A generalized differential constitutive equation for polymer melts based on principles of nonequilibrium thermodynamics

2009 ◽  
Vol 53 (2) ◽  
pp. 309-337 ◽  
Author(s):  
Pavlos S. Stephanou ◽  
Chunggi Baig ◽  
Vlasis G. Mavrantzas
Keyword(s):  
Constitutive Equation ◽  
Nonequilibrium Thermodynamics ◽  
Polymer Melts ◽  
Generalized Differential

Viscosity Models Based on Network Theory for Polymer Melts

2010 ◽  
Vol 129-131 ◽  
pp. 1244-1247
Author(s):  
Hai Hang Xu ◽  
Lei Zhong
Keyword(s):  
Experimental Data ◽  
Kinetic Equation ◽  
Constitutive Equation ◽  
Polymer Composites ◽  
Network Theory ◽  
Polymer Melts ◽  
Structure Parameter ◽  
Viscosity Models ◽  
Model Predictions ◽  
Good Agreement

New shear and extensional viscosity models based on Fredrickson kinetic equation coupled with Dewitt constitutive equation were established to predict viscosities of polymer melts. The experimental data of 125°C LDPE and LDPE filled with 35% glass beads reported from references were compared with the model predictions. The predictions showed good agreement with the measurements. The models are simple and easy to use. Because they contain no structure parameter, they are capable to describe the viscosities of pure polymer and polymer composites.

scholarly journals Simple, Accurate and User-Friendly Differential Constitutive Model for the Rheology of Entangled Polymer Melts and Solutions from Nonequilibrium Thermodynamics

Materials ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 2867 ◽  
Author(s):  
Pavlos S. Stephanou ◽  
Ioanna Ch. Tsimouri ◽  
Vlasis G. Mavrantzas
Keyword(s):  
Large Scale ◽  
Nonequilibrium Thermodynamics ◽  
Polymer Melts ◽  
Fluid Flows ◽  
Second Law Of Thermodynamics ◽  
High Shear Rates ◽  
Entangled Polymer ◽  
Conformation Tensor ◽  
Entangled Polymer Melts ◽  
User Friendly

In a recent reformulation of the Marrucci-Ianniruberto constitutive equation for the rheology of entangled polymer melts in the context of nonequilibrium thermodynamics, rather large values of the convective constraint release parameter βccr had to be used in order for the model not to violate the second law of thermodynamics. In this work, we present an appropriate modification of the model, which avoids the splitting of the evolution equation for the conformation tensor into an orientation and a stretching part. Then, thermodynamic admissibility simply dictates that βccr ≥ 0, thus allowing for more realistic values of βccr to be chosen. Moreover, and in view of recent experimental evidence for a transient stress undershoot (following the overshoot) at high shear rates, whose origin may be traced back to molecular tumbling, we have incorporated additional terms into the model accounting, at least in an approximate way, for non-affine deformation through a slip parameter ξ. Use of the new model to describe available experimental data for the transient and steady-state shear and elongational rheology of entangled polystyrene melts and concentrated solutions shows close agreement. Overall, the modified model proposed here combines simplicity with accuracy, which renders it an excellent choice for managing complex viscoelastic fluid flows in large-scale numerical calculations.

Application of a constitutive equation to polymer melts

1981 ◽  
Vol 26 (6) ◽  
pp. 1847-1863 ◽  
Author(s):  
Ramesh N. Shroff ◽  
Mitsuzo Shida
Keyword(s):  
Constitutive Equation ◽  
Polymer Melts
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