Mechanical properties of impregnated and heat treated Oriental beech wood

Abstract

The main purpose of this study was to investigate mechanical properties such as the modulus of rupture (MOR) and compression strength parallel to grain (CSPG) of impregnated and heat-treated Oriental beech (Fagus orientalis L.) wood. Some copper and boron containing impregnation chemicals such as Wolmanit CX-8 (WCX-8) and Celcure AC-500 (CAC-500) were used. Wood specimens were impregnated 2% aqueous solution of the chemicals according to ASTM D1413-07e1 standard. The wood specimens were heated at 150 and 175 °C for 4 and 8 h, respectively. Results showed that both impregnation and heat treatment decreased the MOR and CSPG of Oriental beech wood. The MOR losses of Oriental beech after both treatments were higher than CSPG losses. The largest reduction of MOR and CSPG were observed with 51.5% and 15.5% for CAC-500 impregnated and heated at 175 °C for 8 h. Except for WCX-8 impregnation and heat treatment at 150 °C for 4 and 8 h, the MOR values of impregnated and heat-treated Oriental beech wood were lower than only heat-treated Oriental beech wood. It was also found that the CSPG values of impregnated and heat-treated Oriental beech wood were higher than only heat-treated Oriental beech wood, except for impregnation and heat treatment at 175 °C for 8 h.

Full Article

Mechanical Properties of Impregnated and Heat Treated Oriental Beech Wood

Turkay Turkoglu,^a,* Ergun Baysal,^b Mehmet Yuksel,^b Huseyin Peker,^c Cevdet Sacli,^d Ihsan Kureli,^e and Hilmi Toker ^b

The main purpose of this study was to investigate mechanical properties such as the modulus of rupture (MOR) and compression strength parallel to grain (CSPG) of impregnated and heat-treated Oriental beech (Fagus orientalis L.) wood. Some copper and boron containing impregnation chemicals such as Wolmanit CX-8 (WCX-8) and Celcure AC-500 (CAC-500) were used. Wood specimens were impregnated 2% aqueous solution of the chemicals according to ASTM D1413-07e1 standard. The wood specimens were heated at 150 and 175 °C for 4 and 8 h, respectively. Results showed that both impregnation and heat treatment decreased the MOR and CSPG of Oriental beech wood. The MOR losses of Oriental beech after both treatments were higher than CSPG losses. The largest reduction of MOR and CSPG were observed with 51.5% and 15.5% for CAC-500 impregnated and heated at 175 °C for 8 h. Except for WCX-8 impregnation and heat treatment at 150 °C for 4 and 8 h, the MOR values of impregnated and heat-treated Oriental beech wood were lower than only heat-treated Oriental beech wood. It was also found that the CSPG values of impregnated and heat-treated Oriental beech wood were higher than only heat-treated Oriental beech wood, except for impregnation and heat treatment at 175 °C for 8 h.

Keywords: Impregnation; Heat treatment; Oriental beech; Modulus of rupture; Compression strength parallel to grain

Contact information: a: Department of Forestry, Koycegiz Vocational School, Mugla Sitki Kocman University, 48800, Mugla, Turkey; b: Wood Science & Technology, Faculty of Technology, Mugla Sitki Kocman University, 48000, Mugla, Turkey; c: Department of Forest Industry Engineering, Faculty of Forestry, Artvin Coruh University, 08000, Artvin, Turkey; d: Department of Material and Material Processing Technologies, Technical Sciences Vocational School, Selcuk University, 42000, Konya, Turkey; e: Wood Science & Technology, Faculty of Technology, Gazi University, 06500, Ankara, Turkey;

