Effect of Thermal Treatment on the Heat of Vaporization of Bound Water by NMR and DSC Analysis

Yingjie Guo, Minghui Zhang, Yanjun Xie, Haiou Chen, Zefang Xiao

Abstract


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%.

Keywords


Vaporized heat; Bound water; Thermal treatment; Radiata pine; Low field nuclear magnetic resonance; Differential scanning calorimetry; Thermogravimetric analysis

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