Study On The Properties Of Nanocellulose Prepare By Sulfuric Acid Hydrolysis And Ammonium Persulfate Oxidation And Its Nanocellulose Gel

As a new material,aerogel has many excellent properties.such as:high specific surface area,high porosity,low density,low thermal conductivity,low dielectric constant,low light index,strong gas adsorption capacity et al.It has been listed as one of the ten popular materials.At present,the research of aerogels is focused on organic aerogel,inorganic aerogel and composite aerogel.As a third generation of aerogels,the cellulose aerogels not only with the excellent performance of traditional aerogel,but also have some excellent performance of the cellulose.such as abundant raw materials,renewable,biodegradable,good biocompatibility,which has broad application prospects.In this paper,the Cellulose Nanocrystal（CNC）and Cellulose Nanofiber（CNF）were prepared by the methods of microwave hydrolysis and ammonium persulfate oxidation usingpulp as raw materials,and their properties were analyzed and characterized by instruments;The hydrogels were prepared by the method of inorganic salt gel using two nano-celluloses as raw materials.The alcohol gel was obtained by solvent exchange.Finally,through supercritical CO₂ drying and freeze drying to get the aerogels.The main conclusions of the paper was as follow.1)The two kinds of nanofibers still maintain the cellulose typeⅠstructure,the crystallinity increases and the thermal stability decreases.The crystallinity of nanocrystalline celluloseis is75.4%,the initial temperature of thermal degradation（T₀）and the maximum weight loss rate(T_max)are 200℃and 265℃,the diameter is mainly distributed in the range of 24-35nm,the length between 250 and 400nm,the surface hydroxyl groups are oxidized to aldehydes and carboxyl groups and thestructure is two ends of the short rod-like;The crystallinity of Cellulose Nanocrystalsis is 68.9%,the initial temperature of thermal degradation（T₀）and the maximum weight loss rate(T_max)are 210℃and 344℃,the diameter is mainly distributed in the range of50-70nm,the length is several microns,the surface hydroxyl groups are oxidized to aldehyde groups and carboxyl groups and it structure is long fibrous.Compared with nanocrystalline cellulose the Cellulose Nanocrystals have higher thermal degradation of the initial temperature and maximum weight loss rate and larger diameter and length,but the crystallinity is low,the shape of the two kinds of nanocellulose is also different.These differences are mainly due to the different in raw materials and preparation methods.2)The best drying process of CNC alcohol gel with the mass fraction of 1.5%is 45℃,2h,12MPa,the optimum drying process of the mass fraction of 2.5%and 3.5%are 45℃,3h,12MPa,The optimum drying process of CNF alcohol gel with the score of 1.5%is 50℃,2h,13MPa,the best drying process of the mass fraction of 2.5%and 3.5%are 50℃,4h,13MPa.3)The mechanical properties were measured by universal testing machine.The compressive strength of CNC aergel and CNF aergel that mass fraction are 1.5%,2.5%and3.5%and drying by supercritical CO₂ drying was 0.32MPa,0.40MPa,0.46MPa and 0.37MPa,0.67MPa,0.77MPa.The compressive strength of CNF aergel that mass fraction are 1.5%,2.5%and 3.5%and drying by freeze-dryingwas 0.85MPa,1.32MPa and 1.47MPa.The compressive strength of cellulose aerogels increases with the increase of the mass fraction of nanofibers.4)Though the Sweep Electron Microscope to observe the aerogel internal microstructure we fond that the aerogels obtained by supercritical CO₂ drying havethree-dimensional network structure in the internal extended region.The aerogels obtained by freeze-drying is a three-dimensional layered structure in the internal extended region,and the higher the mass fraction of nanocapsules,the more dense the internal structure.The higher the mass fraction of nano-cellulose,the more dense the internal structure.5)The N₂isothermal adsorption line of the aerogel conforms to the isothermal adsorption line of the second type that is the multi-layer adsorption.The pore size of the aerogel is mainly mesoporous.With the increase of the mass fraction of nanofibers,the adsorption capacity increased and the pore size decreased.With the increase of the mass fraction of nano-cellulose,the dry shrinkage of alcohol gel decreased and the density of airgel increased.6)When the mass fraction of nanocellulose are the same the dry shrinkage and internal pore size of the aerogel that prepared by CNC are larger than the aerogel that prepared by CNF.The compressive strength and specific surface area of he aerogel prepared by CNC are smaller than the aerogel prepared by CNC;The density,compressive strength and shrinkage ratio of the aerogel that obtained by supercritical CO₂ drying are larger than the aerogel that obtained by freeze-drying,but the specific surface area and the internal pore size are smaller.