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Thermal behavior of Liquidambar orientalis mill wood before and after extraction processes/Ekstraksiyon islemleri oncesi ve sonrasi Liquidambar orientalis mill. odununun termal davranisi.

Abstract: The effect of extractives on the thermal behavior of Liquidambar orientalis Mill. (storax) wood is studied using thermogravimetric analysis (TGA). To evaluate the effects of polar and apolar extractives on the thermal behavior of wood, sawdust samples from the heartwood of L. orientalis are extracted with either cold water (48 h), hot water (48 h), or ethanol/toluene (1:2 v/v) (6 h) prior to thermal analysis. Thermogravimetry (TG) curves show that polar and apolar extractives promote char formation, increase the amount of residue, and improve the thermal behavior of L. orientalis wood. In addition, derivative thermogravimetry (DTG) curves demonstrate that thermal degradation of unextracted and cold water-extracted wood samples occurs in a single step, while a two-step degradation pattern is seen for hot water- and ethanol/toluene-extracted wood samples. It is also observed that first degradation reactions in hot water and ethanol/toluene-extracted wood samples occur faster than those in unextracted and cold water-extracted wood samples. Although there are approximately half the number of extracted apolar compounds compared to polar compounds, the removal of both types of compounds affect the thermal properties of L. orientalis wood to the same degree. It is thus deduced that apolar extractives significantly affect the thermal behavior of L. orientalis wood.

Keywords: Wood extractives, thermogravimetric analysis, Liquidambar orientalis, storax wood, thermal degradation, natural fire retardants

Ozet: Liquidambar orientalis Mill. odununun termal davranisi uzerine ekstraktif maddelerin etkisi termogravimetrik analiz (TGA) yontemiyle incelenmistir. L. orientalis oz odunundan elde edilen ogutulmus odun unu ornekleri termal analizler oncesinde polar ve apolar ekstraktiflerin odunun termal davranisi uzerine etkisinin arastirilmasi amaciyla soguk su (48 s), sicak su (48 s) ve etanol/toluen (1:2 v/v) (6 s) ekstraksiyonlarina tabi tutulmustur. Termogravimetri (TG) egrileri polar ve apolar ekstraktiflerin komurlesmis tabaka olusumunu destekledigini, kalinti madde miktarim artirdigini ve L. orientalis odunun termal davranisini iyilestirdigini gostermistir. Turevsel termogravimetri (DTG) egrileri ise ekstraksiyon islemi uygulanmamis ve soguk su ile ekstraksiyonuna tabi tutulmus odun unu orneklerinde termal bozulmanin tek asamada gerceklesirken sicak su ve etanol/toluen ekstraksiyonuna tabi tutulmus orneklerde termal bozulmanin iki asamada gerceklestigi tespit edilmistir. Ayrica, sicak su ve etanol/toluen ekstraksiyonuna tabi tutulmus orneklerde ilk termal bozulma reaksiyonlarinin ekstraksiyon islemi uygulanmamis ve soguk su ile ekstraksiyonuna tabi tutulmus odun unu orneklerine gore daha hizli oldugu tespit edilmistir. Ekstrakte edilen apolar bilesiklerin miktari polar bilesiklerin yaklasik yarisi kadar olmasina ragmen apolar bilesiklerin ekstraksiyonunun L. orientalis odununun termal ozellikleri uzerine polar bilesikler ile ayni seviyede etkiledigi tespit edilmistir. Bu durum, L. orientalis odununun apolar ekstraktiflerinin odunun termal davranisini onemli derecede etkileyebildigini ortaya koymaktadir.

Anahtar kelimeler: Odun ekstraktiflerin, termogravimetrik analiz, Liquidambar orientalis, sigla odunu, termal bozulma, dogal yangin geciktiriciler

1. INTRODUCTION

Wood may have different thermal degradation profiles depending on its chemical composition. Since cellulose is a thermally stable polymer, the hemicelluloses and lignin are degraded before cellulose during thermal degradation. Different types of wood extractives, on the other hand, can promote or demote of thermal degradation of wood and have an effect on thermal behavior of wood material. Some extractives, however, do not pose any significant impact on the thermal behavior of wood material. Meszaros et al. (2007) compared extracted and unextracted Robinia pseudoacacia woods and found that extracted wood showed slight differences in the thermal behavior compared to the unextracted wood. According to Varhegyi et al. (2004), the removal of extractives from Castenea sativa wood caused a decrease in the fixed carbon content, a decrease in char yield and a displacement of the entire TG curve towards higher temperatures. Compared with C. sativa the effects of extractions were less for beech wood. Shebani et al. (2008) founded that the removal of extractives from Quercus alba, Pinus radiata, Eucalyptus grandis and Acacia cyclops woods TG and DTG curves shifted to higher temperatures and the final amount of residue (char) decreased in all wood species.

