Tablet strength, porosity, elasticity and solid state structure of tablets compressed at high loads

The effects of applying high loads to a powder bed on the properties of compacts of sodium chloride, sucrose and polyethylene glycol were studied. The porosity (apparent zero) and tensile strength levelled off when a high enough load was applied. This levelling off corresponded to a pronounced elasticity, and for polyethylene glycol, an irreversible increase in particle density and melting point was detected. Tablet elasticity (volume increase during decompression) is discussed in terms of two contributing factors. Firstly, rupture of bonds between tabletting particles and, secondly, a pronounced volume expansion of the particles (crystal lattice). The latter mechanism was believed to be important only for polyethylene glycol. The possibility of utilizing the tensile strength at zero porosity as an intrinsic strength value for the tabletted materials was also tested. Significant differences between different size fractions were obtained even when tablets compressed to zero porosity were compared. This was especially pronounced for sodium chloride.