MOISTURE ADSORPTION AND TABLETTING .3. EFFECT ON TABLET STRENGTH-POST COMPACTION STORAGE TIME PROFILES

The effect of air humidity on the Post compaction changes in tensile strength of tablets of three test materials, saccharose, sodium chloride and dicalcium hydrogen phosphate dihydrate, was assessed during storage of the tablets for up to 168 h. For saccharose and sodium chloride also the changes in tablet permeametry surface area at storage times up to 24 h was measured. For tablets of saccharose and sodium chloride, the tablet strength increased generally during the storage. An increased air humidity increased both the rate and the degree of the increase in tablet strength, i.e., the storage time after which measurements of tablet data are performed is of importance when the compactibility of a material is evaluated. However, when tablets were stored at or above the critical relative humidity, the tablet strength decreased after a few hours storage. For tablets of dicalcium hydrogen phosphate dihydrate, the tablet strength did not vary with time or storage condition. For tablets of saccharose and sodium chloride, the surface area generally decreased with storage time and the effect was more pronounced with increased storage humidity. Hence, a relationship between the tablet strength and tablet surface area was found. Thus, the changes in tablet strength during storage are probably a result of a rearrangement of solid material within the tablet which is mediated or facilitated by sorbed water.