These theses that change life: From deliquescence to caking of crystalline powders: sodium chloride
The PhD subject that Marina-Dupas Langlet chose came from “distant parts”, in the Middle East (ME). “Stock cubes used in cooking sent to ME countries tended to degrade during travel and arrived in a sticky, messy state”, she explains. The issue is the same for washing powders and powder forms can be found in numerous uses. Agro-food, rubber, cosmetics, pharmaceuticals … The process transforms the raw matter into a multitude of particles and confers numerous useful mechanical qualities such as fluidity … except when the particles stick together, viz., cake in industrial jargon.
With her diploma from ESPCI (engineering school specialized in industrial physics and chemistry), Marina Dupas-Langlet first did a Master’s degree in Environmental studies followed by a PhD at UTC Compiegne. A placement two years previous on the mechanical properties of powders with an agro-food company showed her the path to follow. That decided her to examine the case of sodium chloride (common salt) to better understand the phenomena of deliquescence and caking.
“As is the case for all divided milieus, powders represent a highly complex form of matter. They must be multifunction, viz., able to adhere before dispersal”, she explains. The ‘public enemy N°1’ both for the consumer and for the industrialized is the risk of caking. For example, the packet of cocoa powder goes solid, or the mashed puree goes lumpy. In the industrial sector the phenomenon is more worrisome: “caked matter gathers and clogs at the bottom of the filters and forces the operators to clean up, which of course slows down production and moreover puts the equipment itself at risk”.
Marina Dupas-Langlet therefore focused her investigations on salt crystals (sodium chloride) to gain an understanding as to how they react to climatic conditions and changes (ambient temperature and/or humidity …) in terms of stability. “What I was seeking was to fully understand the mechanisms that make the material degrade mechanically, notably in transportation”.
The young PhD students chose an original approach: “I started by looking at the microscopic level using micro-gravitational analysis to build my thermodynamic model. The model then enabled me to move up to the macroscopic level, i.e., the industrial scale”.
“Empirically, the phase where the matter is destabilized can be seen visually. It is the model that enables the industrialists to anticipate on possible deleterious phenomena” adds Marina Dupas-Langlet.
The salt crystals degrade when they come into to contact with humidity and then dissolve. To return to their initial “dry” phase, the matter must be dried but this unfortunately leads to caking. “To stop the cakes from forming, the process calls for the addition of large molecules that are refractory to water, such as fatty molecules, for example. Thanks to modelling, we can better understand all the mechanisms at play and thereby avoid the degraded conditionings for the powder. It also contributes to decreasing the amount of fatty molecules needed as anti-caking ingredients in the crystal mixes”.
Thanks to her work, industrialists can now optimize the composite their mixes to obtain a powder that stays bot fluid and moreover has better nutritional features.