* Corresponding author: turkayturkoglu@mu.edu.tr

INTRODUCTION

Wood is one of the oldest construction materials and is used for a variety of purposes because of its unique properties, including a high strength to weight ratio, resiliency, and toughness (Bultman and Southwell 1976). However, wood is susceptible to environmental degradation because it is a biological material (Williams and Feist 1999; Chang and Chou 2000). Thus, it is necessary to treat wood to provide long service life and improve upon some properties of its intended applications (Srinivas and Pandey 2012). Wood treatments such as impregnation using preservatives and thermal modification techniques can improve wood properties (Kamdem et al.2002). Wood modification is the enhancement of wood properties by chemical, biological, or physical means (Hill 2006; Esteves and Pereira 2008; Thybring 2013). Impregnation, as a wood modification technique, provides dimensional stabilization, protects wood against biological deterioration, and reduces cracking (Kumar 1994). However, chemical treatment presents a serious threat to the environment. Environmental awareness has led to increased interest in developing new methods and chemicals (Percin et al. 2015). Thus, new generation wood preservatives such as Celcure AC 500 (CAC-500), micronized copper quat, Tanalith-e, and Adolit KD 5 are less harmful to the environment than previous chemicals containing chromium and arsenic, or they are not harmful at all (Ozgenc et al. 2012; Turkoglu et al. 2015a). Among the impregnation chemicals, borates have several advantages as wood preservative. In addition to imparting flame retardancy, they provide sufficient protection against wood destroying organisms, and they have a low mammalian toxicity and low volatility. Moreover, they are colorless and odorless (Murphy 1990, Drysdale 1994; Chen et al. 1997; Yalinkilic et al. 1999). Increased restrictions on the use of conventional heavy-duty wood preservatives have ensured that copper-based formulations gained wide popularity in the wood preservation industry (Freeman and McIntyre 2008). Therefore, they are commonly used in the forest product industry (Turkoglu et al. 2015a;b). Wood strength is affected when wood is treated with preservatives or fire retardant chemicals (Winandy 1988). Yildiz et al. (2004) investigated modulus of rupture (MOR) of yellow pine (Pinus sylvestris L.) wood impregnated with a 2% aqueous solution of Wolmanit CX-8 (WCX-8) which includes copper and borate. They found that MOR of 2% WCX-8 treated yellow pine wood was slightly lower than an untreated control. Toker et al. (2008, 2009) reported that compression strength parallel to grain (CSPG) and MOR of borate treated Oriental beech and Scots pine were lower compared to untreated control specimen.

Heat treatment is an alternative wood modification method. While heat-treated wood possesses new properties like improved decay resistance and higher dimensional stability, its strength is considerably decreased (Turkoglu et al. 2015c). Heat-treated wood has the advantage in terms of aesthetic properties (uniform and effective change in color) and performance relative to technical guidelines (much reduced swelling and shrinkage, improved resistance to fungi) (Vukas et al.2010; Turkoglu et al. 2015c). Heat treatment leads to significant changes in the chemical structure of the wood cell wall components such as cellulose, hemicellulose, and lignin (Sivrikaya et al.2015). As a result of heat treatment, the wood becomes more brittle, and its mechanical strength and technological properties decrease in relation to the level of heat treatment (Gunduz et al.2008). Jämsä and Viitaniemi (2001) reported that at temperatures over 150 °C the strength properties start to weaken and wood becomes more brittle and bending strength decrease by 10 to 30%. In another study, Unsal and Ayrilmis (2005) determined the CSPG of river red gum specimens decreased about 19.0% when heat-treated at 180 °C for 10 h. Therefore, the effects of solely preservative treatment and thermal modification on the mechanical properties of wood are well known; however, combining effects of these treatments has not been widely researched. According to the authors’ knowledge, there is limited research and a gap in literature. Baysal et al. (2014) researched MOR of Scots pine impregnated with copper and boron containing preservative such as Adolit KD 5 and heat treated. The authors observed a 10.45 to 31.53% decrease in MOR compared with the untreated wood. The present study was conducted on Oriental beech (Fagus orientalis L.) wood specimens impregnated with 2% aqueous solution of water-based wood preservatives containing copper and boric acids, such as WCX-8 and CAC-500. After impregnation, heat treatment was applied at 150 °C and 175 °C for 4 and 8 h.

The objective of study was to determine some mechanical properties such as modulus of rupture and compression strength parallel to grain of WCX-8 and CAC-500 impregnated and heat treated Oriental beech wood.

EXPERIMENTAL

Materials

Preparation of test specimens and chemicals

Wood specimens were prepared from Oriental beech wood, which is commonly used in the forest products industry in Turkey. The specimens were selected from air-dried sapwood pieces which were free of knots and with no visible evidence of infection. They were obtained randomly from the wood. Aqueous solution of WCX-8 and CAC-500 were dissolved in distilled water to a concentration of 2%. According to the technical data sheets, WCX-8 contains 2.8% bis-(n-cyclohexyldiazeniumdioxy)-copper, 13.0% copper (II) carbonate hydroxide, and 4.0% boric acid (Wolman 2007). CAC-500 contains an alkaline copper quaternary system, including 16.63% copper (II) carbonate hydroxide, 4.8% benzalkonium chloride, and 5.0% boric acid (Ozgenc and Yildiz 2014).

