TENSILE SHEAR STRENGTHS OF SOME TROPICAL WOODS BONDED WITH DIFFERENT ADHESIVES Selcuk DEMIRCI 1, Ali KASAL 2, Mehmet ACAR 2, Tolga KUSKUN 2 1 Ege University, Occupatinal High School of Ege, Furniture and Decoration Programme İzmir, Turkey 2 Mugla Sitki Kocman University, Department of Woodworking Industrial Engineering Muğla, Turkey Key words Tropical wood materials, PVAc adhesive, Polyurethan adhesive, Tensile shear strength. Abstract This study aims to determine the tensile shear strength of the three different tropical wood specimens bonded with different adhesives. Iroko (Milicia excelsa), Ayous (Abachi) (Triplochiton Scleroxylon), Anigre (Pouteria spp.) were used as wood species and one PVAc (D4-W) and two Polyurethan (PU), Cosmopur (K-W) and Polyurethan (PU), based adhesive were used as adhesives types in this study. Tensile shear strength of the adhesives was carried in accordance with the standards of BS EN 204 BS EN 205 respectively. According to the results, the highest value of tensile shear strength of wood species was observed from Iroko while the highest value of tensile shear strenght of adhesive observed with PVAc (D4-W) adhesive. In binary interaction of wood species and adhesives types were observed meaningless statistically. Corresponding author: selcuk.demirci@ege.edu.tr. Ege University, Occupatinal High School of Ege, Furniture and Decoration Program, Izmir, Turkey. 1. INTRODUCTION Recent years have seen a clear increase of interest in tropical wood species. Now it is used widely in the manufacture of furniture and elements of garden architecture. Iroko (Milicia excelsa), Ayous (Abachi) (Triplochiton Scleroxylon), Anigre (Pouteria spp.) are kinds of tropical wood which are used widely in furniture industry. Joints are created in form of fixed and demounted in the furniture manufacturing. In fixed joints, adhesives are used with different joint elements. Adhesives are widely used in furniture industry for many years. PVAc and Polyurethane based adhesives are the most used adhesives. These adhesives have a key role in the furniture industry. Gluing of wood parts is among the most effective methods for permanent joining of furniture elements in furniture production. Joints at corners of furniture are very important for the strength of furniture. Demirci et al. (2015). tensile shear strengths of some tropical woods bonded with different adhesives
Swardzevski (2002) asserts the most effective method is gluing in corner joint of furniture and constructional elements which were made by solid wood materials. Mostly, disconnection of glue line cause by technological mistakes during gluing process and applied unheterogen glue line effects cohesion of adhesive. The adhesive bonding of solid wood, wood particles of varying shapes and sizes, and wood fibres is necessary for the production of modern wood products, whether they are used for construction, for furniture, or for other applications. Owing to the importance of adhesive bonding, substantial research activities took place during the last decades. E.g. the influence of various physical and chemical properties of the adhesive and of the adherent was extensively reviewed by Dunky and Niemz (2002). Page 451 Ozcifci et al. (2008) studied the influence of mechanical surface treatment of wood which is to be bonded and the effect of fiber direction in the process of gluing. The wood species used was beech, oak, pine and poplar. The adhesives studied were phenol formaldehyde PVAc, urea formaldehyde and polyurethane. According to the results, the higher strength samples were recorded in beech laminated with PVAc. Researchers 1353 concluded that Beech bonded with PVAc is a great choice for wooden constructions production. Sogutlu et al. (2007) studied tensile shear strength of the local wood specimens which glued with one component PVAc D3, with two components PVAc D4 with the modification of 5 % hardener and polyurethane adhesives. According to result of the study, the tensile shear strength was found high on the high density wood material The highest value of tensile shear strength were observed on acacia wood bonded vith PVAc D4 (14,418 N/mm2 ) and the lowest value were determined on cedar wood bonded with PVAc D3 (6,249 N/mm2 ) adhesive respectively. In this study, it was aimed to determine tensile shear strength of three different tropical wood, Iroko (Milicia excelsa), Ayous (Abachi) (Triplochiton Scleroxylon), Anigre (Pouteria spp.), species bonded with different adhesives, PVAc (D4- W), Cosmopur (K-W) and Polyurethane (PU). As a result of the study, it will be possible to determine wood species and adhesive types for specific uses according to statistical data. This provides economical benefits for furniture industry. 2. MATERIAL AND METHOD Wood Material Iroko (Milicia excelsa), Ayous (Abachi) (Triplochiton Scleroxylon), Anigre (Pouteria spp.) were used as wood species in this study. These woods supplied randomly from local companies in Izmir. Attention has been paid to choose wood species to be without defects.