The aim of the recent study was to investigate the effect of extractives on the thermal behavior of heartwood extractives of Liquidambar orientalis Mill. (storax) wood. L. orientalis trees are ecologically and economically important in Turkey due to balsam content in their barks, which is mainly used in cosmetics and pharmaceutical industry (Ozturk et al. 2008), even though the number of L. orientalis trees have been declined seriously in the country (Alan and Kaya 2003). In recent years, however, various attempts regarding the protection of L. orientalis trees, the formation of new plantations, the regeneration of ecosystem in L. orientalis forests, the formation of novel management plans for balsam production, etc. have been made by The Turkish Government. Since L. orientalis wood has very limited usage as a construction material, such as for furniture, veneer production, ornamental and decoration goods, etc. (Bozkurt et al. 1989; Dogu et al. 2002), no detailed investigations have been made on its various properties. Recently, a series of studies were performed to evaluate the resistance of L. orientalis wood and balsam and its main constituents against wood decay, mold fungi, termite and insects, along with its chemical properties (Kartal et al. 2012; Terzi et al. 2012). In this study, thermogravimetric analysis (TGA) curves were used to quantify the weight loss and thermal degradation steps and to compare the thermal behavior of wood before and after different extraction procedures that removed different types of extractives. Knowledge about thermal effect of wood extractives on wood might be useful to improve natural fire retardants for wood products.

2. MATERIAL AND METHODS

2.1 Heartwood Sawdust

One Liquidambar orientalis Mill. tree was obtained from Mugla, Turkey. Since chemical properties can vary according to the position (from the top to the bottom trunk) in the heartwood from which an item of wood is taken, heartwood portions from the trees to be used in the study was cut from a disk (20 cm thick) obtained at breast height (1.3 m above ground level) of the tree. Heartwood portions were cut from the center area of heartwood discs since properties can change from the heartwood boundary towards the pith. The heartwood portions chosen were free of knots or any visible concentration of resins, and showed no visible evidence of infection by mold, stain, or wood-destroying fungi. The heartwood portions of L. orientalis was ground in the Richter mill and screened through 40 to 80-mesh sieve to obtain sawdust samples.

2.3 Extraction Processes

Sawdust samples were extracted with either cold water (48 h), hot water (48 h) or ethanol/toluene (1:2 v/v) (6 h) in accordance with the Technical Association of the Pulp and Paper Industry (TAPPI) standards TAPPI T 207 cm-99 (TAPPI, 1999a) and TAPPI T 204 cm-97 (TAPPI, 1999b).

2.4 Thermal Analyses

Thermal degradations of extracted and unextracted-wood sawdust samples were carried out by using Perkin Elmer Diamond Thermal Analysis Instrument (Perkin Elmer Diamond TG/DTA), which was calibrated using the melting points of indium ([T.sub.m]=156.6[degrees]C) and tin ([T.sub.m]=231.9[degrees]C) under the same conditions as the sample. The analyses were performed at a heating rate of 10[degrees]C/min. in an atmosphere of nitrogen that had a constant flow rate of 100 ml/min. The sawdust samples (~5 mg) were allowed to settle in standard alumina crucibles and heated up to 800[degrees]C.

3. RESULTS AND DISCUSSION

3.1 Solubility of Heartwood of L. orientalis

Table / Tablo 1 gives solubilities of the heartwood samples of L. orientalis by cold water, hot water and ethanol/toluene. Higher solubilities were obtained by hot water extraction in comparison with those by cold water and ethanol/toluene extractions.

