Study On Preparation And Properties Of Biomass Nanofibrils Based On Sulfation

Sulfated nanofibrils exhibit a great prospects application in some fields such as biomedicine and nanoparticle dispersion due to the advantages properties of high swelling and high dispersibility.Currently,the sulfated nanofibrils are mainly obtained from hydrolysis by sulfuric acid and the esterification by sulfur trioxide and chlorosulfonic acid.However,these methods show some disadvantages such as a low yields and the surface properties was uncontrollable.Hence,it is of great significance to develop a safe,fast,efficient and controllable surface function for the preparation of biomass sulfated nanofibers.In this paper,the waste bagasse,cotton fabric,wood block and chitin powder were used as raw materials.The sulfation biomass nanofibrils were prepared by the strategy of nano-derivatization,that is,the biomass was sulfated by sulfamic acid and follow by treated with mechanical force.In order to realize the controllable preparation of sulfation biomass nanofibrils,the mechanism and kinetics of sulfation,nanofabrication mechanism of biomass,and surface chemistry regulation were studied systematically by means of solid-state ¹³C NMR,Fourier transform infrared spectroscopy,elemental analysis,thermogravimetric analysis,conductometric titration,and atomic force microscopy.In addition,the potential applications of the sulfation nanofibrils were discussed.The main research includes the following aspects:（1）Study on preparation and properties of sulfated cellulose nanofibrils（BSCNFs）by the method of mechanically activated assistance.The waste bagasse was used as raw material and a small amount of N,N-Dimethylformamide（DMF）was used to active the bagasse fibers.The preparation of BSCNFs was carrried out with the sulfated modification by sulfamic acid with the assistance of mechanical shear activation by ball milling.The results showed that the sulfate half-ester groups（-OSO₃^-）formed by the sulfation was beneficial to the nanofabrication of bagasse fibers.Besides,the degree of nanofabrication of bagasse fibers and the surface properties of the obtained BSCNFs could be regulated by changing the mechanical strength and the degree of sulfation.In additon,the degree of substitution of the obtained BSCNFs increased with the mechanical strength or the ratio of esterification reagents,however,the size and degree of polymerization decreased on the contrary.Moreover,the bagasse could be completely nanofabrication the when the degree of substitution was over than 0.04.The diameter,degree of polymerization and degree of substitution of the obtained BSCNFs were about10±5 nm,810-930 and 0.02-0.15,respectively.The properties of BSCNFs were also evaluated and the results showed that BSCNFs exhibited an excllent thermal stability and water dispersibility.（2）Study on Preparation and the properties of nanoparticles dispersion of sulfated cellulose nanofibrils（SCNFs）by heterogeneous derivatization.In order to investigate the reaction mechanism between sulfamic acid and cellulose,the waste cotton cloth with a high purity of cellulose was used as raw material.The results showed that the sulfamic acid mainly reacted with the hydroxyl group at the C6 on the surface of the cotton cellulose.In order to explore the influence mechanism of solvent swelling on the reaction effect,the cellulose raw materials were pretreated with two solvents,DMF and water,respectively,and the highest degree of substitution of 0.34 and 0.39,respectively,were obtained after sulfation for 1 hour.The results showed that the reaction rate and the degree of substitution were positively related to the concentration of the esterification reagent.The SCNFs were obtained by mechanical treatment after sulfation and the degree of substitution,potential and charge density of SCNFs increased with the reaction time and temperature,while the yield,size and degree of polymerization of SCNFs decreased with the same condictions on the contrary.The results showed that the properties of SCNFs could be regulated by changing the reaction conditions.Based on the advantage of the high zeta potential,the SCNFs were used for carbon nanotubes（CNTs）and nano-Zn O dispersion,respectively.The results showed that both of the SCNF/CNT and SCNF/Zn O suspension could be stabled for more then 15 days and the dispersion stability increased with the degree of substitution of the SCNFs.（3）Study on preparation and the properties of anti-UV of sulfated lignocellulose nanofibrils（LCNFs）by heterogeneous derivatization.The birch and sylvestris pine wood powders were used as raw materials for the sulfation,respectively.The results showed that the presence of lignin and hemicellulose did not inhibit the sulfation.Besides,the LCNFs exhibited a higher charge density after the mechnical treatment.The results of kinetics showed that birch exhibited a faster reaction rate and a higher degree of substitution then that of sylvestris pine.The LCNFs preaperd from birch showed the highest surface charge density of about 2.1 mmol/g after sulfated for 2 hours.Based on the inherent UV resistance properties of lignin,the properties of UV resistance properties LCNFs membranes were also evaluated.The results showed that the LCNFs membranes exhibited an excellent UV-light absorption efficiency and the absorption rate increased with the lignin content.The highest absorption rate of excellent UV-light could was as high as 99.6%.However,the LCNFs membranes showed a poor mechanical property and the tensile strength could be significantly improved by compounding with polyvinyl alcohol（PVA）.In addition,the results also showed that the UV resistance of LCNFs/PVA composite films enhanced with the increase of lignin content.（4）Study on preparation and size regulation of sulfated chitin nanofibrils（Ch NS）by heterogeneous derivatization In order to expand the scope of sulfation biomass nanofabrils preparation,the chitin was used as raw material.The Ch NS was obtained after the sulfation with sulfamic acid and followed by mechanical treatment.The results showed that chitin could be sulfated by sulfamic acid effectively.Besides,the results of kinetics showed that the sulfation reaction of chitin followed to the first-order kinetic model,and the reaction rate constant and activation energy were 0.18 min-¹ and 109 KJ/mol,respectively.The Ch NS showed a diameter and length of about 4-6 nm and 100-600 nm,respectively,as well as an excellent water dispersibility.The effects of reaction conditions on the size and properties of Ch NS were further explored by atomic force microscopy,XRD crystal size analysis and turbidity analysis.The results showed that the swelling effect,degree of substitution and charge density of Ch NS increased with the reaction time,temperature and concentration,while the size decreased accordingly.Moreover,it was found that the addition of urea could inhibit the reactivity of chitin and avoid the excessive degradation.Hence,the size and the degree of substitution of Ch NS can be further regulated by adding urea into the reaction system.