Adhesive In this study, PVAc (D4- W), Cosmopur (K-W) ve Polyurethane (PU) were used as adhesive types. Preparation of Test Specimens All wood materials were conditioned under 20 C and 65% ± 3 relative humidity until reached 12% moisture content (MC). Wood blocks were sliced as 5 mm and glue applied as counted 150-200 g/m 2 and pressed under 0.9 N/mm 2 during 60 min. Average MC was measured 12% ± 0,5. Page 452 Test specimens for determine tensile shear strenght were prepared according to TS EN 205. They were dimentioned as 10 x 20x 150 mm (Figure 1.) and in total 90 test specimens were prepared which consist 10 replication for each wood specie and adhesive type. Experimental design of the study was given in Table 1. Figure 1. Test specimen for tensile shear strength Table 1. Experimental design Wood species Adhesive Type Sample Quantity Total Iroko PVAc 10 30 Cosmopur 10 Polyurethan 10 Ayous PVAc 10 30 Cosmopur 10 Polyurethan 10 Anigre PVAc 10 30 Cosmopur 10 Polyurethan 10 Total 90
Test specimens of density were prepared in dimension of 25mm in parallel to grain and 20x20 mm (Figure 2.) according to TS 2740. In total 60 (3x20) density test specimens were prepared which include 20 specimens for each wood species. Page 453 Figure 2. Test specimen of density determination Method Moisture Content Moisture content of test specimens were determined according to TS 2741. For this purpose, weight of samples were measures with an analytical balance that has sensitivity ±0,01 g and dried under 103±2 o C in oven. Moisture content were calculated with following equation. M r M 0 R= -------------- M 0 M r : Wet weight M 0 : Oven-dry weight Density Densities of test specimens were determined according to TS 2472. For this purpose, test samples were conditioned under 20 ± 2 o C and 65% ± 5 relative humidity until samples reached stable weight. In the next step, sample s weight were measured with an analytical balance that is sensitive ±0,01 g and dimentions were measured with a digital calippers that has sensitivity 0,001 mm. Density of test samples at oven-dry were calculated following equation. M 12 δ 12 = ---------- V 12 M 12 : Oven-dry weight V 12 : Oven-dry volume Tensile Shear Strength Tensile shear strength was performed according to TS EN 205. Tests were performed with an universal testing machine which is 5 ton capacity in Mechanical Testing Laboratory of Wood
Science and Technology department at Mugla Sitki Kocman University. Tests were carried out 50 mm/min according to TS EN 205. Test setup was given at Figure 3. Page 454 Figure 3. Test setup With the test, it was tried to broke test samples from glue line by an applied balanced tensile force and get value of maximum strength (F max ) instant of failure. Tensile shear strength was calculated fallowing equation. F max F max σ y =--------- = ----------------------N/mm 2 l.b A A: Glued area (mm 2 ) b: Width of bond surface l: Length of bond surface Assesment of Results Values of tensile shear strength tests were used as data for statistical analyzes. Variance analyzes were done to determine effect of wood and adhesive on capacity of adhesion. In case of significance between groups, it was done LSD test in itself for each factor to determine success rating as split into homogenous group (HG). Statistics were done with MSTAT-C programme according to 0.95 confidence level.
