Wood specimens were prepared from the sapwood part of the tree 150 cm above the ground. While wood specimens were being prepared, especially the parts with smooth fibers, no knots and cracks, and which were not damaged by insects and fungi were selected. Air-dried sapwood specimens of Oriental beech (Fagus orientalis Lipsky) was prepared for WA, and MOR test dimensions of 20 mm x 20 mm x 20 mm, and 20 mm x 20 mm x 360 mm (tangential, radial,

and longitudinal directions), respectively.

Korasit KS, which was preferred in this study, contains 8,4 % N, N-Didesyl-N-methyl-poly (oxethyl) ammonium propionate and 15,2 % copper hydroxide carbonate as impregnation material (Varkim 2022). The Oriental beech was impregnated with Korasit KS in accordance with ASTM D 1413-07el (2007). For 30 minutes, Oriental beech was impregnated with a 760 mm Hg pre-vacuum. After that, the specimens were allowed to diffuse in solution for 30 minutes at atmospheric pressure. The amount of Korasit KS retention was determined using Equation 1.

(1)

G = T₂-T₁

T₂ = After-impregnation specimen weight (kg)

T₁ = Pre-impregnation specimen weight (kg)

V = Volume of the specimen (m³)

C = Solution concentration (%)

Oriental beech was kept in distilled water for 2,5 h, 5 h, 10 h, 20 h, 40 h, 80 h, and 160 h at room temperature as part of the water absorption test. Specimens were removed from the water at the end of each soaking session, dried on paper, and immediately weighed. In order to calculate how much water each specimen absorbed, Equation 2 was utilized.

(2)

Where;

WA = denotes water absorption (%)

M_f = denotes specimen weight after water absorption (g)

M_0i = denotes oven-dry weight after impregnation (g)

According to the TS ISO 13061 (2021) standard, wooden specimens of 20 mm x 20 mm x 360 mm and 30 wooden materials in total, 10 from each specimen group, were prepared for MOR. Prior to testing, wood specimens were conditioned for 6 weeks at 20 °C and 60 % relative humidity. Equation 3 was used to calculate the MOR (MPa) of the wood specimens.

(3)

Where;

P = is the maximum load (N)

l = is the span (mm)

b = is the specimen width (mm)

h = is the specimen thickness (mm)

Thermogravimetry analysis (TGA) and differential thermogravimetry (DTG) studies were carried out in this test using the LABSYS TG-DTA analyzer (France). These tests were conducted in an argon environment at 10 °C / min heating and 50 mL / min purging rates. The temperature was raised to 600 degrees Celsius from ambient. During the heating and pyrolysis of approximately 10 mg of specimen, weight loss was continuously monitored. For each specimen group, the analyzer recorded the pyrolysis's starting and bending temperatures. The TG curve is used to calculate the weight loss rate as a function of time, producing a derivative TG curve.

The data from all tests, the Duncan test at 95 % confidence level, and the analysis of variance were all collected using the computerized SPSS statistical program. In this study, statistical evaluations were carried out on homogeneity groups (HG) containing different letters, with each letter reflecting a distinct statistical significance.

Water absorption (WA) levels of Oriental beech impregnated with Korasit KS are given in Table 1.

Table 1:
WA of O riental beech wood specimens impregnated with Korasit KS.

Each group received ten replicas. At a 95% confidence level, homogeneity group was attained. HG: Homogeneity group.

Results showed that the wood specimens absorbed more water during the first time than during the subsequent periods, which is consistent with earlier investigations (Alma 1991, Hafızoğlu et al. 1994, Yıldız 1994). These outcomes could be the consequence of WA being injected into wood's empty pores at the beginning of soaking and those spaces being smaller with time (Yalınkılıç et al. 1995).

According to the WA values, the highest WA value was determined in the specimens impregnated with 3 % concentration of Korasit KS in all water absorption periods. Korasit KS appeared to facilitate WA in wood. This could be attributed to the chemical components and the hysteresis effect found in wood cavities. Furthermore, specimens of water-based wood preserving-treated wood appeared to be more susceptible to free water retention rather than water impregnation, gave rise to increased WA (Almeida et al. 2021).

However, there was no statistical difference was found in WA values between control group and Korasit KS impregnated Oriental beech in all WA periods. Kirkpatrick and Barnes (2006) found that waterborne copper naphthenate treatments increased WA capacity of wood composite panels. Nicholas et al. (2000) stated that alkali ammonium compounds caused the wood to absorb more water and expand after impregnation as a result of the same kind of mechanism. The findings of Kirkpatrick and Barnes (2006) and Nicholas et al. (2000) are all supported by our findings.

Modulus of rupture (MOR) values of Oriental beech impregnated with Korasit KS are given in Table 2.

Table 2:
MOR values of Oriental beech impregnated with Korasit KS.

- As these are in control group, they are not impregnated. Each group received ten replicas. At a 95 % confidence level, homogeneity group was attained.

