Abstract
Effects of lignin on dynamic sorption and hygroexpansion were investigated. Poplar wood (Populus cathay) [20×20×4 mm3 (radial×tangential×longitudinal)] was delignified at three levels and subjected to dynamic humidity changes, where the relative humidity (RH) changed sinusoidally between 45% and 75% at 25°C during 1, 6 and 24 h. Moisture contents (MC) and dimensional responses were recorded automatically. Scanning electron microscopy (SEM) results show that lignin was partly removed. MC and dimensions also varied sinusoidally with RH. At higher delignification levels, amplitudes, moisture sorption coefficients and humidity expansion coefficients became higher, but the phase lag displayed an opposite trend. The effects were due to the removal of the relatively hydrophobic lignin layers, in the course of which more hydroxyl groups of cellulose and hemicelluloses were accessible to humidity. A linear positive relation was found between the delignification rate and MC, and dimensional changes in the tangential direction. Lignin had a significant effect on sorption and hygroexpansion and this effect was greater for static sorption. Delignification reduced the hysteresis due to matrix stiffness decrement of wood, especially in the RH range of 55–65%.
Funding source: National Natural Science Foundation of China
Award Identifier / Grant number: 31200435
Funding statement: The study is supported by the Fundamental Research Funds for the Central Universities of China (Nos. 2017ZY47, 2015ZCQ-CL-01) and the National Natural Science Foundation of China (Funder Id: 10.13039/501100001809, Grant Number: 31200435).
Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.
Employment or leadership: None declared.
Honorarium: None declared.
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Supplementary Material
The online version of this article offers supplementary material (https://doi.org/10.1515/hf-2017-0198).
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