Mechanical properties of Rowan wood impregnated with various chemical materials

Department of Woodworking Industry Engineering, Faculty of Technology, Gazi University, 06500 Beşevler, Ankara, Turkey. Department of Industrial Technology, Faculty of Industrial Arts Education, Gazi University, 06830 Gölbaşi, Ankara, Turkey. Technology Development Foundation of Turkey (TTGV) 06800 Bilkent, Ankara, Turkey. Department of Forest Industrial Engineering, Faculty of Forestry, Düzce University, 81620 Düzce, Turkey.


INTRODUCTION
The durability of wood is affected by several factors. If the wood materials are used without processing by preservative chemicals (with regard to the area of usage), fungal stains, insect infestation, humidity, fire etc damage the wood. As a result of these damages, the woods require to be repaired, maintained or replaced before its economic life ends (Richardson, 1987). For this reason, in most places the wood materials should be impregnated with the proper chemicals. In the case of the wood not been impregnated but only painted and varnished instead, the prevention on the surfaces is limited to a maximum of two years (Evans et al., 1992). *Corresponding author. E-mail: suleymankorkut@hotmail.com.
It is reported that, in mines, as a result of the impregnation of the beech and spruce wood with watersoluble salts, the bending, tensile, and impact strength decreased a little whereas compression strength increased (Kollmann, 1959). In another research concerning the impregnation of pine, spruce, fir, beech, and poplar woods with Antrasen, it was found that, the compression strength increased by 6 to 40% and bending strength increased by 10 to 22% (Stabnikov, 1957). In the impregnation of pine and beech wood with tar oil and UA salts, the tar oil increased compression strength by 10% and UA salts increased with a small rate. On the other hand, the tar oil increased the bending strength whereas the UA salts diminished the bending strength (Gillwald, 1961). Vologdin (1966) declared that, among the materials used for the impregnation of pine; sodium pentaclorfenet, copper sulphate, and sodium fluoride increased the compression strength, respectively by 95, 25, and 3% whereas zinc chloride decreased by 9%. Sodium pentaclorfenet also increased the bending strength. In another study, pressure treatment caused a decrease of 8 to 10% in the bending strength of different wood types (Isaacs, 1972). It was assessed that, salty impregnation materials increased the compression strength by 4.6 to 9.6%, whereas decreased the bending strength by 2.9 to 16% (Wazny, 1973). In another study, chromate copper arsenate (CCA) and arsenate copper arsenate (ACA) salts did not caused any significant impact on modulus of elasticity in bending (Bendtsen, 1984). After the impregnation of Scotch pine wood samples by hot-cold open tank method with eleven preservatives, no significant difference was observed in the bending strength except the decreasing effects of fluotox containing acid florid (Lutomsky, 1976). Korkut et al. (2009) Özçifci et al. (1999) carried out a research on yellow pine, oriental beech, ash-tree, and oak woods bleached with NaOH+H 2 O, NaOH+Ca(OH) 2 +H 2 O 2 , HCIO, and HCI and varnished with synthetic, polyurethane, acid catalytic varnish to research the impact on surface adhesion strength and brightness. These chemicals have no impact on brightness: Wood type and varnish type was important for brightness. The highest brightness of surface was determined with acrylic varnish and the lowest with acid hardened varnish. HCI decreases adhesion strength of varnishes.  studied static bending strength of yellow pine, oriental beech, ash-tree and oak woods bleached with NaOH+H 2 O 2 , NaOH+Ca(OH) 2 +H 2 O 2 , HCIO and HCI: They determined that HCIO and HCI causes the highest decrease in bending strength. Aytaşkin (2009) studied the impact of impregnation materials on wood types and determined that the impregnation materials increase the density and heat conduction of woods. Impregnation materials also have impacts on the mechanical properties, decreases the bending strength and modulus of elasticity. Compression strength and impregnation relation depends on the type of impregnation material. Impregnation materials decrease the adhesion strength of woods and also the weight loss in combustion tests. Kartal (1998) determined that, impregnation with CCA and drying at a temperature 70°C for 72 h have no impact on the mechanical properties of wood, but the differences between the control samples in bending test with fixation at 20 and 70°C was statistically meaningful at level of 5%.
One well-known technique to protect wood is by impregnating it with chemical products. In this study, naturally growing in Turkey, thin in texture, flexible and hard Rowan wood (Sorbus aucuparia Lipsky) was impregnated with Tanalith-E, Imersol Aqua, Vacsol Azure, and Boron compounds and tested in retention, compression strength, bending strength, and modulus of elasticity in bending.

