The kinetics of water vapour sorption: analysis using Parallel Exponential Kinetics model on six Malaysian hardwoods

Six Malaysian hardwoods, chengal (Neobalanocarpus heimii), kapur (Dryobalanops spp.), keruing (Dipterocarpus spp.), ramin (Gonystylus spp.), acacia (Acacia mangium) and sesendok (Endospermum malaccense) were studied to determine their sorption kinetics behaviour using a dynamic vapour sorption (DVS) apparatus. Experimental data fitted well to the parallel exponential kinetics (PEK) model. The PEK model expresses the sorption kinetics as fast and slow sorption processes, but interpretation of how these can be related to physical phenomena is not yet understood. The Hailwood–Horrobin model was also used to examine the relationship between sorbed monolayer water and polylayer water at different relative humidities. Comparison between the two models was used to verify if the fast and slow sorption processes could be linked to monolayer or polylayer water formation in the cell wall. Characteristic times at various relative humidities showed differences between adsorption and desorption in the slow process for all the species. However, using mass change criterion, sorption hysteresis was found to occur in both the slow and fast processes.