Dry granules manufactured by roll compaction/dry granulation (RCDG) lead often to lower tensile strengths of tablets in comparison to direct compression. Therefore, dry binders are in particular important for RCDG to ensure a sufficient tensile strength, but also to generate large granules and a low fraction of fines.
Eighteen different dry binders were characterised regarding molecular and particle properties. A minimum quantity of three binders per chemical group were chosen to find out, how the behaviour of the chemical types of binders can be described. 3 microcrystalline celluloses, 5 hydroxypropyl celluloses, 3 povidones, 3 copovidones and 4 crospovidones were used as dry binders in a fraction of 10%. The dry granulation and tableting method was kept constant for all batches.
Differences in the results of granules and tablets were obtained regarding granule size, fraction of fines of the granules, tablet tensile strength, friability and disintegration time. Within a chemical type of binder, the behaviour of granule and tablet properties could be described by linear regressions with measured characteristics of dry binders. A differing binding behaviour could be an explanation for the divergent results of PVP polymers. Differences in particle size caused greater effects for small-sized binders on dry granules and tablets.
The two most effective binders in this study, fine grades of HPC and copovidone, were tested with a whole tableting profile. HPC resulted in larger granule size and lower friability, while copovidone led to a lower disintegration time, which can be explained with viscosity effects. Depending on the formulation challenge, both binders can be used as a dry binder in a low fraction.