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Hybrid cellulose films and their applications in papermaking
A PhD project at YKI, in close collaboration with Novozymes A/S, has resulted in techniques for producing cellulose films, and initiation of their use as model substrates for high-resolution studies of adsorption from surfactant or polymer solutions. These films, originally developed at the Mid Sweden University provide a unified basis for investigation of the cellulose interactions that steer paper manufacture, end-use and recycling. The spectrum of applications will be the subject of an upcoming major project at The Forest Products Section, in which the micro-scale interactions between components will be related to macro-scale phenomena and properties, thus providing industry with a clearer link between surface and colloidal mechanisms and product performance. The purpose of the proposed Master's thesis diploma work project is to further generalise the films to cellulose hybrids, and to subsequently characterise these substrates and their performance using Atomic Force Microscopy (AFM), ellipsometry and a range of other surface analysis techniques.
The cellulose films are produced by spin coating a solution of dissolved microcrystalline cellulose onto silica wafers, to which a cationic polymer is pre-adsorbed to enhance adhesion. The thickness of the films depends on the cellulose concentration in the spin-coating solution, and is typically a few hundred Ångströms. ESCA analysis has shown that the films contain no trace of contaminants originating from the cellulose solvent, and AFM tapping mode has indicated a dry film surface roughness of below 50 Å . The films display a reasonable good stability in aqueous solutions after an initial fast swelling process, and the water contact angle is about 18°. The utility of these substrates has been demonstrated by in-situ monitoring of the adsorption of cellulase and its subsequent degradation of the cellulose film.
To broaden the scope for applications, the Masters thesis project shall generalise this versatile synthesis route by introducing other polymers to the spin-coating solution in order to produce modified cellulose surfaces more similar to pulp fibre chemical compositions. In particular, real or model hemicelluloses can be included in the spin-coating solution or applied to the film surface in a post-stage adsorption treatment. The negative surface charge can be further tuned with addition of small amounts of anionic polysaccharides, such as carboxymethyl cellulose or dextran sulfate, to the solution. Further, the hybrid films thus obtained can be compared with the surface charge and chemistry of pulp fibres, either in their natural state or similarly reconstituted using this spin-coating procedure.
The hybrid cellulose films represent a broad range of substrates, with sufficient complexity and robustness to well approximate pulp fibres and their typical environments, while also being sufficiently well-defined to facilitate use of the surface sensitive instruments housed at YKI.
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