Improving mechanical performance and functionality of birch veneer with mechano-enzymatic nanocellulose coating

In this study, we investigated the coating of birch veneers (BVs) with mechano-enzymatically manufactured nanofibrillated cellulose (meNFC) to improve mechanical strength and functionality. The meNFC has a broad particle size distribution and similar chemistry to lignocellulose materials, which are both beneficial properties in the coating of wood products. The veneer coating trials were carried out with a spray coating system developed to coat controllable thin coating layers. The spray coating produced uniform layers, which smoothened the BV surface significantly and was verified with scanning electron microscope imaging and optical profilometer measurements. The surface energy measurements showed that the meNFC is like cellulose, whereas the BV is like lignin. This observation proposes pre-treatment methods to secure a good adhesion level between the meNFC and BVs. The adhesion and compatibility of meNFC with the BV surface were measured with pull-off tests and surface energy measurements. The adhesion on a native BV surface was limited, while pre-treatment with sanding or using a primer significantly enhanced the adhesion. The meNFC coating slightly improved the BV transverse tensile strength (perpendicular to the wood veneer grain direction). A thermochromic functionality was installed on the BVs using meNFC as a binder. The produced thermochromic BVs displayed thermochromic behaviour; the coating could control the warming of the BVs subjected to solar radiation. The activation of a photocatalytic reaction of a meNFC coating containing TiO 2 was studied on the wood surface under both ultraviolet and fluorescent light, indicating in a reduction of formaldehyde concentrations. The results also showed that wood discolouration was inhibited by meNFC with not only TiO 2 but also only the meNFC coating. This study presents a practical approach to surface-treating wood materials with the meNFC to improve the mechanical and functional properties of wood products.