3.2 Thermal Behavior of Extracted and Un-extracted L. orientalis Wood Samples

Thermogravimetry (TG) and derivative thermogravimetry (DTG) curves were obtained from thermal analysis (Figures / Sekil 1 and 2). The initial thermal degradation temperature ([T.sub.i]), the maximum thermal degradation temperature ([T.sub.m]), the final thermal degradation ([T.sub.f]) and the amount of char residue were obtained from TG and DTG curves summarized in Table / Tablo 2. TG and DTG curves were used to determine thermal behavior of extracted and unextracted sawdust samples. All curves showed around 7 to 8% weight loss because of the evaporation of water, which was not evaluated in order to explain the thermal behavior of the wood samples as described in Reaction Step 1 (Table / Tablo 2). The weight loss rate increased above 200[degrees]C for all wood samples. Main weight losses were observed between 200[degrees]C and 400[degrees]C for unextracted and cold water-extracted wood samples, in which the weight losses were approximately 69 and 75%, respectively. This phase was observed to be Reaction Step 2. In contrast, the main weight losses continued until the temperature of 500[degrees]C for ethanol/toluene- and hot water-extracted wood samples. These wood samples exhibited a loss of about 89 and 90%, respectively, during Reaction Steps 2 and 3. Main weight losses can be attributed to the degradation of cellulose, the hemicelluloses and lignin. The TG curves obtained from thermal analysis showed that the extracted wood samples had lower residue (char yield) than the unextracted sawdust sample at 800[degrees]C. The residue yield can be used to explain thermal stability of the wood and higher thermal stability gives rise to a higher amount of residue after thermal degradation. Hot water and ethanol/toluene extractions caused a decrease in thermal stability of L. orientalis wood because of its lower residual yield.

In the case of the extraction of wood samples with hot water and ethanol/toluene, the TG and DTG curves shifted to lower temperatures. This can be attributed to a reduction in thermal stability, which can be supported by decreasing the amount of residue at 800[degrees]C. This validation is necessary because some treatments can shift the curves of TG and DTG for wood samples to a higher temperature while the amount of residue increases (Hirata et al., 1991; Terzi et al., 2009). Ethanol/toluene as an organic solvent can dissolve apolar extractives, such as waxes, fats, resins, some gums, etc. On the other hand, hot water and cold water as an inorganic solvent can dissolve polar extractives, such as tannins, gums, starches, etc. (Shebani et al., 2008). Results showed that polar and apolar extractives of L. orientalis promote char formation, increased the amount of residue and improved thermal stability of L. orientalis wood. This observation could be attributed to how char formation acts as an insulation layer against thermal degradation (Le Van, 1989; Marcovich and Villar, 2003).

Table / Tablo 2 shows the reaction steps, reaction temperatures and amount of residues at 800[degrees]C of unextracted and extracted wood samples. [T.sub.i] is the initial temperature at which degradation starts. [T.sub.m] is the maximum thermal degradation temperature, which produces the most parallel point to the axis on the TG curve and shows peaks in the DTG curves. [T.sub.f] is the final thermal degradation temperature, above which does not appear as shoulders or peaks in the TG and DTG curves within its reaction step. The first degradation event was observed at about 240[degrees]C for unextracted and cold water-extracted wood samples and at about 208[degrees]C and 230[degrees]C for hot water- and ethanol/toluene-extracted wood samples, respectively.

The DTG curves showed that thermal degradation of unextracted and cold water-extracted sawdust samples occurred in a single step (Reaction Step 2), while hot water- and ethanol/toluene-extracted sawdust samples occurred in two steps (Reaction Steps 2 and 3) (Table / Tablo 2). Reaction Step 2 was described as "the main degradation step." It is clear in Figure 2 that the first reaction step related to the thermal degradation of wood samples continues up to around 330[degrees]C, 310[degrees]C, 300[degrees]C, and 310[degrees]C for unextracted, cold water-, hot water- and ethanol/toluene-extracted sawdust samples, respectively. These temperatures produced the appearance of shoulders, which belong to degradation of the hemicelluloses (Orfao et al., 1999; Shebani et al., 2008; Gasparovic et al., 2009; Shen et al., 2009). Shoulder peaks can be observed, particularly with deciduous woods, due to decomposition of the hemicelluloses since the hemicelluloses in those types of woods have a different composition of polysaccharides and react faster than coniferous woods. This fast reaction causes this shoulder formation (Prins et al., 2006; Shen et al., 2009). After the shoulders, reactions continue until 401[degrees]C and 405[degrees]C for unextracted and cold water-extracted sawdust samples, respectively, giving a peak at about 370[degrees]C which belongs to degradation of cellulose dominantly. After temperature levels of 401[degrees]C and 405[degrees]C for unextracted and cold water-extracted wood samples, there are no peaks or shoulders, but weight losses continue due to degradation of the remaining lignin (Orfao et al., 1999; Shebani et al., 2008; Gasparovic et al., 2009; Shen et al., 2009).