Methods

Impregnation process

Wood specimens were impregnated with 2% aqueous solution of WCX-8 and CAC-500 according to ASTM D1413-07e1 (2007). While the specimens tested by CSPG were oven dried at 103 ± 2 °C until unchangeable weight before impregnation, the specimens tested by MOR were oven dried at 55 ± 2 °C until unchangeable weight before impregnation to prevent cracking, deflection, and distortion etc. at higher temperatures. Retention was calculated from Eq. 1,

 (1)

where G = (T₂ – T₁) is the grams of treatment solution absorbed by the wood specimens (T₁ is the weight of the wood specimens before impregnation, T₂ is the weight of the wood specimens after impregnation), C is grams of preservative in 100 g of the treatment solution, and V is the volume of the wood specimen in cm³. Impregnated wood specimens were conditioned at 20 °C and 65% relative humidity for two weeks before heat treatment.

Heat treatment

Heat treatment was performed using a temperature-controlled laboratory oven. Two different temperatures (150 and 175 °C) and two treatment durations (4 and 8 h) were applied to wood specimens under atmospheric pressure and in the presence of air. Heat treated wood specimens were conditioned at 20 °C and 65% relative humidity for two weeks before MOR and CSPG tests.

Modulus of rupture (MOR)

The modulus of rupture of wood specimens was examined according to TS 2474 (1976). Dimensions of air-dried sapwood specimens of Oriental beech were 20 (radial) × 20 (tangential) × 360 (longitudinal) mm for MOR test. The MOR of wood specimens impregnated with WCX-8 and CAC-500 was calculated using Eq. 2,

 (2)

where P is the maximum load (kg), I is the span (cm), b is the width of specimen (cm), and h is the thickness of specimen (cm).

Compression strength parallel to grain test (CSPG)

The compression strength parallel to grain test was determined according to the TS 2595 (1977) standard using a 4000-kp capacity universal test machine, and applying 6 mm/min loading time. Dimensions of air-dried sapwood specimens of Oriental beech were 20 (radial) × 20 (tangential) × 30 (longitudinal) mm for CSPG test.

Evaluation of test results

Mechanical test results were evaluated by one-way ANOVA using the SPSS statistical program. The significance (P<0.05) between the treatments was compared using Duncan’s homogeneity groups. Different letters given with the average values of the tested parameters indicated a significant difference according to Duncan’s homogeneity groups.

RESULTS AND DISCUSSION

MOR of Impregnated and Heat-treated Oriental Beech Wood

Table 1 shows WCX-8 and CAC-500 retention levels and MOR of Oriental beech wood. The retention of WCX-8 and CAC-500 were 12.25 and 12.43 kg/m³, respectively. The highest MOR value was recorded as 1197 kg/cm² for untreated Oriental beech, and the lowest MOR value was 580 Kg/cm² for CAC-500 impregnated and heat-treated at 175 °C for 8 h. The MOR values of untreated wood specimens were higher than those of WCX-8 and CAC-500 impregnated wood specimens. WCX-8 and CAC-500 treatment decreased the MOR of Oriental beech by approximately 15%. There was a significantly statistical difference in MOR levels between untreated wood and preservative treated wood specimens. However, there was no statistical difference in MOR levels between WCX-8 treated and CAC-500 treated Oriental beech wood.

In this study, the waterborne preservatives WCX-8 and CAC-500 chemicals were used. Different research studies have shown that some preservatives, especially waterborne preservatives, have a negative impact on mechanical properties of the wood (Mourant et al. 2008; Toker et al. 2008; Simsek et al. 2010; Simsek et al. 2013). Many of the metallic oxides commonly used in waterborne preservative formulations do react with the cell wall components by undergoing hydrolytic reduction upon contact with wood sugars. This process, known as fixation, oxidizes the wood cell wall components and may reduce wood strength (Winandy 1988). The relative impact of various waterborne preservative systems is directly related to the system’s chemistry and the severity of its fixation/precipitation reaction (Winandy 1996). Simsek et al. (2013) determined that the MOR of Oriental beech and Scots pine decreased after impregnation with copper- and boron-based impregnation chemicals. Yildiz et al. (2004) investigated the effects of a copper-based wood preservative, such as ACQ-2200 treatment, on MOR. They found that there was a significant difference in MOR levels between untreated wood and ACQ-2200 impregnated wood. In another study, Baysal et al. (2014) studied the MOR of Scots pine impregnated with a copper and boron contained chemical, such as Adolit KD 5. They found that the MOR values of wood specimens impregnated with Adolit KD 5 were lower than that of the un-impregnated (control) specimen. Toker et al. (2009) investigated the MOR of Calabrian pine and Oriental beech impregnated with aqueous solutions of borates. They found that MOR levels of both wood specimens were lower than their corresponding un-impregnated wood specimens. Simsek et al.(2010) studied the MOR of Scots pine and Oriental beech wood specimens impregnated with aqueous solutions (0.25, 0.50, 1.50, and 3.00%) of borates. They found that borate impregnation decreased MOR levels of both wood specimens. Moreover, the higher concentration levels of borates resulted in lower MOR for both wood specimens (Simsek et al. 2010). The results reported here are consistent with the findings of the aforementioned studies.

