Rheological and thermo-mechanical properties of Sepifilm-Sepisperse water dispersions and films

"Ready to use" products for the coating of solid dosage forms are constituted by film forming polymers and suitable additives in a fixed ratio. Despite the wide literature available for the single polymers and the impact of additives on their properties, the uncertainty on the composition of the "ready to use" products (for patent reasons) make their behaviour still not well known, at least outside the suggested conditions of use. Among the "ready to use" products, some of them, especially those for coloured films, are formed by two different formulated blends to mix together. The aim of this work is the characterization of one of these coating systems, the Sepifilm-Sepisperse platform, in terms of rheological properties of water dispersions and of thermo-mechanical properties of the free films, highlighting the effect of the ratio of the two products that have to be added together. Polymeric water dispersions were prepared with different concentrations of Sepifilm and several ratios of Sepifilm-Sepisperse. The prepared systems were then analysed in terms of viscosity and viscoelasticity. The results highlighted in both cases that it is the film former polymer concentration to mainly influence the system features. Polymeric free films were prepared by casting the water dispersion and drying the films at ambient conditions. The films were analysed by DMA applying tests able to characterize rheological and thermal properties. The results showed that the ratio of the two products influences the final free film properties, both in terms of glassy phase stiffness and transition from glassy to rubbery phase (glass transition, activation energy and fragility).