Purpose: To analyze the influence of inherent densification and deformation properties of paracetamol on the mathematical parameters derived from Heckel, Walker, Kawakita, and Adams equations and to correlate these with single particle nominal fracture strength and bulk compression parameters using confined compression on a fully instrumented rotary tablet press.
Materials and methods: Force-displacement data were captured during in-die compression for four different particle size fractions (150-250, 300-450, 500-650, and 700-1,000 microm) of paracetamol each at compression force of 5.2, 8.6, and 17.3 kN. Nominal single particle fracture strength was obtained by micro tensile testing.
Results: Apparent mean yield pressure (Py) from Heckel analysis was significantly affected by the applied pressure, and was influenced by elastic energy and Young's modulus. The single particle fracture strength correlated to parameters obtained from Heckel, Walker, Kawakita, and Adams equations. Results obtained from bulk compression and single particle measurements were consistent with, and polynomially related to Py, Kawakita (1/b), and Adams parameter (tau0').
Conclusions: Values of Py, 1/b, and tau0' obtained from Heckel, Kawakita, and Adams equations, respectively, can be interpreted as a measure of single particle nominal fracture strength during confined compression loading. Walker and Adams parameters were less affected, than Heckel and Kawakita parameters, by the applied pressure.