Studies on direct compression of tablets. XIX. The effect of particle size and shape on the mechanical strength of sodium bicarbonate tablets
Alderborn, G.; Börjesson, E.; Glazer, M.; Nyström, C.
Acta Pharmaceutica Suecica 25(1): 31-40
1988
ISSN/ISBN: 0001-6675 PMID: 2842999 Document Number: 311481
Five size fractions of crystalline sodium bicarbonate, a material which reduces in volume mainly by plastic deformation, were prepared by dry sieving. For one of the size fractions, 90-125 .mu.m, both a milled and an unmilled fraction was prepared. All powders were examined by microscopy and then compressed in an instrumented single punch press at two pressures (200 and 300 MPa). Finally, the radial and the axial tensile strength of the tablets were measured. From these data the strength isotropy ratio was also calculated. Porosity changes during compression at 150 MPa were also registered and plotted according to the Heckel funtion. Both the radial and the axial tensile strengths and the values for the strength isotropy ratio were fairly constant over the particle size range studied. For the 90-125 .mu.m fraction, the milled quality gave a significantly higher tablet strength than the unmilled. Even the strength isotropy ratio was higher for the milled quality. The volume reduction behaviour, as evaluated by the Heckel plots, was similar for the unmilled and milled quality of the 90-125 .mu.m fraction.