Fourier Transform Infrared Studies of Heterogeneity, Photodegradation, and Lignin/Hemicellulose Ratios within Hardwoods and Softwoods

There is little information available on the variation in lignin content of growth rings in hardwoods. This study examines whether infrared microscopy can detect intra-incremental differences in the chemical composition of three hardwoods (R. pseudoacacia, P. Americana, and G. triacanthos) and the effect of such differences on the delignification of the hardwoods during weathering. Earlywood has higher lignin content than latewood in R. pseudoacacia and P. americana, but the opposite was found for G. triacanthos. The delignification of the earlywood and latewood during weathering varied for the three species. It was greater in the earlywood of R. pseuoacacia, whereas in P. americana and G. triacanthus it was more pronounced in latewood. Differences in density and lignin content of earlywood and latewood help explain these differences. In addition, a deconvoluting software package was used to determine whether it is possible to estimate the lignin/hemicellulose ratio in softwoods and hardwoods. Results from the 1760–1580 cm−1 region provided data that can be used to estimate the lignin/hemicellulose ratio of softwoods and hardwoods. This information can be obtained far more easily using infrared microscopy than with conventional wet chemical techniques, potentially allowing characterization of greater numbers of species than has hitherto been possible.