THE EFFECT OF MILLING AND ADDITION OF DRY BINDER ON THE INTERPARTICULATE BONDING MECHANISMS IN SODIUM-CHLORIDE TABLETS

In sodium chloride compacts, it has been reported that particles withi n the tablet are held together both by weak distance forces and solid bridges. It was found that milling of the particles or addition of a d ry binder appears to reduce the importance of bonding by solid bridges while increasing that of the weak distance forces. Such changes in th e surface properties of the particles induced either by milling or add ition of a dry binder will not only increase the surface area availabl e for bonding but also increase the number of interparticulate contact points in the compact and, consequently, reduce the stress at each co ntact point. It is suggested that this reduction in the concentration of stress makes rearrangement of material at the particle surfaces, an d thus the development of solid bridges, more difficult. Similarly, it is suggested that milling will increase the surface deformability of asperities on the sodium chloride particles which will also disperse t he concentration of stress within the compacts. The changes in the pro perties of the particle surface also affect fracture propagation durin g the diametral compression test. If it is assumed that cracks mainly occur between particles, milling will probably increase the distance t he fractures will run. (C) 1998 Elsevier Science B.V.