The Crystallinity Control Of Sulfonated Poly(Ether Ether Ketone) Proton Exchange Membrane And The Effects Of Crystallinity On The Membrane Properties

Sulfonated polyether ether ketone(SPEEK)is one of the most ideal substitutes for commercial Nafion membrane because it exhibits superior alcohol resistance performance,excellent mechanical properties and thermal stability,and the cost is low.There have been several studies show that the crystallization of proton exchange membrane has a certain degree of effect on its performance,but the correlation of crystallization and its performance is not clear.In this paper,the SPEEK proton exchange membrane has been studied,and its crystallinity is controlled by three ways: solvents,heat treatment and hot pressing.This article discusses the influence laws of crystallinity on SPEEK proton exchange membrane properties,and the function mechanism has been preliminarily discussed.First of all,SPEEK proton exchange membranes are prepared by using four different solvents(NMP,DMF,DMAc and DMSO).Experiments show that solvents can influence the crystallinity and microstructure of the membranes,or interact with SPEEK molecular,and then affect the performances of the membrane.The influence factors of solvents are too complicated to make sure the effects of crystallinity on SPEEK proton exchange membrane properties.Then the crystallinity of SPEEK proton exchange membrane is controlled by varing the heat treatment temperature,and the crystallinity and proton conductivity is measured.When heat treatment temperature is below the decomposition temperature of sulfonic acid group(about 180℃),the crystallinity of membrane increases with the heat treatment temperature,and the proton conductivity of membrane also increases with the crystallinity.Finally,the crystallinity of different thickness and multilayer SPEEK casting films is controlled via hot-pressing.The relationship between crystallinity and the performance of SPEEK proton exchange membrane is studied,and the function of crystallization to SPEEK proton exchange membrane is discussed.The properties of hot-pressing membranes changes with the crystallinity,and this verifies the correlation of crystallization and membrane performance.In addition,SPEEK hot-pressing membranes were analyzed by TEM and XRD.The results show that SPEEK hot-pressing membranes have similar crystal structure with PEEK.The author speculates that the sulfonated chains of SPEEK are involved in crystallization,and the existence of crystalline phase improves the proton conductivity,tensile strength,and reduces the methanol permeability.