THE EFFECT OF MOISTURE SORPTION ON THE STRENGTH AND INTERNAL SURFACE-AREA OF LACTOSE TABLETS

Tablets compacted from alpha-lactose monohydrate and from roller dried beta-lactose both show time-dependent moisture uptake when exposed to an ambient humid atmosphere. Moisture sorption tends to reach a plateau within 10 min and is accompanied by a decrease in both crushing strength and specific BET-surface area of the tablets. Subsequent storage of the tablets in a dry atmosphere results in an increase in strength but no change in surface area. The tablets show no moisture uptake, nor any change in strength and surface area when transferred immediately after ejection from the die in a dry atmosphere. These changes in crushing strength endorse the need to standardize the time between tablet ejection and strength measurement. Concerning the BET-specific surface area, it is recommended to suppress blocking of small pores by transferring the tablets immediately after ejection from the die into a dry nitrogen atmosphere for transport to the gas-adsorption apparatus.