Preparation,Characterization And Application Of Dilute Sulfuric Acid Method For Nanocellulose

Nanocellulose has unique physical and chemical properties,such as biocompatibility,biodegradability and excellent mechanical properties,etc.,so it plays promising role in application in the fields of nanocomposites,film,supercapacitor,electronics material and other.Therefore,how to produce nanocellulose on a green and efficient scale is of great interest to researchers.In this paper,high yield of cellulose nanocrystals（CNCs）and cellulose nanofilaments（CNFs）were prepared from bleached soft wood kraft pulp（BSKP）by dilute sulfuric acid pretreatment combined with high pressure homogenization.Meanwhile,using chemical pulp as raw material,the lignin-containing cellulose nanofibers（LCNFs）were prepared by the above method.The CNFs and LCNFs obtained by high pressure homogenization were used as the reinforcing phase of PVA composite films to investigate the effects of CNFs on the water resistance and light transmittance of the film material.Nanocellulose aerogels were prepared by TEMPO-oxidation and hydrazine modification of the hydrolysis residue,and the adsorption performance and mechanism of the nanocellulose aerogels for cationic and anionic dyes were investigated.The main researches in this paper were as follows:（1）Using BSKP as raw material,CNCs was prepared by dilute sulfuric acid pretreatment.Through the optimization of single factor reaction conditions,the optimal reaction conditions of acid concentration,reaction temperature,hydrolysis time and cellulose content were 0.3wt.%,160℃,2 h and 3-4 wt.%.Under these conditions,CNCs was typical whisker like cellulose nanocrystal,with a length distribution range of 150-500 nm and a width distribution range of 10-60 nm,and the yield was about 16%.Then,CNFs was prepared from cellulose solid residue（CSR）by high pressure homogenization.The CNFs homogenized for six times at 138 MPa was fibrous like cellulose nanofibers,with a length distribution range of 600-1000nm and a width distribution range of 10-40 nm,and the yield was about 70%.Compared with cellulose nanocrystals prepared by concentrated sulfuric acid method,the CNCs prepared in this paper have better thermal stability.Besides,compared with CNCs,CNFs have higher aspect ratio and are more favorable to be used as reinforcement phase of composites.（2）Using BSKP and chemimechanical pulp（CMP）as raw material,CNF and LCNF were prepared by the above methods.CNF and LCNF were used as reinforcement phase and doped with PVA material.CNF&PVA and LCNF&PVA composite membrane material were obtained by casting method.According to the mechanical characterization,the optimal addition amount of CNF was determined to be 8 wt.%,and then explored the influence of different morphology of CNF and LCNF on the mechanical properties,water resistance,light transmittance and UV barrier performance of the film.The results showed that CNF（homogenized for 6 times）and LCNF（homogenized for 8 times）had the best strengthening effect on the film material,and compared with the pure PVA film material,the tensile strength increased by 32.82%and 92.15%,respectively.Meantime,with the addition of different forms of CNF and LCNF,the water resistance of the composite films was improved.Compared with CNF&PVA films,LCNF&PVA films had poor light transmittance,while LCNF&PVA films had better UV barrier performance,especially in the UVC region of275-200 nm.（3）Using CSR as raw material,TEMPO-oxidation and adipic dihydrazide were used to obtain functionalized nanocellulose,which was cross-linked with aldehydes PEG through hydrazone cross-linking chemistry to prepare nanocellulose aerogel.By investigating the adsorption capacity of the aerogel for cationic and cationic dyes,it could be seen that the aerogel was an anionic aerogel,which can selectively adsorb methylene blue brilliant green cationic dyes,with the maximum adsorption capacity of 85.47 mg·g^-1 and 122.1 mg·g^-1,respectively.According to the adsorption kinetics,adsorption isotherm and diffusion model simulation,the adsorption process of the aerogel was a synergistic process of chemical adsorption and physical adsorption,which was dominated by chemical adsorption.