In wet aqueous stable foams, air bubbles prevent fibre flocculation and sedimentation keeping the fibres separate even after drying of the material.  In addition to the fibres, the foam can carry small, even nano-sized fibrils in the foam vertices and interfaces ensuring their high retention in the final structure. This process, foam forming, opens up possibilities to use raw materials of different size range, from long regenerated or natural fibres up to cellulose nanofibrils in a same material. The interactions between different-scale fibres and the foam provide tools to tailor both structural homogeneity and the micro-scale structure.  In this work we investigated the effect of softwood cellulose and hemp fibres, water-soluble polymers, cellulose nanofibrils and new type of fibrillated wood fines on the strength formation of porous foam-formed fibre networks.  The structure of these materials was studied by using x-ray micro-tomography and image analysis. The fines material made of spruce wood and the cellulose nanofibrils significantly improved the compression and bending strength. Moreover, elasticity was enhanced by natural rubber accumulating at fibre joints and helping the network structure to expand back after compression.  The future applications of the low density foamed structures include e.g. cushioning elements in packaging and acoustic materials in indoor construction. In the current applications, the properties and the production economics of cellulose-based products can be enhanced by the higher processing consistency in the manufacturing phase compared to the traditional water forming and the simultaneous use of longer fibres.

Low density foam-formed fibre structures with enhanced elasticity and strength

255th National Meeting (2018)

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