EFFECT OF PARTICLE-SIZE AND SORBED MOISTURE ON THE COMPRESSION BEHAVIOR OF SOME HYDROXYPROPYL METHYLCELLULOSE (HPMC) POLYMERS

A study has been made of the moisture sorption-desorption and the comp ressional characteristics of some powdered HPMC polymers with differen t particle size, methoxy/hydropropoxy substitution and molecular size. Moisture sorption-desorption isotherms, at 25 degrees C, have been me asured and analysed according to the Young and Nelson and the GAB,equa tions, which distinguish moisture distribution in different physical f orms. Compression data were obtained after storage at various environm ental relative humidities by two methods: the tablet-in-die and the ej ected-tablet method. The rearrangement or packing of HPMC particles an d their deformation under pressure during tableting were determined by means of the Heckel equation. The externally adsorbed and normally co ndensed moisture were found to decrease with the particle size increas e and the methoxy/hydropropoxy substitution ratio while the internally absorbed moisture increased mainly due to the particle size increase. No simple and general change due to molecular size was observed in th e moisture distribution results. The particle packing and deformation of the HPMC powders were found to be related with the moisture distrib ution effects due to the particle size and the methoxy/hydropropoxy su bstitution ratio changes while no correlation was observed with the mo lecular size alteration.