低场NMR技术测定竹材的纤维饱和点  

Determination of fiber saturation point of bamboo using LF-NMR

作　　者：宋路路[1] 高鑫[2] 王新洲[1] 任慧群[1] 陈白 许斌[1] 

机构地区：[1]南京林业大学材料科学与工程学院,南京210037 [2]中国林业科学研究院木材工业研究所,北京100091 [3]浙江省丽水市庆元县松源街道林业工作站,浙江丽水323800

出　　处：《林业工程学报》2017年第1期36-40,共5页Journal of Forestry Engineering

基　　金：国家林业公益性行业科研专项(201304503);江苏高校优势学科建设工程资助项目(PAPD)

摘　　要：以4年生毛竹为试材,利用低场核磁共振(LF-NMR)技术研究了毛竹中的质子H在室温和-3℃条件下的自旋-自旋驰豫时间(T_2)特性,以分析竹材水分分布特征。由于固态冰与液态水的弛豫时间和竹材自由水和结合水凝固点的差异性,本试验采用仅冻结竹材细胞腔内自由水来获取结合水信号的方式,通过对比冷冻前后T_2弛豫信号反演峰的面积,可确定结合水准确含量。结果表明:在室温条件下,T_2分布峰大致为3个,-3℃温度下T_2分布峰为1个,根据毛竹细胞壁内吸着水所处空隙较小、T_2弛豫时间较短可以判断,峰1为结合水弛豫,峰2和峰3为自由水的弛豫。毛竹的纤维饱和点(FSP)均值约为35%,测试结果高于传统外推法结果,与差示扫描量热法(DSC)等实测法的结果相符。试验结果证明核磁共振可以作为快速测定竹材纤维饱和点的有效手段。To explore the water distribution in bamboo, this study examined the spin-spin relaxation time（T2）of water proton H in four years old bamboo using the low field nuclear magnetic resonance（LF-NMR）spectroscopy at room temperature and -3℃. Due to the different freezing points between free water and bound water in bamboo, the different relaxation times between solid ice and liquid water were also measured. Therefore, the experiments were focused on collecting signals of the bound water through freezing free water in cell cavities of bamboo. The bound water content was accurately determined by comparing the T2 inversion peak areas measured before and after freezing separately. The results showed that there was only one distribution peak at -3℃, while there were roughly three T2 distribution peaks at room temperature. At room temperature, based on the small gaps taken by bound water in cell walls of bamboos and short relaxation time of T2 and other qualitative research results, consequent peak 1 with the shortest relaxation time generally represents the relaxation of bound water, while peak 2 and peak 3 with comparatively longer relaxation time should be from the relaxation of free water. The fiber saturation point（FSP）can be calculated as 35% by comparing inversion peak areas. Therefore, all the results indicated that the low field nuclear magnetic resonance（LF-NMR）can be regarded as an experimental method to quickly measure the fiber saturation point of bamboos. In addition, the experimental process is simple and without any damage for bamboos, except making a proper freezing treatment of samples. It was found that the measured values by using this method were mostly higher than the calculated values by traditional extrapolation, and close to the values measured by field methods, such as the differential scanning calorimetry（DSC）.

关 键 词：低场核磁共振(LF-NMR) 弛豫时间T2 纤维饱和点 毛竹 

分 类 号：S781[农业科学—木材科学与技术]