Preparation And Properties Of Imidazolium Ionic Liquids Modified Waterborne Polyurethane Membrane

Water-based polyurethane(WPU)film material has good film-forming properties,selectivity and permeability,etc.,and has become a research hot spot in pervaporation field in recent years.Imidazole based ionic liquids are expected to improve membrane performance due to their high thermal stability,specific selectivity to specific aromatics,and environmental friendliness.In this paper,we design and synthesize five kinds of anionic and cationic imidazolium ionic liquids,one with double bond ionic liquid,and study the influence of preparation process and different modification methods on the structure and pervaporation performance of aqueous polyurethane by optimizing the ionic liquid.The main contents as follows:(1)Five different anionic and cationic imidazolium ionic liquids were designed and synthesized as follows:1-ethyl-3-methylimidazolium hexafluorophosphate(EMIM[PF6]),1-ethyl-3-methylimidazolium tetrafluoride Borate(EMIM[BF4]),1-ethyl-3-methylimidazolium bistrifluorotimide salt(EMIM[T f2N]),1-butyl-3-methylimidazolium hexafluorophosphate BMIM[PF6]),1-hexyl-3-methylimidazolium hexafluorophosphate(HMIM[PF6]),a 1-vinyl-3-butylimidazolium hexafluorophosphate with double bond ionic liquid([VBMIM][PF6]),by means of IR,NMR and other characterization methods,to prove that the prepared ionic liquid has the characteristics of the designed chemical structure.The results of studies on the modified aqueous polyurethane films doped with different anionic and cationic ionic liquids show that the compatibility between EMIM[PF6],EMIM[BF4],EMIM[Tf2N]and WPU gradually increases,and EDX studies the ionic liquid in the membrane.The homogeneity of the distribution is EMIM[PF6]<EMIM[BF4]<EMIM[Tf2N].According to the TG results,the order of thermal stability of different anions is Tf2N->BF4->PF6-;the swelling selectivity data indicate The selection coefficient as for the dissolution of the modified membrane to benzene is EMIM[PF6]/WPU>EMIM[BF4]/WPU>EMIM[Tf2N]/WPU,and the shorter alkyl chain cationic ionic liquid modified membrane benzene has better solubility selectivity.It can be seen from the pervaporation that the separation factors of EMIM[PF6]/WPU membrane,EMIM[BF4]/WPU membrane,and EMIM[Tf2N]/WPU membrane are successively lower,but higher than that of the original WPU membrane;and the permeation flux is rise,and are lower than WPU original film.With the increase of the alkyl chain in the cation,the separation factor gradually decreases and the flux increases gradually.In summary,the EMIM[PF6]ionic liquid doping modified WPU is preferred to optimize its doping process,study of the modified film microstructure and pervaporation properties.(2)The optimal technological conditions were determined by doping with EMIM[PF6]and WPU:the WPU solid content was 10 wt%,the stirring speed of stirring paddle was 600 r/min,the ultrasonic power was 100 W for 1.5 h,the microwave The microwave power was 115 W for 10 min.The EMIM[PF6]ionic liquid prepared had good dispersion and film forming properties in the waterborne polyurethane.The results of structural characterization showed that as the content of EMIM[PF6]gradually increased,it was found that the ionic liquid mainly acts on the soft segment of WPU,and with the increase of content,the glass transition temperature of soft segment of WPU first increases SEM and EDX results show that when the content of EMIM[PF6]is less than 15 wt%,EMIM[PF6]can be more evenly distributed in the polyurethane,and EMIM[PF6]migrates to the membrane surface when EMIM[PF6]tendency.From the swelling results,it can be seen that the swelling of the composite membrane in cyclohexane was essentially unchanged at 3.7%.While the equilibrium DS value of benzene increased from 58%to 98%,indicating that the addition of EMIM[PF6]increased the affinity of the modified membrane for benzene.(3)According to the preferred structure of imidazole-based ionic liquid with better selectivity for benzene,we chose double-bond[VBMIM][PF6]as ionic liquid to graft and modify WPU,high affinity and solubility,to improve the permeability of the membrane components,while free anion and cation electrostatic force bound to the WPU skeleton to ensure the stability of the membrane.By exploring the reaction temperature,the amount of initiator,reaction time and the amount of monomer and other process conditions on the modified emulsion and film-forming properties,optimizing the reaction process conditions.The results showed that the modified water-based polyurethane had good film-forming properties and the film surface was transparent and uniform.However,[VBMIM][PF6]:when the WPU reached 15:100,the film cracked and[VBMIM][PF6]lead to high content of ionic liquid polyaddition increases,is not conducive to the formation of emulsion film.It can be seen from the TG data that as the content of[VBMIM][PF6]increases,the initial decomposition temperature(Tinitiai)of the membrane increases from 170.0 ? to 213.7 ? and the transition decomposition temperature(Tinflection)increases from 353.9 0C to 387.4 ?,the overall decomposition temperature of the film increases,significantly improved heat resistance.Pervaporation performance of a mixture of benzene/cyclohexane(50/50 w/w)at 50 ? showed that the amount of[VBMIM][PF6]ionic liquid increased and the membrane separation factor increased from 3.44 to 8.04,flux increased from 0.21 kg·m-2·h-1 to 0.31 kg·m-2·h-1.