3. RESULTS Density Airdry density of the test specimens were given in Table 3. Table 3. Density of wood species Wood Species Iroko Anigre Ayous X s X s X s 0.65 0.01 0.53 0.01 0.37 0.03 Density value (g/cm 3 ) Page 455 The highest air dry density values were got from Iroko (0,65 g/cm 3 ), Anigre (0,53 g/cm3) and Ayous (0,37 g/cm3) respectively. Tensile Shear Strength Tensile shear strength variance analyzes results of wood species and adhesive types were given in Table 4. Results of wood species and adhesive types were significant however, mutual effects of these factors were meaningless. Table 4. Result of Variance Analyzes Source Degrees of Sum of Squares Mean Square F Value P 0,05 Freedom Wood Specie (Factor A) 2 114943.356 57471.678 38.2786 0.0000 Adhesive Type (Factor B) 2 310738.822 155369.411 103.4826 0.0000 Factor A x Factor B 4 10762.911 2690.728 1.7921 0.1384 Error 81 121613.900 1501.406 Total 89 558058.989 LSD test results of wood species were given in Table 5. Table 5. LSD Results of Wood Species Wood Species X HG Iroko 159.20 A Anigre 128.60 B Ayous 72.87 C LSD : 19.91 X: Average HG: Homogenous Group According to table 5. the highest values were got from Iroko, Anigre and Ayous respectively. LDS test results of adhesive types were given in Table 6.
Table 6. LSD Test results of Adhesive Types Adhesive Type X HG PVAc 198.80 A Cosmopur 104.20 B Polyurethan 57.60 C LSD : 19.91 X: Average HG: Homogenous Group According to Table 5. the highest tensile shear strength values were got from PVAc, Cosmepur and Polyurethan respectively. Page 456 4. CONCLUSIONS In this study, it was investigated tensile shear strength of some tropical woods bonded with polyvinyl acetate and polyurethane based adhesives. According to result of the study, the highest values of tensile shear strength of wood species were got from Iroko ( 159.20 N/mm 2 ), Anigre (128.60 N/mm 2 ) and Ayous (72.87 N/mm 2 ) respectively. On the other hand, the highest values of adhesive types were got from PVAc ( 198.80 N/mm 2 ), Cosmopur (104.20 N/mm 2 ) and Polyurethan ( 57.60 N/mm 2 ). Binary interaction of wood species and adhesive types were analyzed meaningless statistically. As a result of the study, it can be said that tropical wood species of Iroko, Anigre and Ayous can be used more effectively with polyvinyl acetate based adhesives when compared with polyurethane based adhesives. Especially, PVAc adhesive was gave the highest tensile shear strength for all wood species. References BS EN 204, (1991), Non Structural Adhesives for Joining of Wood and Derived Timber Products, British Standards, England. BS EN 205, (1991), Test Methods for Wood Adhesives for Non Structural Applications Determination of Tensile Shear Strenght of Lap Joints, British Standards, England. Dunky M., Niemz P., Holzwerkstoffe und Leime, (2002), Technologie und Einflussfaktoren. Springer- Verlag Berlin-Heidelberg New York. Ozcifci A., Yapici F., (2008), Effects of machining method and grain orientation on the bonding strength of some wood species, Journal of Materials Processing Technology, 202, 353-358. Smardzevski, J., (2002), Technologial Heterogeneity of Adhesive Bonds in Wood Joints, Wood Science and Technology, 36 (3), 213 227. Sogutlu C., Dongel N., (2007), Tensile Shear Strengths of Some Local Woods Bonded with Polyvinyl Acetate and Polyurethane Adhesives, journal of Polytechnic, Vol: 10(3), pp: 287-293. TS 2470, (1976), Odunda Fiziksel ve Mekanik Deneyler İçin Numune Alma Metodları ve Genel Özellikleri, TSE Standardı, Ankara.
TS 2471, (1976), Odunda Fiziksel ve Mekaniksel Deneyler İçin Rutubet Miktarı Tayini, TSE Standardı, Ankara. TS 2472, (1972), Odunda Fiziksel ve Mekaniksel Deneyler İçin Birim Hacim Ağırlığı Tayini, TSE Standardı, Ankara. Corresponding author: Selçuk DEMİRCİ, Ege University, Occupatinal High School of Ege, Furniture and Decoration Program, Izmir, Turkey. Page 457 Author(s) 2015. This article is published under Creative Commons Attribution (CC BY) license.