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The distribution of the plasticizer triethyl citrate between the chains of the polymer ethylcellulose was determined in order to explain the mechanical properties. A knowledge of these properties is indispensable for preformulation studies. As preformulation, the relationship between the mechanical properties and the distribution of the plasticizer was studied. The distribution was investigated with positron annihilation lifetime spectroscopy, and the mechanical properties with breaking hardness tests. Two kinds of ethylcellulose were used. The best film-former with plasticizer was chosen with the optimal concentration. Selection of the optimum type and concentration of the plasticizer is essential in the formulation of pellets and coated dosage forms.

The investigation of free films is an essential part of the preformulation studies, because it is necessary to know, weather the given formulation is suitable to coat the corpus or not. As preformulation, the relationships between surface properties, and the structure of ethylcellulose free films containing different amount of plasticizer were studied. The structure analysis, and the incorporation of the plasticizer was performed with the use of FT-IR analysis. The results showed that the films are suitable to produce diffusion coatings.