| Poly (aryl ether sulfone) s as a class of high performance special engineeringplastics was widely used since the early sixties of last century. Due to good thermaland thermo-oxidative stability, chemical stability, easy processing, PAES was themost important industrial gas separation membrane materials. PS hollow fibers coatedwith silicon rubber were prepared by Ismail, and the gas separation ratios of O2to N2were7.32, CO2to CH4was83.1, which indicated high gas separation performance.By changing the structure of polymer chains and the introduction of nano-inorganicmaterial to the polymer, scientific research workers were continually developing gasseparation membrane material with high gas permeation and separation in recent years.Because carbon nanotubes (CNT) had large aspect ratio and unique structure, theyquickly became the research focus of chemistry, physics and materials science. Due totheir smooth inner wall of the pore structure, the gas permeation rate in CNT wasmuch faster than in other nano-porous materials having comparable pore sizes, thusthey had potential worth in nano-porous materials.A series of pristine multi-wall carbon nanotubes (p-MWNT) and carboxyl multi-wall carbon nanotubes (c-MWNT) were bought from Chengdu institute of organicchemistry and tested as received. The results of FTIR showed that the peak at1722cm1of c-MWNT was assigned to the carboxyl group, which was not seen at1722cm1of p-MWNT. Morphologies of p-MWNT and c-MWNT were observed byTEM. The results showed that the amorphous carbon and other impurities were notseen in c-MWNT, which was opposite in p-MWNT. But the aspect ratio remainedrelatively high. The results of Raman spectrum reflected that the tube structure of p-MWNT was extremely perfect. Because2.86wt%carboxyl groups in c-MWNTexisted, the tube structure was not as perfect as that of p-MWNT, but tube structurewas still existed without obvious damage. Since a large number of surface polargroups in c-MWNT existed, therefore c-MWNT could be dispersed in the polarsolvent NMP.In order to design PAES chains,(4-Amino) phenylhydroquinone (4-AmPHQ)and3,3’-dially-4,4’-dihydroxybiphenyl (DABP) were successfully synthesized respectively and characterized by MS, DSC, FTIR and1H-NMR separately. Theresults were consistent with the expected structures. A series of copolymers weresynthesized by nucleophilic substitution reaction with adjustable ratio the twomonomers,4,4’-dichlorodiphenylsulfone (DCDPS) and4,4’-biphenol (BP). Fourkinds of crosslinkable poly (arylene ether sulfone) s with amino group (AP-PAES)were synthesized, whose structures were proved by FTIR and1H-NMR, whichconsistent with the expected structures. The molecular weight of copolymers rangedfrom50,000to70,000. The solubility of AP-PAES in polar solvents was very good.Thermal properties of copolymers were characterized by DSC. With the increase of4-AmPHQ or DABP, the glass transition temperature (Tg) of copolymers decreasedsignificantly.We chosen A10P15to crosslink from a series of copolymers we synthesizedbefore. Crosslinked membrane was achieved by heating membranes with2wt%BPOas curing agent at the temperature of180°C for1.5h in nitrogen atmosphere. Heatingthe polymer induced crosslinking of propenyl groups and lead to the formation ofthree-dimensional crosslinkage network. Because the curing time, curing temperatureand curing time had direct effect on the membrane properties, we did a lot ofexperiment and ensured the most suitable curing condition.Four kinds of membranes which were A10P15, CA10P15, A10P15-2, andCA10P15-2were prepared by solution evaporating. From the FTIR result of A10P15-2it showed that red shift of amino group appeared due to hydrogen bondinginteractions compared to A10P15. Macroscopic phase of the four membranes wereobserved by SEM. It showed that the macroscopic phase of CA10P15did not changedcompared to A10P15, which indicated that macroscopic phase did not change inheating; A10P15-2and CA10P15-2dispersed uniformly, no obvious macroscopicphase separation observed, and the morphology of MMM was different from A10P15.The results showed that the c-MWNT didn’t aggregate in the matrix after sonicatingfor6h, which was due to the hydrogen bonding interactions between carboxy group ofc-MWNT and amino groups of the copolymer.The thermal properties of A10P15, CA10P15, A10P15-2, and CA10P15-2wereinvestigated by differential scanning calorimetry (DSC) and thermogravimetricanalysis (TGA). The glass transition temperature (Tgs) of the A10P15membrane was 214C and addition of2%Carboxyl-MWCNTs did not increase the glass transitiontemperature. Tgs of CA10P15and CA10P15-2were not observed after curing. Itcould be attributed to the formation of three-dimensional crosslinkage network, whichdecreased the mobility of chains and lead to the invisible of Tgs. The TGA ofmembranes were tested under nitrogen and air respectively. The membranes showedgood thermal stability up to400oC and began to lose weight at higher temperaturesand had a char yield of59-64%at800oC in the atmosphere of nitrogen. Thetemperatures for5%weight loss (T5%s) were in the range of507-515oC. Themembranes also had excellent thermo-oxidative stability with the temperatures above350°C in air atmosphere. The temperatures for5%weight loss were in the range of449-493oC. In addition, the residual weight retentions were found to be58-79%onfurther heating to600oC, implying that these polymers possessed good oxidativestability. From DMA results it showed that the values of the tangent of loss angle ofCA10P15raised3℃compared to the A10P15, probabaly due to the formation ofthree-dimensional crosslinkage network, which decreased the mobility of chains andlead to the increase of Tgs. The Tgs of A10P15-2was raised to218℃compared toA10P15, probabaly due to the hydrogen bonding interactions between carboxy groupof c-MWNT and amino groups of the copolymer. The Tgs of CA0P15-2was thehighest in the four copolymers, which accord to the inference above.The mechanical properties of all the membranes were tested. The resultsindicated that the Young’s modulus went from1891MPa for pristine A10P15to1927MPa for the CA10P15. While the tensile strength increased from70MPa to98MPa,which increased obviously than tensile modulus. The A10P15-2membrane exhibitedhigher tensile modulus and tensile strength after doping2wt%c-MWCNTs. It couldbe explained that well dispersion of MWCNTs was attributed to hydrogen interaction between carboxyl groups and amino groups of A10P15. When curing and dopingMWNTs were introduced to a membrane, the increasing of Young’s modulus andtensile strength were more obvious. The elongation at break of the membranesdecreased with heat-curing and the addition of MWCNTs overall. This may beascribed to that the formation of three-dimensional crosslinking and the introductionof inorganic filler reduced the chain flexibility, hence the membranes became fragileand the elongation at break fell off.The morphology of the prepared membranes was investigated by measuring theWAXD. All the membranes showed completely amorphous structure. It could be seenthat2values of membranes shifted to low values with introduction of curing, andthe mixing of c-MWCNTs further enhanced the trend, indicating the increase ofintersegment distance or the packing of polymer chains, which could gain gaspermeability coefficient.The gas separation performance of membranes was studied. The results showedthat the permeability coefficient of CA10P15was much higher than that of A10P15; itmay be the formation of three-dimensional crosslinkage channel after curing, thus gascould permeate quicker through it and increase the permeability coefficient. Thepermeability coefficient of A10P15-2also increased after doping2wt%c-MWNT, ofwhich gas could permeate quicker through the smooth tube than that of chain gap. Sowhen cuing and doping c-MWNT were introduced to the same membrane,permeability coefficient of CA10P15-2was the highest among the four membranes.For five kinds of gases, the trend of gas separation coefficient accord to that ofpermeability coefficient, it also could be speculated that curing and doping c-MWNTwas help to improve the permeability and separation coefficient of membrane. |
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