The influence of vacuum heat treatment on the pore structure of earlywood and latewood of larch

Abstract

To investigate the changes in the pore structure of earlywood and latewood (EW and LW) in larch during the heat treatment process, this study applied nitrogen adsorption and mercury intrusion porosimetry (MIP) to measure wood pore characteristics. Wood samples were heat treated within a vacuum atmosphere at temperatures between 180 and 220 °C for 6 h. Analysis conducted on nitrogen adsorption isotherms indicated that the micropores and mesopores in the cell walls were present in both untreated and heat-treated EW and LW, and that the mesopores appeared as slit-shaped pores. More pores were detected in EW compared to LW, and these primarily absorbed in the range of 1.5–4 nm. Compared with the untreated wood, the total pore volume of treated wood decreased with increasing temperatures, with decreased pore volumes at 220 °C of 63 and 42% for EW and LW, respectively. The MIP results showed a greater porosity of EW compared to LW. Compared with the untreated wood, the porosity of heat-treated EW and LW first increased with increasing temperature, and then decreased at 220 °C. For treatment temperatures lower than 200 °C, heat treatment increased the proportion of macropores with pore sizes in the ranges of 100–1000 nm and 10,000–40,000 nm.

Layer-by-layer assembling redox wood electrodes for efficient energy storage

“…The freeze-dried TrW samples showed enhanced adsorption in the micro and mesoporous region [Supplementary Figure 1C and D], and a characteristic sharp step-down in the desorption curve is called "cavitation" -a sign of a significant level of micro-and mesoporosity [21,22] . All samples showed H4-type hysteresis loops with non-limiting adsorption at high relative pressure [23] . The distribution of loops over a wide relative pressure range proves the presence of pores with varied diameters in wood.…”

Effects of heating mediums on microstructure and chemical properties of thermally modified Matoa

“…This was partly inconsistent with the results reported by Liu et al ( 2023), who claimed that the S BET and V total were both decreased no matter in saturated steam or in air condition at 180 and 210°C. However, Sun et al (2022) found that the porosity of thermally modi ed pine rst increased and then decreased with the increasing modi cation temperature, indicating the change of porosity was related with the intensity of TM. Higher modi cation temperature and leaching post-treatment mostly induced an increase in porosity, however, the higher TM temperature also resulted in a decrease in the average mesopore diameter.…”

“…TM results in weight loss (Czajkowski et al 2020), changes in mechanical strength, and reduction in equilibrium moisture content (EMC) and hygroscopicity, which subsequently improves the dimensional stability (Borůvka et al 2019) and decay resistance (Cao et al 2011). These property changes mainly deriving from the degardation of chemical constituent (hemicellulose, cellulose, and lignin) ) and changes of pore structure (Sun et al 2022). During TM process, the decrease of -OH groups (Xu et al 2022) due to the degradation of hydrophilic hemicellulose, and the increase of relative crystallinity (Andersson et al 2005) due to the reduced amorphous cellulose would decrease the hygroscopicity of thermally modi ed wood (TMW).…”

“…Simultaneously, the crystallization state of cellulose is also affected by the moisture content of TM. The crystallinity of TMW treated under dry conditions signi cantly decreases after the dry-wet cycle, while the sample treated under wet conditions does not show signi cant changes (Sun et al 2022).…”