Wood materials
Test samples were obtained from Kastamonu Forestry Regional Directory, Küre Directory, Kösreli Department number 200. Test samples were cut from the trees in accordance with TS 4176 (1984) standard. Test samples were prepared in accordance with TS 2470 TS 53 (1981). Accordingly, non-deficient, knotless, normally growth (without zone line, without reaction wood and without decay and insect mushroom damage) wood materials was selected. Test samples cut to 70 × 70 × 800 mm were air-dried at a temperature of 20 ± 2°C and 65 ± 3% relative humidity conditions up to reaching 12% humidity level.

Tanalith-E
Tanalith-E is an impregnation material used against the attacks of agent, yeast, insect, and termite. It is a new generation of impregnation material consisting of copper and organic biocide (triazole) and not harmful to plant, animal, and human health. Tanalith-E, light green in color, odorless, pH 7, 1:04 g/cmP 3 density, smooth and completely water-soluble, water-based, non-corrosive to metal parts are available in the form of ready solution. Tanalith-E was applied to woods used in fences, railings, garden furniture, barns, silos, farm buildings, the wood used in children's play areas by vacuum -pressure method (Hickson's Timber Impregnation Co. (GB), 2000).

Vacsol Azure
Vacsol Azure a product of a new technology developed by using active ingredients, used in the process, ground wood materials on the level of fungi, insects (Propiconazole and tebuconazole), and termites (permethrin) to prevent decay by protecting against transparent impregnating agent. This solvent-based material is water-insoluble, pale yellow in color, flammable, density 0.806 g/cm3 at 20 ± 2°C, contains 64% of volatile organic compounds (VOC) (Hickson's Timber Impregnation Co. (GB), 2000).

Imersol-Aqua
Imersol-Agua, used as an impregnation material in this study was supplied from Hemel (Hemel-Hickson Timber Products Limited), Istanbul. Imersol-Aqua is non-flammable, odorless, fluent, water-based and completely soluble in water and non-corrosive material with a pH value of 7 and a density of 1.03 g cm -3 . It is available as a ready-made solution. It contains 0.5% w/w tebuconazole, 0.5% w/w propiconazole, 1% w/w 3-Iodo-2-propynl-butyl carbonate, and 0.5% w/w cypermethrin. Before the application of Imersol-Aqua on the wood material, all kinds of drilling, cutting, turning, and milling operations should be completed and the relative humidity should be in equilibrium with the test environment. In the impregnation process, dipping duration should be at least 6 min and the impregnation pool must contain at least 15 liters of impregnation material for 1m 3 of wood. The impregnated wood should be left for drying for at least 24 h at 20 ± 2°C and 65% ± 3 (Hickson's Timber Impregnation Co. (GB), 2000).

Determination of density
The densities of wood materials, used for the preparation of test samples were determined according to TS 2472TS (1976. For determining the air-dry density, the test samples with a dimension of 20 × 30 x 30 mm were kept under the conditions of temperature at 20 ± 2°C and 65 ± 3% relative humidity until they reached to a stable weight. The weights were measured with an analytic scale of ± 0.01g sensitivity. Afterwards, the dimensions were measured with a digital compass of ± 0.01mm sensitivity. The air-dried densities (δ12) of the samples were calculated by the formula: (1) Where, W12 is the air-dry weight (g) and V12 is the air-dry volume (cm 3 ). The samples were kept at a temperature of 103 ± 2°C in the drying oven until they reached to a stable weight for the assessment of full dry density. Afterwards, the full dried samples were cooled in the desiccators containing phosphorus pentoxide (P2 O5). Then, they were weighted on a scale of ± 0.01g sensitivity and their dimensions were measured with a digital compass of ± 0.01mm sensitivity. The volumes of the samples were determined by stereo metric method and the densities (δo) were calculated by the formula: (2) Where, Wo is the full dry weight (g) and Vo is the full dry volume (cm 3 ).

