Modeling the Kinetic of Sorption of Alcohols in Glassy Matrimid 5218 Using a Non Equilibrium Theory for Glassy Polymers (NET-GP) Approach

<>Modeling the Kinetic of Sorption of Alcohols in Glassy Matrimid 5218  Using a Non Equilibrium Theory for Glassy Polymers (NET-GP) Approach

Giovanni Cocchi,  Marco Giacinti Baschetti, Maria Grazia De Angelis, Ferruccio Doghieri*, Giulio Cesare Sarti

Department of Civil, Chemical, Environmental and Material Engineering - University of Bologna, Via Terracini 28, 40131 Bologna, Italy

* Corresponding Author Email Address: ferruccio.doghieri@unibo.it

Matrimid 5218 is a polyimide that exhibits several interesting mechanical and thermal properties. Its most striking feature is a really high glass transition temperature, that is reported to be around 310°C [1]. Therefore, Matrimid 5218 can be used for membrane separation processes in the glassy state and it has indeed been proposed for gas separation and organic solvent nanofiltration modules. In the latter application, in particular, solvent- induced plasticization effects can significantly affect the membrane properties with respect to the dry state. The kinetics of sorption and pseudoequilibrium solubility of liquid methanol,  ethanol and 1-propanol  in Matrimid 5218  at 308 K has been measured through the common blot and weight method, while the kinetics of sorption and the pseudoequilibrium solubility of methanol in vapor phase has been measured in a Quartz Spring Balance [2]. The liquid sorption experiments are integral sorption experiments with the largest possible activity jump, while the vapor sorption experiments had been done at different vapor activity and performing differential sorption experiments. The results had been successfully modeled through a comprehensive approach, in which the thermodynamics and the kinetics of sorption are being described  taking into account the out of equilibrium nature of the glassy matrix [3,4]. The non equilibrium thermodynamics of glassy polymers (NET-GP) has been applied to describe the thermodynamic properties of polymer-solute mixtures in out of equilibrium conditions. The lattice fluid model by Sanchez and Lacombe was used to represent the equilibrium thermodynamic properties of alcohol-Matrimid systems within the NET-GP procedure. A one dimensional model for sorption and dilation in polymeric films was developed by considering a simple rheological description of the relaxation processes of the glassy state enables to predict the dilation kinetics. Use of concentration dependent bulk viscosity in the rheological model allowed for the representation of relaxation phenomena in vapor sorption and liquid sorption experiments. The mass transport of the alcohols inside the bulk of the polymer film was then described through the Fick's constitutive equation with composition dependent diffusivity. The model has been numerically implemented through a finite element scheme. The Figure 1 show the comparison between the experimental sorption kinetic of liquid 1 Propanol in Matrimid 5218 at 308 K and the results of the model.

Figure 1: Mass Uptake of 1 Propanol in Matrimid 5218 at 308 K as a function of the square root of time.

 

 

[1] A.C. Comer, D. S. Kalika, B. W. Rowe, B. D. Freeman, D. R. Paul, Dynamic Relaxation Characteristics of Matrimid® Polyimide, Polymer, 50, 2009, 891-897.

[2] E. Piccinini, M. Giacinti Baschetti, G. C. Sarti, Use of an Automated Spring Balance for the Simultaneous Measurement of Sorption and Swelling in Polymeric Films, Journal of Membrane Science, 234, 2004, 95-100.

[3] M. Minelli, F. Doghieri, A Predictive Model for Vapor Solubility and Volume Dilation in Glassy Polymers, Industrial & Engineering Chemistry Research 51, 2012, 16505-16516.

[4] V. Carlą, Y. Hussain, C. Grant, G.C. Sarti, R.G. Carbonell, F. Doghieri, Modeling Sorption Kinetics of Carbon Dioxide in Glassy Polymeric Films Using the Non Equilibrium Thermodynamics Approach, Industrial & Engineering Chemistry Research 48, 2009, 3844-3854.