Evaluation of strength-enhancing factors of a ductile binder in direct compression of sodium bicarbonate and calcium carbonate powders

This study evaluated the effectiveness of a ductile binder in direct compre ssion of sodium bicarbonate and calcium carbonate powders. Properties assoc iated with both the binder and the compound were studied. The addition of b inder materials, such as polyethylene glycols (PEGs) of differing molecular weights or microcrystalline cellulose, generally resulted in an increase i n the axial tensile strength of the corresponding compacts. The increase in tablet strength was generally greater with the PEGs than with microcrystal line cellulose. The results indicate that the improvement in tablet strengt h caused by the binder is dependent on properties of both the binder and th e compound. By utilising different methods it was established that the frac ture during tablet strength testing mainly occurred around the compound par ticles. As a consequence of this, it appears that the ability of the binder to fill the voids between the compound particles isa determinative factor for increasing tablet strength. The binder appeared to have less effect whe n added to compounds that fragmented during compaction. Characteristics of the binder resulting in the greatest decrease in porosity, and thus the,gre atest increase in the tensile strength of the compound, included a high deg ree of plastic deformation with a Limited elastic component and a small par ticle size. Obviously, the amount of binder added to the mixture also affec ted the results. (C) 2000 Elsevier Science B.V. All rights reserved.