Functional encapsulation of small particles : quantification and control of the morphology of the coating layers : quantification and control of the morphology of the coating layers

Increasingly conscious consumers seek more values in the products. For e.g. pharmaceutical products, this means higher efficacy, easier administration and longer shelf-life. Such attributes can be provided by applying functional encapsulation, with the right properties of coating layer around small particles. In this thesis, a quantitative image analysis method was developed to quantify the morphology i.e. thickness distribution, porosity, and (spatial) pore size distribution of the coating layers. Such quantification will allow the coating formulation and the process parameters to be adjusted more rationally. The process parameters (of fluidized bed coating process) affecting the coating morphology were further investigated. The process environments required to achieve the best coating quality were suggested. Scaling-down to particle-droplet level, it was found that the control of droplet deposition and drying mode is crucial to attain the desired coating morphology. Not only the bulk porosity but also the pore location are determining factors for the transport properties of the coating film. The possibility to also control the spatial distribution of pores in the coating film was demonstrated. This was by avoiding the droplet to dry out before deposition and providing sufficient coating time/layering cycles. Also, the interactions between the coating films and components in the environment e.g. moisture and oxygen and their effect on coating transport properties were studied. Quantitative correlations, which describe the relation between the coating transport properties and the changes of coating properties, i.e. internal stress and free volume during moisture sorption at different ambient, were proposed. Such correlations would facilitate better screening of the coating formulations.