Determination of humidity
The humidity of test samples before and after the impregnation process was determined according to TS 2471TS (1976. Thus, the samples with a dimension of 20 × 20 x 20 mm were weighed and then oven dried at 103 ± 2°C till they reach to a constant weight. Then, the samples were cooled in desiccators containing phosphorus pentoxide (P2O5) and weighed with an analytic scale of 0.01 g sensitivity. The humidity of the samples (r) was calculated by the formula;

Mo
Mo Where, Mr is the initial weight (g) and Mo is the full-dry weight (g).

Preparation of the test samples
The rough drafts for the preparation test and control samples were cut from the sapwood parts of massive woods and conditioned at a temperature of 20 ± 2°C and 65 ± 3% relative humidity for three months until reaching an equilibrium in humidity distribution. The samples for compression strength test, with a dimension of 20 × 20 × 30 mm were cut from the drafts having an average humidity of 12% according to TS 2595TS (1977. The samples for bending strength and modulus of elasticity in bending test, with a dimension of 20 × 20 × 400 mm were cut from the drafts having an average humidity of 12% according to TS EN 408 (2011). The densities and humidity values of all test samples were measured before the impregnation process. The test samples were impregnated according to ASTM-D 1413ASTM-D -76 (1976, TS 344 (2012) and TS 345 (2012). Accordingly, test samples were subject to 60 cm HgP -1P (vacuum) for 60 min and to diffusion at normal atmospheric pressure. Impregnated test samples were air-dried and then, weighed with 0.001g precision analytical balance and retention amount were calculated. The processes were carried out at 20 ± 2°C. Retention of impregnation material (R) was calculated by the formula: Where, G is the amount of impregnation solution absorbed by the sample (g), T2 is the sample weight after the impregnation (g), T1 is the sample weight before the impregnation (g), C is the concentration (%) of the impregnation solution and V is the volume of the samples (cm 3 ). Impregnated test samples were kept under a temperature of 20 ± 2°C and 65 ± 3% relative humidity until they reach a stable weight. Five types of impregnation materials (Tanalith-E, Imersol Aqua, Vacsol Azure, Boric acid and Borax), four test types (retention amount, compressive strength, flexural strength and modulus of elasticity) plus one control and ten replications for a total of 250 test samples were prepared.

Compression strength
The tests for compression strength parallel to grains of wood materials were carried out with Universal Testing Machine shown in Figure 1 , according to TS 2595, according to TS (1977. The capacity of Universal Testing Machine was 400 N. The speed of testing machine was adjusted to 5 mm/min. for crashing to occur in 1 to 2 min. Compression strength was calculated by the formula: Where, Fmax is the breaking load on the scale (N), a is the crosssectional width of test sample (mm), b is the cross-sectional thickness of the test sample (mm).

Bending strength
The tests for bending strength were carried out with the Universal Testing Machine shown in Figure 2 , according to TS 2474, according to TS (1976. The capacity of the Universal Testing Machine was 400 N. The speed of the testing machine was adjusted to 5 mm/min for breakage to occur in 1 to 2 min. Bending strength was calculated by the formula: Where, Fmax is the breaking load on the scale (N), L is the distance between the lower tension rods (mm), L1 is the distance between two loads (mm), b is the cross-sectional width of test sample (mm), and h is the cross-sectional thickness of the test sample (mm).

Modulus of elasticity (MOE) in bending
The tests for modulus of elasticity in bending were carried out with the Universal Testing Machine shown in Figure 2, according to TS 2478 (1976). The capacity of the Universal Testing Machine was 400 N. Deformations on the test samples were measured in the middle of the sample within a zone of five times the width of the sample by comparator. The deformations by incrementally increasing the forces were assessed with a sensitivity of ± 0.01mm. In the elastic deformation zone, modulus of elasticity was calculated by the formula: Where, ∆F is the difference between the arithmetic average of the upper and lower limits of applied force in the elastic deformation zone (N), ∆f is the net elastic deflection -difference between the measured elastic deflection in the upper and lower loading  limits-(mm), L is the span (mm), b is the cross-sectional width of test sample (mm), h is the cross-sectional thickness of the test sample (mm).

