No abstract

Due to their bio-based character, oil-based coatings become more and more prevalent in wood surface finishing. These coatings impart appealing optical and haptic properties to the wood surface, but lack sufficient protection against water and mechanical influences. The present study reports a simple green route to improve the performance of linseed oil coating by the addition of nanofibrillated cellulose (NFC). In order to achieve surface chemical compatibility with linseed oil, NFC was chemically modified with acetic anhydride and (2-dodecen-1-yl)succinic anhydride, respectively, using propylene carbonate as a solvent. NFC/linseed oil formulations were prepared and applied to wood substrates. The wear resistance of oil-coated wood surfaces was assessed by a newly developed test combining abrasive loading with subsequent contact angle measurement. As revealed by infrared and nuclear magnetic resonance (NMR) spectroscopy, as well as X-ray diffraction (XRD), NFC has been successfully modified without significantly affecting the structure of cellulose. In abrasion tests, all NFC-modified oil coatings performed better than the original oil. Interestingly, NFC only suspended in propylene carbonate, i.e., without chemical modification, had the strongest improvement effect on the coating's wear resistance. This was primarily attributed to the loose network structure of this NFC variant which effectively prevents the oil from penetration into the wood surface, thus forming a protective NFC/oil composite layer on the wood surface.

The mechanical reinforcement of porous materials made of microfibrillated cellulose by in situ polymerisation of furfuryl alcohol prior to freezedrying from aqueous slurry was studied. Besides a slight improvement in the modulus of elasticity measured in compression testing, no beneficial effects of furfuryl alcohol addition on porous materials produced from microfibrillated cellulose derived from bleached softwood pulp were observed. By contrast, when microfibrillated cellulose containing substantial amounts of residual non-cellulosic cell wall polymers, termed microfibrillated lignocellulose, was used, clear mechanical reinforcement effects due to furfuryl alcohol addition were measured. By means of SEM, significantly improved wetting of the cellulosic fibrillary architecture of porous materials with furfuryl alcohol was observed for microfibrillated lignocellulose compared to microfibrillated cellulose. It is proposed that the specific surface-chemical character of microfibrillated lignocellulose enables wetting of fibrils with furfuryl alcohol, thus providing micron fibre-reinforced structures with improved strength after in situ polymerisation. Besides mechanical properties, the density and thermal stability of cellulose-based porous materials were found to increase with increasing amounts of furfuryl alcohol added to the initial reaction slurry.