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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.

In this study, a multiparticulate matrix system was produced, containing two different active pharmaceutical ingredients (APIs): enalapril-maleate and hydrochlorothiazide. The critical control points of the process were investigated by means of factorial design. Beside the generally used microcrystalline cellulose, ethylcellulose was used as matrix former to achieve modified drug release ensured by diffusion. The matrix pellets were made by extrusion-spheronization using a twin-screw extruder. Some pellet properties (aspect ratio, 10% interval fraction, hardness, deformation process) were determined. The aim of our study was to investigate how the two different APIs with different solubility and particle size influence the process. The amount of the granulation liquid plays a key role in the pellet shaping. A higher liquid feed rate is preferred in the pelletization process.

The aim of our research was to investigate the effect of the length of the polymer chain and the concentration of triethyl citrate used as a plasticizer on the thermal stability of the film structure in the case of two ethyl cellulose films (EC 10 and EC 45) used for preparing MR dosage forms. The influence of storage time was studied by monitoring the changes in the thermoanalytical parameters and by performing TG–MS examinations. It was found that the decomposition of the plasticizer from the arising film structure is retarded and a more homogeneous sample, therefore a better film can be prepared from EC 45. Mass spectrography performed as a coupled technique also proved that the films stayed stable until approximately 200 °C. Based on the above results, the composition prepared from EC 45 polymer with 5% triethyl citrate as plasticizer is recommended for making MR dosage forms.