Table 1. MOR of Impregnated and Heat-treated Oriental Beech Wood

The results of this study showed that heat treatments decreased the MOR of Oriental beech wood specimens. The findings from previous studies on heat-treated wood MOR are not always compatible with each other because heat treatment temperature, treatment time, size of specimen, treatment method, and chemical composition of wood affect MOR loss in heat-treated wood. In this study, heat treatments decreased the MOR of Oriental beech by 7.7 to 32.2%. Generally, the results of this study on the effect of heat treatment on the MOR of Oriental beech are compatible with the findings of previous research related to the effects of heat treatment on MOR. When heating wood without oxygen, hemicellulose is degraded first, followed by cellulose, and finally lignin. Therefore, heat-treated wood has a higher percentage share of lignin than normal wood (Vukas et al. 2010). Hemicelluloses are more affected than other constituents of wood due to their relatively lower thermal stabilities (da Silva et al. 2015). Changes in hemicellulose determine the strength properties of woods heated at high temperatures (Hills 1984). The first reason for the loss of strength is the degradation of hemicelluloses, which are not as stable to the heat as cellulose and lignin. The close relationship between hemicellulose content and bending strength was reported by a number of researchers (Winandy and Morrell 1993; Winandy and Lebow 2001; Esteves and Pereira 2008). Kartal et al. (2007) found a relationship between strength and the hemicellulose content of specimens. They reported that a lower hemicellulose content in the specimens resulted in lower MOR of wood specimens. The current study showed that the MOR values of Oriental beech wood specimens decreased with increasing treatment temperature and duration. This result is consistent with previous studies (Gunduz and Aydemir 2009; Korkut and Hiziroglu 2009; Aydin et al. 2015).

In this study, the MOR decreased 1.4 to 46.6% for WCX-8 treated and heat-treated Oriental beech. The MOR decreased 10.0 to 51.5% for CAC-500 treated and heat-treated Oriental beech. Baysal et al. (2014) investigated the MOR of Adolit KD 5 impregnated into Scots pine (Pinus sylvestris L.) wood specimens that were subsequently heat-treated. They found that the MOR levels of impregnated and heated Scots pine were lower than that of the un-impregnated and un-heated Scots pine wood specimens. Moreover, they found that the MOR values of Scots pine wood specimens decreased with increasing treatment temperature and duration. The results of the present study are in good agreement with the data provided by Baysal et al. (2014). According to these results, except for WCX-8 impregnation and heat treatment at 150 °C for 4 and 8 h, combining impregnation and thermal modification resulted in lower MOR of Oriental beech, compared to only heat treated Oriental beech wood. For example, while the only heat treatments group decreased 7.7 to 32.2% MOR of Oriental beech, combining impregnation and heat treatments decreased the MOR of Oriental beech by 1.4 to 51.5%. The decrease in MOR of Oriental beech wood specimens may be due to the combined effect of chemicals and heat treatment.

CSPG of Impregnated and Heat-treated Oriental Beech

The compression strength parallel to grain (CSPG) and retention values are given in Table 2. The retention of WCX-8 and CAC-500 were 10.26 and 10.87 kg/m³, respectively. The compression strength parallel to grain value of untreated beech was higher than treated Oriental beech wood. The highest CSPG value was 714 kg/cm² for untreated Oriental beech. The lowest CSPG was 603 kg/cm² for CAC-500 impregnated and heat-treated at 175 °C for 8 h. These results showed that preservative treatments decreased the CSPG values of Oriental beech wood specimens.

