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

Abstract

Spruce samples (Picea abies Karst.) were irradiated by a strong ultraviolet (UV) light emitter mercury lamp, and another 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 10 days. One treatment cycle consisted of 24 h of UV irradiation, followed by 6 h of water leaching. This cycle was repeated 10 times. The chemical changes were determined by IR spectroscopy, and the difference spectrum method was used for evaluation. The IR measurement was carried out after each UV radiation as well as after water leaching, to determine the effect of UV radiation and water leaching separately. The lignin degradation was more significant for the leached samples than for the pure UV treated samples. The chemical components most sensitive to leaching were the unconjugated carbonyl groups generated by the photodegradation. As a consequence of photodegradation, two absorption bands of unconjugated carbonyl groups emerged at 1714 and 1750 cm−1 wavenumbers. The band at 1750 cm−1 was much more sensitive to leaching by water than the band at 1714 cm−1. This band almost disappeared after eight cycles. The water was able to leach out carbonyl groups (absorbing at 1741 cm−1) that had been present in the wood originally as well.