Dried cell wall nanopore configuration of Douglas-fir, western red cedar and aspen heartwoods

Abstract

Wood cell wall pores are essential for understanding nanostructure and subsequent application to wood processing and new product design. CO2 and N2 sorption isotherms were used to explore nanopores in dried cell walls of Douglas-fir, aspen and western red cedar heartwood specimens. The total cell wall pore volume was estimated as sum of detected micropore volume from the CO2 isotherm and the volume of pores that are less than 10 nm from the N2 isotherm. The estimated pore volumes from the gas sorption method were statistically lower than those obtained from the classical pycnometer method using water and white mineral oil as replacing liquids. Large open hysteresis was observed in CO2 sorption isotherms. Further pore distribution analysis assigned the detected 10–36 nm pores to those in pit membranes. Extraction of western red cedar heartwoods largely affected the detected 0.4–0.6 nm pores, which strongly suggests penetration of extractives into cell walls. Despite the exploratory nature of this study on western red cedar, CO2 sorption analysis shows great potential in exploring micro-distribution of extractives.