Comparison of lubricant efficiencies during compaction of lactose powder.

Abstract

Sodium, calcium, magnesium, zinc and aluminium stearates and behenic, stearic, palmitic, myristic and lauric acids were tested as lubricants during the compaction of lactose powder. Lactose powder, lactose mixtures with lubricants and lubricant powders were compressed in a cylindrical die with flat-surfaced punches. As the upper punch pressure required to compact a given lubricant to a certain porosity increased, the pressure required for the lactose mixture with that lubricant decreased. As regards the pressure-transmission ratio, the higher the value that the lubricant powder showed, the higher the value for the lactose mixture with that lubricant. The Heckel's constants were determined, and a larger k-value (the slope of Heckel's plot at high pressure) for lubricant powder resulted in a smaller value for the mixture. It is suggested that lubricants with higher melting points (metal stearates) provide more effective lubrication on the die wall and between lactose particles than lubricants with lower melting points (fatty acids).