INFLUENCES OF DIFFERENT DRYING CLIMATES ON Eucalyptus camaldulensis WOOD PROPERTIES

One of the most important disadvantages of the wood material, whose usage is becoming more and more widespread, is the dimensional instability that occurs in its interaction with water. Therefore, studies to improve these drawbacks of wood, remain always up to date. For the mentioned purpose in this study, some chemical, morphological, physical and mechanical properties of Eucalyptus camaldulensis woods, which were naturally dried in outdoor and indoor climate in Eastern Mediterranean (Kahramanmaraş province) atmosphere conditions of Turkey, were investigated. According to the results of the study, chemical properties of Eucalyptus woods dried indoor were measured as merely 0,23 % higher than dried ones outdoor. The results of morphological measurements indicated that the fiber dimensions of eucalypt wood dried in indoor were average 1,48 % lower than the ones dried out outdoor. Also, as a result of statistical analysis, it was found that there were significant differences (ρ < 0,000) between the physical properties of Eucalyptus wood samples indoor and outdoor according to the t-test. At the same time, as a result of the t-test applied to determine the effect of drying conditions on mechanical properties of Eucalyptus wood, modulus of elasticity, compression, tensile, dynamic bending and shear strength did not cause any significant difference between indoor and outdoor, while bending and Janka hardness strengths showed significant differences at ρ < 0,000 level. Finally, when the data obtained as a whole is considered, it can be said that testing of Eucalyptus wood which requires a very sensitive drying in different climates has important contributions on the subject. Regarding eucalypts, which has a high distribution area (20 million hectares) in the world, it is recommended to relevant institutions and organizations to expand and maintain such study in the future. Lastly, according to obtained data from this study, it can be said that the experiments of Eucalyptus woods which require a very delicate drying in different environments provide important contributions on the subject.


INTRODUCTION
One the most important disadvantages is the change in the dimensions of wood material during its interaction with water. As a result of the reduction of wood-based resources, demand for wood cannot be adequately met and price increases are higher than expected. For these and similar reasons, the studies on reducing the objectionable aspects of the wood material and increasing their positive properties are always keep up-to-date (Kocaefe et al. 2008, Aytin et al. 2015, Cetin and Gunduz 2016. As is known, wood is an anisotropic material and its properties differ in various directions (Dahl andMalo 2009, Dackermann et al. 2016). Knowing of the physical, mechanical and chemical properties of wood makes it easier to compare wood materials with others and gives ideas about processing and usage characteristics (Sancak 2010, Duzkale et al. 2014, Cetin and Gunduz 2017. Mechanical properties are defined as the degree and condition of the wood to resist external forces and various types of loads, such as mechanical and external forces, which lead to dimension and deformation, stress and rupture (Bozkurt and Goker 1996). Due to its hygroscopic properties, wood material or any wood-based product can reach certain equilibrium moisture content by adapting to weather conditions in various places of use. In dimensions of wood material, which is not dried sufficiently changes occurs such as shrinkage or swelling during utilization (Kantay 1993, Bergman 2021. Because of these changes, defects such as cracking, separation from joints, and deformation of wood material can take place (Ors and Keskin 2008). There are two main components in wood: lignin (18 % -35 %) and carbohydrates (cellulose and hemicellulose) (Ors and Keskin 2008). These components are complex and polymeric materials. There are minor extraneous materials in structure of wood, which are organic extractives and inorganic minerals (ash). Generally, wood has an elemental composition of about 50 % carbon, 6 % hydrogen, 44 % oxygen, and trace amounts of several metal ions (Pettersen 1984).
Australia is the homeland of the genus Eucalyptus. Eucalyptus camaldulensis is cultivated for commercial purposes in Turkey and this plant of foreign origin has become native (Davis 1988). Eucalypts, which is grown especially in the southern regions of Turkey, is a type of tree that has an important role for forest industry in the world due to its large diameter arises in a short time and has smooth trunk. This plant, which has been grown in Turkey since 1939, obtains different forest products for various purposes, primarily for railroad tie and bridge production, followed by cellulose, which is the raw material of paper industry (Karsavuran 2008). Eucalyptus, which was considered as a packing case at first, is nowadays used in many areas such as building constructions, veneer, furniture, chest, turnery, agricultural tools, musical instruments, sports equipment, stull, trolley pole and fiber-chip wood (Yaltirik andEfe 1994, Korkut et al. 2008).
The water present in new-cut trees should be eliminated from wood before using as end product. Hence, rough and fresh timber should be exposed to drying process. Depending on species, weather conditions, timber dimensions and the season when the wood piled, natural-drying times vary widely. Temperature, relative humidity and airflow effect the drying process of wood piles (Bektas et al. 2017). Different timber dimensions, bark content and piling specifications may strongly affect natural-drying times (Simpson andWang 2004, Bown andLasserre 2015). The drying process has several important advantages such as increases some strength properties and improves dimensional stability of wood (Forest Products Laboratory 1999). However, drying defects such as cracks, hardening, cell collapse, shape changes, color changes adversely affect the quality of the wood material (Kantay 1993).
As far as can be researched, no studies have encountered effect of different drying climates on the properties of Eucalyptus wood. Closest to the subject of this study, mechanical properties of Eucalyptus urophylla wood (Lahr et al. 2017) and Eucalyptus grandis wood ) of different moisture (12 %, 30 %) levels were investigated. Eventually, Lahr et al. (2018) found that mechanical properties were significantly affected by moisture content, and the behavior pattern consisted in increasing the values of the properties with reduction of moisture content. Other researchers also investigated Eucalyptus saligna (Nogueira et al. 2019) and Eucalyptus maidenii wood's properties in abovementioned moisture contents . In another study, pine (Pinus sylvestris) and beech (Fagus sylvatica) woods were subjected to steam kiln-drying. Modulus of elasticity and bending strength for steam dried, air-steam mixture dried and air-dried samples as reference were measured. They concluded that steam and air-steam mixture drying cause changes of the mechanical properties of analyzed wood species (Baranski et al. 2014).
In the light of the above explanations, the effects of natural drying climates on some chemical, morphological, physical and mechanical properties of Eucalyptus wood, one of the fast growing tree species with high distribution areas, was investigated in this study.

