| Cellulose nanocrystals (CNC), one kind of natural organic polymernano-materials, are isolated or extracted from native plant and animal tissues.Benefiting from its high purity, high crystallinity, high young’s modulus, as well astheirs intrinsic renewability, biodegradability, biocompatibility et al, CNC are widelyapplied in biological medicine, food industry, textile and compound reinforcements.Through the study of the chemical functionalization of CNC surface modification, aswell as the quantitative control of CNC material crystal type and crystallinity, morehigh quality performances of CNC material will be given, making a wider applicationprospect for CNC in more fields in the futureThe paper focuses on the preparation of jute CNC, structure research and thecharacterization applications of synchrotron radiation small/wide angle X-rayscattering (SR-SAXS/WAXS), aiming to explore quantitative controllable preparationon crystallinity and crystal type of cellulose for jute CNC. There are three main stepsas follows:(1) the preliminary preparation of jute CNC;(2) the effects of pretreatmentconditions on cellulose crystallinity and crystal typeof jute fiber and CNC;(3)preparation of jute CNC under optimized conditions and corresponding structurecharacterization.NaOH and DMSO chemical pretreatments are conducted to jute fibers, followingby TEMPO mediated oxidation of jute CNC. In the end we obtained CNC with lateralsize of12~30nm and radial size of hundreds nano. The SR-SAXS/WAXS resultsshow that NaOH and DMSO have different impacts on jute cellulose crystallinity,crystal type and CNC sizes. In detail, the sizes of CNC from jute fibers after theDMSO are larger than that of jute fibers only pretreated by NaOH. What’s more, the crystallinity indexes as well as the crystal forms of CNC and pretreated jute cellulosestay uniform. As to the jute CNC aerogels obtained from freeze-drying have porousand lamella spatial structure, the SEM results show that the CNC concentrations havedirect influence on the macrostructure of lamella CNC and aerdgels.The SR-WAXS characterization and analysis are operated on jute cellulosecrystallinity and cellulose II content by changing the concentration of NaOH,temperature and duration time of NaOH pretreatments. It’s found that the pretreatmentof NaOH and DMSO solvent have different influences on cellulose crystallinity andcrystal forms owing to their opposite effects on the size of OH-and Na+. Thecrystallinity of all CNC samples are above70%, higher than that of mercerized jutecellulose, and has a similar changing trends with that of jute cellulose, however, thecellulose II content has very close value to that for mercerized jute cellulose. TheFTIR and DSC results provide the detailed information of the composition changesfor hemi-cellulose and lignin, together with the hydrogen bonds and chemical groupschange before and after the pretreatments and TEMPO-mediated oxidation.An optimized process for the preparation of jute CNC by TEMPO-mediatedoxidation is obtained according to the different influences of pretreatments on jutecellulose and CNC. After the optimization, the productive rate of CNC increases by27%, the energy consumption reduces sharply, the preparation period shortens by1/3,and about57%TEMPO is recycled by adding H2O2. The final product jute CNC hassimilar crystallinity and size of12~15nm for sectional dimension and100~250nmfor radial dimension with that of pristine jute cellulose. The SR-WAXS resultsprovide the shape and size of cellulose crystallites in CNC as well as theircorresponding changes after the TEMPO-mediated oxidation. In combination with theTEM characterization, the schematic structure of CNC composed of cellulosiccrystallites is also obtained. |
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