Some preservatives, especially waterborne preservatives, have a negative impact on the mechanical properties of wood (Mourant et al. 2008). It can be said that preservative impregnation increased the rate of hydrolysis in the wood, thereby causing loss in strength. Bal (2006) studied the CSPG of Scots pine impregnated with a copper-based wood preservative such as ACQ. He found that ACQ treatments decreased 1 to 3% of CSPG of Scots pine. However, there was no significant difference between untreated and ACQ treated wood specimens in this study. Simsek et al. (2013) reported that borate preservative treatments decreased 7.69 to 9.98%, and 7.88 to 10.87% of CSPG for Oriental beech and Scots pine, respectively. This study showed that WCX-8 and CAC-500 treatment decreased the CSPG of Oriental beech by 5.7 and 10.0%, respectively. However, there was no statistical difference between untreated Oriental beech and treated Oriental beech. Furthermore, heat treatments decreased the CSPG of Oriental beech wood specimens. Heat treatments decreased the CSPG of Oriental beech 2.5 to 7.0%. Aydin et al.(2015) reported that percentages of compression strength losses for 2, 6, and 10 h were 4.32, 15.92, and 18.85% at 185 °C for Oriental beech wood. In another study, Korkut et al. (2009) determined that percentages of compression strength losses for 2, 6, and 10 were 10.36, 11.94, and 16.31% at 180 °C for European hophornbeam (Ostrya carpinifolia Scop.) wood. Gunduz et al. (2009) reported that the compression strength losses for 170 °C and 4 h was 7%, while for 210 °C and 12 h, it was 34.7%.

Table 2. CSPG of Impregnated and Heated Oriental Beech

The effect of thermal modification on mechanical properties of wood is complex, and the magnitude of this effect is a function of parameters such as exposure time, temperature, medium rate of heating, and the moisture content of wood (Yildiz et al. 2006; Korkut and Hiziroglu 2009). The decrease in compression strength was due to the holocellulose content degradation, in which the first constituent affected was probably the hemicellulose (da Silva et al. 2013). Nuopponen (2005) found that thermally treated wood specimens showed higher lignin contents than unheated wood specimens, which was the result of the degradation of hemicellulose.

This study showed that CSPG values of Oriental beech wood specimens decreased with increasing treatment temperature and duration. This result is consistent with previous studies (Yildiz 2002; Gunduz et al. 2009; Aydin et al. 2015). In this study, while CSPG decreased 0.8 to 9.5% for WCX-8 treated and heat-treated Oriental beech, it decreased 2.2 to 15.5% for CAC-500 treated and heat-treated Oriental beech. Percin et al. (2015) investigated CSPG values of oak (Quercus petraea Liebl.) wood impregnated with borates and heat treated. They found that CSPG of oak wood clearly increased after impregnation and heat treatments. In another study, Can et al.(2010) studied CSPG of boric acid impregnated and then heated at 212 °C for 2 h. They found that CSPG values of both wood specimens decreased after treatments. According to these results, except for impregnation and heat treatment at 175 °C for 8 h, combining this impregnation and thermal modification caused a higher CSPG of Oriental beech compared to Oriental beech wood that was only heat-treated.

CONCLUSIONS

1. The MOR and CSPG of unheated Oriental beech (control) were higher than heat-treated Oriental beech. Thus, higher treatment duration and temperature resulted in lower MOR and CSPG of Oriental beech.
2. Except for WCX-8 impregnation and heat treatment at 150 °C for 4 and 8 h, combination of impregnation and thermal modification caused lower MOR of Oriental beech compared with only heat-treated Oriental beech wood.
3. Except for impregnation and heat treatment at 175 °C for 8 h, combination of impregnation and thermal modification caused higher CSPG of Oriental beech compared with only heat-treated Oriental beech wood.
4. Impregnation and then heat treatment caused a greater decrease in MOR than in the CSPG of Oriental beech.
5. Preservative treatment and then heat treatment at 150 °C for 4 and 8 h decreased 1.4 to 13.1% of MOR for Oriental beech wood and it decreased 0.8 to 4.2% of CSPG for Oriental beech. As the National Design Specification for Wood Construction (NFPA) requires a 10 to 20% reduction in allowable design stress, these treatments met the NFPA requirements for design purposes. However, MOR of preservative treated and then heat-treated at 175 °C for 4 and 8 h Oriental beech did not met the NFPA requirements for design purposes.
6. In all treatment applications, the lowest MOR and CSPG losses were obtained from Oriental beech wood impregnated with WCX-8 and heat treatment at 150 °C for 4 h.
7. Higher temperature and durations and then preservative treatment of structural members for applications when strength is a dominant factor is usually not recommended.
8. Preservative impregnation before heat treatment is recommended only where a relatively mild heat treatment is involved.

