Effect of Heat Treatment on Water Absorption of Chinese fir Using TD-NMR

Knowledge of the dynamic changes in the water absorption process of heat-treated wood is important for providing a scientific basis for the reasonable application of heat-treated wood, especially for outdoor applications. Nuclear magnetic resonance (NMR) techniques provide detailed information about the moisture components and moisture transport processes in wood, which are not available with other methods. In this work, water absorption of untreated and heat treated Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) heartwood was investigated using various NMR methods. The heat treatment temperatures were varied between 160 degrees C and 220 degrees C. According to the spin-spin relaxation time (T-2), there were two components of water in the samples heat-treated at 160 degrees C and 180 degrees C as well as the untreated sample, while three components of water were found in the samples heat-treated at 200 degrees C and 220 degrees C, and the mass of each component was calculated by the integral peak areas of the T-2 curve. The amount of bound water and free water in heat-treated samples were less compared to the untreated ones, and the water absorption decreased correspondingly, due to the increasing heat-treated temperature. The results obtained by one dimensional frequency coding indicated that the heat treatment made wood difficult to be accessed by moisture. Besides, NMR images revealed that the free water absorption in latewood was faster than in earlywood, but earlywood could absorb more water than latewood.