Effect of binder to solid ratio on mechanical properties of granules processed using reactive and non-reactive binder

In wet granulation of powders in high shear granulators, the properties of granules formed can be altered by controlling a number of parameters. One of the crucial parameters responsible for granule properties is the quantity of the binder used for granulation. This can be expressed as binder to solid ratio (B/S) or liquid to solid ratio (L/S). Researchers have reported in the past the effect of liquid to solid ratio on granulation mechanism and growth, granule structure and consequently on the deformation behavior of the granules. Some researchers have also reported the distribution of the binder and the size distribution of the granules formed as a function of the concentration of the binder used in the process. However, there is limited work reported in the literature on the effect of binder to solid ratio on the physical and mechanical properties of granules. The mechanical properties of the granules can determine the behavior of granules at various stages such as usage, handling, transportation and storage under compression. The work reported in this paper investigates the effect of binder to solid ratio (B/S) on the mechanical properties of soft detergent granules made via wet granulation in a high shear mixer. The effect of binder to solid ratio in wet granulation can vary depending upon the nature of the binder used. Hence two different types of binders were used viz. reactive (reacts with base powder) and non-reactive (acts only as a binder) to granulate sodium carbonate as primary particles. The mechanical properties were studied by conducting single and bulk compression measurements. Known models of Heckel and Kawakita and Ludde were also used to predict mechanical properties of the granules. The granulation time required to achieve similar physical properties (particle size distribution and circularity) of the granules decreased with increase in binder to solid ratio. Single granule compression measurements showed that apparent granule strength decreases with increase in binder to solid ratio for both reactive and non-reactive granules which may be due to more liquid binder content in the granules. The Heckel parameter was observed to be approximately 2.5 to 3 times the apparent granule strength obtained from single granule compression measurements for both reactive and non-reactive granules. Packing coefficient increased with increase in binder to solid ratio indicating higher compressibility behavior under similar load for both reactive and non-reactive granules. (C) 2012 Elsevier B.V. All rights reserved.