Modelling the dissolution of structured particles for enhanced wash performance

Andreu-Cabedo, Patricia (2019). Modelling the dissolution of structured particles for enhanced wash performance. University of Birmingham. Ph.D.

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Abstract

Dissolution of solid particulates is a critical step in a wide range of processes across different industrial sectors including food, pharmaceutical and the domestic sector. Typical particulate product forms are flakes, pellets, tablets and granules. The latter is one of the most common forms of solid detergents made by the popular spray drying process.

The dissolution kinetics of particles have been of interest to researchers for the last centuries. Particle dissolution consists of a complex sequence of phenomena, including wetting, sinking, disintegration and finally dissolution. The internal structure of spray dried particles plays a key role in the dissolution process. However, there is still a need for a thorough understanding of the influence that the internal structure of the particles has on the dissolution behaviour of each of the particle components. Particularly, for complex formulations of detergent powders. This forms the main motivation of this Ph.D. study.

Powder detergents are usually formulated with a wide range of components with different functions in the end-use application. In light of this, simplified blown powders produced with three main components present a good model of porous powders in order to investigate the effect of structure on the dissolution kinetics.

Different particle structures were obtained by varying the fraction of the components and key production parameters (such as primary particle size of components and air injection) during the spray drying process. These model particles were used in this study, which consists of three main areas.

Firstly, the characterization of the bulk powders has been done by combining computational image analysis with traditional characterization methods. This combination has proven to be an excellent approach to evaluate both qualitatively and quantitatively the internal structure of the particulate materials. The variations of intra-particle porosity were detecting by both methods, however, the pore size distributions showed a different range of pore sizes in the mercury porosimetry and x-ray tomography. The latter was combined with a novel approach for the evaluation of the spatial distribution of the pores within the particles. This allowed for the identification of the key parameters for the production of particles with thick shells, micronised sodium sulphate and high binder content.

Secondly, the dissolution process of structured particles consists of a complex sequence of physical and chemical mechanisms, which can be affected by various factors. As a result, controlled dissolution analyses were performed with UV-Vis spectroscopy and electrical conductivity measurements. This combination of techniques allowed for the individual evaluation of the dissolution kinetics of the particle constituents (sodium sulphate and binder). From the use of these two techniques, the influence of particle structure was readily observed in that the dissolution profiles of the binder and the salt did not coincide depending on the structure.

Lastly, a one-dimensional model has been developed in order to simulate the dissolution profiles observed from the dissolution kinetics experiments with the addition of structural parameters (such as shell thickness, in the case of hollow spherical particles and a radial distribution of components) evaluated from the image characterization of the structured particles. This model accounts for the central cavity that the hollow spherical particles contain as well as the mass transfer resistance arising from the presence of one of the binder components (sodium silicate).

With these main threads of study the structural parameters were correlated with the dissolution behaviour of the powders.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):