Materials
The freshly sawn lumbers were obtained from Mersin-Karabucak Forest Sub-district Directorate. Lumbers were cut into the dimensions of 6 cm x 15 cm x 300 cm and the ends of edged timbers were not sealed. When the timbers were brought to drying environments, their starting moisture content (MC) varied between 57 % to 72 %. Twenty timbers were dried in each environment in order to minimize random variations and the test samples were randomly selected from the piles.

Drying process
Air drying method was applied to the timbers stacked in Kahramanmaraş Province. Timbers were piled in two different environments: Outdoor (OD) and Indoor (ID). Drying process was began in summer period (effective drying) on June and followed during one year. The data were taken from meteorological station for OD and Geratech DT-172 was used to measure temperature and relative humidity of ID.

Determination of physical and mechanical properties
Test specimens were obtained from eucalypts (Eucalyptus camaldulensis Dehnh.) timbers supplied in Mersin-Karabucak territory. Test specimens were prepared on the basis of TS 2470 (1976). Some physical properties such as air-dry density, oven-dry density and basic density values were determined with the sample dimension of 20 mm × 20 mm × 30 mm, based on TS 2472 (1976). Additionally, volumetric shrinkage and swelling was calculated according to TS 4083 (1983), TS 4084 (1983), TS 4085 (1983), TS 4086 (1983 with the sample dimension of 20 mm × 20 mm × 30 mm. As for the mechanical properties, static bending strength and modulus of elasticity was designated on the sample dimensions of 20 mm × 20 mm × 300 mm based on TS 2474 (1976)  The Independent Samples t-test was performed to determine if there were statistically significant differences between the properties of ID and OD dried wood.

Determination of chemical and morphological properties
Eucalyptus samples were chipped to matchstick size and in order to determine chemical components, chips were ground in a laboratory type Wiley mill according to TAPPI T257 om-85 standard. Samples passing through 40-mesh sieve and remaining over 60-mesh sieve were stored in closed containers for chemical analysis and moisture contents were determined. Holocellulose, cellulose, alpha cellulose, lignin, extractive and ash contents of the samples were determined according to Wise and Karl (1962), Kurschner and Hoffer (1969), TAPPI T203 cm-99 (1999), TAPPI T222 om-15 (2015), ASTM D1107-96 (2013) and TAPPI T211 om-16 (2016), respectively. Cold water, hot water and 1% NaOH solubilities of the samples were determined according to TAPPI T207 cm-08 (2008) and TAPPI T212 om-18 (2018) standards.
The maceration process was carried out with chlorite method to make the woody fibers individual. Fiber slides were prepared for determination of fiber dimensions by using Nikon FS1 photo microscope; the average fiber width, length, lumen diameter, and cell wall thickness of 100 fibers were measured.

