This thesis addresses both the theory and simulation of diffusion of moisture in water-based biopolymer films, whose preliminary use is as adhesives on glass bottles in the labelling industry. The first part explores the kinetics of dehydration of thin films of these biopolymer materials. The second part of the thesis deals with moisture intake into both dried thin films and into the wet biopolymer gel network.
Mathematical simulations based on Fick's laws of diffusion have been developed as a tool to understand the underpinning mechanisms of diffusion and of evaporation to discover which, if either plays a more dominant role in controlling the dehydration process. By inputting a series of different initial and final moisture contents, a full spectra of scenarios has been examined to aid understanding of the dehydration process. Numerical calculations where diffusion is the controlling mechanism as well as simulations where evaporation controls the process have been considered and discussed. Models in which a combination of both diffusion and evaporation are equally important are also studied. Fixed and moving boundary conditions are applied to the models and compared with dehydration results obtained experimentally. A simple method has been developed to assess the rehydration process of a dried biopolymer film and similar simulations have also been constructed to describe the rehydration of a water droplet into the thin, dried films.
A novel method to investigate the migration of water into casein biopolymer gels using acoustic techniques has been developed and validated. The preliminary results are promising, highlighting the potential capability of the method. As the composition of a material changes, the speed of a wave of sound being passed through the material changes, so by monitoring this change as a function of time, concentration profiles of the biopolymer material can be constructed. Simulated concentration profiles were successfully produced based on Fick's second law of diffusion, to obtain a diffusion coefficient dependent on both time and position.. By fitting these curves to the experimental data, diffusion coefficients are obtained with values of the same order of magnitude as those calculated from the experiments on a dehydrating thin film of the same composition
