THE SWELLING AND WATER-UPTAKE OF TABLETS .3. MOISTURE SORPTION BEHAVIOR OF TABLET DISINTEGRANTS

Water vapor sorption properties and the thermal behavior of four disintegrants including microcrystalline cellulose (Avicel PH102), croscarmellose sodium (Ac-di-sol), com starch, and sodium starch glycolate (Primojel), were studied. They all exhibited type II-like isotherm. The apparent monolayer sorption for each of disintegrants was found to be significantly greater than the specific surface obtained from nitrogen adsorption. It is proposed that water molecules interact with specific sites on the disintegrant glassy polymer. Water tends to stay as a condensed phase on the polymer, rather than to diffuse into the bulk. Water plasticization caused glass transition temperature (T(g)) of all disintegrant polymers to decrease. It facilitated a change from glass to the rubber state. Because the sorption sites were in the glassy state, the change from glass to rubber, which in tum kinetically reduced the available sites, would reflect the sorption capacity of a disintegrant polymer. In addition, the difficulty in freezing a disintegrant's sorbed water was encountered.