mined from results with ejected tablets indicate that higher pressures are needed to fill the interparticulate void space than are in fact necessary. The effect of particle size is less clearly defined in the values of kl and kz but, again, there is the indication that the 75-104-pm. size fraction is the most resistant to deformation.
These results deal only with samples of lactose. When taken in conjunction with the previous work (1,2,4), the conclusion possibly could have application to other materials. CONCLUSIONS 1. For tablet volumes determined at pressure, the smaller the original particle size, the greater is the relative volume at all applied pressures.
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For tablet volumes determined after ejection from the die, the difference in relative volume between the two larger particlesize fractions is considerably reduced. The relative volumes for tablets prepared at slow compaction are lower than those of the two larger particle-size fractions, but the opposite is true for tablets prepared at the higher rate of compaction.
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Calculation of the densification due to particle rearrangement by the method of Heckel (2) shows that the smallest size fraction undergoes the greatest rearrangement both at slow and high speed compaction. Particle rearrangement is generally greater for the spray-dried lactose.
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Calculation of the densification due to particle rearrangement by the method of Cooper and Eaton (4) confirms this finding for crystalline lactose. The results for spray-dried lactose are, however, inconclusive.
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The yield pressure calculated from the slope of the densifxation-pressure curves of Heckel (2) indicates that the middle size fraction has the highest value for both compaction systems and methods of measuring tablet density. The yield pressures are higher for tablets ejected from the die.
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The yield pressure for spray-dried lactose is generally lower than for crystalline lactose.
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The pressures necessary to fill the voids of smaller sizes than the particles, i.e., those required to cause particle fracture and plastic flow, are always higher than the pressures necessary to fill the voids of the same dimensions as the particles, i.e., to effect particle rearrangement.