Preparation And Properties Of Nanocrystalline Cellulose Via Ultrasonication Assisted Method

Nanocrystalline cellulose (NCC) was a hotspot in nanotechnology field for its advantages of abundant, renewable, biodegradable and excellent mechanical properties. It had high Young’s modulus and strength, and also the properties of lightweight, biodegradable, biocompatible and renewable had exhibited great application prospects in preparing the high-performance composite materials. NCC was prepared form different plant materials through controlling chemical, mechanical or biologic methods. Some special bacterial and tunicate were also excellent materials to prepare NCC. How to expand raw materials, as well as through optimizing the preparation method to produce low costs, efficient and environmental friendly NCC had great theoretical meaning in further application.This paper aimed to preparing NCC with different morphologies through using different cellulose materials via ultrasound assisted method. PVA composites were prepared using rod-shaped and the long web-like NCC as enhanced materials. Magnetic nanomaterials were prepared using long web-like NCC as matrix. Mesoporous TiO2spheres prepared by an acid catalyzed hydrolysis method using rod-shaped NCC as template. SEM, TEM, XRD, DRS, N2adsorption isotherm and VSM were used for characterization of NCC, nanocomposites and SP-TiO2photocatalyst.Nanocrystalline cellulose (NCC) with small particle size and high crystallinity was prepared via the combined method of ultrasonication and acid hydrolysis from bleached softwood kraft pulp (BSKP). The analyses revealed that rod-shaped NCC particles with diameter of10to20nm can be obtained. Ultrasonication can induce cellulose folding, surface erosion, and external fibrillation of BSKP, together with the shorter average length of NCC (96nm) than that prepared without ultrasonication (150nm). Due to the smaller size and larger number of free ends of chains, the thermal stability of NCC was lower than BSKP. The degradation of BSKP exhibited one significant pyrolysis stage within the range of300to420℃. In contrast, UH-NCC exhibited three pyrolysis stages within the range of210to450℃. NCC prepared with ultrasonication decomposed at lower temperature and over a wider temperature range, together with higher char yield of43%(compared with27%for that without ultrasonication). The obtained NCC had similar surface chemical structures but higher crystallinity (82.3%) compared with that of the starting BSKP (74.9%).Rod-shaped NCC was prepared from microcrystalline cellulose (MCC) using the purely physical method of high-intensity ultrasonication. The reinforcement capabilities of the obtained NCC were investigated by adding it to poly (vinyl alcohol)(PVA) via the solution casting method. The results revealed that the prepared NCC had a rod-shaped structure, with diameters between10-20nm and lengths between50-250nm. X-ray diffraction results indicated that the NCC had the cellulose I crystal structure similar to that of MCC. The crystallinity of the NCC decreased with increasing ultrasonication time. The ultrasonic effect was non-selective, which means it can remove amorphous cellulose and crystalline cellulose. Because of the nanoscale size and large number of free-end chains, the NCC degraded at a slightly lower temperature, which resulted in increased char residue (9.6%-16.1%), compared with that of the MCC (6.2%). The storage modulus of the nanocomposite films were significantly improved compared with that of pure PVA films. The modulus of PVA with8wt%NCC was2.40×larger than that of pure PVA.Optically transparent reinforced poly (vinyl alcohol) composites were prepared using NCC from bleached hard kraft pulp (BHKP) isolated by high-intensity ultrasonication. The obtained NCC was used to reinforce PVA to make nanocomposites via the solution casting method. The results revealed that the prepared NCFs were long web-like structure, with diameters between20-80nm and lengths more than500μm. X-ray diffraction results indicated that the NCFs had the cellulose I crystal structure similar to that of BHKP. The crystallinity of the NCFs increased from77.3%(BHKP) to78.3%. The initial pyrolysis temperature shifted to a lower temperature than that of the Al-CFs, because of increased the number of hydroxyl groups of NCFs. The tensile modulus and Young’s modulus of PVA composites were significantly improved with the NCC loading of4%which was1.86×and1.63×that of neat PVA and also retained an excellent transparency.NCC aerogels were prepared from poplar alkaline peroxide mechanical pulp (APMP) using physical ultrasonication method. As raw materials, the unique mechanical effects of APMP cause the fiber folding and loose during the pulping process, which was beneficial to further chemical purification and subsequent treatment for long and entangled NCC. The obtained NCC exhibited higher crystallinity (77.8%) compared with that of APMP (72.6%) together with diameters range from20to90nm and self-assembled to network. The primary thermal degradation of NCC occurred at331.5℃. The prepared NCC network aerogels acted as a novel matrix which can prevent the growth and aggregation of ferromagnetic CoFe2O4nanoparticles. The magnetic properties were all increased with increasing the reaction concentration of FeSO4/CoCl2salt.Mesoporous nanosize TiO2spheres (SP-TiO2) were prepared using rod-like NCC as template. The results showed that SP-TiO2was uniform in size with a diameter of100-200nm. SP-TiO2was composed of smaller crystal particles (10-20nm). The average mesoporous pore diameter of SP-TiO2was8.2-13.5nm, which increased with increasing calcination temperature. A nano-scale reactor that was formed by bonding between the hydroxyl groups of NCC long-chain can inhibit the growth and aggregation of the TiO2precursor, promote its self-assembly into spherical structure, and inhibit the phase transformation from anatase to rutile. SP-TiO2prepared at600℃exhibited the highest activity with the phenol degradation percentage of89%.