Purpose: We hypothesize that if the kinetics and the mechanisms involved in tablet compression are more fully understood and quantified, the parameters which influence tablet behavior in production may be controlled. The objective of our work was to obtain two deformation kinetic parameters for the predominant barrier to deformation, the activation volume (Vact) and the activation energy (Eact) of poly (methyl methacrylate-co-methacrylic acid) (PMMA/coMAA), a viscoelastic polymer similar to the commercial Eudragit.
Methods: Stress relaxation studies were performed and monitored at varying temperatures on compacts using an instrumented Instron testing apparatus. Solid density, microindentation hardness and contact area testing served to quantify the shear stress rates.
Results: The Vact was found to be 64.4 +/- 4 b(3), 63.8 +/- 11 b(3) and 79.1 +/- 8 b(3) for the applied strain rates of 1, 2, and 5 mm/min. The Eact for flow was determined to be 145 +/- 7.7, 235 +/- 8.0, and 506 +/- 2.8 x 10(1) kJ/mole(-1) for the applied strain rates of 1, 2, and 5 mm/min respectively.
Conclusions: The average activation energies are indicative of strain hardening effects. The activation volumes and energies obtained will serve as estimates of these state variables for input into a particle deformation model of time-dependent compaction which is underway.