Preparation Of Nanofibrillated Cellulose By The Combination Of Chemical And Mechanical Treatment

Environmental wood-based nanofiber papers possess many unique properties, such as excellent mechanical strength, porous structure, high transparency, et al., these properties make nanocellulose paper have a potential charm in wearable electronic equipment, flexible battery diaphragm paper and flexible display, super capacitor to replace the plastic and glass membrane in electronic devices. High energy input, wide size distribution and poor dispersibility of nanofibrillated cellulose(NFC), however, hinder the development of nanofiber materials for commercial application.Based on the knowledge of wood fibers structure and morphology, NFC was prepared by the combination of chemical and mechanical treatment, including cutting, hammering, kneading, TEMPO-oxidation and high-pressure homogenization. The high yield NFC has narrow size distribution and retains uniform dispersion using these technologies. The main conclusions are as follows:According to the relationship between microfibrillar angle and fibers length, the fibers could be crushed overall and cracked in longitudinal axis, when the length of fibers were cut to 0.20-0.64 mm in length and with 1 or 2 laps of the winding number of microfibrils around the fiber axis, as well as the length of preliminary microfibrillated fibers could be effectively controlled under in the process of kneading.At pH 10-10.5, mechanical hammering pretreatment promote fibrous fracture and fibrillation in longitudinal direction of cellulose fibers which were in the length of 0.40 to 0.64 mm. The increase of specific ratio of cellulose fibers which made hydrated Na+ easily permeate to break the intramolecular hydrogen bonds, with the ongoing swelling, the P and S1 layers of cell wall were destructed and cut into fragmentation. The fiber length was less than 0.40 mm, the effect of fibers swelling was more apparent. However, it could mainly occurred in local position or cross section of fibers when the length was longer than 0.64 mm.The microfibrills layers with by above pretreatment weakening hydrogen bond could be easily defibrillated using kneading, and obtain preliminary nano-scaled microfibril bundles. The surface of microfibrils were introduced carboxy groups undergoing TEMPO/NaClO/NaBr oxidation system treatment and showed higher hydrophilicity. In combination of TEMPO/NaClO/NaBr oxidation and high-pressure homogenization, we obtained uniformly fibrillating NFC suspensions with the diameter in the range from 10 to 20 nm and in 1000 nm longitudinal length.Therefore, though the process of cutting, hammering, kneading, carboxylation and shearing successively, pulp fibers could be fibrillated into nanoscale in higher yield with uniform dimensions, high transparency and stable suspension.