Effect of previous history on kinetics of sorption by wood cell walls

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

“…The use of a dm/dt criterion becomes critical when considering sample drying which in many studies is performed initially. The results of Christensen and Hergt (1969) show that the longer the time under constant climate before a given change in RH, the slower the rate of sorption. Thus, if a sample is initially dried out using a dm/dt criterion after experiencing stable conditions for a long while, it will exhibit a slower rate of desorption than in a subsequent second drying stage after re-wetting.…”

“…Instead, sorption might be controlled by relaxation of stresses arising from swelling of the dense and stiff wood cell walls (Christensen 1959(Christensen , 1960Christensen and Kelsey 1959). 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).…”

A critical discussion of the physics of wood–water interactions

“…In adsorption experiments, Christensen and Hergt (1969) observed a slower rate of adsorption and longer time to equilibrium the longer samples were conditioned at 53 % RH prior to the initiation of sorption. Furthermore, Christensen (1959) and Christensen and Kelsey (1959) found that the halftime to equilibrium was inversely proportional to swelling pressure, that is, smaller steps in RH gave a longer time to equilibrium.…”

“…Thus, as stress relaxation progresses, the equilibrium surface concentration changes. Several researchers have described sorption of water in the cell walls by a twostage process (Christensen 1965;Christensen and Hergt 1969;Xie et al 2011;Hill et al 2012) for which moisture uptake in the initial stage resembles a process controlled by Fickian diffusion. The second stage is slower and becomes increasingly dominant as the initial concentration of bound water is increased (Christensen 1965).…”

The Sorption of the Tertiary Butyl Alcohol-Water Binary Mixture on Wood

“…The composition of both liquid and vapor phases of binary mixture was verified and the total pressure recorded at the end of the sorption cycle. (Christensen and Hergt 1969;Hergt and Christensen 1965). Compare with initial value …”