WOOD RESEARCH Volume 69, Number 2, 2024
EDINA PREKLET, LASZLO TOLVAJ, and DENES VARGA

INFRARED SPECTRUM CHANGE OF UV IRRADIATED AND NATURAL WOOD SAMPLES DURING 12 YEARS OF STORAGE IN TOTAL DARKNESS

The stability of the surface of UV-irradiated wood samples was investigated after 12 years of storage in total darkness at room temperature. The investigated specimens were earlywood and latewood of Scots pine sapwood, earlywood and latewood of spruce, earlywood of ash, beech and hybrid poplar. The thin (1 mm tick) samples contained only earlywood or latewood, and the tangential surfaces were used for infrared spectrum measurement. For comparison, the non-irradiated natural surface (back side) of the specimens was used for infrared spectrum measurement. Natural wood surfaces were stable during the storage. Only ether linkages in hemicelluloses showed minor degradation at 1175 cm-1 wavenumber. Lignin molecules remained stable during the 12-year storage period on both UV irradiated and non-irradiated side of the specimens. In contrast, UV irradiated samples suffered alterations during the 12 years of thermal treatment at low temperature (20-25°C). Hemicelluloses in photodegraded surface layers underwent thermal degradation and oxidation processes, generating new carbonyl groups. Extractives also presented absorption increase in the conjugated carbonyl region

WOOD RESEARCH Volume 66, Number 4, 2021
DENES VARGA, LASZLO TOLVAJ, and EDINA PREKLET

Colour stability of steamed black locust, beech and spruce timbers during short-term photodegradation

Black locust (Robinia pseudoacacia L.), beech red heartwood (Fagus sylvatica L.) and spruce (Picea abies Karst.) wood samples were treated in saturated steam at 100, 110 and 120°C then irradiated using a UV emitter mercury lamp in order to test their colour stability. Colour change was evaluated and presented in the CIE Lab colour coordinate system. Untreated black locust, beech and spruce specimens as control samples were irradiated using the same mercury lamp. Results revealed that beech produced the greatest colour stability during both steam treatment and the following UV treatment while spruce was the most sensitive species to photodegradation. Steaming reduced the colour change intensity only for black locust during photodegradation. Both redness and yellowness change demonstrate this colour stability increase. Steaming at 120°C resulted in the greatest protection against the colour alteration of black locust caused by photodegradation. The investigated thermal treatments did not change the photodegradation properties of beech and spruce specimens. A considerable increase in colour saturation of the specimens was generated by steaming, and the saturation value further increased during the UV treatment.

WOOD RESEARCH Volume 64, Number 5, 2019
EDINA PREKLET, LASZLO TOLVAJ, Endre A. Banadics, Tibor Alpar, and DENES VARGA

Colour modification and homogenisation of larch wood by steaming

Larch (Larix decidua L.) wood samples were steamed applying broad range of steaming time (0-20 days) at 90°C and 110°C steaming temperatures. The colour change was monitored by objective colour measurement using the CIE Lab colour system. The initial colour of earlywood and latewood within sapwood and heartwood has highly different values for larch wood. Wide range of colours was created by steaming between the initial colour and brown colour depending on the steaming time and temperature. The steaming produced excellent colour homogenisation and resulted in an increase of saturation. The redness showed the greatest homogenisation effect. The redness value difference among the tissues was seven times smaller after 9 days of steaming at 110°C than the initial redness difference. The yellowness values increased and moved toward each other during steaming. The results showed that the best visualisation effect of homogenisation can be presented on the a*-b* plane. The colour saturation of the examined tissues increased considerably and showed homogenisation effect as well. Because of the colour homogenization, it was difficult to differentiate sapwood and heartwood at the end of the steaming process at 110°C. The effective steaming time for colour homogenisation was 5 and 2 days at 90°C and 110°C, respectively.

WOOD RESEARCH Volume 65, Number 6, 2020
Zoltan Pasztory, LASZLO TOLVAJ, and DENES VARGA

Effect of water leaching on photodegraded poplar wood monitored by IR spectroscopy

Poplar (Populus x euramericana cv. pannonia) samples were irradiated using ultraviolet light emitter mercury lamp. Other series of specimens were treated with the combination of UV radiation and water leaching. The total duration of UV radiation for both series of specimens was 20 days. The total duration of water leaching was 10 days. One cycle of the combined treatment consisted of 2-day UV radiation followed by one day water leaching. The IR measurement was carried out after both UV radiation and water leaching to monitor both effects separately. Lignin degradation of water leached samples was found to be greater than that of the solely UV treated samples. The guaiacyl and the syringyl lignin showed similar degradation properties. The unconjugated carbonyl groups generated by the photodegradation proved to be the most sensitive chemical components to leaching. As a consequence of photodegradation, two absorption bands of unconjugated carbonyl groups were grown up at 1715 and 1759 cm-1 wavenumbers. The band at 1759 cm-1 was much more sensitive to water leaching than the band at 1715 cm-1. Ten days of water leaching was long enough to remove all unconjugated carbonyls generated by the photodegradation. The water was able to leach out carbonyl groups (absorbing at 1745 cm-1) originally presented in poplar wood as well.