How relevant is ribbon homogeneity in roll compaction/dry granulation and can it be influenced?

A homogeneous distribution of solid fraction in ribbons is generally assumed to be beneficial during roll compaction/dry granulation. Numerous attempts have been made to increase this homogeneity by modification of the machine, i.e. the roll design and the design of the feeding unit. It has however not been critically tested how relevant this homogeneity really is during subsequent processing. This study investigated two resulting questions: How can process parameters used to increase homogeneity in ribbons and how relevant is this homogeneity for properties of resulting tablets? For that, a statistically designed experiment were performed and ribbon homogeneity analyzed using X-ray micro-computed tomography. Independent from the sealing system used during manufacturing, larger gap widths led to higher homogeneity. The effect of specific compaction force was strongly dependent on the sealing system. When using the cheek plate system, higher specific compaction forces decreased the ribbon homogeneity, while it had no influence when rim rolls were used. In a subsequent study, ribbons of different homogeneity were milled and the resulting granules compressed to tablets. Tablets from homogeneous and inhomogeneous ribbons showed comparable strength and tablet mass variability. Reduced tabletability from highly densified regions of inhomogeneous ribbons was compensated by higher amounts of fines which originate from the more porous regions of ribbons. It was concluded that the relevance of ribbon homogeneity in roll compaction might generally be overestimated.