| Development and utilization of renewable resources fully become inevitable trend, under the current situation of the exhausting non-renewable resources such as coal, oil and natural gas. Natural cellulose is the most abundant biomass resources in nature, and is the most popular biological macromolecular, which exists in various organisms such as bacteria and some plants, animals, etc. Nanocrystalline cellulose (NCC) extracted from natural fiber is nanoscale cellulose, which not only has the features of nanoparticles, but also has some unique strength and optical properties, which makes it prospective in the industry.In the thesis, sulfuric acid hydrolysis and enzyme hydrolysis were used to prepare NCC, respectively. The surface morphology and optical properties of NCC extracted from bleached hardwood Kraft pulp by sulfuric acid hydrolysis were investigated by X-ray diffraction (XRD), particle charge detector (PCD), atomic force microscopy (AFM) and polarized light microscopy. The effects of hydrolysis conditions on the crystallinity, yield and surface charge density were also studied. The experimental results demonstrated that reaction temperature and acid-to-pulp ratio had a decisive influence on the properties and yield of NCC. A yield between 23.32% and 33.56% could be extracted using 64wt% sulfuric acid. AFM observation showed that the prepared NCCs were parallelepiped rod-like structures with cross-sectional dimensions in the nanometer range with high aspect ratio and high crystallinity (over 80%). When suspensions of NCC in water were allowed to evaporate on Yattria-stabilized Zirconia single-crystal (100) surface, a film with typical optical properties was formed. The film reflects circularly polarized light that changed color with viewing angle, when observed in polarized light microscope.The preparation of NCC using enzyme hydrolysis method was explored. Research found that white uniform NCC suspension could be hardly prepared using MCC as the raw material when changed the dosage and species of the enzyme. When bleached soft wood Kraft pulp was used as the substrate,18.37% yield of NCC with no surface charge could be prepared with cellulase. The cellulase dosage was 80000IU/g, pH4.8, hydrolyzed for four days at 50℃Cationic modification of NCC was investigated. The experiment showed that NCC could be successfully cationic modificated with 3-Chloro-2-hydroxypropyltrimethyl ammonium chloride (CHTMAC). The surface charge density of modified NCC decreased as the pH increased. The physical and chemical properties of modified NCC were preliminarily studied. NCC modified by quaternary ammonium salt lost its performance of liquid crystalline chiral nematic phase, and became gel. The film formed by NCC had no special optical properties observed under the polarizing microscope.Borate was used in the anion modification of NCC. The results showed that the surface charge density of anion charged NCC could be increased, and its performance of liquid crystalline choral nomadic phase and unique optical properties remained. It was found that the surface charge density of modified NCC decreased as the pH decreased. This may be because of the neutralizing between borates with negative charge and hydrogen ions with positively charge.The applications of NCC and modified NCC in papermaking were explored. Paper tensile strength and tear strength were improved when NCC and modified NCC were used in the wet end in a certain dosage range. The breaking length of the paper increased 15.7% when the dosage of anionic modified NCC was 2.5%, and the tear index increased 14.9% as the dosage of modified NCC was 0.5%. The breaking length of the paper increased 11.2% and the tear index increased 29.4% when the dosage of cationic NCC is 0.2%. The physical properties could be improved more by modified NCC than the unmodified.It was helpful for the retention of small components of pulp when NCC or cationic NCC was used alone or accompany with CPAM or cationic starch. The retention of fines and fillers and the draining speed could also be improved when cationic NCC was used as the retention aid.
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