Cellulose Acetate Micro Nanofiber Preparation And Their Applications In Aerosol Filtration Materials

The manufacturing technology of industrialized cellulose fibers in traditional textile industry is quite mature.With the rising prices of raw materials,labor and other factors like financing and channel costs,orders are gradually transferred to the surrounding Asian countries.The traditional textile industry is squeezed,while the non-renewable resources such as oil,coal and natural gas are decreasing day by day.It gives a huge space for the development of renewable resources such as regenerated cellulose fiber.As a pillar industry,China's textile industry had a total output value of RMB 6893.565 billion,accounting for 8.3% of GDP in 2017.In 2017,the total output of cellulose fibers(viscose,cellulose acetate,copper and ammonia fibers)in the world was 5.36 million tons.China,accounting for 71%,was the largest producer in the world.The 13 th Five-Year Plan outlined the progress of science and technology in the textile industry.In the guidance of high and new technology for fiber materials,independent innovation technology is highly recommended to promote industrial restructuring,while the functional modification and differentiation toward the direction of functionalization,thin and green cellulose fibers.Cellulose acetate(CA)is mainly used in the field of textiles and cigarette filter.With the development of nanotechnology,micro-nano cellulose acetate fiber is gradually used in other fields like air filtration,water filtration,wound dressing,biomedical scaffold materials,energy storage components,flexible display screen,personal care products and so on.The paper took CA as the research objects.To begin with,the preparation methods and application fields of cellulose and its derivatives were reviewed,as well as the needle and needleless electrospinning spinnerets for mass production.The air filtration theories and characterization were also reviewed.Secondly,it was our first attempt to synthesize cellulose acetate from tobacco stalk pulp(TSP).We have also prepared cellulose diacetate(CDA)from different types of wood pulp.The spinnability of CDA from cheap tobacco pulp was proven by electrospinning.Then,cellulose triacetate(CTA)was hydrolyzed to cellulose monoacetate(CMA)to change its water affinity.The Janus micro nanofiber membrane with asymmetric water affinity was prepared by two-step electrospinning.Afterwards,the spinnability of CDA micro nanofiber was explored by needleless electrospinning when dissolved in acetone/ dimethyl sulfoxide(DMSO).The output was further improved by adjusting the electrospinning parameters.Finally,CDA micro nanofiber filters were prepared by needleless electrospinning.Different structures were designed according to simulation results with high filtration efficiency and low resistance.The research had comprehensively analyzed the preparation of CA micro nanofiber filter and its potential use in air filtration.Firstly,the chemical composition of different pulps were analyzed by high performance liquid chromatography(HPLC).Took TSP for example,the reaction time,solid-liquid ratio of reaction system,catalyst amount and pre-treatment conditions of low temperature acetylation method were explored.TSP CTA was prepared under the modified reaction procedure.The method was also suitable for the preparation of CTA from softwood and hardwood pulps.The relationship between DS and hydrolysis time of commercial CTA was explored.The spinnability of TSP CDA is verified by blend electrospinning.A large number of beads were obtained by pure TSP CDA electrospinning.The electrospinning of TSP CA after hydrolysis with different proportion of commercial CDA was carried out to verify its spinnability.The blending of TSP CDA into commercial CDA reduced the broken fiber amount and the diameter of electrospun submicron CA fiber with increasing blending ratio.Then,the effect of reaction variables on CA DS was studied.Secondly,the hydrophilic submicron fiber membrane of commercial dissolved pulp(DPA)cellulose monoacetate(CMA)were prepared after hydrolysis.The degree of substitution(DS)of CTA prepared by DPA was calculated by 1H-NMR.The contact angles of electrospun DPA CTA and CMA fiber membranes were measured and compared respectively.The average fiber diameter was also reduced with lower DS.Then,CDA and CMA were prepared from CTA at different hydrolysis time in high temperature.The DS at different carbon position was calculated by 1H NMR.As the DS decreases,the average electrospun fiber diameter,average porosity and water contact angle decreased gradually.The reduced Ag NPs by UV were loaded on the asymmetric water affinity Janus CA membranes with excellent antimicrobial properties by a two-step electrospinning method,CMA electrospinning and CTA electrospinning on the same collector.The mechanism of this phenomenon was also analysis.The resistance of antimicrobial fiber membrane against Staphylococcus aureus and Escherichia coli was measured by the colony count method and the inhibition zone method.Thirdly,the solution viscosity and conductivity were measured.The solution viscosity increased with increasing CDA concentration,while the conductivity remained unchanged.CDA submicron nanofibers could be obtained continuously and stably with a disc-shape needleless electrospinning spinneret in acetone/ DMSO solvent system.The addition of amphiphilic surfactants(SAA)dodecyl trimethyl ammonium bromide(CTAB)affected the solution viscosity,conductivity and surface tension at different CDA concentrations.With the increase of CTAB content,the solution viscosity decreased,and the conductivity increased,while the surface tension decreased gradually and tends to be stable eventually.The partial correlation analysis between solution properties(viscosity,surface tension,conductivity)and average fiber diameter and their coefficient of variation(CV)value was studied by SPSS.Solution viscosity was highly correlated to average fiber diameter,and surface tension was weakly correlated with average fiber diameter,while conductivity was negatively correlated to average fiber diameter.The addition of CTAB changed the solution viscosity,conductivity as well as the surface tension,but the combination of the three factors has no effect on the average fiber diameter CV.The linear regression relationship between solution viscosity and average fiber diameter was obtained by SPSS.The fitting relationship between the actual average fiber diameter and the predicted value was also illustrated.The influence of electrospinning ambient temperature applied voltage and bubble size in solution on CDA micro nanofiber output was studied by response surface analysis.The influence significance order of different factors on the CDA micro nanofibers output is ambient temperature,applied voltage and bubble size respectively.The electrospun CDA nanofiber for mass production by needleless spinneret was successfully prepared with different solvent systems.The output of CDA micro nanofiber was further improved by parameters adjustment.Finally,CDA nanofiber filters were prepared by needleless electrospinning.The fluid motion towards different filter thickness with different fiber diameters in the computational domain were studied through COMSOL Multiphysics 5.4.With the same filter thickness and solid volume fraction(SVF)for comparison,filtration efficiency and pressure drop increased with decreasing fiber diameter,while the quality factor reached maximum when the fiber diameter was 0.5 ?m,which indicated that the decrease of fiber diameter did not contribute to higher QF with all else being equal.Similarly,the increase of filter thickness increased filtration efficiency with lower QF.Then,three different structures with different diameters ranges were designed to simulate the effect of diameter distribution on filtration effect.The results showed that the filtration efficiency increased gradually with decreasing fiber diameter CV.When CV equaled to 0,the pressure drops increased slightly with a decrease of QF,indicating that the QF value could not be improved continuously with completely uniform fiber diameters with all else being equal.Then,by changing the angle ? between the filter and fluid velocity direction,the filtration efficiency and QF of the filter increased significantly when ? was lower compared to the other samples with same thickness and SVF value,which was mainly due to the increase effective filtration area of the filter in the simulation domain.With lower ? value,the QF value of the filters could be improved.CDA filters with different diameter ranges and CV were obtained by electrospinning.The results showed that smaller average fiber diameter and CV were conducive to improving the filtration efficiency and QF with rather low pressure drop.The filtration efficiency of the combined structure of the aforementioned CDA filter was even enhanced.In this work,CA preparation and CA micro nanofiber were studied for various applications.It was intended to broaden the applications of CA micro nanofiber,which may provide with some reference for more researchers in related fields.