Yazar "Yildiz, Umit C." seçeneğine göre listele

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    Effect of artificial weathering on the properties of heat treated wood
    (Elsevier Sci Ltd, 2013) Yjidiz, Sibel; Dizman Tomak, Eylem; Yildiz, Umit C.; Ustaomer, Derya
    This study aims to investigate the change in chemical composition, surface characteristic and mechanical properties of heat treated four wood species (ash, iroko, Scots pine and spruce) during artificial weathering from 400 h to 1600 h in relation to their color changes, surface roughness, compression strength, modulus of elasticity, modulus of rupture and surface composition. Original color of wood species was significantly changed by heat treatment and artificial weathering. Artificial weathering decreased color change of heat treated wood samples except for iroko. Color change significantly increased with longer weathering exposure for heat treated wood samples however similar trend was not observed for control samples exposed to weathering factors. In general, heat treatment alone did not have a considerable effect on surface roughness of wood. Heat treatment seemed to protect wood surface to become rougher after weathering for softwoods. Compression strength and MOR of samples decreased while MOE increased during heat treatment. Compression strength, MOR and MOE of samples decreased considerably with longer weathering exposure both for heat treated and control samples. Softwood species seemed to be more affected by heat and weathering than hardwood species did with respect of loss on the strength properties. Severe delignification and hemicellulose degradation occurred in heat treated and control samples for all wood species during weathering from 400 h to 1600 h evident from rapid decrease at 1504/1508 cm(-1) and 1730 cm(-1), respectively. Heat treatment did not fully protect hemicellulose degradation and delignification occurred by weathering with longer exposure periods. (C) 2013 Elsevier Ltd. All rights reserved.
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    An FT-IR study of the changes in chemical composition of bamboo degraded by brown-rot fungi
    (Elsevier Sci Ltd, 2013) Dizman Tomak, Eylem; Topaloglu, Elif; Gumuskaya, Esat; Yildiz, Umit C.; Ay, Nurgul
    The objective of this study was to use FT-IR analysis to investigate the chemical composition of aged and un-aged bamboo specimens, with and without node sections, decayed by brown-rot fungi. Specimens were exposed to two brown-rot fungi, Coniophora puteana and Poria placenta, for 8 weeks after which decay was assessed by weight loss and FT-IR spectra analysis. Depending on the bamboo section examined, the aging process reduced decay resistance of specimens. Weight loss (measured as a percentage) decreased from the top to the bottom portion of bamboo culms. The presence of nodes in the specimens increased weight loss caused by P. placenta attack, and caused only a slight increase in weight loss from C puteana attack. Significant chemical changes in bamboo were observed after fungal degradation, as revealed by FT-IR analyses. Consistent with the degradation mechanism of brown-rot fungi, lignin was essentially un-degraded or modified. Both brown-rot fungi caused a sharp decrease in the carbonyl absorption area. Surprisingly, cellulose peaks of degraded specimens were nearly similar to the peaks of control specimens. Aging treatments and biodegradation affected the crystalline structure of bamboo specimens. Poria placenta degraded wood components faster and changed the crystallinity more than C puteana did, in accordance with the weight losses due to decay. (C) 2013 Elsevier Ltd. All rights reserved.