Physicochemical properties of granulating liquids and their influence on microcrystalline cellulose pellets obtained by extrusion-spheronisation technology

The use of ethanol or ethanol/water mixtures as granulation liquids in the extrusion-spheronisation process results in the formation of pellets with significantly different mechanical and structural properties from those prepared using water alone. The product of surface tension (γL), relative permittivity (ɛR) of the granulation liquid and the cosine of contact angle (Θ) of granulation liquid on pellets solid has been introduced in order to explain the mechanism of this phenomenon. A correlation is shown between the factor γL × cos(Θ) × ɛR and the properties of the pellets produced. We have introduced the γL × cos(Θ) × ɛR which can be considered to represent the driving and counteracting forces of pellet contraction during drying. The contact angles and surface tensions were evaluated using the Wilhelmy plate method. Pellets were produced by extrusion-spheronisation technique using water, ethanol and ethanol/water mixtures as granulation liquids. Subsequent characterization of the pellets showed that their tensile strength and disintegration times increase with increase in the proposed factor γL × cos(Θ) × ɛR, while friability, average pore diameter and porosity decreases. The observed correlations show, that the granulation liquid influences the mechanical and structural properties of the pellets through the contraction driving and contraction counteracting forces during drying.