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Multiple-Scale Approach to Understanding Formulated Product Production
[Thesis]. Manchester, UK: The University of Manchester; 2011.
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Abstract
Consumer- and pharmaceutical-based products are a major component of the chemicalindustry. In the personal care industry, formulations often consist of a mixture ofsurfactants and fatty alcohols. The addition of surfactants aids the stability of the formulation.The formulated product microstructure depends upon the preparation conditionsas well as the ingredients. Controlling which microstructures form during the productionof a formulated product is important as different microstructures can have wildly differentphysical properties, making some far more favourable than others.This thesis examines several of the processes undertaken in the manufacture of formulatedproducts. The dissolution of a surfactant in a bulk water phase is examined. Thisis examined in a number of ways; firstly, the dissolution times of the surfactants are measuredusing electrical resistance tomography. It is found that the dissolution time varieswith the agitation rate, agitator size, and addition method. The dissolution is also examinedusing dissipative particle dynamics to gain insight into the dissolution on a molecularscale. It is found that the surfactant breaks into wormlike micelles on dissolution. If an oilis added to the initial bulk then the dissolution process is modified so that long cylindersare produced with some spherical micelles. Finally, the break-up rate is predicted usinga breakage model based on the agitator shear rate and a network-of-zones model. Thisproduces good results.The production and post-shear processing of a sample formulated product, hair conditioner,is examined. Firstly, the mixing in a vessel is examined with electrical resistancetomography. Problems are encountered when the production method involves the useof distilled water as the conductivity is very low; however, the mixing time of the finalproduct in the vessel can be determined. It is also shown that the majority of the structuralchanges in the post-shearing process are caused by the in-line rotor-stator mixer.The viscosity of the product increases in a linear fashion with the shear rate, while theconductivity increases as a function of the shear rate and the recycle rate. This allowsthe monitoring of the post-shearing process to be carried out using electrical resistancetomography.This thesis also looks at the possibility of producing a multiple frequency electricalresistance tomography device to monitor formulated product production; however, it hasbeen shown that the conductivity does not vary with the voltage frequency over a usablerange. This meant that no further effort was put into developing this, as it gave no advantageover the traditional single frequency technique. Nevertheless, important advancestowards better understanding of mixing processes resulted due to the investigations carriedout.