Research Of Proton Exchange Membrane Preparation By Alkaline Treatment PVDF

Proton exchange membrane(PEM) could act as a proton exchange medium in fuel cell,which play a very important role within the fuel cell,so much attention has been concerned by lots of people about its research.At present,the hot spot in the field was researching low-cost and high-performance membrane materials. In this paper,The PEM was prepared by film-forming in solution method and hot-pressing forming film method and corresponding alkaline treatment,grafting and sulphonation process.Film-forming in solution method was directly using alkaline treating PVDF powder and then grafting on SSS monomer;on the process of PEM by this method,the paper expanded from alkaline concentration and alkali treatment time influenced on related properties and systematic researched PEM related to solubility property、electrical property、IEC value、mechanical property and surface morphology,It provided a theoretical basis for PEM preparation and performance improvement.Hot-pressing forming film method was using alkaline treating PVDF hot-pressing film and then grafting a-methyl styrene monomer followed by sulfonation in concentrated sulfuric acid;the paper expanded from a-methyl styrene monomer content and hot-pressing frequency influenced on PEM performance and changing and provided a theoretical support for quantitative studying related performance with hot-pressing film.We systematic characterized PEM related to grafting rate、swelling rate、IEC value、electrical property、 crystal structure and molecular chain structure、mechanical property and morphology characterization.The function group structure changing was analysed firstly on the PEM preparation process with film-forming in solution.FT-IR results show that the film have obvious C=C double bond or little triple bond to form and successfully introduced into SSS monomer. The conductivity could reach0.024S.cm-1and the Nyquist figure showed the curve was high regularity and approximate compared with Nafion117membrane. The maximum IEC value could reach3.87and its changing trend and conductivity trend was consistent. SEM and swelling ratio test show that the modified film still have micro polymer network structure with sponge shape,the film surface micro hole distributed more closely and uniformly and the modified film swelling rate increased greatly.The PEM grafting rate was quantitative researched firstly on the PEM preparation process by hot-pressing forming film method.The result show it’s more advantage to adopt a-methyl styrene as grafting monomer than styrene monomer;film grafting rate have a larger degree upgrading on repeated hot-pressing process,the largest grafting rate could reach29.13%. The swelling performance test showed PVDF had been successfully sulfonated. Through XRD and DSC test,it proved that PVDF main chain structure basically hadn’t changed after modification,crystal structure change from disorder to orderly.lt increased the amorphous area and thereby enhanced the film electrical performance.PEM prepared by this method had good electrical and mechanical properties;The film conductivity could reach0.018S/cm and repeated hot-pressing could improve its electrical property;The tensile strength maximum could reach45.38MPa which have greater degree increased compared with film-forming in solution. SEM test showed that pure PVDF hot-pressing film structure was relatively dense and uniform compared with the alkaline treatment film,its images was almost no change;the surface of grafted film presented polymer crumb structure,its surface became more smooth and uniform after sulfonation and the reunion crumb also reduced a lot.Through the BEC test,it proved that the polymer was uniform phase distributed throughout the whole film and didn’t happen micro-phase separation phenomenon.The above test result showed that the alkaline treatment PVDF preparing PEM was a better method,it have a important meaning to prepare high performance PEM.