Effect of matrix composition on the flowability of spray-dried detergent powders

[Display omitted] •Flow behaviour of four simple model formulations was investigated.•Slurry water content plays a key role in composition of the composite matrix formed on drying.•Matrix micro-structure has significant effect on powder flow.•Micro-structural properties, and mechanical robustness, were more important to the flowability than the shape. The flowability of spray-dried laundry detergent is important for manufacturing process performance and reliability, and product quality; it is strongly dependent on formulation. In this work, a detailed study of four model formulations provides fundamental understanding of the role of particle composition, and micro-structure, on spray-dried detergent powder flow behaviour. All spray-dried powders studied contained the sodium salt of linear alkylbenzene sulphonate (NaLAS) and sodium sulphate. However, their formulation varied depending on either the initial water content (30.0 or 63.0wt%) of the slurry or the addition of sodium silicate with molar-ratios of 1.6 and 2.35 SiO2:Na2O. The nil-silicate powder, made from low water content slurry, had the poorest flow characteristics. The addition of the silicate binder, significantly improved flowability, 2.35 ratio silicate, providing better flowability than 1.6 ratio. Remarkably, increasing the water content of the slurry also improved flowability significantly. Detail analysis showed that this was due to changes in composition and micro-structure of the composite matrix formed on drying the liquid components of the slurry, and that the improved flowability was due to improvements in mechanical strength of this matrix. These changes in mechanical robustness were significantly more important to the flowability than the powder shape.