Table 2 shows that although there is no statistically significant difference between the control and Korasit KS impregnated test specimens, the control specimens have the highest modulus of rupture (MOR) (118,04 MPa) and the Korasit KS-treated specimens have the lowest MOR (103,61 MPa). MOR was higher in the control group than in the impregnated Oriental beech wood. Lower MOR levels of oriental beech were produced by Korasit KS concentrations that were higher. When wood is treated with fire retardant chemicals or wood preservatives, the strength of the wood is impacted (Winandy et al. 1988).

Mechanical factors have an impact on preservative chemical structure, chemical pH, pre- and post-treatment of wood, impregnation parameters, and interactions with microstructure. The Korasit KS treatment had no statistically significant impact on the MOR of the Oriental beech, supporting the negligible impact of copper and quaternary ammonium compounds on the bending properties of wood. In certain investigations, similar outcomes have been found (Pizzi 1983, Topaloğlu 2019).

It has been discovered that protective impregnation reduces the modulus of fracture of some hardwoods, indicating that applications may have negative impacts on mechanical qualities (Winandy and Lebow 2001).

In our study, specimens impregnated at 3 % and 6 % concentrations showed a respective drop of 10,97 % and 13,92 % from the control. It is well known that the treated wood's lower strength is significantly influenced by the treated wood's initial pH value, treatment solution concentration, and blast furnace drying temperature (Shukla et al. 2019).

The MOR values of Oriental beech impregnated with compounds containing copper, such as 2 % aqueous solutions of Wolmanit CX-8 and Celcure AC 500, were examined by Türkoğlu et al. (2016). They discovered that the MOR values for Oriental beech impregnated with Wolmanit CX-8 and Celcure AC 500 fell by 15 % and 15,50 %, respectively.

Şimsek et al. (2013) examined the MOR of woods treated with copper-containing compounds such 4 % aqueous solutions of Adolit KD 5 and Tanalith-e preservatives on Oriental beech (Fagus orientalis Lipsky) and Scots pine (Pinus sylvestris L.). Their findings showed that the MOR value of the chemically treated wood specimens was lower than that of the untreated control group. Our findings substantially agree with the information provided by Şimsek et al. (2013) and Türkoğlu et al. (2016).

The thermal behavior of the wood which was impregnated with and without Korasit KS under a nitrogen atmosphere was conducted using TGA and DTG. The results were given in Table 3 and Figure 1.

Table 3:
Initial and maximum temperature (°C) of thermal degradation and the char yield (%) after thermogravimetric analysis.

T_i% was found within the temperature range of 230 °C to 280 ºC. T_{max %} was found between 330 °C and 358 ºC. As a result of thermal degradation at 600 ºC, the highest char yield was obtained impregnated with 6 % concentration of Korasit KS with 50,69 %, and the lowest char yield was obtained from the control with 29,42 %. It was shown that the use of Korasit KS which have copper hydroxide enhanced the thermal stability of the specimens. Metal hydroxide compounds increased the amount of residue at 600 ºC (Chen et al. 2006, Choi et al. 2009). Water and oxide were generated in the environment with the thermal decomposition of copper hydroxide. This endothermic reaction cooled the polymer surface and increased charring (Kong et al. 2008, Li et al. 2010).

TGA thermographs and derivative thermogravimetry (DTG) curves of control and Korasit KS impregnated Oriental beech were given in Figure 1. DTG curves refer to the velocity of mass loss during thermal degradation.

Figure 1:
TGA and DTG results of specimens.

Temperature values corresponding to initial and maximum mass loss were obtained to be considerably lower in impregnated specimens compared to control specimens. Baysal et al. (2017) found that while the amount of some commercial wood preservatives increased in the wood, the maximum decomposition temperature decreased.

The initial weight loss in the TG and DTG curves occurred at about 100 ºC because of moisture removal. Cellulose and hemicelluloses were dramatic diminished in the range of 200 ºC - 350 ºC. Hemicellulose occurred acetic acid through deacetylation during thermal degradation (Bianchi et al. 2010).

Degradation of cellulose which led to the production of volatile flammable components were taken place through dehydration, decarboxylation, oxidation, hydrolysis, and free radical formation. Free radicals led to the production of hydrogen peroxide, carboxyl, and carbonyl groups, and these groups were responsible for the thermal degradation (Junges et al. 2019).

The degradation of lignin started at approximately 200 °C, however, the mass loss occurred across a wide temperature range. Temperatures above 600 °C, which are higher than the maximum degradation temperatures of cellulose and hemicellulose, can be reached during the slow disintegration of lignin. The literature revealed similar three-stage thermal degradation processes (Shebani et al. 2008, Kim et al. 2010, Popescu et al. 2011).

Korasit KS impregnated Oriental beech wood specimens that included copper ions had a lower weight loss than the control specimens. The copper ions can expedite the decomposition of wood at lower temperatures and char oxidation (Fu et al. 2009, Hirata et al. 1992).

Cellulose was catalyzed by metals and decomposed rapidly. In this case, it caused to increase in the char yield (Helsen and Bulck 2000). Also, charring was very slow due to metal compounds complexed with or precipitated on lignin (Tomak et al. 2012). Previous studies determined that as the amount of copper impregnated into wood increased, thermal degradation of wood decreased (Lu et al. 2008, Koo et al. 2014, Junges et al. 2019).

^♠Corresponding author: caglar.altay@adu.edu.tr