Differences in the mechanical strength of dried microcrystalline cellulose pellets are not due to significant changes in the degree of hydrogen bonding.

Abstract

The mechanical strengths of oven-dried pellets of microcrystalline cellulose, MCC, prepared by extruder/marumerizer technology are weaker when ethanol/water mixtures are used as granulating solutions than when granulated with water. Previously, the difference in the strengths of these pellet systems were thought to be due to changes in the degree of hydrogen bonding within these systems. This work reports the results of studies using magic-angle-spin nuclear magnetic resonance (NMR), x-ray diffraction and degree of crystallinity, and oxygen combustion calorimetry studies of various MCC systems developed to test this hypothesis. Carbon-13 cross polarization magic-angle spin NMR studies of MCC pellets with and without 10% theophylline showed no differences in the spectra of these systems. X-ray diffraction studies and heats of combustion data obtained from oxygen combustion calorimetry of oven-dried pellets of MCC granulated with either water, deuterated water, or a 70/30 ethanol/water mixture were found to have no significant differences in their diffraction patterns, degree of crystallinity, or internal energies. None of these results provide any evidence that a significant net change in the degree of hydrogen bonding is responsible for the observed changes in the strengths of these systems. It is hypothesized that the strength of these dried pellets may, in part, be due to the conversion of some of the intramolecular hydrogen bonded amorphous fibrils at the surface of the MCC particles to intermolecular hydrogen bonded fibrils with other MCC particles.