Structural Changes in Wood under Artificial UV Light Irradiation Determined by FTIR Spectroscopy and Color Measurements – A Brief Review

Spruce and beech samples were irradiated by UV light in humid (100% air humidity) and dry conditions to clarify the effects of vapor on photodegradation. UV-irradiated samples were also soaked in distilled water for comparison. The color change and the IR absorption spectra were measured. The wet condition generated considerably greater discoloration than did the dry condition. The intensity of the color change was higher at elevated temperature (53 °C) than at 32 °C. The results showed that the presence of water as vapor increased the degradation of lignin. The nonconjugated carbonyl groups absorbing around 1760 cm -1 were found not to be stable, and the number of these chemical groups decreased in the presence of vapor when compared against the dry condition. The rising temperature amplified this degradation effect.

Section: Infrared Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of Air Relative Humidity and Temperature on Photodegradation Processes in Beech and Spruce Wood

Tolvaj¹,

Popescu²,

Molnár³

et al. 2015

“…Light-induced ageing is a complex and dynamic process of photodegradation, primarily related to lignin decomposition by UV light through a stepwise mechanism involving formation of phenoxyl free radicals and their further reaction with oxygen to produce carbonyl-containing chromophore groups (Fengel and Wegener 1984;Williams 2005;Teacă et al 2013). Visible light up to 515 nm, which penetrates deeper into wood, also contributes to surface and especially sub-surface color changes (Živković et al 2014), though it does not affect lignin (Kataoka et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Effects of Ageing on the Color and Surface Chemistry of Paulownia Wood (P. elongata) from Fast Growing Crops

Liu¹,

Timar²,

Varodi³

et al. 2016

The behavior of paulownia wood (Paulownia elongata) was investigated using three different ageing tests: simulated natural ageing under the influence of light under indoor conditions, temperature-induced ageing in the dark, and UV-induced ageing. Ageing effects were evaluated by color measurements in the CIE Lab system. Simulated natural ageing of wood in indoor conditions (6 months) and UV-accelerated ageing (72 h) are complex and dynamic processes, which resulted mostly in yellowing of the samples due to photo-degradation. Temperature-induced ageing (288 h at 100 C) resulted mostly in a rapid and visible darkening of the paulownia wood. Comparative in-time evolution of color changes during accelerated UV ageing testing and simulated natural ageing testing under indoor conditions allowed the estimation of an acceleration index of about 50X. Fourier transform infrared spectroscopy (FTIR) was used to examine specific chemistry changes occurring during these ageing tests. UV light from natural or artificial sources caused primarily lignin degradation followed by oxidative processes leading to carbonylcontaining chromophores. Temperature-induced partial degradation of hemicelluloses and oxidative processes resulted in the formation of chromophores containing mostly conjugated carbonyl groups. This research highlighted that paulownia wood (P. elongata) is quite sensitive to ageing under the action of light and temperature, which cause notable color and surface chemistry changes.

“…In the case of the pine wood samples treated with acid and alkaline buffer, yellowing of the surface under light exposure was the primary colour change caused by the photodegradation. The changes in this coordinate indicate alternation of lignin and hemicellulose with the occurrence of unstable products (Müller et al 2003;Teacă et al 2013). Samples treated with acid buffer and then exposed to 340 nm light were the yellowest (Fig.…”

Section: Colour Changes Due To Irradiationmentioning

confidence: 99%

“…coating, chemical and thermal modification as well as surface impregnation). The influence of wood finishing has been previously described (Jankowska and Szczęsna 2011; Hochmańska et al 2014;Teacă et al 2013). In the furniture industry it is very important to improve aesthetics and protective properties such as resistance to light.…”

Section: Introductionmentioning

confidence: 98%

Analysis of Photodegradation Process of Pinus sylvestris L. Wood after Treatment with Acid and Alkaline Buffers and Light Irradiation

Zborowska¹,

Stachowiak-Wencek²,

Nowaczyk-Organista³

et al. 2015

The purpose of this investigation was to evaluate the effect of acid and alkaline treatment of pine wood on photodegradation. The work presented here deals with changes in the wood colour and infrared spectrum caused by UV light. The colour changes were monitored with a reflectance spectrophotometer. The analysis of the colour changes in wood surfaces was carried out by measuring CIE L*a*b* parameters. Infrared spectroscopy was used to study chemical changes occurring on the surface of wood samples caused by light. Wood treated with alkaline buffer was characterized by higher brightness changes than wood treated with acid. The surface of samples treated with alkaline buffer revealed similar resistance to photodegradation against both outdoor and indoor light. Greater changes in colour were detected in the case of samples treated with acid and exposed to outdoor light in comparison to indoor light. FTIR results showed degradation in the lignin structure both in the case of samples treated with acid and alkaline buffer and exposure to outdoor and indoor irradiation. The difference between the samples treated with UV 340 nm and UV 351 nm irradiation was seen in the 1512 cm -1 band.