Time domain-NMR studies of average pore size of wood cell walls during drying and moisture adsorption
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Time domain‑NMR studies of average pore size of wood cell walls during drying and moisture adsorption Xinyu Li1 · Zhihong Zhao2 Received: 25 January 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The change in the pore size of cell walls affects many physical properties of wood. In this paper, the dynamic changes in the pore size of wood cell walls during drying and moisture adsorption were studied at four relative humidities. The results showed that the average pore size of cell walls of Qingpi poplar (Populus- platyphylla var. glauca) was larger than that of pine wood (Pinus sylvestris var. mongolica Litv.) under the same experimental conditions, and the changes in pore size of Qingpi poplar cell walls were more sensitive to ambient humidity no matter whether during drying or moisture adsorption. Moreover, the average pore size of cell walls at saturated-water state is about 2.5 times of the average pore size of cell walls when woods reached the moisture absorption equilibrium from the oven-dry state. This article is useful for the wood manufacture industry and for wood modification. It is not only important for wood processing and utilization but also for the research on other porous materials.
Introduction Wood is widely used in furniture and building industry, although it is easily affected by the change in moisture content (MC). It is generally believed that below the fiber saturation point (FSP), the moisture molecules combine with wood by hydrogen bonds. Representative theories of moisture adsorption are the monomolecular layer adsorption theory and the multimolecular layer adsorption theory. The former is represented by the Langmuir theory (Hailwood and Horrobin 1946: Langmuir 1918) and the latter by the BET (Brunauer, Emmett and * Xinyu Li [email protected] Zhihong Zhao [email protected] 1
Institute of Carbon Materials Science, Shanxi Datong University, Datong 037009, China
2
College of Materials Science and Art Design, Inner Mongolia Agricultural University, Hohhot 010018, China
13
Vol.:(0123456789)
Wood Science and Technology
Teller) theory (Brunauer et al. 1938) and the Polanyi adsorption potential theory (Dubinin 1966). The pore size of cell walls shrinks with drying and increases with moisture adsorption, which has a great impact on the macrosize and physical properties of wood. Hence, the study of wood pore size is important for wood modification and wood building industry. The International Union of Pure and Applied Chemistry (IUPAC) classified the pore size of porous materials into micropores ( 50 nm) (Everett 2009). Many methods have been proposed to study the pore size, some of which are also applicable to wood. Mercury intrusion porosimetry is an effective way for macropore measurement in wood (Vitas et al. 2019). However, the wood sample needs to be dried, and during mercury intrusion, the pore structure might be destroyed. Gas adsorption isotherms are capable of detecting micropores and mesopores (Yang and Tze 2017; Yin et al. 2015). However, f
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