Moisture adsorption and tabletting. I. Effect on volume reduction properties and tablet strength for some crystalline materials

The presence of water in a powder mass is known to influence the behaviour of the powder during compaction as well as the mechanical strength of the tablets obtained. To study the influence of moisture content, 6 substances (sodium chloride, sodium bicarbonate, saccharose, lactose, acetylsalicyclic acid, sodium citrate and Emcompress) were compressed in a range of RH (33–100%)_. The compression characteristics of the materials in terms of porosity-pressure displacement profiles and surface area-pressure profiles as well as the tablet strength by diametral compression were evaluated. The results showed that water absorbed at particle surfaces has a very limited effect on the volume reduction behaviour of a particulate solid. The exception is when a fairly large amount of “condensed” water is present in the powder mass. In this case it seems that water can facilitate volume reduction, probably because water can reduce friction between particles and between powder and die wall. It was also found that the air humidity during storage markedly affected the tablet strength, showing both increases and decreases. Adsorbed water vapour the tensile strength for most of the tested materials at low and medium relative humidities. Condensation of water vapour at high relative humidities led to a decreased tablet strenght in most cases.