On the other hand, after the shoulders, reactions continue until about 380[degrees]C and 400[degrees]C for hot water-and ethanol/toluene-extracted sawdust samples, respectively, which belongs to the degradation of cellulose primarily. After 380[degrees]C and 400[degrees]C for hot water-and ethanol/toluene extracted-sawdust samples, a peak appears due to degradation of the remaining lignin unexpectedly. In general, DTG curves obtained from the thermal degradation of wood in an inert atmosphere do not yield a peak due to the thermal degradation of lignin. In contrast, DTG curves obtained from the thermal degradation of wood in an oxygen environment generally yield a peak due to the thermal degradation of lignin (Chauvette et al., 1985; Cordero et al., 1991; Orfao et al., 1999; Fang et al., 2006; Emandi et al., 2011; Niu et al., 2011).

4. CONCLUSIONS

In contrast to previous studies on the effect of extractives on the thermal properties for wood of various tree species, it is found that the extractives of L. orientalis wood increased the yield of char of L. orientalis wood (Varhegyi et al., 2004; Meszaros et al., 2007; Shebani et al., 2008). The extraction of the polar and apolar extractives caused a decrease in the thermal stability of L. orientalis wood. The cold water, hot water and E/T extracted-wood samples produced less char formation than unextracted wood. On the other hand, it is known that tannins are effective in improving the fire resistance of wood as a natural fire retardant. Also, tannins could be used with boron and phosphorus to produce fire resistance wood (Tondi et al., 2012; Gonzalez-Laredo et al., 2015).

In addition, thermal degradation started later for unextracted wood than it did for hot water and E/T extracted wood samples. Despite the relatively low amounts of apolar comounds that could be extracted by E/T, which were about two times less than H/W extracted polar compounds, the removal of apolar compounds affected the thermal properties of L. orientalis wood to the same degree as the polar compounds.

Apolar extractives significantly improved the thermal stability of L. oriantalis wood. These extractives are also leach resistant potentially under wet conditions depending on their chemical structures. Apolar extractives of the L. orientalis wood could be further investigated individually.

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Evren Terzi (1*)

(1) Istanbul University, Faculty of Forestry, 34473, Istanbul, Turkey

(*) Corresponding author e-mail (Iletisim yazari e-posta): evrent@istanbul.edu.tr

Received (Gelis): 14.02.2017 - Revised (Duzeltme): 06.04.2017 - Accepted (Kabul): 25.04.2017

Cite (Atif) : Terzi, E. 2017. Thermal behavior of Liquidambar orientalis mill wood before and after extraction processes. Journal of the Faculty of Forestry Istanbul University 67(2): 150-156.
Table 1. Solubility of L. orientalis heartwood samples
Tablo 1. L. orientalis oz odununun cozunurlugu

Solubility Type             Solubility (%)

Ethanol/toluene solubility  2.66
Cold water solubility       1.36
Hot water solubility        5.80

Table 2. Thermal degradation temperature and amount of char residue of
extracted and unextracted sawdust samples
Tablo 2. Ekstrakte edilmis ve edilmemis odun orneklerinin termal
degradasyon sicakliklari ve kalinti komur miktari

Sawdust Type    Reaction    [T.sub.i]      [T.sub.m]      [T.sub.f]
                  Steps    [[degrees]C]   [[degrees]C]   [[degrees]C]

Un-extracted        1         25.26          62.56         119.71
                    2        241.23         371.43         401.81
Cold-water-         1         17.19          60.41         107.29
extracted           2        243.53         374.65         405.41
Hot-water-          1         33.01          60.83         110.20
extracted           2        229.80         334.80         379.30
                    3        379.30         462.74         502.38
E/T-extracted       1         29.96          60.64         132.46
                    2        208.46         338.84         400.20
                    3        400.20         462.26         519.43

Sawdust Type      Char Residue
                at 800[degrees]C (%)

Un-extracted          15

Cold-water-           11
extracted
Hot-water-
extracted              1.5

E/T-extracted
                       1.2
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Title Annotation:Research Article / Arastirma Makalesi
Author:Terzi, Evren
Publication:Journal of the Faculty of Forestry Istanbul University
Article Type:Report
Date:Jul 1, 2017
Words:3566
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