Coprocessing of powdered cellulose and magnesium carbonate: direct tableting versus tableting after roll compaction/dry granulation.

Mixtures of magnesium carbonate (MC) with three types of powdered cellulose (M80, P290, A300) were tableted directly or after roll compaction/dry granulation. The fraction of powdered cellulose in the mixture was varied from 0% to 25% (w/w). The properties of the granules, blends, and their corresponding tablets were analyzed. Granules with a low amount of A300 showed the best flow properties, whereas the fibrous shape of the binding agents M80 and P290 impaired the free flow. Heckel plots showed clearly the different behavior of powdered cellulose in blends and granules during the tableting process. The Heckel-Plots for pure MC powder and granulated MC (MCgr) were similar. Increasing the fraction of powdered cellulose resulted in a fan-shaped set of curves, which is a reflection of an increased densification. Physical mixtures of all three powdered celluloses and granulated mixtures of M80 resulted in a higher densification compared with pure MC. In contrast, the granulated mixtures of P290 and A300 resulted in a diminished densification during tableting, which means that the coprocessed mixtures behaved differently during tableting compared with the physical mixtures. The curves were lower than those of pure MC and MCgr most pronounced at a fraction of 5% powdered cellulose. The tablet pore structure was evaluated by mercury porosimetry. The addition of P290 and A300 to the dry granules resulted in tablets with a higher fraction of smaller pores. Comparably high values for tablet tensile strength and low friability resulted from this special tablet structure. Roll compacted/dry granulated MC, coprocessed with 5% of P290 or A300, seems to be a promising excipient for direct compression. This coprocessed product combines good flow and tablet properties, and is superior to pure MC or a physical mixture of MC and PC.