Comparison of changes in micropores and mesopores in the wood cell walls of sapwood and heartwood

Abstract

The objective of this paper was to investigate size distribution of micropores and mesopores within the wood cell walls between sapwood and heartwood by using nitrogen adsorption method and to find out implications for the biological durability and further processing such as in drying and preservation treatment. The pore shape, specific surface area and pore size distribution of Chinese fir (Cunninghamia lanceolata) were evaluated using the hysteresis loops, Brunauer-Emmett-Teller (BET) and density functional theories, respectively. Both the sapwood and heartwood exhibited slit-shaped pores with regard to the H3 type of hysteresis loop of the isotherm. However, more mesopores were found in the sapwood, while the micropores increased with a decrease in mesopores in the heartwood. Furthermore, the earlywood and latewood in the sapwood had a higher BET-specific surface area (2.088 and 1.255 m 2 g -1 , respectively) compared with the earlywood (1.058 m 2 g -1 ) and latewood (0.787 m 2 g -1 ) in the heartwood. This could be caused by an increase in depositions in the extractive that partly filled the mesopores of the heartwood cell walls during the transformation from the sapwood. Additionally, a larger amount of mesopores existed in the earlywood in comparison with the latewood in the sapwood. However, there was no significant difference in the amounts of the micropores and mesopores, when comparing the earlywood with the latewood in the heartwood.

Comparison of Micropore Distribution in Cell Walls of Softwood and Hardwood Xylem

“…Both earlywood and latewood tracheid cell walls in high-temperature-dried Norway spruce (Picea abies) contained a similar amount of micropores (Borrega and Kärenlampi, 2011). Micropores have been described as slit-like spaces between adjacent lamellae (Stone and Scallan, 1965;Yin et al, 2015). Lamellae-shaped pores were observed in Norway spruce wood or pulp fibers infiltrated with polyethylene glycol in both the micropore and mesopore ranges, associated with aggregates of cellulose microfibrils or with cell wall checking, using atomic force microscopy and scanning electron microscopy under dry conditions Salmén, 2002, 2005).…”

“…Micropores and mesopores may be infiltrated with extractives during heartwood formation (Yin et al, 2015). Sapwood may contain more mesopores than heartwood, and this may reflect the filling of mesopores by extractives in the heartwood, resulting in a relative increase in the number of smaller micropores.…”

“…The highly lignified middle lamella, and lumen surface, act as a barrier to probe movement and, therefore, water movement in both softwood and hardwood. important during heartwood formation, where cell walls may replace their water with gums and extractives involved in defense responses, resulting in reduced permeability (Yin et al, 2015). In aspirated xylem, cell wall micropores can provide an alternative route for water movement and potentially allow for the refilling of conduits (Brodersen and McElrone, 2013;Ryu et al, 2016).…”

“…The spatial distribution of micropores in native wet cell walls of different cell types and in different cell wall regions has not been investigated (Yin et al, 2015). Methods for detecting and measuring micropores in wood cell walls using fluorescence microscopy have been developed recently (Donaldson et al, 2015).…”

Pore structure changes from wood to vitrain: a casy study from New Zealand coal

“…Porosity studies in wood have been conducted using different methods from mercury injection to small angle x-ray scattering (Almeida and Hernández, 2007;Kalliat et al, 1983;Kojiro et al, 2010;Nakatani et al, 2008;Papadopoulos et al, 2003;Plötze and Niemz, 2010;Stamm, 1973;Yin et al, 2015;Zauer et al, 2014). Plötze and Niemz (2010) conducted B A 8 a porosity study on 24 different types of hardwood and softwood using mercury injection porosimetry (MIP) and water vapour adsorption technique.…”