Processing a detergent powder formulation: Direct compression, and high shear wet granulation followed by compression

In this paper, detergent tablets processing for industrial multi-purpose uses, i.e., hard surfaces cleaning, has been investigated. The detergent formulation is a complex blend of over 95% of powders: inorganic salts of alkaline metal called builders, and a system of surfactants composed of anionic and nonionic organic molecules. Two processes were examined: wet granulation prior to compression (processing 1), and direct compression (processing 2). Wet granulation is performed in a laboratory high shear mixer with a blend of powdered raw materials excluding one of the salts, the metasilicate. This blend is called “initial blend for granulation.” The granulation parameters studied are the intensity of shear related to the impeller speed, and the amount of liquid added, water being used as liquid binder. Powdered and granulated formulations are characterized in terms of particle size distribution, flowability, and compressibility. Compression is performed on a uniaxial laboratory press, either with the granules mixed with sodium pentahydrated metasilicate for processing 1, or with a mix of powdered and pre-granulated raw materials, called here “initial blend for direct compression,” for processing 2. The following features of the compacts are considered: mechanical strength, friability, density, solubility in cold water, and microscope observation of fractured surfaces. Comparison of compacts showed that prior granulation leads to increased mechanical properties due to higher plasticity and stronger binding with water, while it slightly deactivates the alkaline product. Compression of the material significantly increases dissolution times in both cases.