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【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T_2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T_2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。
【Objective】 The objective of this study was to determine the sorption water content and pore distribution in the swelling state of fir and poplar cell wall by means of NMR freeze-thaw analysis, and to provide a method for selection and modification of particle size of modifier. 【Method】 The total amount of T_2 relaxation signal in the sample was obtained at room temperature. The sample was cooled by the NMR system to measure the un-frozen water content of the samples under different freezing temperature conditions. According to the Gibbs-Thomson effect The freezing point reduces the relationship with the pore size and analyzes the pore size distribution. 【Result】 The results of NMR and FTIR analysis showed that the adsorption water saturation of Chinese fir and poplar was about 38%, higher than that estimated by hygroscopic extrapolation method, which was similar to the results of solvent excretion, porous plate and centrifugation. Avoiding the phenomenon that the content of adsorbed water is small according to the T_2 relaxation distribution at room temperature; the porosity of pores in the two cell walls of the samples for quick-curing biomass is less than 1.59 nm, and the proportion of pores larger than 4.56 nm does not exceed 6%, consistent with solvent discharge and spectral labeling. 【Conclusion】 NMR freeze-thaw analysis can obtain the sorption water content and cell wall pore distribution of wood easily and accurately. The results can be used to guide the choice of modifier particle size and the evaluation of modification effect.