Multi-Scale Characterisation of Interactions between Cellulose Interfaces and Polymers

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The aim of the sub-project is a better understanding and better control of the binding of polymers to paper fibres. An important research approach of the package application is to functionalise papers with the help of polymers and thus impart new or improved properties to them, such as increased wet tensile strength and better transport properties. The challenge is to achieve a long-term stable bonding of the polymers to the paper via chemisorption or physisorption while maintaining the swelling capacity. In order to better understand and control the immobilisation of different polymer systems at the interface of the paper fibre and the influence on the properties of paper, precise investigations on smaller length scales are particularly necessary. In the present project, the adhesion-mediating function of polymers is investigated on different small length scales (nm - some µm). Since many methods (ellipsometry, AFM, reflectometry) for interface characterisation require a planar interface, water-stable planar model surfaces of cellulose, which chemically imitate a paper fibre surface, were prepared in the first funding period. In the second funding period, the focus will be placed even more strongly on different roughness and topography differences (pores, oriented structuring) of the model surface in order to simulate different surface structures of fibres. For this purpose, thin films of microcrystalline cellulose (MCC), cellulose fibres (nanofibrillated cellulose, NFC) and trimethylsilyl cellulose (TMSC) will be produced on planar substrates. Furthermore, the relationship between the structure, swelling behaviour and mechanical properties of polymers and cellulose surface will be understood. In addition to swellability in water, swelling in ionic liquids is also investigated (C1). In a next step, polymer accumulation at the fibre crossing points and its effect on the mechanical behaviour of the fibre crossing points is to be better understood (B1, B3). For this purpose, the model system is extended by adsorbing a paper fibre (diameter: a few µm) onto the cellulose surface and investigating the polymer adsorption in the vicinity of the paper fibre by means of atomic force microscopy. In this context, the influence of the orientation of the paper fibres on the polymer binding with simultaneous mobility of the polymers shall be understood and controlled.In addition to the polymers from A3, the polymer microgel particles produced in our research group will be used. The soft microgel particles are strongly adhesive and therefore have a fibre-bonding effect. These microgels react to external stimuli such as temperature and pH value and are to be used in the long term to build up papers with sensor properties. In addition to polymers, the binding of peptides is also to be investigated with C2.