Preparation And Application Of Polymer Membranes Prepared By Atomization Assisted Non-solvent Induced Phase Separation Method

The separation performance of polymeric membranes is determined by the membrane material and the morphological structure of the prepared membranes,which is affected by the preparation process.Non-solvent induced phase separation,also known as L-S phase separation,is the commonly used method to prepare asymmetric polymer membranes.In this dissertation,the membrane preparation process was adjusted and improved.An atomization pretreatment was added to the non-solvent induced phase separation process to slow down the phase separation speed,aiming at controlling the membrane microstructure.Microfiltration membranes with bicontinuous network pore structure were prepared by this optimized method.Superwettability surfaces with micro-nano composite structure were obtained by combining this method with polymer blending,high-pressure spraying.The formation mechanism was revealed and the application potential of the membranes in adsorption,oil-water separation,and fog collection,was thoroughly investigated.The following are the main research contents:1.A novel polymer membrane preparation method,the atomization assisted non-solvent induced phase separation（AA-NIPS）method,was developed.Using this method,membranes based on commercial polymer polyacrylonitrile（PAN）were prepared,of which the microstructure can be regulated by adjusting polymer concentration of the casting solution,the atomization pretreatment time and the fog amount.With the increase of the atomization pretreatment time,the microstructure of the membranes gradually changed from ultrafiltration membrane with small pore size to microfiltration membrane with bicontinuous network pore structure,and the porosity also showed an increase trend.The atomization pretreatment time also affected the membrane surface wettability and specific surface area,and then affected the adsorption performance of the membrane.With the increase of the atomization pretreatment time from 0s to 40 s,the adsorption capacity of methylene blue on the PAN membranes with a concentration of 8 wt%in the casting solution increased from 53 mg·g^-1to 117 mg·g^-1,and the adsorption capacity increased by 2.2 times.By fitting the experimental data,it was found that the adsorption of methylene blue on the PAN membrane was caused by the synergistic effect of physical adsorption and chemical adsorption,and the adsorption process could be described by the Langmuir isotherm adsorption equation.2.Inspired by the three-dimensional fiber network structure of loofah,microfiltration membranes with a bicontinuous network pore structure based on commercial polymer PAN and polyvinylpyrrolidone（PVP）were prepared by AA-NIPS method.The effects of PVP content and atomization pretreatment time on membrane structure and wettability were studied.PAN/PVP membranes with a layer of nano-protrusions distributed on the entire membrane fiber skeleton were obtained.It was proposed that the formation of nanoprotrusions was caused by the microphase separation of the two polymers and the entanglement of polymer chains,as confirmed by the ATR-FTIR,NMR and AFM characterizations.The micro-nano composite structure endowed the membrane surface with underwater superoleophobicity and excellent anti-oil adhesion properties.Surfactant-free and surfactant-stabilized oil-in-water emulsions could be effectively separated at low pressure.In addition,the long-term performance of the membrane was proved by ultrasonic treatment,mixed solvent treatment and cycle test.The excellent performance of the membrane in separating oil-in-water emulsions and its preparation process with easy to scale-up feature showed that the membrane would have a good application prospect.3.Inspired by the superhydrophobic/superhydrophilic patterned water collection mode of natural organisms,porous membranes with hybrid wettability of micro-nano composite structure were prepared by combining AA-NIPS method with high-pressure spraying.The membranes were capable of collecting fog droplets effectively owing to the patterned membrane surface with both superhydrophilicity and superhydrophobicity.By adjusting the atomization pretreatment time and the high-pressure spraying time,the microstructure of the membrane surface and the coverage of the hydrophobic part were tuned to optimize the fog collection efficiency,reaching the maximum of 46.0mg·cm^-1·min^-1.At the same time,the membrane could be used continuously for a long time because of its excellent interface stability.4.A continuous AA-NIPS process was realized by reforming the roll-to-roll production equipment in the laboratory.The non-woven fabric support,the scraper machine speed,the feeler gauge thickness and the scraping process were optimized so that efficient oil-water separation membranes can be prepared.Using the optimal process parameters,the flat sheet membrane module was prepared and used for the oil-water separation performance test.The separation flux of the membrane fabricated by the continuous process to the emulsifier-stabilized diesel/water emulsion could reach 1312 L·m^-2·h^-1,with a corresponding separation efficiency of 98.9%.The cycle test proved that the flat sheet membrane obtained by the continuous preparation process could effectively separate the emulsified oil for a long time,indicating of great practical application potential.