Preparation Of Cellulose Nanocrystals And Chiral Membranes By Swelling And Oxidizing Cotton With Ammonium Persulfate

The suspension of nanocrystalline cellulose(NCC)has chirality after drying and forming films.If water-soluble substances or water-soluble substances that are soluble after reaction are added,nanocrystalline cellulose suspension as chiral template can be used to construct chiral composites,and it has become a research hotspot in chemistry,medicine and other fields.The morphology and length-to-diameter ratios of nanocrystalline cellulose are important for preparation of chiral complexes,and yield of NCC plays a crucial role in the industrialization of nanocrystalline cellulose and chiral complexes.In this paper,in order to improve the yield of nanocrystalline cellulose and reduce reaction time,nanocrystalline cellulose was prepared from the raw material of cotton linter by the method of ammonium persulfate(APS)swelling followed by oxidation and hydrothermal ammonium persulfate swelling followed by oxidation.The effects of different preparation conditions on the yield,crystallinity,morphology and size of nanocrystalline cellulose particles were investigated in details.The natural drying film formation of nanocrystalline cellulose suspension prepared under two optimal conditions is proved to be chiral by characterization.(1)At the same condition of oxdition time at 12 hours and oxidation temperature at 60°C,the one-step of ammonium persulfate swelling followed oxidation was the method to prepare nanocrystalline cellulose suspension with the series condition of different swelling temperature,swelling time and solid-liquid ratio,which represents the mass of cotton linter divided the volume of ammonium persulfate volume.The swelling effect of cotton linters and yield,particle size,crystallinity,the average degree of polymerization and Zeta potential of nanocrystalline cellulose were analyzed by optical microscope,X-ray powder diffraction(XRD),atomic force microscopy(AFM),Zeta potentiometer and Fourier infrared spectrometer(FT-IR),respectivelly.The XRD and FT-IR characterization analysis showed that the cellulose structure of nanocrystalline cellulose prepared by the method of ammonium persulfate swelling followed oxidation was not destroyed,and the crystallinity was greatly increased compared with the raw materials cotton linter.The C-OH of C6 was oxidized to-COO-.The Zeta potential characterization proved that the same negative charges repel each other among nanocrystalline cellulose,thus maintaining the stability of nanocrystall ine cellulose suspension.According to the AFM characterization showed that the morphology of nanocrystalline cellulose was spindle.The ratio of length and diameter is in the range of 1?100.The optimal preparation conditions of the nanocrystalline cellulose is swelling temperature at 25°C,swelling time at 3.0h and the solid-liquid ratio of 1:50,which have the best swelling effect on the cotton linters.The yield,the crystallinity,the distribution of length and width and Zeta potential was 95.75%,93.51%,136±90nm,10±5nm and-30.5m V,respectively.(2)To reduce the swelling time and reaction time,the hydrothermal ammonium persulfate swelling followed oxidation was the method to prepare the NCC suspension with the series condition of different swelling temperature,swelling time and reaction time at the same condition of the solid-liquid ratio at 1:50 and oxidation temperature at 60°C.The yield,particle size,crystallinity,average degree of p olymerization and Zeta potential of NCC were analyzed by optical microscope,XRD,AFM,Zeta potentiometer and FT-IR.The analysis results showed that the morphology of nanocrystalline cellulose was spindle,the cellulose structure of nanocrystalline cellulose was not destroyed,and the crystallinity was greatly increased compared with the raw materials cotton linter.The C-OH of C6 was oxidized to-COO-and the nanocrystalline cellulose suspension can still exist stably.The results show that the optimal preparation conditions of the nanocrystalline cellulose is swelling temperature at 25°C,swelling time at 2.0h and reaction time of 8.0h.The higest yield,the highes crystallinity,the minimum length distribution and Zeta potential of nanocrystalline cellulose were 92.21%,92.98%,117±61nm and-29.7m V,respectively.Compared to the optimal results of ammonium persulfate swelling followed oxidation,the morphology of spindle,yield and crystallinity of nanocrystalline cellulose were similar.The length distribution of NCC is narrow.The raw cotton is placed in the hydrothermal reactor.The gas and hydrogen peroxide were produced by the decomposition of ammonium persulfate and the hydrolysis of persulfate,respectively.Hydrogen peroxide was heated to produce oxygen.The swelling time and oxidation time was reduced by strengthening the pressure of the reaction system in a closed reacter.The mechanism of preparation of nanocrystalline cellulose by ammonium persulfate swlling followed oxidation cotton was put forward.The first process is the swelling of cellulose molecular chain in the ammonium persulfate solution.The second process is the oxidation of the amorphous and crystalline regions of cellulose by hydrogen peroxide and sulfate radical produced by the hydrolysis and thermal decomposition of persulfateradical in the ammonium persulfate solution.The last process is that the surface of nanocrystalline cellulose has the carboxyl group with the negative charge,which maintains the stablity and unagglomeration of the nanocrystalline cellulose suspension.(3)The nanocrystalline cellulose suspension prepared by the ammonium persulfate swelling followed oxidation and the hydrothermal ammonium persulfate swelling followed oxidation under the optimal conditions were drought to film at the room temperature.Polarized light microscopy and the field emission scanning electron microscopy were used to characterize whether nanocrystalline cellulose films had irsident and the cross sectional morphology,repctively.The results show that the irisident began to appear in the drying process of nanocrystalline cellulose films and the irisident appeared in the surface of it when completely dried.The morphology of cross section showed a layer by layer stacked structure,indicating that the nanocrystalline cellulose films were chiral.