Polymer extrudate-swell: From monodisperse melts to polydispersity and flow-induced reduction in monomer friction

Robertson, Ben; Thompson, Richard L.; McLeish, Tom; Robinson, Ian

doi:10.1122/1.5058207

Cited by 13 publications

(12 citation statements)

References 29 publications

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“…Specifically, Ianniruberto et al observed that modeling alignment‐dependent friction is more important to capture PS extensional rheology, compared to melts of other chemistries, due to its small N eK . Furthermore, Robertson et al showed that including alignment‐dependent friction in the tube model produces much‐improved predictions of extrudate swell in PS, particularly for near‐monodisperse polymers. In solutions reduced friction is expected to be absent because the local environment is dominated by the solvent .…”

Section: Resultsmentioning

confidence: 99%

Nonlinear shear of entangled polymers from nonequilibrium molecular dynamics

Anwar

Graham

2019

J Polym Sci B Polym Phys

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This study aims to use molecular dynamics (MD) simulations of Kremer–Grest (KG) chains to inform future developments of models of entangled polymer dynamics. We perform nonequilibrium MD simulations, under shear flow, for well‐entangled KG chains. We study chains of 512 and 1000 KG beads, corresponding to 8 and 15 entanglements, respectively. We compute the linear rheological properties from equilibrium simulations of the stress autocorrelation and obtain from these data the tube model parameters. Under nonlinear shear flow, we compute the shear viscosity, the first and second normal stress differences, and chain contour length. For chains of 512 monomers, we obtain agreement with the results of Cao and Likhtman (ACS Macro. Lett. 2015, 4, 1376). We also compare our nonlinear results with the Graham, Likhtman and Milner‐McLeish (GLaMM) model. We identify some systematic disagreement that becomes larger for the longer chains. We made a comparison of the transient shear stress maximum from our simulations, two nonlinear models and experiments on a wide range of melts and solutions, including polystyrene (PS), polybutadiene, and styrene–butadiene rubber. This comparison establishes that the PS melt data show markedly different behavior to all other melts and solutions and KG simulations reproduce the PS data more closely than either the GLaMM or Xie and Schweizer models. We discuss the performance of these models against the data and simulations. Finally, by imposing a rapid reversing flow, we produce a method to extract the recoverable strain from MD simulations, valid for sufficiently entangled monodisperse polymers. We explore how the resulting data can probe the melt state just before the reversing flow. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1692–1704

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Section: Resultsmentioning

confidence: 99%

Nonlinear shear of entangled polymers from nonequilibrium molecular dynamics

Anwar

Graham

2019

J Polym Sci B Polym Phys

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“…A better agreement at low Wi number for the bidispersed PS is observed compared to that in Figure 10a, which indicates the necessity of additional stretching or nonstretching modes for more accurately representing the melts with a broader MMD. These authors also revealed that the polymer stretch relaxation governed by the Rouse motion time played a main role in controlling the extrudate swell, [ 9,151 ] which appears to be inconsistent with the report by Cao et al. [ 150 ] As stated by Robertson, [ 9 ] interesting future work would therefore be to include the evaluation of how versatile the Rolie‐poly model is to capture swelling variations for an increasing dispersity value.…”

Section: Modeling Tools and Applicationmentioning

confidence: 87%

“…These authors also revealed that the polymer stretch relaxation governed by the Rouse motion time played a main role in controlling the extrudate swell, [9,151] which appears to be inconsistent with the report by Cao et al [150] As stated by Robertson, [9] interesting future work would therefore be to include the evaluation of how versatile the Rolie-poly model is to capture swelling variations for an increasing dispersity value.…”

Section: Molecular-based Constitutive Modelsmentioning

confidence: 89%

“…Furthermore, Robertson et al. [ 9,62,151 ] systemically investigated the extrudate swell of PS melts applying the Rolie‐poly model with the in‐house FEM‐based tool “flowSolve.” It is seen in Figure a that the predicted swelling assuming a monodispersed polymer with an M m of 340 kg mol −1 only agrees with the experimental data for the bimodal polymer P672‐S with the multipass rheometer (MPR), which contains a peak with a high M m of 340 kg mol −1 and another with a low M m of 160 kg mol −1 , at higher Wi numbers. Hence, it is worthwhile to improve the Rolie‐poly model to capture the impact of dispersity on the viscoelastic properties.…”

Section: Modeling Tools and Applicationmentioning

confidence: 99%

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State of the‐Art for Extrudate Swell of Molten Polymers: From Fundamental Understanding at Molecular Scale toward Optimal Die Design at Final Product Scale

Tang

Marchesini

Cardon

et al. 2020

Macro Materials & Eng

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Exit velocity profiles for parallel die and die optimized using conical widening or narrowing. Reproduced permission. [164] Copyright 2010, Elsevier Ltd. c) Average velocity of each outflow subsection of the slit die (width = 100 mm and height = 1.5 mm), Reproduced with permission. [173] Copyright 2012, Elsevier Ltd. d,e) The geometry profiles of the Catheter cross section covered as case study. f) The velocity distribution at the die outflow for different trials-T0: the original die profile; T1: r 2 varies from 0.9 to 0.95 mm; T2: r 2 varies from 0.95 to 0.9 mm, θ 2 varies from 45° to 43°; T3: r 2 varies from 0.9 to 0.95 mm; T4: θ 2 varies from 43° to 40°; T5: r 3 varies from 0.7 to 0.65 mm. Reproduced with permission. [166] Copyright 2013, Elsevier. g) The corresponding objective function evolution in consecutive trials. Reproduced with permission. [166] Copyright 2013, Elsevier Ltd.

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“…A single stretching mode version of the Rolie-Poly equation was used to simulate monodisperse melts and the multi-mode Rolie-Double-Poly equation [32] was used for simulation of bidisperse and polydisperse melts. A modified version was used to include finite extensibility for the single stretching Rolie-Poly element of monodisperse melts and the two stretching elements used in models of the bidisperse melt [27][28][29]. Experimentally we demonstrated that the isothermal die swell for polystyrenes with molecular weights in the range of 100-400 kDa showed the behaviour reported in literature.…”

Section: Tube Theory Explanations Of Die Swellmentioning

confidence: 62%

Shear processing maps: a new design guide for melt processors

Robertson

Robinson

Stocks

et al. 2020

Plastics, Rubber and Composites

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A method for predicting the optimal conditions for polymer extrusion, which relies only on gramscale laboratory experiments for two commercial polystyrene samples with two molecular weights is demonstrated by oscillatory rheology. These enable a shear viscosity map vs. temperature and shear rate to be constructed, together with the positions for the major molecular timescales. Alternative methods for characterising rheology, including melt flow index and capillary rheology measurements were also employed, but these do not give the same level of understanding of flow behaviour. The capillary tests generates die swell and this complex behaviour can be seen to collapse onto a single line regardless of temperature when plotted using the Rouse-Weissenberg number. The full shear viscosity map, together with the polymer timescales serves as a design tool to predict processing behaviour for melt processors. The work represents and builds on major academic-industry collaborative research programmes.

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Polymer extrudate-swell: From monodisperse melts to polydispersity and flow-induced reduction in monomer friction

Cited by 13 publications

References 29 publications

Nonlinear shear of entangled polymers from nonequilibrium molecular dynamics

Nonlinear shear of entangled polymers from nonequilibrium molecular dynamics

State of the‐Art for Extrudate Swell of Molten Polymers: From Fundamental Understanding at Molecular Scale toward Optimal Die Design at Final Product Scale

Shear processing maps: a new design guide for melt processors

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