Variation in polymer film structure and thickness‐dependent permeability

Abstract

Fick's laws have been applied to permeation processes in polymer films, and in Fickian permeation flux and film thickness vary inversely,' thus allowing prediction of film performance at various thicknesses. In a film having a porous asymmetric structure (a porous core bounded by compact surface zones), the relative proportions of the various zones in the barrier and indeed the pore structure of each zone may vary during a change in film thickness, thus resulting in non-Fickian permeation. This aspect was investigated in the present study.An acrylate-methacrylate copolymer (ERI-100, Rhom Pharma, Darmstadt) was used to form films of various thicknesses by casting the polymer solution on FTFE molds2 The films contained a plasticizer, glycerol triacetate (GTA) or glycerol tributyrate (GTB), 16.6%. Film permeability was determined after Abdel-Aziz and others (1975Y at 30°C using 10% urea or sodium chloride as permeant. Film lower surface (in contact with mold during casting) was upstream in the permeation experiments. Permeability coefficient P was calculated from the quasi-steady-state equation1Where C-, and C, are the concentrations initially and at time t in the donor fluid. L is film thickness, and Vis the volume of each compartment. Film pore structure was determined by electron microscopy2; the plasticizer leached from the films under conditions of the permeation experiment was determined by a gas-liquid chromatographic (GLC) m e t h~d .~ Permeability coefficients increased linearly with increase in film thickness when urea was used as permeant (Fig. 1). The effect was most pronounced in the GTRplasticized film and least pronounced in films from which the plasticizer GTA had been leached prior to permeation experiments; for instance, the overall increases in permeability coefficients for each 10 pm increase in film thickness were 0.963,0.233, and 0.041 x cm2 s-l for the GTB, GTA, and deplasticized GTA films, respectively. The use of sodium chloride as permeant resulted in a decrease in film permeability with increase in film thickness; observed values of the permeability coefficient were 0.025,0.014,0.004, and 0.002 x lo-' cm2 s-l obtained with

Solute adsorption and concentration-dependent permeability in certain polymer films

“…Abdel- Aziz et al (1975) and Okor (1982) have indicated the potential of acrylatemethacrylate copolymer films in controlled release applications. Solutes permeate these films by a pore flow mechanism, (Okor & Anderson 1986a). In a preliminary report aimed at developing an ocular delivery system of sulphaceta-mide sodium, it was shown that the permeability coefficient versus concentration profile of the solute exhibited an initial increase followed by a decrease (Okor & Anderson 1986b).…”