Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı

Utilization of Bark Tannins from Oriental Spruce (Picea orientalis) and

Oak (Quercus spp.) in Bioadhesive Production
In this PhD dissertation, bio-based tannin adhesives were developed by using tannins from spruce (Picea orientalis) and oak (Quercus spp.). The barks were obtained from wood based panel industry and forest residues. Spruce barks were obtained from Artvin and Trabzon area while oak barks were supplied by Kastamonu Integrated Wood Industry and Trade Inc., Kastamonu Turkey.
Basic chemical analyses were performed to determine chemical composition of the bark samples. Then hot water, sodium sulfite, sodium carbonate, and urea solutions were used for tannin extraction from bark with different extraction parameters and then the extraction stage were optimized. Afterwards, the tannin powders were produced with a spray dryer based on the observations during the extraction process. Chemical analyzes were performed to determine the chemical structure of the spruce and oak tannins. After that bioadhesive synthesis experimentals were carried out using the spruce and oak tannins. In the experimentals, the bioadhesive synthesis parameters such as pH, formaldehyde:tannin molar ratio, viscosity, and free formaldehyde content were optimized. Physical and chemical properties of the bioadhesives were determined. Finally, the adhesion performance of the bioadhesives were determined using a TMA instrument with three-point bending test.
Ash content values of the barks obtained from Artvin and Trabzon area were 4,31% and 3,99%, respectively, while the oak bark samples were 10,02%. Hot water solubility of the spruce bark samples were higher than the oak bark samples. Residual lignin contents of Artvin spruce, Trabzon spruce, and oak were 19,53%, 20,61%, and 18,49%, respectively, while α-cellulose contents were 37,28%, 37,92%, and 41,59%, respectively. The results of the total phenol and butanol-HCl assay showed that Artvin spruce barks had higher values than other bark samples. As hydrolysable tannins, there were gallo tannins in the samples of spruce and oak barks whereas ellagic tannins were not found.
At the bark extraction stage, 2,5% sodium sulfit + 0,50% sodium carbonate solution, 1:8 bark:solution ratio, and one hour extraction time were obtained as an optimum result. The pH of hot water extraction solutions were around 4,5 while the pH of sodium sulfide and sodium carbonate solutions were about 7. The hide powder method used in this study indicated that non-tannin fraction of the oak tannin and oak sulfited tannin were higher than the spruce tannin and spruce sulfited tannin.
Many adhesive formulations were developed with the spruce and oak tannins. The results obtained in this work clearly showed that the shelf life and free formaldehyde content values of the adhesives were affected by the formaldehyde:tannin molar ratios. As for the maximum shelf life values of the bioadhesives, the spruce tannin adhesive had 72 days shelf life, whereas the oak tannin adhesive had 38 days. The gelation time values related with pH were also examined. The findings demonstrated that the spruce and oak sulfited tannins had higher gelation time values than those of the water tannins. To determine adhesion performance of the bioadhesives, modulus of elasticity (MOE) were carried out by a TMA instrument with 3-point bending test. It was concluded that the spruce tannin based bioadhesives had similar adhesion performance as compared with a commercial phenol formaldehyde adhesive