Study On The Preparation And Properties Of PVC-based Alkaline Anion Exchange Membranes

Today's environmental pollution and resource shortages are becoming more and more serious.As a new type of energy conversion device,fuel cells have received widespread attention from scholars and industry in recent years.As one of the core components of PEMFC,ion exchange membrane directly affects the performance of fuel cell.At present,proton exchange membrane fuel cell(PEMFC)is widely studied.However,the high cost of noble metal catalyst limits the commercial application of PEMFC.Anion exchange membrane fuel cell(AEMFC)can be used without noble metal as catalyst,so it has broad development prospects.As a general-purpose plastic,PVC has been used in all walks of life due to its advantages of cost-effectiveness,easy manufacturing,high chemical stability,high tensile properties.Because PVC contains-Cl group,it is easy to have substitution reaction with amine group,mercapto group and other groups,which provides the possibility of functional modification of polyvinyl chloride.In this thesis,a series of PVC functionalized with heterocyclic ammonium was successfully prepared through substitution reaction with N-methylpiperidine and N-methylpyrrolidine by using PVC as raw material.The PVC-based anion exchange membrane(PIP-PVC,PYR-PVC)was prepared by solution casting method.The Cl^-ionic conductivity,mechanical properties and oxidation stability of the series of ionic membranes were characterized.The results showed that the PYR-PVC membrane had the highest ion conductivity of 79.4 m S·cm^-1,respectively,while their water uptake and swelling ratio remained at low levels.The tensile strength of PIP-PVC and PYR-PVC ionic membranes ranged from 19.3 to 30.0 MPa,and the elongation at break ranged from 42.5 to 70.2%.On the basis of monoammonium functionalized PVC,a series of different crosslinked PVC anion exchange membranes were prepared by further reaction of N,N,N',N'',N''-pentamethyldiethylenetriamine and N,N,N',N'-tetramethyl-1,6-hexanediamine as crosslinking agents,in order to improve the heat resistance and the mechanical properties.The ionic conductivity,mechanical properties and oxidation stability of the series of ionic membranes were characterized.The results showed that the highest ionic conductivity of PEN-PIP-PVC cross-linked ionic membrane reached 48.8 m S·cm^-1 at 80°C,while that of PEN-PYR-PVC was44.9 m S·cm^-1.Several cross-linked PVC ionic membranes have excellent mechanical properties compared to uncross-linked PVC ionic membranes.Among them,the tensile strength of PEN-PIP-PVC is 34.3 MPa,and the elastic modulus is 812.2 MPa,which is higher than that of uncross-linked PIP-PVC-1.5 membrane increased by 46%and 46.7%respectively.The water absorption and swelling degree of the cross-linked membrane are a little lower than that of the uncross-linked membrane,indicating that the prepared cross-linked PVC ion membrane has significantly improved mechanical properties than the uncross-linked PVC ion membrane,while the heat resistance and dimensional stability are not improved much.In this thesis,the monoammonium ion functionalized PVC anion membranes were synthesized,and then crosslinked with polyamine.The ionic membranes prepared can achieve the balance of ionic conductivity,dimensional stability and mechanical properties.The PVC cross-linked ionic membranes have a good application prospect in the fields of low-temperature alkaline fuel cell,membrane separation,chlor-alkali industry and seawater desalination.