Preparation Of Cellulose Nanofibers Aerogels By Adding Cryoprotectant And Its Application

Aerogels,as the lightest solid materials in the world,have a unique three-dimensional porous network structure,with an increasing population.Celluloses Aerogel is the third generation aerogel after the inorganic aerogel and synthetic polymer aerogel.Not only is the cellulose green and renewable,but also natural cellulose material is non-toxic and biocompatibility.Celluloses Aerogel has become a central issue in the field of cellulose material.The paper involves the preparation of TEMPO-oxided cellulose,which consist of PFI mechanical pretreatment and TEMPO-oxided cellulose in the presence of Na2CO3/NaHCO3 buffer solution,and the results showed that the structure of the fiber becomes porous and loose,which enhanced the accessibility of cellulose.Therefore remarkably contributing to TEMPO-oxided efficiency,the carbonate buffer solution can maintain a relatively constant pH in the process of oxidation process,thus improving the selectivity of TEMPO-oxided and decreasing the excess degradation of cellulose.Compared TEMPO-oxided cellulose by Na2CO3/NaHCO3 buffer solution with traditional method,the carboxyl content of TEMPO-oxided cellulose prepared by Na2CO3/NaHCO3 buffer solution and traditional process was 1.15mmol/g and 0.48mmol/g respectively,and the total charge density and Zeta potential were 1.66mmol/g,-70mV and 0.63mmol/g,-59mV respectively.The transmission electron microscopy(TEM)results showed that cellulose nanofibers(CNF)by this method has a narrow size distribution,and is stabilized well in solution.Compared with traditional nanofibrillated cellulose preparation method,Na2CO3/NaHCO3 buffer solution has higer surface density of negative charges and high aspect ratio.But the CNF aerogels has low strength and non-uniform pore size.In order to improve the strength of aerogels,different kinds of cryoprotectants including sorbitol,sucrose and mannitol were added to the nanocellulose suspension to improve the strength of CNF aerogel.The structures and properties of CNF aerogels were characterized.The results showed that cryoprotectant could reduce the viscosity of CNF suspension.The density rose a little,and the range was 0.0120～0.0139 g·cm-3.The results of TEM showed that the CNF size was uniform and the diameter was 10～20 nm.The results of BET showed that the specific surface area was increased and the pore size distribution of aerogels tended to be uniform after cryoprotectant added.The results of SEM showed that the pore distribution of the pure CNF aerogel was uneven,and the pore distribution of aerogel tended to be uniform after adding different cryoprotectants,and the effects of sorbitol was the best.The results of compression experiments showed that the compression strength of CNF aerogel was increased to a large extent after cryoprotectant added.The results of XRD and TG showed that the addition of cryoprotectant would not affect the crystal structure and thermal stability of the aerogels.The adsorption effect of CNF aerogel prepared by different cryoprotectant on methylene blue was researched.As the specific surface area of the aerogel increased,the decolorization rate increased.The decolorization time was 150 min,the temperature was 40 and pH was 11,the decolorization effect was the best.