title: Understanding the effect of environmental history on bilayer tablet interfacial shear strength.
abstract: OBJECTIVE
  To understand the effect of post production environmental conditions on the interfacial strength of bilayer tablets.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors: Drexel University, Philadelphia, Philadelphia, USA.
authors: Gerard
authors: G
authors: Klinzing
authors: Antonios
authors: A
authors: Zavaliangos
mesh_terms: D002130:Calcium Phosphates / Q000737:chemistry*; D002482:Cellulose / Q000737:chemistry*; D006813:Humidity; D033081:Shear Strength; D013607:Tablets / Q000737:chemistry*
chemical_list: D002130:Calcium Phosphates; D013607:Tablets; D002482:Cellulose; C485829:calcium phosphate, dibasic, anhydrous; C109691:microcrystalline cellulose