Understanding the Effect of Environmental History on Bilayer Tablet Interfacial Shear Strength
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To understand the effect of post production environmental conditions on the interfacial strength of bilayer tablets.
Bilayer tablets of microcrystalline cellulose/dicalcium phosphate were exposed to several humidity conditions higher/lower than production conditions and tested in shear to assess interfacial strength. Specific failure mechanisms were observed using x-ray microtomography and scanning electron microscopy.
Transients in moisture diffusion of bilayer tablets with significant differential moisture absorption characteristics are responsible for the reduction of strength in both high and low moisture environments. X-ray microtomography and SEM experiments have shown that two different mechanisms of interfacial crack formation are present. For low moisture exposure, interfacial cracks close to the surface were produced, whereas at high moisture conditions, internal interfacial cracks were created. In both cases the fracture modes are consistent with the tensile stresses that develop locally due to the volumetric strains induced by moisture absorption.
The insight gained from this work will be useful for material selection and packaging of bilayer tablet systems. While additional work is needed to develop specific guidelines for the optimization of bilayer strength, the results presented here provide a rational basis upon which such work can be conducted.
KEY WORDSbilayer tablets cracking humidity interfacial strength transient diffusion
ACKNOWLEDGMENTS AND DISCLOSURES
The authors would like to acknowledge the NSF GOALI project #0900476 for funding and Merck Inc & Co for the use of the compaction simulator.
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