Preparation And Study On Modified Nanocellulose And Miscibility Mechanism Of Membranes Based On Nanocellulose And Polyethersulfone

Cellulose is biodegradable,environmental friendliness,renewable,and is the most abundant natural macromolecular material in the world.Its down-stream product,nanocellulose,which has some excellent features,like high hydrophilicity,intensity,hyperfine structure and high surface activity.To improve the properties of nanocellulose and enlarge its utilization range,preparation methods and chemical properties of composite membranes have been continuously studied to investigate the required properties in order to prepare high performance of membranes in this thesis.The preparation and characterization of nanocellulose were studied which was used cotton pulp and sodium chlorite.The mechanism was that amorphous area and the crystallization of defective area were broken up by using phosphoric acid.According to the investigation of effect on grain diameter and yield of nanocellulose,the results showed that the efficient reaction conditions were as follows: H3PO4,65%,reaction time,100 min,temperature,120°C.Under the conditions,the diameter was 247 nm,yield was up to 75.85%.The product was characterized by FTIR,SEM and XRD.The results showed that crystalline structure was not destroyed and the crystalline was 61.25% which was higher than cotton pulp.The acetylation and urea modification were carried out.The FTIR of urea modification which was effected by swelling time,catalytic reaction time and urea was characterized.The results showed that the efficient reaction conditions were as follows: swelling time,150 min;catalytic reaction time,60 min;urea,87%.Through the TGA of nanocellulose and urea modified nanocellulose,the thermostability of urea modified nanocellulose was lower than nanocellulose.Then,substitution degree of acetylation modification was tested,and the results showed that the efficient reaction conditions were as follows: reaction temperature,80?;reaction time,2 h;acetic anhydride,83%;H2SO4,0.4%.FTIR showed that –CH3 bending vibration peak and C=O absorption peak were occurred in 1375 cm-1 and 1757 cm-1 which suggested the successful of acetylation modification.XRD also showed the case in 2?=22.7°.The hydrocarbon ration of acetylation was examined through element analysis.According to calculation,the substitution degree of acetylation was 1.78.Though the thermostability of A-NCC was lower than nanocellulose,higher than thermostability of urea modified nanocellulose,so A-NCC was selected as raw material in next research.The compatibility of nanocellulose with polyethersulfone blend system was studied by group-contribution method which indicated that the solubility parameter of NCC and PES was close.And we investigated the determination of viscometric methods,scanning electron microscopy?SEM?,polarized optical microscopy?POM?,fourier transform infrared spectrophotometric?FTIR?.SEM infrared spectrophotometric and differential scanning calorimetry results were obtained from the transparent films cast from the blended solutions.The results showed a partial compatibility existed in the blends system,which may result from the strong hydrogen-bonding interaction between the hydroxyl group of NCC and the sulfonyl group of PES.The mechanism can be studied by scientific methods which provides theroretical basis for preparation of membrane materials,broadens the range of membrane and plays important role in industrial production.Then,the composite film based on A-NCC and PES was carried out by using PVP K30 as an initiator.The preferable reaction conditions of the preparation reaction were confirmed by considering the pure water flux and tensile index which effected by A-NCC,PES and PVP K30.The results showed that the efficient reaction conditions were as follows: PES concentration,18%;A-NCC concentration,3%;PVP K30 concentration,4%;DMAc as solvent;pre-evaporation time,15 s;gel-bath temperature,20?;coagulation bath was water.The results showed that both of them were asymetric membrane and full of finger holes.The addition of A-NCC and PVP K30 made the more holes and higher pure water flux.FTIR showed the structure was not destroyed which indicated the physical combination between A-NCC and PES.Using A-NCC and PES as base materials of the membranes,A-NCC/PES composite ultra films were prepared by L-S phase inversion method.DMAc was used as the casting solvent,PEG 2000 and nano-TiO2 was used as polymer additives.The influence mechanism of the various factors in the membrane preparation process was explored and the mechanical properties,the filtering capabilities?including pure water flux and BSA rejection?,the thermal stability,the morphology,the anti-fouling property of composite membranes were analyzed and characterized.The best preparation conditions of A-NCC/PES composite membranes were as follows: PES concentration,18%;A-NCC concentration,3%;PEG 2000 concentration,4%;Nano-TiO2 concentration,1.5%;pre-evaporation time,15 s.The contact angle of composite membrane was 78° compared with 55° of pure PES membrane and the surface energy was from 87.9 mN/m2 to 114.5 mN/m2 which showed that the hydrophilia of A-NCC/PES composite membrane was higher than pure PES membrane.The decreasing of m and FR showed the higher anti-fouling property.SEM occurred more holes in the surface of composite membrane and pore size was 10-20 nm which can be used as ultrafiltration film.A-NCC/PES composite membrane had good thermal stability below 300?.After immersed by HCL,NaOH and H₂O₂,the pure water flux and rejection still kept good performance which suggested the composite membrane had good chemical stability for the application of industrial production.Combined nano-ZSM-5 molecular sieve with A-NCC/PES microfiltration membrane,organic-inorganic hybrid membrane was prepared to improve the pure water flux and rejection.The influence mechanism of ZSM-5 concentration in the membrane preparation process was investigated and the mechanical properties and filtration properties were analyzed.The results showed that pure water flux of hybrid membrane was 310.65 L·m-2·h-1 and salt rejection was 97.35% when ZSM-5 concentration was 0.3%.By comparing conventional dispersion,ultrasonic agitation and pretreatment of the solvent?DMAc?dispersion,the pretreatment of the solvent?DMAc?dispersion was the best way to improve its dispersibility.The contact angle of composite membrane was 78° compared with 45° of microfiltration membrane and the surface energy was from 87.9 mN/m2 to 124.3 mN/m2 which showed that the hydrophilia of hybrid membrane was higher than microfiltration membrane.The surface and cross images of hybrid membrane SEM showed lots of holes and distributed aperture,some inorganic particles fixed on experimental hole which increased the rejection.And the pore size was close to 2-3 nm belonging to ultrafiltration which laid the foundation for the preparation of reverse osmosis membrance.XRD confirmed the existence of ZSM-5 and the crystal structure was not destroyed.