Effects of moisture on tablet compression of chitin

Direct compression of chitin was studied with special reference to the effects of moisture content on tablet formation and properties. Two cellulosic direct compression materials, microcrystalline cellulose (MCC) and spray-dried lactose-cellulose (SDLC, (Cellactose®) were used as reference materials. The compaction studies were carried out using an instrumented single-punch tablet machine. For physical material characterisation, water sorption isotherms were determined gravimetrically and the effects of moisture on the solid-state properties were studied by means of FT-NIR spectroscopy and X-ray powder diffractometry (XRPD). The sorption isotherms showed that the moisture sorption capacity of chitin is clearly higher than that of SDLC and only slightly higher than that of MCC, especially in the high humidity range. The maximum crushing strength for the chitin tablets was obtained at the moisture content ranging from 7% to 9%, approximately double the corresponding monolayer moisture content (mo). Lower and higher humidity levels clearly reduced the mechanical strength of the tablets. It was also found that the elasticity and plasticity factors of chitin, MCC and SDLC were strongly dependent on the level of moisture present during compaction.