With the environmental awareness towards a sustainable society, great efforts are nowadays invested to replace conventional plastics and hence decrease the dependency of materials generated from fossil fuel. Modern nanofibre reinforced bio-composites produced from renewable materials will in the future most probably be made exclusively from aqueous dispersions containing both the matrix polymer and nanofibres for reinforcement. In order to fully utilise the excellent inherent properties of the nanofibres it is essential to distribute them homogeneously throughout the formed nanocomposite and to avoid aggregation. In aqueous systems this is a challenging task since the particle stability will be determined both by the surface charge of the nanofibres and the matrix polymer as well as the interaction between the polymer and the nanofibres. The colloidal stability of nanofibres is not only affected by electrostatic repulsions, but can also be improved by steric interactions by grafting or physically adsorbing polymers to the surface. Hence, in our initial work we have aimed to firstly study the coupling efficiency of different types of “grafting to" mechanisms as well as physical adsorption onto the cellulose nanofibrillar system and how these grafting mechanisms affect the colloidal stability. Among others, EDC-coupling has been utilised to covalently graft the nanocellulose surface with poly(ethylene glycol) (PEG) chains (see Figure 1). The aim is to create a true cellulose nanofibrillar system with a small amount of stabiliser and not the opposite. Systematic approaches in conducting the studies as well as understanding the fundamentals in regards to how polymer structures interact with nanofibrillar surface are important key factors. Our studies show that the EDC-coupling is not as efficient as previously reported in grafting polymers to the nanofibrillar surface. This is among others supported by quartz crystal microbalance measurements. Moreover, choosing the correct purification step post-grafting is crucial in ensuring a pure grafted colloidal system. Hence, a more sophisticated method for purifying the system post-grafting has been devised.

Controlling colloidal stability in nanofibrillar systems by surface modification

251st National Meeting (2016)

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