Temperature dependence of wood photodegradation. Part 2: Evaluation by Arrhenius law

Abstract

The temperature dependence of photodegradation for wood was evaluated applying the Arrhenius law. Hardwood (beech, Fagus sylvatica L. and poplar, Populus x euramericana cv. Pannonia) and softwood (Scots pine, Pinus sylvestris L. and spruce Picea abies Karst.) species were involved in the test. Samples were irradiated by a strong UV emitter mercury lamp at 30 °C, 80 °C, 120 °C and 160 °C. The chemical changes were detected by diffuse reflectance infrared spectroscopy. The absorption changes were determined by difference spectrum method. After IR data processing, the dominant seven IR bands were selected for generating the Arrhenius plots for all examined species.The results show that the Arrhenius law is useful in interpreting the kinetics of some photochemical reactions during the photodegradation of wood. The photodegradation of guaiacyl lignin absorbing at 1270 cm−1 was found a single rate-limited, thermally activated process for all examined species. These results indicated that the temperature dependence of this degradation was exponential. The absorption increase of quinones at 1596 cm−1 and the absorption decrease of ether bond in cellulose and hemicellulose at 1175 cm−1 also showed exponential temperature dependence for conifers.In most of the cases, at least two different (and sometimes antagonistic) types of chemical changes generated absorption change at the same wavenumber region. In these situations, the Arrhenius equation was unable to indicate whether the temperature dependence is exponential or not.