (Na) is found, Θ ~ Na0.72, from which the fluid temperature rise due to viscous heating as well as the resultant viscosity change can be predicted.

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“…This work does not include the infinite-shear-rate viscosity (as an estimable parameter) for the modified Cross model because all the experimental data did not present the characteristic Newtonian plateau of the high shear-rate region. This consideration is regularly used in the literature according to the shear rate range investigated, [4,29] which regularly applies when the polymer melts have high zero-shear viscosity values (≥10 4 Pa s). For the Bird-Carreau and Carreau-Yasuda, this work used 𝜂 ∞ = 1 × 10 −5 Pa s after performing a sensitivity analysis test, which showed that this parameter is not significant (small influence on the results) due to the shear rate range investigated.…”

Section: Theoretical Approachmentioning

confidence: 99%

“…It has been found the shear stress data could be more accurately described over the wide shear rate range by the newly suggested models. The accuracy of curve fitting decreases in the following order: Modified Quemada model, Modified Carreau [ 23,24] 56-76 𝜂 = f(T, p) [4,25] No informed by the authors 𝜂 = f ( λ, T) [ 8,26,27] No informed by the authors 𝜂 = f(MFI) [17] No informed by the authors.…”

Section: Introductionmentioning

confidence: 99%

Multivariable Rheological Models for Commercial Polypropylene with High Molar Masses

Castor

Fialho

Oechsler

et al. 2023

Macro Reaction Engineering

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This work investigates the fitting performance of conventional rheological models and the development of multivariable rheological models to reproduce experimental rheological data of different industrial grades of linear isotactic polypropylene (iPP) having high mass average molar masses, Mm (164–404 kg mol−1), at three temperature values (180–220 °C) over a wide range of shear rates (10−1–104 s−1). A shear thinning behavior is found in all investigated conditions. However, a low shear rate primary Newtonian plateau for a short shear rate range is only identified for the smallest Mm among those investigated, and for higher Mm such primary plateaus are even found at shorter shear rate range. Among the investigated models, only Cross and Carreau–Yasuda models are effective to reproduce the data for a specific PP grade. Two modified models are proposed that incorporate three variables. In the modified Cross Model, it has been shown that the characteristic time (λ) between the Newtonian plateau at the low shear rates and the shear‐rate range with shear‐thinning behavior depends exponentially on the Mm, and it does not depend on the temperature. Both proposed models fit very well with the experimental data with shear thinning behavior for a wide range of Mm.

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Rheological Properties Related to Extrusion of Polyolefins

Cited by 12 publications

References 77 publications

Open-Celled Foams from Polyethersulfone/Poly(Ethylene Glycol) Blends Using Foam Extrusion

Open-Celled Foams from Polyethersulfone/Poly(Ethylene Glycol) Blends Using Foam Extrusion

Retrieving Equivalent Shear Viscosity for Molten Polymers from 3-D Nonisothermal Capillary Flow Simulation

Multivariable Rheological Models for Commercial Polypropylene with High Molar Masses

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