Use of tannin-based bioadhesives prepared from different barks in particleboard production and performance properties

The production of wood composites is mainly based on petrochemical-based and formaldehyde-containing adhesives such as urea formaldehyde (UF), phenol formaldehyde (PF) and melamine urea formaldehyde (MUF), which may pose health and environmental problems under certain conditions. The aim of this study is to reveal the effect of a renewable tannin-based adhesives on the potential values for particleboard production. In this PhD dissertation, the production of bio-based tannin adhesive has been carried out. The tannins used in the synthesis of bioadhesive were obtained from industrial waste red pine (Pinus brutia) bark emerged from Kastamonu Integrated Wood Industry and Trade Inc. in Balıkesir and waste maritime pine (Pinus pinaster) bark in the raw material warehouse of Industrial Timber Design and Trade Inc. (ENAT) located in Bursa Karacabey Region. For tannin extraction from the bark samples, the extraction studies were carried out with hot water, sodium sulfite+sodium carbonate, urea and borax solutions at the determined ratios. Afterwards, the properties of 40% tannin solutions such as tannin solid content, viscosity, pH and density were revealed by determining the styasny and yield values in the obtained aqueous tannin solutions. In the next stage, bioadhesive production was carried out using red pine and maritime pine tannin. In order to reveal the properties of the obtained bioadhesive, the solid, gel time, viscosity, pH and density values of the glue were determined, structural characterization of the bioglue samples was performed using FTIR analysis, and their thermal decomposition was used through Thermogravimetric Analysis (TGA) and Differential Scanning Calorimeter (DSC) was used to elucidate curing process. In addition, surface tension and adhesion test (lap shear) values were determined in the glues. At the same time, XRD analyzes were performed on powdered tannin solutions and tannin bioadhesives. In tannin yield values in bark aqueous tannin solutions, the highest yield was determined in the sodium sulfite extraction of red pine with 23,72%, while the lowest yield value was determined in samples extracted with maritime pine water with 6.11. In terms of Stiasny number values, the highest was determined as 107,65% in red pine urea tannin solution, while the lowest was determined as 74,12% in red pine sulfide tannin solution. After identifying the bioadhesive properties, particle board production with a thickness of 16 mm and a density of 640 kg/m3 was carried out with each bioadhesive sample. The physical and mechanical properties of the obtained particle boards were identified. Additionally, formaldehyde emission value on the particle boards, contact angle, bioadhesive-wood surface interaction imaging with light microscope (LM), microstructural characterization using scanning electron microscopy (SEM) and finally the fire resistance values of the boards samples were determined. When the test results were examined, the highest moisture content values of the boards produced with red pine and maritimepine bioadhesive were determined in the boards produced with red pine sulfide bioadhesive (KSB), whereas the lowest value was determined in the boards produced with maritime pine urea bioadhesive (SÜB). In general, the moisture values given in the three-layer particle board standards were provided only by the boards produced with maritime pine urea bioadhesive (SÜB) from bioadhesive, while the closest values were identified in the boards produced with red pine urea bioadhesive (KÜB). All the boards produced with bioadhesives meet the standard values for water absorption rates, while in terms of thickness swelling (2 hour) high values were obtained in boards produced with adhesives other than KÜB and maritime pine sulfite bioadhesive (SSB). No statistical difference was found on the density distributions of the boards. According to the mechanical tests results, the values closest to UF were found in the case of KÜB boards in the relationship between bending resistance and elasticity modulus in bending. The highest value in terms of the effect on surface strength is also observed in the KÜB sample. With regard to tensile strength values, the control group showed results closest to UF in the boards produced with KÜB, while the highest values after KÜB were found in the SSB, SÜB, KSB and KB boards samples, respectively. Whereas formaldehyde emission in the boards gave low (good) results in all bioadhesives, the highest (bad) formaldehyde emission values were seen in commercial UF. In addition to these, studies such as contact angle, light microscopy imaging, SEM, and fire resistance were also conducted. With a view to the contact angle test result, the highest contact angle was found in the KÜB sample, following UF. The light microscopy imaging and SEM analysis results demonstrated that the boards produced with KÜB and SSB samples, along with UF, indicated better penetration properties. Based on the fire resistance results, the flame height was found to be lower in the boards produced with all bioadhesives compared to UF.