Common hornbeam (Carpinus betulus L.) is a highly underused wood species despite its great hardness, strength, wear-resistance and toughness. It is mainly used as firewood in Hungary because of its wood defects, irregular shape and low-dimensional stability. These wood defects and small breast height diameter result in a low yield. It is non-durable outdoors as it tends to turn grey, crack and be attacked by wood-decaying organisms. Indoors it lasts for hundreds of years. One technology that could improve the stability and durability properties is acetylation. Hornbeam was acetylated with the Accoya® method under industrial conditions. The aim of this research was the assessment of acetylation affecting the chemical properties of hornbeam wood and how these are related to the change in physical and mechanical properties. Main wood constituents (cellulose, hemicellulose, Klason lignin, extractives and ash content) were determined and compared. Chemical parameters related to the degradation of structural polymers were also evaluated (total phenolic and soluble carbohydrate contents, pH and buffering capacity, furfural, levulinic acid, formic acid, acetic acid). Structural changes in acetylated wood and in the Klason lignin fraction were also assessed using FTIR spectroscopy.

Hornbeam wood is known for its high density, hardness, toughness, and wear resistance, but due to its low durability (Class 5 according to EN 350), limited wood quality, and rather small sawmill yield, it is mainly utilized as firewood today. The potential for hornbeam to be used as solid, high-quality wood material exists if its durability and dimensional stability can be increased. Hornbeam boards were acetylated under industrial conditions and tests were carried out to evaluate the treatability of this wood species by acetylation. In this study, the examination of physical, mechanical, and durability properties of acetylated hornbeam wood are described and compared to untreated hornbeam and to acetylated beech, which has a similar anatomical structure to hornbeam. Acetylated hornbeam was also compared to acetylated radiata pine, which is the main product of Accsys Technologies. These comparisons include the determination of the equilibrium moisture content, density, dimensional stability, accelerated checking, color change, water uptake, decay resistance, compression strength, modulus of rupture (MOR), modulus of elasticity (MOE), impact bending strength, Janka hardness, Brinell hardness, and impact bending strength. The aim of this project is the creation of a new product thereby widening the usage of this species.

In this research, acetylation was applied under industrial conditions to improve the properties of Turkey oak and Pannonia poplar wood. Both species are potential “climate winners” in Hungary, yet they are currently underused due their low durability and poor dimensional stability. The acetylation modification process may be a suitable method to improve their properties. In order to verify the effectiveness of the process, comparative chemical analyses (cellulose, hemicelluloses, lignin, extractives, ash, buffering capacity, and pH) of the untreated and acetylated heartwood and sapwood were carried out for both species for the first time. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was also used to support the evaluation of the chemical analyses. The weight percent gain was 11.54% for poplar and 0.94% for Turkey oak, indicating poor treatment efficiency for the latter. The cellulose, hemicelluloses, and lignin contents changed significantly in poplar, with the highest change (+81%) induced by acetylating the hemicelluloses. Only the alpha-cellulose content decreased significantly in Turkey oak, presumably due to the degradation of the non-crystalline part of the cellulose. Acetylation may improve the resistance of Pannonia poplar against moisture, weather, decay, and wood-boring insects, but the process parameters need to be optimized in order to prevent degradation and discoloration in poplar. Turkey oak was found to be less suitable for acetylation due to its low permeability and tendency to crack.

Nine different environmentally friendly coatings were tested on natural and acetylated hornbeam wood, during natural weather exposure and xenon lamp irradiation. The coating performance of acetylated hornbeam, and the photostability properties of tested coatings were evaluated to offer suggestions regarding suitable and less-suitable coatings for the exterior use of acetylated hornbeam. On the one hand, acetylation decreased the coating absorbance of hornbeam. On the other hand, it made the wood more durable and dimensionally stable, all of which influences the outdoor performance of acetylated hornbeam. The color of acetylated hornbeam is not photostable; it brightens during photodegradation, and greys after leaching. For long-lasting color, acetylated hornbeam should be coated with dark pigmented stains and maintained regularly. Fungal degradation and cracking did not occur, but the wood is just as susceptible to wasp stripping as untreated hornbeam. In this study, 200-h-long xenon lamp irradiation resulted in a color similar to that caused by 1 month of weather exposure (April to May 2018, Sopron, Hungary).

In this study, the effect of acetylation and coating with boiled linseed oil was evaluated concerning the photodegradation of common hornbeam wood (Carpinus betulusL.). To measure colour stability, a 10-month-long outdoor weather resistance test without soil contact was performed as well as artificial aging using a 200 hour mercury-vapour lamp irradiation test. The measurements were done on hornbeam, acetylated hornbeam, boiled linseed oil-treated hornbeam, and acetylated and boiled linseed oil-treated hornbeam samples. The control and treated samples’ colour change was determined by comparing them to the original colour in all cases. The photodegradation process was examined with Fourier Transform Infrared (FTIR) spectra. Acetylated hornbeam was less prone to crack, but the modification did not hinder the fading and greying caused by UV irradiation. Coating the samples with boiled linseed oil decreased the rate of colour change and cracking. The photodegradation of lignin was confirmed by the FTIR spectra.

The present study aimed to determine how acetylation affected the bonding properties of European hornbeam wood. The research was supplemented with the investigation of wetting properties, wood shear strength, and microscopical studies of bonded wood, as these all have strong relationships with wood bonding. Acetylation was carried out on an industrial scale. Acetylated hornbeam showed a higher contact angle and lower surface energy than untreated hornbeam. Although the adhesion of the acetylated wood surface is lower due to its lower polarity and porosity, the bonding strength of acetylated hornbeam was similar to that of untreated hornbeam when bonded with PVAc D3 adhesive, and it was higher in the case of PVAc D4 and PUR adhesives. Microscopical studies proved these findings. After acetylation, hornbeam could be used in applications where it is exposed to moisture, as its bonding strength after soaking or boiling in water was significantly higher than that of untreated hornbeam.