A feasibility study to investigate caking in washing powder formulations using a Freeman FT4 powder rheometer [Conference paper]

Using conventional powder flow analysis methods to quantify the formation of a crust on the surface layer of a powder formed from moisture ingress is a challenge, as cake formation is not uniform throughout the powder sample. This study examined the feasibility of using a dynamic flow tester to compare the caking tendencies of washing powder formulations. A Freeman FT4 powder rheometer was used to investigate crusting caused by 80% relative humidity in washing powder formulations at room temperature. Formulations of 27%, 31%, 33% and 37% sodium carbonate were exposed for 7 days to high humidity before being tested using a twisted blade powder rheometer. Successive test cycles showed the breakdown of agglomerates caused by caking, with the greatest effect on formulations of 27% and 37%. Visual inspection of these powders indicated a hard caking layer of approximately a third of the depth, beneath which free-flowing powder was present. Variations from weak caking, caused by interparticle liquid bridges, were also detected using this method. The study demonstrates the viability of this methodology for optimising new formulations for caking resistance.