Molecular simulations of crystalline cellulose interfacial interactions

Crystalline nanocellulose, especially cellulose nanocrystals (CNCs), is widely used in many fields, such as pharmaceutical and biomedicine materials, paper making and alimentation industries, in reinforcement of polymer composites, but also as support matrices and packaging materials. The interactions between CNC surfaces and other materials can influence the properties of CNCbased materials, which can widen the usage of CNC materials. In this thesis, CNC interactions with water, ions, and lignin-carbohydrate complexes (LCCs) are studied, since these interactions can heavily affect the properties of CNC materials but also the wood-like and wood-based materials. We first studied the interactions between CNC surfaces and Na+ and Cl- ions in water solutions. After that, the interactions between CNC surfaces and LCCs were studied. A very small amount of ions can affect CNC surface interactions strongly. In this thesis research, in a 0.6 %wt CNC solution, 0.25 mM NaCl in the solution was sufficient to significantly change the viscosity. Our results show that the presence of NaCl as ions can change the water dipole orientation, which influences the interactions between CNCs. The hydration layer ordering at the position of the ion can increase. The change at the binding sites is enough to change the interaction between CNC surfaces, affecting solution viscosity. This kind of water molecule orientation change can help merge the hydration layers of surfaces, which increases the connections of CNCs in solution. Thus the viscosity increased. The interactions between LCCs and CNCs are dependent on the CNC surface crystal facet. We examined simple model LCCs to obtain insight. The main driving force of interaction between hydrophilic CNC surfaces and the model LCCs was hydrogen bonding, with lignin playing a bigger role when the hemicellulose chains are short. For hydrophobic CNC surfaces, the interaction was more through van der Waals and dipole-dipole forces. In summary, interactions between CNC surfaces common in CNC solutions and in wood-like and wood-based materials are studied in this thesis. This can help understanding and control the properties of these materials. The findings may help product design in these fields to be more productive and environment-friendly.