Investigation of water vapour sorption mechanism of starch-based pharmaceutical excipients.

Starch-based excipients are commonly used in oral solid dosage forms. The effect of particle size and pregelatinisation level of starch-based excipients on their water absorption behaviour have been evaluated. The results showed that starch-based excipients have type ii isotherms, indicating that the principal mechanism of sorption is the formation of monolayer coverage and multilayer water molecules (10-80 RH %). It was found that the particle size of starch-based excipients did not have any influence on the rate of water sorption, whereas the level of pregelatinisation changed the kinetics of water sorption-desorption. Results showed that the higher the degree of pregelatinisation, the higher the rate of water absorption, which is irrespective of particle size. SEM images showed that a partially gelatinised starch had a firm granular structure with small pores and channels on the surface while a fully gelatinised starch had more irregular and spongy like surface with a degree of fractured particles.