Effect of high-intensity microwave (HIMW) treatment on chemistry of radiata pine

This study investigated the effect of high-intensity microwave (HIMW) treatment on the chemistry of sapwood and heartwood of radiata pine. The wet chemical method, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) were utilized to assess and evaluate the effect of different microwave energy densities (0, 60, 80, and 100 kWh/m 3 ) on the chemical composition, chemical structure, and cellulose crystallinity of both sapwood and heartwood. The results indicated that the greatest changes in the relative content of lignin and cellulose were observed at a microwave energy density of 80 kWh/m 3 . Furthermore, XPS analysis demonstrated a decrease in the O/C ratio as the microwave energy density increased. When the energy density of microwave reached 100 kWh/m 3 , the O/C ratio of sapwood and heartwood decreased by 10.2% and 19.6%, respectively. At the same time, no notable changes were detected in the FTIR spectra of the microwave-treated samples. Due to the recrystallization of cellulose and the presence of aromatic C=O groups, which could be linked to the rise in lignin content, there were slight variations in several absorption intensities and peak positions, such as O–H groups. As microwave energy density increased, both the crystallinity index (CI) and cellulose crystal width ( D 200 ) of HIMW-treated samples increased accordingly. The findings indicated that the chemistry of radiate pine’s sapwood and heartwood was affected differently by the microwave treatment. Notably, the heartwood exhibited a more pronounced impact compared to the sapwood.