Leaching effect of water on photodegraded hardwood species monitored by IR spectroscopy
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Leaching effect of water on photodegraded hardwood species monitored by IR spectroscopy Denes Varga1 · Laszlo Tolvaj1 · Zsolt Molnar2 · Zoltan Pasztory3 Received: 15 March 2020 / Published online: 19 September 2020 © The Author(s) 2020
Abstract Black locust (Robinia pseudoacacia L.), beech (Fagus sylvatica L.), aspen (Populus tremula L.) and sessile oak (Quercus petraea Liebl.) hardwood samples were irradiated by a strong ultraviolet (UV) emitter mercury lamp at 50 °C. Other series of specimens were exposed to a combined treatment of UV irradiation and water leaching. Ratio of UV radiation and water leaching time was 2:1. While the total duration of UV radiation was 20 days for both test series that of water leaching was 10 days. IR measurement was taken after both UV radiation and water leaching to monitor both effects separately. Lignin degradation proved to be more intensive in leached samples than in purely UV-irradiated samples. Guaiacyl and syringyl lignin showed similar degradation properties. Unconjugated carbonyl groups generated by the photodegradation were the most sensitive chemical components to leaching. Photodegradation generated two absorption bands of unconjugated carbonyl groups at around 1710 and 1760 cm−1 wavenumbers. The band at 1760 cm−1 was much more sensitive to water leaching than the band at 1710 cm−1. Three to ten days of water leaching was enough to remove all unconjugated carbonyls generated by the photodegradation, depending on the species. Sessile oak was the most sensitive species to water leaching, whereas black locust proved to be the most stable against both photodegradation and water leaching. Water was able to leach out unconjugated carbonyl groups (absorbing at 1745 cm−1) originally present in all investigated wood species.
* Laszlo Tolvaj tolvaj.laszlo@uni‑sopron.hu 1
Institute of Physics and Electrotechnics, University of Sopron, Bajcsy‑Zs. u. 4, Sopron 9400, Hungary
2
Institute of Wood Machinery, University of Sopron, Bajcsy‑Zs. u. 4, Sopron 9400, Hungary
3
Innovation Center, University of Sopron, Bajcsy‑Zs. u. 4, Sopron 9400, Hungary
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Vol.:(0123456789)
1408
Wood Science and Technology (2020) 54:1407–1421
Introduction Wood is a renewable material bonding large amounts of carbon. Growing trees absorb carbon dioxide from the atmosphere and convert it to woody biomass (Bravo et al. 2017). Half of the total wood mass is bonded carbon absorbed from the atmosphere. From an environmental aspect, it is important to store this carbon in wood products as long as possible ensuring slower wood decomposition and a long-term carbon cycle (Sathre and Gustavsson 2009; Keith et al. 2015). Taking into account the forested area of our planet, a significant amount of carbon can be stored in wood material for decades or even centuries, depending on the application. Therefore, wood products can play a significant role in the fight against global warming induced by greenhouse gases. Whether trees naturally decompose or burn, carbon dioxide is emitted back into the atmosphere. Carb
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