RESULTS AND DISCUSSION
The results obtained from the experiments on the chemical contents of Eucalyptus wood dried in indoor and outdoor conditions are given in Table 1. According to Table 1, toluene-acetone-ethanol solubilities and lignin contents of Eucalyptus wood dried ID and OD were found to be similar. Hot-water solubility of woods dried OD is lower than that of ID. The coldwater solubility of OD dried Eucalyptus wood was about 5,1 % lower than that of the ID. The holocellulose content of the OD dried wood was 0,5 units higher than that of the ID. In terms of cellulose and alpha cellulose contents, woods dried ID are richer than woods dried OD. When Table 1 is examined in general, there are significant differences between water solubility values of Eucalyptus wood dried ID and OD climates, but there is no significant difference between other chemical components and solubilities. Ayata (2008) determined holocellulose and lignin contents of Eucalyptus grandis wood as 81,2 % and 25,7 %, respectively. In the same study, ash and extractives contents were found to be 0,3 % and 2,4 %. It was found that holocellulose content was lower and lignin and extractive contents were higher than those of undried Eucalyptus wood. Table 2 indicates the differences revealed in fiber dimensions of Eucalyptus samples dried in ID and OD climates. When fiber dimensions of Eucalyptus woods dried in different climates are examined, it is seen in Table  2 that there are no differences between fiber lengths and cell wall thicknesses. The most significant difference is in fiber width, and wood dried OD is about 5,4 % wider than the one dried ID. Likewise, lumen diameter of wood dried OD was found to be wider 0,52 units than that of dried ID. It can be thought that these differences can be occurred due to relative humidity of OD climate being higher than that of ID. In the literature, no study has been found on the effects of drying climates on fiber morphological properties. However, it is seen that the fiber dimensions of the samples dried in both conditions are similar with the literature (Bhat et al. 1990, Gurboy and Ozden 1994, Trevisan et al. 2017. Statistical analysis data of air-dry, oven-dry and basic density values are given in Table 3. According to data in Table 3, differences of drying condition on air-dry density, oven-dry density and basic density values were found to be significant at ρ < 0,000 level. In same table, it can be seen that the air-dry density, oven-dry density and basic density values of the samples dried in OD were higher than those of dried in ID. These increases were determined as 10,88 % in air-dry density, 13,50 % in oven-dry density and 9,91 % in basic density. In a study conducted in the literature, air-dry density, oven-dry density and basic density values were found as 670 kg/m 3 , 620 kg/m 3 , 510 kg/m 3 , respectively (Aslan et al. 2008). In another study performed between two different types of Eucalyptus, these values were found to be 530 kg/m 3 , 520 kg/m 3 , 460 kg/m 3 for Eucalyptus grandis. and 700 kg/m 3 , 680 kg/m 3 , 570 kg/m 3 for Eucalyptus camaldulensis Dehn., respectively (Ayata 2008). The results obtained from this study are similar with the literature.
Shrinkage values made to determine the dimensional stability of the Eucalyptus wood dried in ID and OD conditions are given in Table 4. As it can be seen in Table 4, tangential shrinkage values constitute significant differences (ρ < 0,000) between Eucalyptus timber dried in ID and OD climates, however in radial, longitudinal and volumetric shrinkage values did not demonstrate same trend.
When shrinkage percentages of the samples dried in ID and OD were evaluated, radial shrinkage showed a decrease of approximately 3 % in OD (5,08 %) measurements compared to ID (5,24 %). Tangential and longitudinal shrinkage values of samples dried ID were found to be lower about 19 % and 30,8 % than those of samples dried OD, respectively. Finally, volumetric swelling is less with a rate of 9,4 % compared in ID climate (10,89 %) to OD (11,91 %). All shrinkage and deformations in the wood, from cutting to usage area, are the main reasons why the need to be dried before use (Kilic Ak 2016). In this study, volumetric swelling results (ID: 10,89 %, OD: 11,91 %) different when compared from other species of Eucalyptus: lower than that mentioned by Lima et al. (2014) for Eucalyptus resinifera (16,67 %), by As et al. (2001) for Eucalyptus rostrata (12,7 %). Moreover, similar results were found for Eucalyptus camaldulensis as 11,4 % and 11,8 % (Aslan et al. 2008, Ay et al. 2008. Table 5 shows percentages of swelling calculated in Eucalyptus samples dried in ID and OD climates. According to the results of t-tests applied to swelling measurements presented in Table 5, tangential and longitudinal swelling values have significant differences in terms of drying climate, whereas the effect of climate is found to be insignificant on the radial and volumetric swelling percentages. When swelling values of the samples dried in OD compared with ID, a decrease of approximately 11,4 % was observed in the radial direction, whereas in increase was observed 26,1 % in the tangential, 72 % in the longitudinal direction and 8,6 % in the volumetric dimension. The values found for volumetric swelling were determined to be lower to those reported in the literature (Aslan et al. 2008, Ay et al. 2008. From these results, it can be said that a more protective drying was performed in ID climates.
