Nanostructural Cell Wall Changes Due to Thermal Degradation in Wood

Pyrolysis of wood involves the thermal degradation of the wood polymers and the formation of char. Understanding how char forms, particularly, in terms of the nano-structural changes that take place during pyrolysis will inform fire models to ensure fire safety in timber structures. Here, small- and wide-angle x-ray scattering (SAXS/WAXS) based tomography were used to study how thermal degradation changes wood nanostructure across the pyrolysis zone in Douglas-fir. The changes in the aggregation of cellulose elementary fibrils (via SAXS) as well as changes in the cellulose crystallinity (via WAXS) were measured. Tomographic reconstructions from the scattering contrast and absorption data were computed to visualize and quantify these changes across the entire cellular structure of the samples. Preliminary results revealed relatively abrupt changes in the cellulose crystallinity as the wood polymers are thermally degraded. With SAXS we observed changes in the overall intensity as a function of thermal degradation, which suggests that the packing of the elementary fibrils may be modified as some of the polymers are degraded.