Modification of Fagus sylvatica (L.) with 1,3-dimethylol-4,5-dihydroxyethylene urea (DMDHEU): Part 1. Estimation of heat adsorption by the isosteric method (Hailwood-Horrobin model) and by solution calorimetry

The differential heat of adsorption (ΔH s ) of Fagus sylvatica wood modified with 0.8 M, 1.3 M, and 2.3 M solution of 1,3-dimethylol-4,5-dihydroxyethylene urea (DMDHEU) was determined at different equilibrium moisture contents (EMCs) by both the isosteric method, using the Hailwood-Horrobin model at 20, 30, and 40°C and by solution calorimetry. Both methods revealed that at 1% EMC, the 2.3-M modified wood releases approximately double the amount of energy as does unmodified wood. At EMC below approximately 5%, DMDHEU-modified wood appears to be more hygroscopic than unmodified wood, indicating that more OH groups are available for adsorption. The bulking effect of the cell wall and the increase of OH groups caused by the modification with DMDHEU are probably the reason for this observation. As expected, higher EMC led to a reduction of ΔH s .