Mechanical properties and statistical analysis of the wood samples dried in ID and OD climates are presented in Table 6. The results of the t-test given in Table 6, which were applied to reveal effect of ID and OD drying climates showed differences on mechanical properties. Significant differences were found between the bending strength and modulus of elasticity of the samples dried in ID and OD climates according to t-test results at ρ < 0,050 significance level. Likewise, Janka hardness values measured in cross sectional, radial and tangential directions constituted significant differences at ρ < 0,000 level according to ID and OD drying climates. T-test results introduced that there is no significant effect of drying climate differences on compression, tensile, dynamic bending and shear strength samples. On the other hand, calculations based on data in Table 6 revealed that the compression strength and dynamic bending strength for the samples dried in OD were 2,3 % and 9,8 % lower than those dried in ID, respectively. However, the modulus of elasticity, static bending strength, tensile strength and shear strength values of the samples dried in ID were determined as 8,6 %, 11,3 %, 0,80 % and 2,11 % lower than those of dried in OD climates, respectively.
As it can be seen from Table 6, effect of drying climates difference on the tensile strength parallel to the fibers was calculated as much lower (0,80 %) than OD climate, in contrast to the compressive and bending strengths. Another interesting data is also that the dynamic bending strength value of samples (0,51 MPa) dried in ID climate is approximately 10 % higher than the other one (0,46 MPa). Since dynamic bending strength is particularly prominent for using structural wood in the seismic zones, the effect of the drying environment difference in such usage areas should be take into account. Regarding Janka hardness values, it can be seen from the data in Table 6 that the difference between the samples dried in OD and ID is much higher than other mechanical properties. The Janka hardness values measured in ID all three directions (C rs , R, T) are lower than those measured in the OD. These decreases were calculated as 12,17 %, 25,74 % and 19,29 % according to C rs , R and T directions, respectively. There are many studies on the mechanical properties of Eucalyptus woods in the literature; however, there have been any research dealing with the differences in drying climates (Aslan et al. 2008, Ay et al. 2008, Bektas et al. 2008).
On the other hand, temperature and relative humidity, which are two of main drying factors of environment where this research was carried out, were investigated by Kilic Ak (2016) and obtained data are illustrated in Figure 1. The most effective period for fast drying is summer period called "effective drying period". This period is between intersection points of curves showing the change of air temperature and relative humidity within one year at place of drying (Kantay 1993). The effective drying periods were indicated in Figure 1 with arrows. According to Figure 1, the temperature in summer is higher in OD than ID, but it is lower in winter.
Relative humidity values are generally higher in ID than those of in OD. It is understood from Figure 1 that the fastest drying in both (ID, OD) climate took place between June and September, when the temperature was higher and the relative humidity was lower. Furthermore, these data indicate that the effective drying period in Kahramanmaraş province occurred between June and September.

CONCLUSIONS
The results of the tests to investigate effect of drying climate on the chemical, morphological, physical and mechanical properties of Eucalyptus woods can be summarized as follows; There was no significant difference between the chemical compositions of Eucalyptus woods dried in ID and OD. The fiber width and lumen diameters of the wood dried in OD were wider than those of dried in ID due to differences relative humidity.
As a result of the physical tests, significant differences were found between the air-dry and oven-dry density, basic density, tangential shrinkage, tangential and longitudinal swelling values at the level of ρ < 0,05, while there was no significant difference between radial-, volumetric-swelling, radial-, longitudinal-, volumetric-shrinkage.
Significant differences were found between the some mechanical properties such as static bending strength, modulus of elasticity and Janka hardness (cross section, radial, tangential) of the Eucalyptus samples dried in ID and OD climates. On the other hand, it was found that drying climate had no significant effect on compression, tensile, dynamic bending and shear strength values.
Finally, in the light of the data obtained in this study, it is suggested to take into account the differences in chemical, morphological, physical and mechanical properties of Eucalyptus wood in drying process and solid usage areas.