Tailored cellulosic materials by physical adsorption of polyelectrolytes

Abstract: The growing interest in using bio-based resources has made forest-based cellulose (used as fibre and nanofibril building elements) a good candidate for the development of new materials. In order to be used in commercial applications, cellulose must however be processed and/or functionalized to provide the final material with specific properties. This thesis presents (a) a way to improve the mechanical properties of traditional cellulose-based materials (paper), (b) an investigation into the structural and adhesive properties of the self-assembled hyaluronic acid thin films used to tailor the mechanical properties of paper materials, and (c) the preparation and functionalization of cellulose aerogels.In the first part of this thesis, the adsorption of polyelectrolytes onto pulp fibres (either as a monolayer or as multilayers) was studied as a way to improve the mechanical properties of paper materials. It was found that low amounts of adsorbed cationic amines were able to significantly improve the tensile properties of sheets made from treated fibres. Tensile testing of fibre crosses and microtomography revealed that this improvement in mechanical properties was due to an increase in both the interfibre joint strength and the interfibre contact area. By building up polyelectrolyte multilayers of hyaluronic acid (HA) and polyallylamine hydrochloride (PAH) onto the fibres, a threefold increase in both strain at break and tensile strength was achieved.Finally, wet-resilient porous cellulose aerogels were developed by freezedrying and crosslinking cellulose nanofibrillar gels. This material with high porosity and a high specific surface area was then used as a template to build three dimensional (3D) energy-storage devices using the Layer-by-Layer approach. Thin films of conductive materials were ivdeposited into the bulk of the material, and 3D-interdigitated supercapacitors and batteries were built. The devices showed high capacitance and operated under extreme conditions of compression and bending, opening up numerous possibilities in the field of flexible electronics.