(170e) Modeling the Kinetic of Sorption of Alcohols in Glassy Matrimid 5218 Using a Non Equilibrium Theory for Glassy Polymers (NET-GP) Approach

Cocchi, G., University of Bologna
Baschetti, M. G., Alma Mater Studiorum - Università di Bologna
Doghieri, F., University of Bologna
Sarti, G., University of Bologna

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. Carlà, 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.