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

In this study, we investigated the coating of birch veneers (BVs) with mechano-enzymatically manufactured microfibrillated cellulose (meMFC) to improve mechanical strength and functionality. The meMFC 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 meMFC is like cellulose, whereas the BV is like lignin. This observation proposes pre-treatment methods to secure a good adhesion level between the meMFC and BVs. The adhesion and compatibility of meMFC 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 meMFC coating slightly improved the BV transverse tensile strength (perpendicular to the wood veneer grain direction). A thermochromic functionality was installed on the BVs using meMFC 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 meMFC coating containing TiO₂ 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 meMFC with not only TiO₂ but also only the meMFC coating. This study presents a practical approach to surface-treating wood materials with the meMFC to improve the mechanical and functional properties of wood products.