| At present,the problem of air particulate matter pollution is still severe,which has caused serious impact on people's health and production activities.The controllable emission of industrial dust-laden gas is one of the key methods for prevention of air particulate pollution.Filtering technology is the main approach to purify the dust-laden gas,and it can efficiently entrap the fine particles.Industrial emissions of air pollutants are mainly emitted from high-temperature flue gas,while the current domestic filter for the core components of the filter are almost all dependent on imports,such as PPS,Aramid,PTFE.These fiber filters have a poor temperature resistance,limited production and high prices,which is not conducive to their use and promotion.Therefore,it is of great significance to study a lightweight fiber filter material with excellent high temperature and chemical corrosion resistance for high-temperature industrial dust-laden gas purification,industrial process intensification energy saving and emission reduction.Aromatic polyimide(PI),characterized by superior thermal and chemical stability,has a wide range of promising applications.The PI nanofibers prepared by electrospinning technology possess high porosity,porous interconnected structure,good air permeability and gas permeability selectivity,and have a great potential for application in the field of high-temperature gas purification.Nevertheless,the preparation of high-performance PI fibers is still challenging presently.In this work,a soluble semi-crystalline heterocyclic aromatic PI was used as the raw material to study and prepare high-performance PI nanofiber membranes.First,the method and concentration range of the PI solution for preparing nanofibers by electrospinning were investigated.The parameters of the spinning process were adjusted and optimized,and a series of PI nanofiber membranes were successfully prepared.Then,a series of performance-enhanced f-Gr/PI composite nanofiber membranes were successfully prepared by adding graphene oxide(GO),fluorinated graphene(FG)and aminated graphene(NG)as the nano-reinforced filler.Finally,the chemical corrosion and high temperature treatment of the as-prepared composite nanofiber membranes were tested.The research and results of this work mainly include the following five aspects.1?By comparing and analyzing the surface characteristics of the PI fibers prepared from PI solutions and the spinning process,a suitable solvent system for the electrospinning solution of PI nanofibers was determined.The PI solution were prepared by settling different additive contents,solvent systems and dissolved environment.And the solvent system is a homogeneous dispersed NMP/LiCl system and the content of LiCl is 1.0 wt%.The homogeneous PI electrospinning solution was prepared in 105 ? oil bath with constant temperature and magnetic stirring.A set of electrospinning parameters for the preparing PI nanofibers was determined by analyzing the characteristics of the as-prepared fiber surface,morphology,etc.Before electrospinning,its parameters are set as follows:applied voltage:18.0 kV,feeding rate:0.5 mL·h-1,rotating speed:300 r·min-1,injection needle inner diameter:0.41 mm,syringe pump sliding speed:4 m·min-1,receiving distance:180 mm,ambient temperature and humidity:25 ± 2 ? and 45 ± 5 RH%.2?The influences of concentration,viscosity and conductivity of the different PI electrospinning solutions on the diameter distribution and morphology of the prepared nanofibers were investigated,and the suitable concentration range of PI was 6.0-12.0 wt%.The optimal PI concentration was 10.0 wt%,and the corresponding fiber average diameter was 264 ± 54 nm.The as-prepared electrospun PI nanofiber membranes exhibited good hydrophobicity,excellent thermal stability with an initial thermal decomposition temperature(Td)of 544 0C,and poor mechanical properties with tensile strength,Young's modulus,breaking elongation of 10.5 PMa,0.9 GMa,and 7.8%,respectively.At the same time,the 10.0 wt%electrospun PI nanofiber membrane represented good filtration performance for ultra-fine oily substances(0.3?m DOP),and it achieved a best filtration efficiency of 90.4%.3.The GO/PI composite electrospinning solution was prepared by solution blending method,and the composite nanofiber membranes with different GO contents were prepared by electrospinning.The results showed that the addition of GO improved the distribution uniformity of the PI nanofibers.When the GO content was 0.5 wt%,the average diameter of the electrospun GO/PI composite nanofibers was at least 231 ± 36 nm,and the porosity was as high as 90%.Thermal analysis results indicated that the thermal stability of the electrospun GO/PI composite nanofiber membranes was improved by 15 ? compared with that of pure PI nanofiber membranes,and its Td and heat resistance temperature(THRI)reached 551.7 ? and 193.9 ?,respectively.In addition,the addition of GO can effectively improve the mechanical properties of the electrospun PI nanofiber membrane,and its tensile strength,Young's modulus,and breaking elongation reached 14.4 MPa,1.4 GPa,and 8.9%,respectively.The filtration testing results revealed that the filtration efficiency of the electrospun PI composite nanofiber membranes was effectively improved with the highest value of 96.5%,which was 8%higher than that of the pure PI nanofiber membranes.Through the quality factor(QF)evaluation,it was found that the overall filtration performance of the electrospun GO/PI composite nanofiber membranes achieved the best effectiveness when the GO content was 0.75 wt%.4.The f-Gr/PI composite electrospinning solution was prepared by suing the solution blending method and hierarchical ultrasonication-centrifugation,and the composite nanofiber membranes with different f-Gr types were prepared by electrospinning.It was found that the uniformity of diameter distribution of PI nanofibers was effectively improved by adding f-Gr.The diameter distribution of the electrospun f-Gr/PI composite nanofibers was 80-200 nm,and the fiber diameter of the electrospun NG/PI composite nanofibers represented the lowest value of 151 ± 26 nm,and the porosity reached 92.7%.The electrospun FG/PI and NG/PI composite nanofiber membranes exhibited high hydrophobicity and the water contact angles reached 129.6° and 125.6°,respectively.Moreover,the tensile strength,Young's modulus and breaking elongation of the electrospun NG/PI composite nanofibers were increased by 102.8%,190.1%and 55.8%respectively,achieving 45.0 MPa,10.9 GPa and 17.6%,respectively.In addition,the electrospun f-Gr/PI composite nanofiber membrane exhibited excellent thermal stability with the Td of 554.5-567.8?.The filtration efficiency of the electrospun f-Gr/PI composite nanofiber membrane for the 0.3 ?m DOP increased by nearly 12%,and reached 99.99%.5?Chemical corrosion resistance and high temperature resistance of the electrospun f-Gr/PI composite nanofiber membranes were studied by using solution soaking method and high temperature treatment.The experimental results showed that the electrospun PI,GO/PI and NG/PI composite nanofiber membranes possessed remarkable acid corrosion resistance,and the breaking strength retention and elongation retention were maintained at 72-88%and 68-72%after the acidic solution treatment,respectively.Meanwhile,the filtration efficiency still remained around 97%.While those composite nanofiber membranes represented relatively poor alkali corrosion resistance,and the corresponding mechanical properties were maintained at about 60%and 50%respectively after alkaline solution treatment.Additionally,the filtration efficiency still reached 86%.The high-temperature treatment has a great influence on the mechanical properties of electrospun PI,GO/PI and NG/PI composite nanofiber membranes.The breaking strength retention and elongation retention were maintained at 80-88%and 76-80%after heat treatment at 260 ?,respectively.And they are maintained in the range of 63-68%and 52-56%respectively after the heat treatment at 300 ?.With the increase of treatment temperature,the filtration performance of the electrospun composite nanofiber membranes showed a downward trend,and still maintained at about 82%after heat treatment at 300 ?.It can be inferred that the continuous operating temperature of the electrospun GO/PI and NG/PI composite nanofiber membranes reaches 260-300 ?. |
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