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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.

The vaporized heat of bound water in radiata pine wood sapwood, which was thermally treated at 200 °C, via N2 protection for 24 h, were studied using low-field nuclear magnetic resonance (LFNMR) and differential scanning calorimetry (DSC) analysis. The bound water was divided into two states using LFNMR, which were absorbed water bonded with cell wall polymers and condensed bound water in the micro-pores of cell wall, respectively. The mass of the two states of bound water vaporized during DSC test was calculated based on the total mass of bound water vaporized and the moisture content of different water states in the water-saturated sapwood obtained, respectively. The reduction of moisture during DSC test was monitored synchronously using thermogravimetric analysis. The results showed thermal treatment decreased the spin-spin time (T2) of absorbed bound water and increased T2 of condensed bound water. The moisture content of the two states of bound water was reduced by thermal treatment. The vaporized heat of the bonded bound water was increased and that of the condensed bound water was reduced, which agreed with the change of T2 in the LFNMR experiment. The results suggest that bound water in the thermal treated wood is easier to vaporize when the relative humidity condition is more than 60%.