Modified foam process to produce homogeneous laboratory sheets with 24mm fibers

Using foam as a carrier phase instead of water is an alternative way to produce fibre-based webs. This old technology has attracted great interest recently as the approach gives many positive influences on sheet properties. Since fibers are locked between foam bubbles during transportation to the wire, they do not flock as easily as in water, which leads to improved formation. Moreover, consistency can be increased, and thus the amount of water in the process and the drying energy can be reduced. In addition, bulk is often increased when applying the foam forming technology. Generally, formation of a fiber sheet deteriorates as fiber length increases. Here we aimed to produce sheets with very long fibers with foam forming. In order to change the fiber length systematically, model 1.7 dtex viscose fibers were used. Fibers were provided as small straight wet bundles that were dispersed in the foam. Sodium dodecyl sulphate (SDS) was used as foaming agent. Floc-free sheet of upto 12 mm fibres could be produced fairly easily by the conventional foam-forming method in laboratory scale. However, longer 24 mm fibers required several developments in the pre-processing phase. Homogeneity of the sheet structure was sensitive to foam properties. The effects of SDS dosage, air content, foam volume and mixing speed were quantitatively characterized for laboratory forming process. In particular, a parameter window for producing homogeneous sheet structure could be found. In the modified process, wet fiber bundles were fed into foam with enlarged bubble size and high foam viscosity. The crowding number characterizing the flocking tendency was reduced by increasing the foam volume. Finally, surfactant concentration affected the air content and the bubble size distribution of the foam and thus its viscosity. The technique could make a way for producing novel fashion and technical textiles, which requires the handling of long fibers in the process. The study was mainly focused on laboratory scale, but necessary development steps in upscaling of the process to the pilot scale were considered as well.