XXVIII Congreso Interamericano de Ingeniería Química Cuzco Perú _____________________________________________________________ Drying of a Multicomponent Polymeric Coating Film: Modelling and Experiments Fabio Luna 1 , Apolinar Picado 1,2 , Joaquín Martínez 1 1 Dept of Chemical Engineering and Technology, KTH Royal Institute of Technology Teknikringen 42, SE-100 44 Stockholm, Sweden picado@kth.se 2 Faculty of Chemical Engineering, National University of Engineering (UNI) Avenida Universitaria, Managua 11127, Nicaragua Keywords: Diffusion equation; Multicomponent diffusion; Polymeric solution Abstract The convective drying of a multicomponent polymeric solution containing two volatile components (acetone and ethanol), one non-volatile (cellulose acetate hydrogen phthalate), and an optional non-volatile component (ethylene glycol) as a softener was studied. Experiments were carried-out on a flat thin film geometry in batch mode. A mathematical model was presented to describe the composition profiles in the film as a function of time. Experiments showed that the drying rate exhibits two distinct falling periods. Addition of a softener changed the drying behaviour. Experiments where the softener was present show a higher and faster decrease of evaporation rates during initial stage of the drying process. Physically, the film developed a membrane on the surface at the beginning of the evaporation, becoming thicker as the solvents were depleted. Lateral or edge drying was observed along the exposed evaporation surface. Simulation results have a good qualitative agreement with experiments. 1. Introduction A step in the manufacture of various products—such as photographic films, magnetic storage media, adhesives, membranes, synthetic fibbers, and coatings—is to apply a thin film of a polymeric solution to provide for additional characteristics that enhanced the quality of such products. The drying of multicomponent polymeric solutions consisting of at least one polymer and one or more solvents is important because of its influence on the quality of the product. For instance, to improve the quality of pharmaceutical products, tablets are coated to provide physical and chemical protection for the drug, to control the release of the drug from the tablet, to mask the taste, odour or colour of the drug, or to simply improve the appearance of the tablet. In another pharmaceutical application, an active substance is embedded in a polymeric film for intradermal-controlled release. In such cases, an even distribution of the active substance will determine the efficiency of its release. Therefore, the simulation of the drying process can be useful to optimise and ensure product quality. Drying of polymeric solutions has focused mainly on one or two solvents in experimental and modelling approaches. Vrentas and Vrentas [1] provided an analytical solution for the