利用核磁共振测定木材润胀细胞壁的水分含量与孔径分布

【目的】利用核磁共振冻融分析技术测定杉木与杨木两种速生材细胞壁润胀状态吸着水含量与孔隙分布情况,为改性剂粒径选择与改性效果评价提供方法。【方法】常温下获得试样内水分T₂弛豫信号总量,通过核磁冻融分析系统对试样进行降温处理,检测不同冷冻温度条件试样内未冻结水分信号量; 依据Gibbs-Thomson效应确定凝固点降低与孔径的关系,并以此分析孔径分布。【结果】核磁冻融法测定杉木和杨木吸着水饱和含量约为38%,高于通过吸湿外推法估算数值,与溶剂排出法、多孔板法、离心法结果相近; 核磁冻融分析法避免了常温条件按照T₂弛豫分布确定吸着水含量偏小的现象; 两种速生材试样细胞壁润胀状态孔径小于1.59 nm的孔隙占比约为75%,大于4.56 nm的孔隙占比不超过6%,与溶剂排出法、光谱标记法结果相符。【结论】核磁共振冻融分析技术可较为便捷准确地获得木材吸着水含量与细胞壁孔隙分布,其结果可用于指导改性剂粒径的选择与改性效果评价。

Bound water content and pore size diameter distribution in swollen cell walls determined by NMR cryoporometry

【Objective】 The purpose of this study was to determine the bound water content and pore size diameter distribution in the swollen cell walls of two fast-growing trees(Cunninghamia lanceolata(Chinese fir)and poplar)using nuclear magnetic resonance(NMR)cryoporometry. The results should be valuable in the selection of particle size for wood modification. 【Method】The T₂ signal amplification of specimens at normal temperature and different frozen temperatures was compared to avoid the phenomenon that bound water content is lower than the theoretical value determined by T₂ relaxation distributions at normal temperature. The maximum moisture content and pore size diameter distributions of the swollen cell wall were determined from the total signals of samples according to the Gibbs-Thomson equation, and inversion calculations were omitted. 【Results】 The saturated bound water content of Chinese fir and poplar was approximately 38%, which was clearly higher than the fiber saturation point(approximately 30%)measured by the extrapolation method, but was in accordance with solute exclusion, porous plate and centrifugal methods. The proportion of pore diameters smaller than 1.59 nm was approximately 75%, and the proportion of pore diameters larger than 4.56 nm was below 6%; this result was also in accordance with solute exclusion and spectral methods. 【Conclusion】 The bound water content and pore size diameter distributions of the cell wall could be conveniently and accurately determined by NMR cryoporometry, which could be used in the selection of modification agents and evaluation of modification effects.