Some physical properties of gelatin films in relation to hard capsule production
Hard gelatin capsules are manufactured from blends of limed ossein (LOG), acid ossein and acid pigskin gelatins, with LOGS usually forming the main portion of the blend. Unfortunately, the quality of the finished capsule cannot be predicted by routine quality control tests and 'poor' batches of LOG are encountered which form unsatisfactory capsules. In addition, differences between gelatin types are encountered in practice but the supporting literature is sparse and conflicting. This work examines some properties of gelatins pertinent to hard capsule manufacture in an attempt to relate these to gelatin type and known performance on capsule machines. Molecular mass distributions (MMD) were examined by polyacrylamide gel electrophoresis. Each different gelatin type possessed a characteristic shape of MMD which could be related to the source tissue and the treatment undergone during gelatin manufacture. MMDs, isoionic point determinations and an assessment of the content of protein impurities by ultraviolet spectrophotometry failed to resolve differences between 'good' and 'poor' LOG batches. The drying rates of freshly-cast gelatin films were studied under conditions of controlled humidity, temperature and air velocity. No significant differences between gelatin types were observed. Small variations in equilibrium moisture content were seen and were tentatively ascribed to the generation of water binding sites (free carboxyl groups) during gelatin manufacture. The mechanical properties of dry gelatin films were examined by tensile stress-strain and stress-relaxation measurements. Viscoelastic behaviour typical of a polymer in the glass transition region was observed, and significant differences in film fracture strain were observed but these were not related to gelatin type. Optical rotation measurements indicated similar orders of film crystallinity and determinations of frictional characteristics similarly revealed no varietal differences. Overall, few differences related to gelatin type were seen within the properties examined. There was no evidence in these studies to explain the unsatisfactory behaviour of 'poor' LOG batches in capsule manufacture. NB. This ethesis has been created by scanning the typescript original and may contain inaccuracies. In case of difficulty, please refer to the original text.