Examination of the fracture of tablets in a strength test has revealed two types of failure. Where the interparticulate bond is strong, fracture occurs across the grains and the strength of tablet is a simple function of the particle size. If the interparticulate bond is weak, fracture occurs around the grain and particle size has little effect. A thin coating of stearic acid was used to weaken the interparticulate bond when the effect of grain size on strength disappeared or was reversed. The relation of bonding and capping is discussed and it is shown that capping can be reduced by weakening the interparticulate bond.

A motorised single-punch eccentric tablet machine has been fitted with instruments to measure the forces operating during the compression cycle. Apparatus has also been designed to measure the resistance to crushing of the final compact. Sodium chloride was compressed at varying pressures and the relationship between compaction forces, ejection force, strength and voidage investigated.FUNDAMENTAL research on the problems of tabletting was begun in 1950 by Higuchi, Arnold, Tucker and Bussel and in subsequent investigations many aspects of formulation and production were described. Train2 has studied the transmission of forces through a powder under compression and other contributions have been made by Munzel and Kagi3, and by Seth4.This investigation is concerned with the factors affecting tablet strength. Sodium chloride was used since it forms a satisfactory tablet without the addition of excipients, and in this way, a simple system could be studied.

The effect of moisture on the behaviour of sodium chloride under compression was investigated by measurement of compaction forces and ejection forces. Saturated solution present at the crystal surfaces effected a reduction in friction at the interparticulate boundary and between the particles and the die wall. Dry material formed compacts of higher strength than wet material except at low pressures. Subsequent drying of compacts prepared in the presence of moisture resulted in an increase in strength due to interparticulate recrystallisation.

The effect of maize starch on the particle sizes recovered from sulphadiazine tablets subjected to the B.P. disintegration test has been examined. A size analysis of the resulting suspension was made using a combination of wet sieving techniques and the Coulter Counter. Intragranular starch resulted in the recovery of finer particles than when extragranular starch was used, but the disintegration time was longer with intragranular starch. The use of both intra-and extragranular starch in a tablet gave intermediate disintegration time and mean diameter.