Effect of Water Leaching on Photodegraded Scots Pine and Spruce Timbers Monitored by FTIR Spectroscopy

Eszter Visi-Rajczi,Tamás Hofmann,Edina Preklet,László Tolvaj

doi:10.3390/f12070833

Abstract

The goal of this research was the systematic study and comparison of the divided individual effects of UV light irradiation and water leaching during artificial weathering. Spruce (Picea abies Karst.) and Scots pine (Pinus sylvestris L.) samples were irradiated by ultraviolet (UV) light. Another sequence of samples was treated with the combination of UV irradiation and water leaching. The total extent of UV treatment was 20 days for both series of samples. Time relation of UV irradiation and water leaching was 2:1. The chemical changes were observed by FTIR spectroscopy. The difference spectrum was used for determination of the chemical changes. Degradation of lignin was greater for the leached samples than for the pure UV treated samples. Scots pine suffered greater lignin degradation than spruce, and produced higher absorption increase on the absorption region of unconjugated carbonyls. The unconjugated carbonyl groups were the most responsive chemical elements to leaching. Spruce was more susceptible to leaching of unconjugated carbonyl groups than Scots pine. Two absorption bands of unconjugated carbonyl groups at 1706 and 1764 cm−1 wavenumbers were produced by photodegradation. The absorption band at 1764 cm−1 was more sensitive to water leaching than the band at 1706 cm−1.

Highlights

Sunlight, rain, heat, frost, air humidity, atmospheric pollutants and other environmental factors affect the surfaces of wooden objects placed outdoors [1,2]
The chemical changes produced by the UV irradiation and water leaching were monitored by diffuse reflectance IR spectroscopy
The free radicals produced by the photodegradation react with oxygen and produce unconjugated carbonyl groups

Summary

Introduction

Rain, heat, frost, air humidity, atmospheric pollutants and other environmental factors affect the surfaces of wooden objects placed outdoors [1,2]. The attractive colour hue and colour variety of wood is sensitive to these environmental factors. Greying is generated mainly by the leaching effect of rain. Rain is able to leach out the water-leachable extractives and partly leach out the degradation products of lignin [2,3]. Afterwards, the pure grey cellulose remains on the surface [4]

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