Vaporization heat of bound water in wood chemically modified via grafting and crosslinking patterns by DSC and NMR analysis

Radiata pine wood (W) was modified with acetic anhydride and glutaraldehyde (GA) resulting in WAc and WGA to various weight percent gains (WPGs), whereas in WAc the effect is due to grafting and in WGA, crosslinking. The heat of vaporization of bound water (BW) of the modified woods was studied by differential scanning calorimetry (DSC) and the mass loss (due to water loss) of the samples by thermogravimetry (TG). The temperature program was in both cases from 25 to 40°C with 10°C min−1. The adsorbed or condensed water in wood were observed via low-field nuclear magnetic resonance (LFNMR). At a comparable WPG level, the LFNMR analysis showed that the interaction of water with WGA was stronger than that with WAc. In both modified woods, a considerable reduction in the vaporization heat of BW was visible due to cell wall hydrophobization and bulking. The reduction of condensed water in micropores was lower for WGA than WAc, probably because BW needs more energy to evaporate from the crosslinked stiff WGA cell walls.