The role of detergent formulation on the cleaning of a complex carbohydrate-fat food soil from stainless steel surfaces was studied using a modified version of the millimanipulation device described by Ali et al. (2015b) which allowed the force required to scrape the soil from the surface to be measured as the soil is immersed, in situ and in real time. This allowed the influence of temperature, solution chemistry and time on the mechanical forces (rheology) and removal behaviour of the soil to be studied-in effect quantifying the relationships in Sinner's cleaning circle. The soil simulated a burnt-on baked-on deposit and featured regular cracking in the 300 m thick layer. The removal force decreased noticeably on hydration: the cleaning mechanism was then determined by the agents present. At 20C, below the temperature at which the fat phase was mobile, removal was characterised by cohesive failure except in the presence of the cationic surfactant CTAB, which promoted adhesive failure and fast decay in removal force. At 50C, when the fat was mobile, a transition between cohesive and adhesive failure was observed at pH 7 which was inhibited at higher pH. Adhesive failure and fast decay in removal force was observed at higher pH and 50C in the presence of the anionic and non-ionic surfactants, SDBS and TX-100, respectively.
Extended or repeated heating of food fats promotes polymerisation reactions that produce difficult-to-remove soil layers. Cleaning of these baked-on/burnt-on fat deposits was investigated using model layers generated by baking lard on 316 stainless steel discs. Rigorous characterisation of the layer material was difficult, as it was insoluble in most solvents. Cleaning was studied using the scanning fluid dynamic gauging technique developed by Gordon et al. (Meas Sci Technol 21:85–103, 2010), which provides non-contact in situ measurement of layer thickness at several sites on a sample in real time. Tests at 50 C with alkali (sodium hydroxide, pH 10.4–11) and three surfactant solutions indicated two removal mechanisms, related to the (1) roll-up and (2) dispersion mechanisms reported for oily oils, namely (1) penetration of solvent at the soil–liquid interface, resulting in detachment of the soil layer as a coherent film, observed with linear alkylbenzene sulfonic acid (LAS) and Triton X-100 and aqueous sodium hydroxide at pH 10.4–11; and (2) the breakdown promoted by the agent penetrating through the layer, observed with cetyl trimethyl ammonium bromide (CTAB), in which CTAB antagonised the cleaning action of LAS.
Ten commercial portland cement clinkers with their slowly and quickly cooled counterparts were examined microscopically. Methods are given for the conduction of the microscopical examination.The appearance of the clinker phases after the different heat treatments is described and the structure of the clinkers discussed.In general, for all clinkers, the phase compositions as calculated with consideration of glass agreed better with the microscopically determined phases than did those based upon the calculations in which complete equilibrium crystallization was assumed. The microscopically determined 3CaO.Si02 was nearly always greater and the 2CaO.Si02 lower than that calculated by either of the other methods. The 3CaO.AhOa was always less than that calculated from chemical analyses. Generally the 4CaO.AI20a.Fe20a found microscopically exceeded that calculated by either of the other methods. The glass determined microscopically and the values obtained from the heat of solution method agreed better for slowl y and plant cooled than for quickly cooled clinkers.
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