Study On Preparation Of Biomass Nanofibers From Choline Chloride Deep Eutectic Solvents And Stabilization Of Pickering Emulsion

Cellulose and chitin are two of the most abundant biomass resources on the earth.Because they are insoluble in water,their applications are limited.By reducing the size of cellulose and chitin,they can form stable suspension in aqueous solution,which is beneficial to expand their application scope.Based on the development of a non-toxic and environmentally friendly natural eutectic solvent(NADES)for controllable preparation and functional application of biomass nanomaterials,the technological conditions of preparing nanocellulose and nanochitin from different compositions of deep eutectic solvent(DES)were studied.The feasibility of applying it to stabilize Pickering emulsion was discussed,combined with Transmission Electron Microscope(TEM),Atomic Force Microscope(AFM),Thermogravimetric Analysis(TGA),X-ray Powder Diffractometry(XRD),Fourier Transform Infrared spectroscopy(FTIR),Zeta potential and other analytical methods,reveal the mechanism of DES in the preparation of biomass nanomaterials and emulsion stabilization.The specific research contents and conclusions are as follows:(1)Chitin nanocrystals were successfully prepared at 100 ? with choline chloride and five acids,including oxalic acid dihydrate,lactic acid,malonic acid,citric acid monohydrate and DLmalic acid,respectively.Further analysis showed that the treatment time of DES had a significant effect on the performance of Ch NCs.All the prepared chitin nanocrystals underwent O-acylation.The average diameter of single chitin nanocrystals is 42 nm-49 nm and the average length is 257nm-670 nm.After acidic DESs treatment,the crystallinity of chitin nanocrystals was increased by the removal of amorphous regions.Choline chloride/lactic acid system DES is the best system for the preparation of chitin nanocrystals.The pretreatment time is short,the yield of Ch NCs is the highest(up to 87.5 %)and the stable water suspension can be formed.Therefore,acidic DESs is a non-toxic and environmentally friendly solvents for the production of functionalized/polymerized chitin nanocrystals.(2)Composed of lactic acid(LA)/choline chloride(CC)NADES in milder conditions of preparation of nano cellulose,reaction time,reaction temperature can be reduced to 3 h can be as low as 100 ?,the yield of 75 % ? 89 %,and nanocrystallization of cellulose and esterification reaction happened at the same time.The crystallinity of nanocellulose is lower than that of raw materials due to the influence of mechanical action.TEM analysis showed that nanocellulose crystals(290±65 nm)and nanocellulose fibers(610±50 nm)with different lengths could be prepared by controlling the reaction conditions of choline chloride/lactic acid NADES pretreatment.(3)Both nanocellulose and chitin can be directly used as emulsifiers to prepare oil-in-water(O/W)type Pickering emulsion.The stability of the emulsion increases with the increase of the concentration of nanoparticles,and too large length to width ratio of nanoparticles is not conducive to the stabilization of the emulsion.In comparison,the Pickering emulsion prepared by nanocellulose is more stable.In particular,cellulose from eucalyptus pulp was added to NADES with a LA:CC molar ratio of 3:1 at a solid-liquid mass ratio of 1:100,CNC(CLA4H-3M120)prepared by pretreatment of eucalptus pulp for 4h at 120 ? showed the best stability of emulsion(M3-2808)at a concentration of 0.8 wt% and an oil/water mass ratio of 20/80,with a Zeta potential of-38.4 m V.The droplet size was the most uniform,with an average diameter of 770 nm.(4)Nanocellulose and nanochitin pretreated with deep eutectic solvent(DES)can be used as emulsifiers to prepare Pickering emulsion.However,the mechanisms of Pickering emulsion stabilized by the two biomass-nanofibers are different.Chitin nanocrystal(LA-Ch NC1)is mainly due to its close arrangement on the surface of the droplet,forming a thin layer of isolation film,which achieves the function of mechanical barrier.CNF(CLA4H-1M120)mainly maintains the emulsion stability by forming a three-dimensional network structure on the surface of the droplet.CNC(CLA4H-3M120)not only forms a layer of compact nanocellulose shell on the surface of the droplet,but also forms a three-dimensional network structure around the droplet,so the emulsion has better stability.