木质纤维素纳米纤丝制备及形态特征分析

以阔叶树材杨木木粉为原料,始终保持纤维处在水润涨的状态下,利用亚氯酸钠在酸性条件下脱除木质素,氢氧化钾脱除半纤维素,然后借助高强度超声波的空化作用,依次制备了综纤维素、纯化纤维素及木质纤维素纳米纤丝(WCNF).通过傅里叶变换红外吸收光谱(FTIR)、X射线衍射(XRD)、扫描电镜(SEM)对WCNF制备过程中的化学组分、晶型结构、结晶度及形态特征变化进行了表征,并进一步利用图像分析系统对WCNF的直径分布进行了测量统计.结果表明,WCNF的主要成分为纤维素,其晶型结构仍为纤维素Ⅰ型,结晶度为65.68%,较之原料木粉提高了12.33%.所得纤丝的直径集中分布在5～32nm之间,长度大于10μm,长径比高于300,纤丝间相互交织成网状缠结结构.WCNF的高结晶度、高长径比、纳米尺度、网状缠结结构,显示其为一种十分理想的增强增韧材料.

A METHOD FOR ISOLATING CELLULOSE NANOFIBRILS FROM WOOD AND THEIR MORPHOLOGICAL CHARACTERISTICS

Toward exploiting cellulose nanofibrils with high aspect ratio and nano-order-unit interconnected web-like structure from poplar wood,a novel route was demonstrated,which combined the usual chemical procedures with high intensity ultrasonic treatment of the material in the water-swollen state. Firstly,lignin in the sample was removed using an acidified sodium chlorite solution. Secondly,the sample was treated with potassium hydroxide in order to leach hemicellulose. Lastly,the sample was processed with high intensity ultrasonication. Never-dried holocellulose,never-dried purified cellulose and wood cellulose nanofibrils (WCNF) were obtained,respectively. The changes of WCNF on the chemical composition,crystalline structure,crystallinity and morphologies during the preparation process were characterized by means of Fourier transform infrared spectroscopy (FTIR),X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the diameter distribution of WCNF was further calculated and analyzed by image analysis method. The results showed that the main composition of WCNF was cellulose with crystalline structure of Ⅰ type,and the crystallinity of WCNF was 65. 68% ,12. 33% higher than that of the raw material wood. The diameters,lengths and aspect ratio of WCNF were about 5 ～ 32 nm,longer than 10 μm and larger than 300,respectively. The nanofibrils of WCNF were also interconnected into unique web-like structure. The characteristics including high crystallinity,high aspect ratio,nano-order-scale,web-like entangled structure,and so on,indicate that WCNF is a perfect reinforcing and toughening material.