Water vapor sorption kinetics of wood modified with glutaraldehyde

Abstract

The modifying effects of Scots pine (Pinus sylvestris L.) wood with the crosslinking agent glutaraldehyde (GA) on the water vapor sorption kinetics were studied by curve fitting the experimental isotherm sorption data obtained using a Dynamic Vapor Sorption apparatus using the parallel exponential kinetics model (PEK model) and the Hailwood-Horrobin model (H-H model) for the isotherm. Both the H-H model and the PEK model provided good fits to the experimental data. Modification of wood with GA reduced both the time to equilibrium and the equilibrium moisture content (EMC). According to the PEK and H-H models, the reduction in EMC was mainly due to the decrease of moisture content (MC) associated with the slow sorption processes and polylayer water. The fast sorption processes and monolayer water were little affected by GA modification. Compared to the untreated control, the estimated total water absorbed by wood treated to a WPG of 20.9% at 100% RH decreased by 52.2%, by extrapolating the fitted curves derived from the H-H model. V

Experimental techniques for characterising water in wood covering the range from dry to fully water-saturated

“…As only a small sample mass (typically in the 5-20 mg range) is needed like in the quartz helix spring systems, a faster approach to equilibrium is observed compared with conditioning larger samples over saturated salt solutions or in climate chambers. As automated sorption balances are becoming a common research tool in wood research laboratories, the literature is abundant with sorption isotherms determined with such equipment, also for various types of modified wood Jalaludin et al 2010a, b;Popescu and Hill 2013;Xie et al 2010Xie et al , 2011. While the low sample mass makes possible detailed studies of differences in water sorption between earlywood and latewood (Fredriksson and Thygesen 2017), even at the growth ring level (Hill et al 2015;Song et al 2014), it also requires the user to consider how to collect representative samples for the study in question.…”

“…While the low sample mass makes possible detailed studies of differences in water sorption between earlywood and latewood (Fredriksson and Thygesen 2017), even at the growth ring level (Hill et al 2015;Song et al 2014), it also requires the user to consider how to collect representative samples for the study in question. For generating representative samples of larger wood volumes, several studies have used milled wood Himmel and Mai 2015;Xie et al 2010;Zaihan et al 2009Zaihan et al , 2011, but it could be speculated if this gives a representative material or might produce unwanted side effects, for example a change in sample chemistry. Milling is not as intense a method for subdividing wood as ball milling which has been shown to change the material chemistry (Mao et al 2006) and internal chemical bonding (Schwanninger et al 2004).…”

“…This also explains why samples conditioned for longer times after a change in RH exhibit slower rate of sorption as observed by Christensen and Hergt (1969). Due to the two-stage nature of the sorption process, it has often been analysed by the parallel exponential kinetics (PEK) model featuring two moisture sorption processes (fast and slow exponentials) using data for both untreated ) and modified wood (Hill et al 2012a;Himmel and Mai 2016;Jalaludin et al 2010a;Popescu et al 2014;Xie et al 2010). It may be difficult to compare the results across studies due to differences in sample mass and geometry as diffusion into the sample at some point becomes relevant, at least in the low-RH regime (Christensen 1965).…”

The water vapour sorption behaviour of three celluloses: analysis using parallel exponential kinetics and interpretation using the Kelvin-Voigt viscoelastic model

“…The isotherms and sorption kinetic behaviour of the celluloses was measured using a Dynamic Vapour Sorption Intrinsic apparatus (DVS, Surface Measurement Systems Ltd, London, United Kingdom) as previously reported (Hill et al 2010d;Xie et al 2010c). The mass of the cellulose sample (approximately 5 mg), running time, actual relative humidity (RH) were real-time recorded in a thermostatically controlled cabinet at 25°C during the sorption experiment.…”

Modification of beech veneers with N-methylol-melamine compounds for the production of plywood

“…Moisture (vapour) sorption is a process which proceeds due to the uptake and incorporation of water molecules into the cell wall, whereas no water is deposited in the lumens of the cells. For this reason, moisture sorption can only be reduced, when hydroxyl groups of cell wall polymers are replaced by less polar groups or when chemicals are stably incorporated in the cell wall matrix and fill cell wall nano-pores (Xie et al 2010).…”