Microfibril angle, crystalline characteristics, and chemical compounds of reaction wood in stem wood of Pinus densiflora

This study aimed to observe and to compare the microfibril angle (MFA), crystalline characteristics, and chemical compounds in compression wood, lateral wood, and opposite wood in the stem wood of Korean red pine (Pinus densiflora). The MFAs of compression wood, lateral wood, and opposite wood were determined using iodine methods and optical microscopy, and the crystalline characteristics and chemical composition were measured by an X-ray diffraction method and FTIR spectroscopy, respectively. The compression wood had the greatest MFA, whereas the opposite wood showed the smallest MFA. The relative crystallinity of compression wood was the lowest, whereas the opposite wood showed a slightly greater value than lateral and compression woods. The crystal widths of compression wood were slightly smaller than those of lateral wood and opposite wood. Compression wood and lateral wood showed more significant peaks for lignin in juvenile wood, while opposite wood showed higher peaks due to the carbohydrate peaks. Compression wood showed greater peaks representing lignin in mature wood, while lateral and opposite woods showed higher peaks in carbohydrates. The MFA of P. densiflora was decreased with increasing growth ring number. The relative crystallinity from each part was increased with increasing growth rings, whereas the crystal width showed no radial variation. Juvenile wood showed more significant peaks for lignin, while mature wood showed higher peaks for carbohydrates. In conclusion, compression, lateral, and opposite woods showed a distinct difference in the MFA, crystalline characteristics, and chemical compounds, whereas the MFA, relative crystallinity, and chemical compounds of compression, lateral, and opposite woods showed a radial variation.