REFERENCES CITED

Anonymous (2007). “Wolmanit® CX-8 technical leaflet,” (www.wolman.de), Accessed 16 March 2016.

ASTM D1413-07e1 (2007). “Standard test method for wood preservatives by laboratory soil-block cultures,” ASTM International, West Conshohocken, PA, USA.

Aydin, E., Baysal, E., Toker, H., Turkoglu, T., Deveci, I., Ozcifci, A., and Peker, H. (2015). “Decay resistance, physical, mechanical, and thermal properties of heated oriental beech wood,” Wood Research 60(6), 913-928.

Bal, B. C. (2006). Investigation of Some Physical and Mechanical Properties of Scots Pine (Pinus sylvestris L.) Wood Treated with Ammonical Copper Quat (ACQ), Master’s Thesis, Department of Forest Industrial Engineering, Kahramanmaras Sutcu Imam University, Kahramanmaras, Turkey.

Baysal, E., Degirmentepe, S., Toker, H., and Turkoglu, T. (2014). “Some mechanical and physical properties of AD-KD 5 impregnated and thermally modified Scots pine wood,” Wood Research 59(2), 283-296.

Bultman, J. D., and Southwell, C. R. (1976). “Natural resistance of tropical American woods to terrestrial wood-destroying organisms,” Biotropica 8(2), 71-95. DOI: 10.2307/2989627

Can, A., Yildiz, S., Yildiz, U. C., and Tomak, E. D. (2010). “Effects of boron impregnation and heat treatment on some physical and mechanical properties of spruce and pine wood,” in: The 1^stInternational Symposium on Turkish Japanese Environment and Forestry, Trabzon, Turkey, pp. 753-766.

Chang, S. T., and Chou, P. L. (2000). “Photodiscoloration inhibition of wood coated with UV-curable acrylic clear coatings and its elucidation,” Polym. Degrad. Stabil. 69(3), 355-360. DOI: 10.1016/S0141-3910(00)00082-3

Chen, P. Y. S., Puttmann, M. E., Williams, L. H., and Stokke, D. D. (1997). “Treatment of hardwood lumber with borate preservation,” Forest Prod. J. 47(6), 63-68.

da Silva, M. R. D., Machado, G. D. O., Brito, J. O., and Junior, C. C. (2013). “Strength and stiffness of thermally rectified eucalyptus wood under compression,” Mater. Res. 16(5), 1077-1083. DOI: 10.1590/S1516-14392013005000086

da Silva, M. R., Brito, J. O., Govone, J. S., de Oliveira Machado, G., Junior, C. C., Christoforo, A. L., and Lahr, F. A. R. (2015). “Chemical and mechanical properties changes in Corymbia citriodora wood submitted to heat treatment,” Int. J. Mater. Eng. 5(4), 98-104. DOI: 10.5923/j.ijme.20150504.04

Drysdale, J. A., (1994). Boron treatments for the preservation of wood—A review of efficacy data for fungi and termites (IRG/WP 94-30037), The International Resource Group on Wood Preservation, Stockholm, Sweden.

Esteves, B., and Pereira, H. (2008). “Wood modification by heat treatment: A review,” BioResources 4(1), 370-404. DOI: 10.15376/biores.1.1.1-2

Freeman, M. H., and McIntyre, C. R. (2008). “A comprehensive review of copper based wood: with a focus on new micronized or dispersed copper systems,” Forest Prod J 58(11), 6-27.

Gunduz, G., Korkut, S., and Korkut, D. S. (2008). “The effects of heat treatment on physical and technological properties and surface roughness of Camiyanı Black Pine (Pinus nigra Arn. subsp. pallasiana var. pallasiana) wood,” Bioresour. Technol. 99(7), 2275-2280. DOI: 10.1016/j.biortech.2007.05.015

Gunduz, G., and Aydemir, D. (2009). “The influence of mass loss on the mechanical properties of heat-treated black pine wood,” Wood Research 54(4), 33-42.

