The physical and mechanical properties of thermally modified wood (TMW) have been comprehensively studied; however, the quantitative analysis of water states and cell wall pores of TMW is limited. In this work, Douglas fir and Norway spruce were thermally modified at 180, 200 and 220 °C, and then studied by NMR cryoporometry method. The results show that thermally modified samples had lower fiber saturation point and the bound water content than the reference samples at all the experimental temperatures, indicating the reduced hygroscopicity due to thermal modification (TM). In addition, TM decreased number of hygroscopic groups, which can be implied by the decreased proportion of bound water sites, and TM also increased the proportion of small voids for bound water clusters. An increase in TM intensity resulted in lower bound water content and a smaller number of hygroscopic groups. In summary, the NMR method detected the water states and pore size distribution and confirmed that TM decreased the fiber saturation point and hygroscopicity of wood by reducing the bound water content and proportion of bound water sites in wood cell walls.

中文翻译：

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NMR研究热改性木材的束缚水含量和孔径分布

已经对热改性木材（TMW）的物理和机械性能进行了全面研究。然而，对TMW的水状态和细胞壁孔的定量分析是有限的。在这项工作中，花旗松和挪威云杉在180、200和220℃下进行了热改性，然后通过NMR低温法进行了研究。结果表明，在所有实验温度下，热改性样品的纤维饱和点和结合水含量均低于参考样品，表明由于热改性（TM）导致的吸湿性降低。此外，TM减少了吸湿性基团的数量，这可能是由于结合水位的比例降低所暗示的，并且TM也增加了结合水团簇的小孔隙的比例。TM强度的增加导致较低的结合水含量和较少的吸湿性基团。总之，NMR方法检测了水的状态和孔径分布，并证实TM通过减少木质细胞壁中的结合水含量和结合水位的比例降低了木材的纤维饱和点和吸湿性。