**Preface to "Advances in Surface Modification and Treatment of Wood"**

Timber is a biosynthetic end-product. The photosynthetic formation of wood is a function of the gene expression and catalytic rates of structural enzymes under different environmental factors. Thus, to achieve a full understanding of wood formation, as a later subject of our studies, each component of the full set of intrinsic processes must be studied (i.e., chemical reactions and physical changes) and known, investigating how each one of those components is affected by other processes in a complex form. Differences in the wood surfaces occur between the manufacturing and post-treatment processes within single trees. Wood surface attributes can be established by examining its several different physical or chemical properties. Understanding how their unique anisotropic molecular organization, chemical linkages, branching, and other molecular features govern microand macroscale accessibility is essential for coating and complex modification processes. It is therefore important for scientific as well as practical reasons to qualify and quantify the effects of wood surface treatments and modifications.This Special Issue contains nine scientific works from a wide spectrum of research with a specific focus on the surface modifications, potential applications, and natural-artificial weathering treatments. The interfacial interactions of the wood surface components are key concerns for the reliability of structural changes after modifications. Wood surface modification is a comprehensive concept, which, in time, has been as successful as challenging in terms of improving the resistance during its life cycle in both indoor and outdoor applications. The review paper in this Special Issue offers an systematic overview of some of the most recent advances reported in the field. Another study deals with the effects of nanosilver impregnation and heat treatment on the gas permeability and pull-off strength, as these properties depend to some extent on the porous structure of the wood species. Impregnation can increase the thermal conductivity of the specimens and decrease the heat treatment gradient. The structural and fundamental changes occurring in naturally aged wood surfaces was the objective of another study to compare the performance of transparent and pigmented coating systems. To follow artificial ageing in different wood species' using surface chemical compounds without coatings, a novel evaluation method was developed. Confocal profilometry and macro-photography were used to quantify the image shelling of flat-faced deckboards exposed to natural weathering for seven months. A different study was dedicated to examining the changes in the adhesion strength between transparent acrylic and alkyd coatings on wood due to weathering changes. In parallel, some other impacts were evaluated, including the presence of hindered amine light stabilizer or hydroxyphenyl-benzotriazoles UV additives in coatings and the fungicidal pre-treatment of wood with boric acid or benzalkonium chloride, as well as plasma modification. A following study examined how the overall service life of the acrylate and oil coating system is affected by the initial surface modification of wood using caffeine solutions, dispersion of TiO2 nanoparticles, and their combinations. The method of artificial-accelerated weathering in a UV chamber was used with a subsequent test of mold growth on both ageless and weathered surfaces of treated wood. The authors observed that, in service, wood treated with copper-based preservatives tends to change from green/blue to a brown color as the surface of the wood oxidizes. The aim of the following scientific contribution was to understand the efficacy of this approach in yielding a brown, photo-stable wood surface with the potential to eliminate or reduce the need for the addition of colorants. Finally, spruce with different heat pre-treatments was studied with the effect of diffuse coplanar surface barrier discharge plasma

treatment, which was evaluated by measuring the changes in wood surface free energy, chemical composition, and micro-morphology.Challenges are still exist to fully understanding the effect of the numerous applied chemicals and the wide range of treatment processes on wood surfaces, which can be overcome to some extent by further collaborative efforts between scientist, laboratories, and industries.

> **Levente Cs ´oka** *Editor*
