Aqueous foam as the carrier phase in the deposition of fibre networks: Dissertation

The use of foam, rather than water, as a material carrier in the manufacturing of novel paper-like structures has recently been studied intensively. This new technology provides potential savings in terms of raw materials, energy and water in comparison with traditional water forming. Such foam forming technology can not only produce materials with properties such as improved material homogeneity and reduced density, but also tailor the microporous structures with the foam properties. The pore structures of the foam-formed sheets and water-formed sheets were compared using imaging techniques such as X-ray microtomography, scanning electron microscopy, and light microscopy, which showed that their pore size distributions differed significantly. The relationship of the fibre network and foam properties was investigated by comparing the pore structure with the measured bubble size distribution and it was shown that both the pore structure and corresponding macroscopic sheet properties could be affected by the mean bubble size. The foams were generated with axial mixing, where the bubble size and its distribution was affected by several factors such as rotational speed, air content and surface tension. Responses of wet foam to inclusion of natural and regenerated cellulose fibres were quite different. The mean bubble size became smaller for natural fibres than for regenerated fibres. In addition, the bubble size distribution became narrower for natural fibres. The reason behind this behaviour is likely to be the rough surfaces of the natural fibres and their fine particle fraction, which are absent with regenerated fibres.