Dissolution of spray-dried porous particles: from single to bulk

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Karampalis, Dimitris (2019). Dissolution of spray-dried porous particles: from single to bulk. University of Birmingham. Ph.D.

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Abstract

This thesis demonstrates a detailed understanding and investigation of the dissolution behaviour of spray dried porous structured particles. This topic is crucially important for many industries as the control of the dissolution performance of the powders will allow them to modulate their essential properties. The formulation of the slurry was linked to the physicochemical properties of the detergent particles via characterisation
techniques. SEM and XRT results show that high slurry mix moisture (62%) results in mush less amount of undissolved Na2SO4 (0.6%) and high levels of porosity (82%) which has been confirmed by Mercury Porosimetry. On the other hand, the presence of binder in the formulation results in high bulk density, lower porosity and high degree of agglomeration. Focusing on the effect of material components, dissolution conditions and particle structure on dissolution, a combination of experimental measurements and numerical simulation have been used. Novel dissolution methods have been developed for conducting single particle diffusion and convective dissolution. The single particle dissolution mechanisms have been visualised for the first time. Results indicate that under stagnant conditions the effects of binder and porosity on dissolution are dominant. Powder samples with high slurry mix moisture dissolve smoother, faster (up to 68%) and more controllable than the low slurry mix moisture samples. Silicate binder due to polymerisation slows down the dissolution while the presence of Citric Acid in the binder formulation is critical as it enhances disintegration and as a result dissolution. However, in convective dissolution significant role play the hydrodynamic conditions. Single particle convective dissolution results indicate dissolution under laminar flow is up to 42% and up to 79% faster than diffusion for particles below 250 μm and 250-500 μm respectively. Numerical models developed to link single particle diffusion dissolution to bulk and to predict single particle convective dissolution using experimentally evaluated particle velocity. Results show good fitting for both conditions. Bulk dissolution experiments on the chemical release of components demonstrate that Conductivity can be used as an accurate tool for the detection of chemical release of Na2SO4 while UV-Vis and CatSO3 titration can measure the release of the anionic surfactant, linear alkyl benzene sulphonate (LAS). At the initial moments of dissolution, the release of Na2SO4 is blocked by either LAS or binder. A dissolution model found in the literature has been used to predict LAS (R2=0.833 ± 0.18) and Na2SO4 (R2=0.972 ± 0.01) release. In general, the generated insights, and the assays developed in this study can be of critical importance for the industry on powder performance evaluation. Also, can be used in the development of a new formulation strategy to produce highly soluble, and fast releasing spray-dried powders.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):