Color changes in wood during heating: kinetic analysis by applying a time-temperature superposition method

This paper deals with the kinetics of the color properties of hinoki (Chamaecyparis obtusa Endl.) wood. Specimens cut from the wood were heated at 90-180°C as accelerated aging treatment. The specimens completely dried and heated in the presence of oxygen allowed us to evaluate the effects of thermal oxidation on wood color change. Color properties measured by a spectrophotometer showed similar behavior irrespective of the treatment temperature with each time scale. Kinetic analysis using the time-temperature superposition principle, which uses the whole data set, was successfully applied to the color changes. The calculated values of the apparent activation energy in terms of L*, a*, b*, and ΔE*ab were 117, 95, 114, and 113 kJ/mol, respectively, which are similar to the values of the literature obtained for other properties such as the physical and mechanical properties of wood. Introduction Kinetic analysis has been successfully used to describe the temperature dependence of the reaction rate in chemical reactions. Applying kinetic analysis to wood and wood compounds allows one to predict the pyrolysis or deterioration of lignocellulosic materials. The kinetics of pyrolysis has been widely studied in the high temperature zone due to growing demand for lignocellulosic biomass as an alternative energy resource [1-5], while at the lower temperature zone they have been applied to the accelerated aging phenomena of materials to understand their natural aging [6-10]. Among the wood properties that change during low temperature heating, as reviewed by Esteves et al. [11], wood aging kinetics generally applies to properties such as weight loss, modulus of elasticity (MOE), modulus of rupture (MOR), and thermogravimetric data. However, these properties may require a destructive test on defect-free specimens, and the initial values that are needed, especially for ha l-0 07 02 69 6, v er si on 1 31 M ay 2 01 2 Author manuscript, published in "Applied Physics A: Materials Science and Processing 99, 1 (2010) 47-52" DOI : 10.1007/s00339-010-5542-2