(38b) Determination of the Critical Stress Intensity Factor for Microcrystalline Cellulose (MCC) Using a Developed Tensile Stress Method and Its Application to Double-Layer Tablets

Tablets that have layered compaction zones, produced by different compaction pressures have been found to enable a controlled release rate profile of active ingredients: a desirable characteristic of powder compacts that can be difficult to achieve with singly compacted tablets. An observed disadvantage of some multi-layered tablets is the interfacial weakness between the individual layers, which can cause the tablet to fracture by capping. Single and double layered tablets of the excipient Microcrystalline Cellulose (MCC), FMC Corp., have been studied using an axial tensile stress method, originally developed to determine the tendency of a single compacted tablet to fracture by capping (Nystrom et al., 1977). The methodology was assessed by finding the critical stress intensity value at zero porosity (KIC0), using conventional fracture mechanics principles, for singular compacted MCC. The result of 0.86 MPa.m0.5 has been found to be in good agreement with other published work (Roberts and Rowe, 1989, Roberts et al., 1993, Mashadi and Newton, 1987, Mashadi and Newton, 1988, York et al., 1990, Hancock et al., 2000). The interface tensile strength of double layered compacts has been found to increase with a rise in applied stress on the upper layer (when initial compaction stress is held constant). Initial investigations to explain the discrepancies of interface strength of compacts subjected to different applied stresses have begun.

KEYWORDS: Multi-layered tablets, Microcrystalline Cellulose, Critical stress Intensity factor