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.