关键词: 木粉, 脱化学成分, 动态, 水分吸着

Abstract: [Objective]In order to obtain the information about interactions among the main components of wood and to provide theoretical basis to analyze the behaviors of moisture sorption and wood deformation, the effects of chemical components on moisture sorption of wood under dynamic conditions were investigated.[Method] Populus euramericana flour (40-60 meshes) was subjected to extractives, hemicellulose extraction and matrix (hemicellulose and lignin) removal treatment, respectively. The effects of partial removal of chemical component treatments were detected by X-ray diffraction (XRD). The control and treated samples were placed into dynamic conditions where RH changed sinusoidally between 45%-75% for cyclic periods of 1, 6, and 24 h at 25℃, during which moisture changes were measured. The changes of relative humidity and wood moisture content were fitted by the Fourier analysis, giving the following result.[Result] 1) XRD tests suggested that the positions of the diffraction peaks for crystal planes in cellulose of the samples did not change after partial removal of chemical component treatments. The crystallinity of extractives removed samples, hemicellulose removed samples and matrix removed samples was determined as 36.4%, 41.3% and 48.5%, respectively. 2) In dynamic conditions, the Fourier analysis proposed by a previous study showed a good agreement with experiment result in this work for both RH and moisture changes of the samples at each cyclic period. 3) Dynamic sorption isotherms of the samples were characterized by several overlapped oval curves, where sorption hysteresis could be obviously observed with hysteresis ratio ranging from 0.881 to 0.955. 4) The moisture sorption coefficient of the untreated samples, extractives removed samples, hemicellulose removed samples and matrix removed samples was 0.090 8, 0.094 8, 0.089 2 and 0.087 4, respectively, when the cyclic period was sufficiently long. These values were half of the static values.[Conclusion]1) Hemicellulose of the samples was removed without breaking the crystallize structure in cellulose. 2) Moisture of the samples were generally sinusoidal but lagged behind the imposed RH and steady-state was reached as dynamic sorption proceeded. 3) The amplitude and moisture sorption coefficient increased and the phase lag decreased with increasing cyclic period. 4) A comparison among the samples by different partial removal of chemical component treatments demonstrated that the extractives removed samples exhibited the highest amplitude and moisture sorption coefficient, followed by the untreated samples, hemicellulose removed samples and matrix removed samples for all cyclic periods.

Key words: wood flour, removal of chemical component, dynamic condition, moisture sorption