Gunduz, G., Korkut, S., Aydemir, D., and Bekar, I. (2009). “The density, compression strength and surface hardness of heat treated hornbeam (Carpinus betulus L.) wood,” Maderas Cienc. Tecnol. (11)1, 61-70. DOI: 10.4067/S0718-221X2009000100005

Hill, C. A. S. (2006). Wood Modification: Chemical, Thermal and Other Processes, John Wiley & Sons Ltd, Chichester, UK.

Hillis, W. E. (1984). “High temperature and chemical effects on wood stability,” Wood Sci. Technol. 18(4), 281-293. DOI: 10.1007/BF00353364

Jämsä, S., and Viitaniemi, P. (2001). “Heat treatment of wood-better durability without chemicals,” in: Proceedings of special seminar held in Antibes, France.

Kamdem, D. P., Pizzi, A., and Jermannaud, A. (2002). “Durability of heat-treated wood,” Holz Roh. Werkst 60(1), 1-6. DOI: 10.1007/s00107-001-0261-1

Kartal, S. N., Hwang, W. J., and Imamura, Y. (2007). “Water absorption of boron-treated and heat-modified wood,” J. Wood Sci. 53(5), 454-457, DOI: 10.1007/s10086-007-0877-9

Korkut, S., and Hiziroglu, S. (2009). “Effect of heat treatment on mechanical properties of hazelnut wood (Corylus colurna L.),” Mater. Desig. 30(5), 1853-1858. DOI: 10.1016/j.matdes.2008.07.009

Korkut, S., Alma, M. H., and Elyildirim, Y. K. (2009). “The effects of heat treatment on physical and technological properties and surface roughness of European Hophornbeam (Ostrya carpinifolia Scop.) wood,” Afr. J. Biotechnol. 8(20), 5316-5327.

Kumar, S. (1994). “Chemical modification of wood,” Wood Fiber Sci. 26(2), 270-280.

Mourant, D., Yang, D. Q., Riedl, B., and Roy, C. (2008). “Mechanical properties of wood treated with PF-pyrolytic oil resins,” Holz Roh. Werkst. 66(3), 163-171. DOI: 10.1007/s00107-007-0221-5

Murphy, R. J. (1990). “Historical perspective in Europa,” in: Proceedings of the First International Conference on Wood Protection with Diffusible Preservatives, Nashville, Tennessee, pp. 9-13.

Nuopponen, M. (2005). FT-IR and UV Raman Spectroscopic Studies on Thermal Modification of Scots Pine Wood and its Extractable Compounds (Reports Series A 23), Helsinki University of Technology, Laboratory of Forest Products Chemistry, Helsinki, Finland.

Ozgenc, O., Hiziroglu, S., and Yildiz, U. C. (2012). “Weathering properties of wood species treated with different coating applications,” BioResources 7(4), 4875-4888.

Ozgenc, O., and Yildiz, U. C. (2014). “Surface characteristics of wood treated with new generation preservatives after artificial weathering,” Wood Research 59(4), 605-616.

Percin, O., Sofuoglu, S. D., and Uzun, O. (2015). “Effects of boron impregnation and heat treatment on some mechanical properties of oak (Quercus petraea Liebl.) wood,” BioResources10(3), 3963-3978.

Simsek, H., Baysal, E., and Peker, H. (2010). “Some mechanical properties and decay resistance of wood impregnated with environmentally-friendly borates,” Const. Build. Mater. (24)11, 2279-2284. DOI: 10.1016/j.conbuildmat.2010.04.028

Simsek, H., Baysal, E., Yilmaz, M., and Culha, F. (2013). “Some mechanical properties of wood impregnated with boron and copper based chemicals,” Wood Research (58)3, 495-504.

Sivrikaya, H., Can, A., de Troya, T., and Conde, M. (2015). “Comparative biological resistance of differently thermal modified wood species against decay fungi, Reticulitermes grassei and Hylotrupes bajulus,” Maderas Cienc. Tecnol. 17(3), 559-570. DOI: 10.4067/S0718-221X2015005000050

Srinivas, K., and Pandey, K. K. (2012). “Photodegradation of thermally modified wood,” J. Photochem. Photobiol. B 117(5), 140-145. DOI: 10.1016/j.jphotobiol.2012.09.013

Thybring, E. E. (2013). “The decay resistance of modified wood influenced by moisture exclusion and swelling reduction,” Int. Biodeter. Biodegr. 82, 87-95. DOI: 10.1016/j.ibiod.2013.02.004

Toker, H., Baysal, E., Ozcifci, A., Altınok, M.., Sönmez, A., Yapıcı, F., and Altun, S. (2008). “An investigation on compression parallel to grain values of wood impregnated with some boron compounds,” Wood Research 53(4), 59-67.

