THE EFFECT OF FILM COMPOSITION ON THE DIFFUSION OF ETHANOL THROUGH SOFT GELATIN FILMS

Changes were made in the composition of plasticized gelatin gels, anal ogous to those used in the manufacture of soft shell capsules, and the effect of these changes on the diffusion of ethanol through the films was investigated. The substitution of glycerol by higher polyols such as xylitol, sorbitol and lycasin (hydrogenated corn syrup) caused a s ignificant reduction in the diffusion process, as indicated by a reduc tion in the apparent diffusion co-efficient. When allowance was made f or film moisture content, a 5-10-fold reduction in the apparent diffus ion co-efficient was observed with the greatest reduction occurring in films having lower moisture contents. This reduction in apparent diff usion co-efficient is believed to be due to a 'phobic' interaction bet ween ethanol and the higher polyols which increases the energy barrier to the diffusion process. A general case is postulated whereby any di ffusion process will be modified by the inclusion of 'diffusantophilic ' (increased rate of diffusion) or 'diffusantophobic' (reduced rate of diffusion) components in the barrier. The implications of the changes in the formulation of the films for the filling of soft shell capsule s by the rotary-die method is discussed. Attempts to modify diffusion by inclusion of solid particles or liquid crystals in the gel structur e were unsuccessful, as was the replacement of part of the gelatin by hydrolyzed gelatin. (C) 1998 Elsevier Science B.V.