Data analysis
SPSS 15.0 for Windows program is used in the statistical analysis of the technological properties of the wood material tested. F-test was used to determine the differences between the technological properties of the impregnated samples. In this case, difference between the groups was significant (α = 0.05) confidence level compared with Duncan test.

Retention quantities
The amount of retention by Rowan wood according to the impregnation period is shown in Table 1. Retention amounts varied according to the type of impregnation material. The amount of retention multivariate analysis of variance of the effects of type of impregnation materials are given in Table 2.
According to the F test for the quantities of wood preservatives retention, retention volumes showed statistically significant score differences according to the type of wood preservatives (F (4; 45) = 168 926, P < 0.05). Duncan test results were given to determine the severity of the differences between the two groups in Table 3.

Compression strength
The statistical values of impregnated Rowan wood were given in Table 4. Compressive strength was approximately equal for all types of impregnating agents. Impregnation-treated samples gave better results than control samples. Multivariate analysis of variance on the effects of impregnation materials to compression strength was given in Table 5.
Compression strength values of Rowan wood impregnated with different agents showed statistically important differences in F test given in Table 5. (F (5; 54) = 15.142, P < 0.05) Duncan test results to define the degree of importance between the groups and were given in Table 6. Compression strength was the highest with Boric acid followed by Vacsol Azure, Borax, Imersol Aqua, Tanalith-E, and control samples as shown in Figure 3.

Bending strength
Bending strength values of impregnated Rowan wood were given in Table 7. Bending strength values of Rowan wood impregnated with different impregnation materials showed statistically important differences in F test given in Table 8. (F (5; 54) = 10.404, P < 0.05). Duncan test results to define the degree of importance between the groups and were given in Table 9. The highest bending    Compression strength (N/mm 2 ) Impregnation material       strength was measured in Imersol Aqua, Boric acid, and Tanalith-E' followed by Borax, Vacsol Azure, and control samples. Bending strength values were given in Figure 4.

Modulus of elasticity in bending
Modulus of elasticity in bending values of impregnated Rowan wood was given in Table 10. Modulus of elasticity in bending values of Rowan wood impregnated with different impregnation materials showed statistically important differences in F test F(5; 54) = 22.050, P < 0.05) as shown in Table 11. The highest Duncan test results was found for samples impregnated with Tanalith-E followed by Imersol Aqua, Borax, Boric acid, control, and Vacsol Azure (Table 12). Modulus of elasticity in bending was given in Figure 5.

RESULTS
According to the type of impregnation materials, retention amounts showed a statistically significant difference. This may be due to different concentration of impregnation solutions. The highest value retention was obtained in Vacsol Azure followed by Imersol Aqua, Tanalith-E, Borax, and boric. According to the type of impregnation material, the highest retention amounts were in Vacsol Azure samples (  . According to F test, modulus of elasticity in bending of impregnated samples was found significant (F (5; 540) = 22, P < 0.05). According to Duncan test, the highest modulus of elasticity was in Tanalith-E followed by Imersol Aqua, Borax, Boric acid, and Vacsol Azure As a result, the highest values in compression strength of Rowan wood was measured in samples impregnated with Boric acid, in bending strength impregnated with Imersol Aqua and in modulus of elasticity in bending impregnated with Tanalith. The lowest values were with Tanalith-E in compression strength, with Borax in bending strength, with Vacsol Azure in the modulus of elasticity in bending. According to this results Rowan wood may be impregnated with Tanalith-E to be used in the fields where compression strength, bending strength, and modulus of elasticity in bending are critical.
In general the results of this study on the mechanical properties of Rowan wood impregnated with various impregnation materials are compatible with the findings in literature on the effect of various impregnation materials on mechanical properties of different tree species. Togay (2009) found that except for oak samples, one time impregnation with timbercare aqua due to the increasing MOE and impregnation with timbercare aqua can be useful for the wood material subject to bending stress, which needs high elasticity.