Toker, H., Baysal, E., Simsek, H., Senel, A., Sonmez, A., Altinok, M., Ozcifci, A., and Yapici, F. (2009). “Effects of some environmentally-friendly fire-retardant boron compounds on modulus of rupture and modulus of elasticity of wood,” Wood Research 54(1), 77-88.

TS 2474 (1974). “Wood-determination of ultimate strength in static bending,” Institute of Turkish Standards, Ankara, Turkey.

TS 2595 (1977). “Wood-testing in compression parallel to grain,” Institute of Turkish Standards, Ankara, Turkey.

Turkoglu, T., Baysal, E., and Toker, H. (2015a). “The effects of natural weathering on color stability of impregnated and varnished wood materials,” Adv. Mater. Sci. (2015), 526570, 1-9, DOI: 10.1155/2015/526570

Turkoglu, T., Baysal, E., Kureli, I., Toker, H., and Ergun, M. E. (2015b). “The effects of natural weathering on hardness and gloss of impregnated and varnished scots pine and oriental beech wood,” Wood Research 60(5), 833-844.

Turkoglu, T., Toker, H., Baysal, E., Kart, S., Yuksel, M., and Ergun, M. E. (2015c). “Some surface properties of heat treated and natural weathered oriental beech,” Wood Research 60(6), 881-890.

Unsal, O., and Ayrilmis, N. (2005). “Variations in compression strength and surface roughness of heat-treated Turkish river red gum (Eucalyptus camaldulensis) wood,” J. Wood Sci. 51(4), 405-409. DOİ: 10.1007/s10086-004-0655-x

Vukas, N., Horman, I., and Hajdarević, S. (2010). “Heat-treated wood,” (http://www.tmt.unze.ba/zbornik/TMT2010/031-TMT10-153.pdf), Accessed 10 May 2016.

Williams, R. S., and Feist, W. C. (1999). “Water Repellents and Water-repellent Preservatives for Wood,” (Gen. Tech. Rep. FPL-GTR-109), U. S. Department of Agriculture, Forest Products Laboratory, Madison, WI.

Winandy, J. E. (1996). “Effects of treatment, incising, and drying on mechanical properties of timber,” (Gen. Tech. Rep. FPL-GTR-94), U. S. Department of Agriculture, Forest Products Laboratory, Madison, WI.

Winandy, J. E., and Morell, J. J. (1993). “Relationship between incipient decay, strength, and chemical composition of Douglas-fir heartwood,” Wood Fiber Sci. 25(3), 278-288.

Winandy, J. E. (1998). “Effects of treatment and re-drying on mechanical properties of wood,” in: Conference on Wood Protection and the Use of Treated Wood in Construction, Memphis, TN, USA.

Winandy, J. E., and Lebow, P. K. (2001). “Modeling strength loss in wood by chemical composition. Part I, An individual component model for Southern pine,” Wood Fiber Sci. 33(2), 239-254.

Yalinkilic, M. K., Gezer, E. D., Takahashi, M., Demirci, Z., Ilhan, R., and Imamura, Y., (1999). “Boron addition to none or low formaldehyde cross-linking reagents to enhance biological resistance and dimensional stability for wood,” Holz Roh Werkst 57(5), 351-357. DOI: 10.1007/s001070050358

Yildiz, S. (2002). Physical, Mechanical, Technological and Chemical Properties of Fagus orientalis and Picea orientalis Wood Treated by Heat, Ph.D. Dissertation, Blacksea Technical University, Trabzon, Turkey.

Yildiz, U. C., Temiz, A., Gezer, E. D., and Yildiz, S. (2004). “Effects of wood preservatives on mechanical properties of yellow pine (Pinus sylvestris L.) wood,” Build. Environ. (39)9, 1071-1075. DOI: 10.1016/j.buildenv.2004.01.032

Yildiz, S., Gezer, E. D., and Yildiz, U. C. (2006). “Mechanical and chemical behavior of spruce wood modified by heat,” Build. Environ. (41)12, 1762-1766. DOI: 10.1016/j.buildenv.2005.07.017

Article submitted: May 27, 2016; Peer review completed: July 14, 2016; Revised version received and accepted: July 29, 2016; Published: August 11, 2016.

DOI: 10.15376/biores.11.4.8285-8296