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 m2 g−1, respectively) compared with the earlywood (1.058 m2 g−1) and latewood (0.787 m2 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.