Single and bulk compression of pharmaceutical excipients: Evaluation of mechanical properties

Abstract

The compaction of powders into tablets is widely used in the pharmaceutical industry to convert drugs, in the form of small particles, into coherent and robust metered solid dosage forms. In order to produce robust tablets with the required properties, it is essential to understand the elastic, viscoelastic and plastic properties and rupture strength of the feed particles, which can be as small as a few microns in diameter. The objective of this work is to characterise the mechanical properties of single particles using a micromanipulation diametrical compression technique and relate the parameters to the compression behaviour of powders. Mechanical parameters, such as the Young's modulus, hardness and nominal rupture stress, were thus determined for each sample. The bulk compression data of the powders were analysed to calculate the parameters of the Heckel (Heckel, R.W., 1961a An analysis of powder compaction phenomena, Trans Metal Soc. AIME, 221, 1001–1008; Heckel, R.W., 1961b Density–pressure relationships in powder compaction, Trans Metal Soc. AIME 671–675), Kawakita (Kawakita, K. and Ludde, K.H., 1971 Some considerations on powder compression equations, Powder Technology, 4, 61–68) and Adams (Adams, M.J., Mullier, M.A. and Seville, J.P.K., 1994 Agglomerate strength measurement using a uniaxial confined compression test, Powder Technology, 78, 5–13.) models. These parameters will be compared with each other, and with the mechanical properties of the individual component particles. A correlation has been found between the nominal rupture stress of single particles and the apparent strength derived from the Kawakita and Adams models.