Feasibility study to investigate caking in washing powder formulations using a Freeman FT4 powder rheometer

Because of legislation and environmental concerns, washing powder manufacturers have phased out phosphate builders in favour of substitutes such as sodium carbonate. This has meant that the new formulations have a greater tendency towards unwanted agglomeration (caking), based on moisture uptake and migration. This study examines the feasibility of using a Freeman FT4 powder rheometer to examine the effect of moisture migration, using the Basic Flow Energy (BFE) value to compare formulations of sodium carbonate content 27-37% and sodium sulphate content 10-20% by mass after 7 days exposure to 80% relative humidity at 20°C. The results showed that 31% and 33% sodium carbonate formulations were the most resistant to caking, with 27% and 37% being the most susceptible under the test conditions. Using the method of Brockbank et al. (2015), the FT4 was also used to detect the presence of a hard crust; under the test conditions, no hard crust was found. However, the presence of soft caking was detected in the force-height profile, showing a less abrupt transition.