Synergistic effects of partial hemicellulose removal and furfurylation on improving the dimensional stability of poplar wood tested under dynamic condition

Two-step treatment involving partial hemicellulose removal and furfurylation was proposed to improve the dynamic dimensional stability of fast growing poplar wood (Populus euramericana Cv.). Moisture content (MC) and dimensional changes were automatically measured during cyclic process where relative humidity changed sinusoidally from 45% to 75% at 25 degrees C. Hemicelluloses were partially removed and furfural resin chemically in situ polymerized in wood from both results of Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). Hemicellulose removal caused many voids in cell walls, and partial furfural resin polymerized in these voids suggested by the results of scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM). The distribution of modifier was more uniform and the cell wall bulking was more obvious for the furfurylated wood with low hemicellulose content (LHF). After the two-step treatment, MC and dimensional changes were presented as similar sinusoidal shapes to RH. The average MC was reduced by over 50% and tangential dimensional change decreased by over 40%. MC and dimensional amplitudes both fell with the most scope above 50%. Moisture sorption coefficient and humidity expansion coefficient dropped by more than 50% and 30% respectively. The two-step treatment could reduce the hygroscopicity and improve the dimensional stability greatly by varying the physical-chemical environment for water in modified wood. Chemically, the effective hydroxyl groups decreased after hemicellulose removal. Physically, furfural resins blocked water exchange paths and reduced the space to accommodate water or covered the adsorbed sites as a resin film and caused permanent bulking of cell wall.