Analysis of stress relaxation on the basis of isolated relaxation spectrum for wet wood

In this study, we investigated the relaxation properties of wet wood based on spectra isolated from the whole wood relaxation spectrum, calculated using Alfrey’s approximation at temperatures ranging from 25 to 85 °C. Three relaxation processes were identified, I, II, and III, in the order of low to high temperature, and these were attributed to local molecular motions of hemicellulose, lignin, and cellulose, respectively. Processes I and II (but not III) depended on temperature and the apparent activation energy, which was calculated from the temperature dependence of their relaxation time and was approximately 85 kJ/mol (20 kcal/mol) for both processes. The peak positions and intensity of the isolated relaxation spectra indicated that the molecular motion of the relaxation processes in the temperature range studied represent not whole molecular motion, but rather local molecular motion of the hemicellulose and lignin matrix. This study also demonstrated that the isolation procedure using a Gaussian function can be used to analyze the relaxation process of wood.