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Classical nucleation theory applied to homogeneous bubble nucleation in the continuous microcellular foaming of the polystyrene−CO2 system / Shunahshep Shukla in Industrial & engineering chemistry research, Vol. 48 N° 16 (Août 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 16 (Août 2009) . - pp. 7603–7615 Titre : Classical nucleation theory applied to homogeneous bubble nucleation in the continuous microcellular foaming of the polystyrene−CO2 system Type de document : texte imprimé Auteurs : Shunahshep Shukla, Auteur ; Kurt W. Koelling, Auteur Année de publication : 2009 Article en page(s) : pp. 7603–7615 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Polymer−physical  foaming  agent  solution  Bubble  nucleation  Hydrodynamic  constraints Résumé : In the continuous production of microcellular thermoplastic foam, a polymer−physical foaming agent (PFA) solution is subjected to a rapid pressure drop through an extrusion foaming die. Simulations were run for the flow of a polymer−PFA solution through an extrusion foaming die with an abrupt axisymmetric contraction. The pressure drops across the die obtained through the simulations showed good qualitative agreement with experimental pressure drop measurements on the foaming extrusion die obtained in our laboratory. Field values of pressure, temperature, and velocity were obtained at each point in the foaming die. Once the values of pressure and temperature were obtained along each point in the foaming die, classical nucleation theory for bubble nucleation was invoked to predict the local bubble nucleation rate downstream of the saturation surface. The hydrodynamic constraints to the nucleation rate were calculated by using a modified form of the classical nucleation theory that accounted for the diffusional and viscosity constraints to the rate of homogeneous nucleation. The capillarity approximation was found not to be valid for bubble nucleation of CO2 in polymers; a correction accounting for the curvature dependence of surface tension was applied to get nonzero nucleation rates for the system to reconcile theoretically predicted rates with experimental observations. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie8011243 [article] Classical nucleation theory applied to homogeneous bubble nucleation in the continuous microcellular foaming of the polystyrene−CO2 system [texte imprimé] / Shunahshep Shukla, Auteur ; Kurt W. Koelling, Auteur . - 2009 . - pp. 7603–7615. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 16 (Août 2009) . - pp. 7603–7615 Mots-clés : Polymer−physical  foaming  agent  solution  Bubble  nucleation  Hydrodynamic  constraints Résumé : In the continuous production of microcellular thermoplastic foam, a polymer−physical foaming agent (PFA) solution is subjected to a rapid pressure drop through an extrusion foaming die. Simulations were run for the flow of a polymer−PFA solution through an extrusion foaming die with an abrupt axisymmetric contraction. The pressure drops across the die obtained through the simulations showed good qualitative agreement with experimental pressure drop measurements on the foaming extrusion die obtained in our laboratory. Field values of pressure, temperature, and velocity were obtained at each point in the foaming die. Once the values of pressure and temperature were obtained along each point in the foaming die, classical nucleation theory for bubble nucleation was invoked to predict the local bubble nucleation rate downstream of the saturation surface. The hydrodynamic constraints to the nucleation rate were calculated by using a modified form of the classical nucleation theory that accounted for the diffusional and viscosity constraints to the rate of homogeneous nucleation. The capillarity approximation was found not to be valid for bubble nucleation of CO2 in polymers; a correction accounting for the curvature dependence of surface tension was applied to get nonzero nucleation rates for the system to reconcile theoretically predicted rates with experimental observations. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie8011243

Shear viscosity of CO2-plasticized polystyrene under high static pressures / Maxwell J. Wingert in Industrial & engineering chemistry research, Vol. 48 N° 11 (Juin 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 11 (Juin 2009) . - pp. 5460–5471 Titre : Shear viscosity of CO2-plasticized polystyrene under high static pressures Type de document : texte imprimé Auteurs : Maxwell J. Wingert, Auteur ; Shunahshep Shukla, Auteur ; Kurt W. Koelling, Auteur Année de publication : 2009 Article en page(s) : pp. 5460–5471 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Shear  viscosity  measurements  Polymer/supercritical  fluid  systems  Pressure Résumé : High-pressure shear viscosity measurements of polymer/supercritical fluid systems are numerous, but most involve pressure-gradient equipment such as a capillary or slit die with pressure drops exceeding 10%. Pressure change across the measurement region introduces some errors when quantifying the effect of blowing agents and other diluents on viscosity. This source of errors was removed by using a static-pressure, Couette rheometer. The viscosity of polystyrene (PS)/carbon dioxide (CO2) was measured from 140 to 180 °C and from 3 to 6 wt % CO2. The effect of pressure on diluent-free PS viscosity was required to calculate the CO2 concentration shift factor. Thus, viscosities at both atmospheric and elevated pressure (via helium, an insoluble gas) were measured using the same equipment and method. The Fillers−Moonan−Tschoegl (FMT) model was overdefined for obtaining free volume parameters, but it was a helpful correlation tool to obtain the pressure effect on viscosity. Pressure and concentration shift factors obtained from the experiments were compared with empirical free-volume plasticization models, one based on glass transition temperature, the other on P−V−T behavior. Unfortunately, neither model demonstrated quantitative agreement with the experimental data within the 3−6 wt % CO2 range examined. The WLF−Chow model, based on Tg data, fared better than the P−V−T-based model. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800896r [article] Shear viscosity of CO2-plasticized polystyrene under high static pressures [texte imprimé] / Maxwell J. Wingert, Auteur ; Shunahshep Shukla, Auteur ; Kurt W. Koelling, Auteur . - 2009 . - pp. 5460–5471. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 11 (Juin 2009) . - pp. 5460–5471 Mots-clés : Shear  viscosity  measurements  Polymer/supercritical  fluid  systems  Pressure Résumé : High-pressure shear viscosity measurements of polymer/supercritical fluid systems are numerous, but most involve pressure-gradient equipment such as a capillary or slit die with pressure drops exceeding 10%. Pressure change across the measurement region introduces some errors when quantifying the effect of blowing agents and other diluents on viscosity. This source of errors was removed by using a static-pressure, Couette rheometer. The viscosity of polystyrene (PS)/carbon dioxide (CO2) was measured from 140 to 180 °C and from 3 to 6 wt % CO2. The effect of pressure on diluent-free PS viscosity was required to calculate the CO2 concentration shift factor. Thus, viscosities at both atmospheric and elevated pressure (via helium, an insoluble gas) were measured using the same equipment and method. The Fillers−Moonan−Tschoegl (FMT) model was overdefined for obtaining free volume parameters, but it was a helpful correlation tool to obtain the pressure effect on viscosity. Pressure and concentration shift factors obtained from the experiments were compared with empirical free-volume plasticization models, one based on glass transition temperature, the other on P−V−T behavior. Unfortunately, neither model demonstrated quantitative agreement with the experimental data within the 3−6 wt % CO2 range examined. The WLF−Chow model, based on Tg data, fared better than the P−V−T-based model. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800896r