Physical Properties of Shellac Material Used for Hot Melt Extrusion with Potential Application in the Pharmaceutical Industry

Hot melt extrusion offers an efficient way of increasing the solubility of a poorly soluble drug. Shellac has potential as a pharmaceutical matrix polymer that can be used in this extrusion process, with further advantages for use in enteric drug delivery systems. The rheological property of a material affects the extrusion process conditions. However, the literature does not refer to any published work that investigates the processability of various shellac materials. This work explores various types of shellac and explores their physicochemical and thermal properties along with their processability in the hot melt extrusion application. Physicochemical characterization of the materials was achieved using differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Additional processability characterization was achieved using melt flow index and rheology analysis. The results indicated that there was no chemical difference between the various shellac types compared in this study. However, the extrudable temperature ranges and rheological properties of different shellac types varied; SSB 55 Pharma FL had the lowest processing temperature and glass transition temperatures. Due to the shear-thinning behaviours, shellac can be extruded at lower temperatures. This study provides necessary data to determine the processing conditions in hot melt extrusion applications for the range of shellac materials.