Study On Preparation And Properties Of Nanocrystal Cellulose/Sulfonated Polymer Composite Proton Exchange Membrane

Because of their excellent thermal,chemical,and mechanical durability,sulfonated polyether ether ketone have attracted much attention for their potential use in proton exchange membrane.However,the increasing number of sulfonic acid groups would lead to the loss of the mechanical strength and dimensional stability under the circumstances of high temperature and high humidity.Extensive efforts to well get the balance between proton conductivity and dimensional stability are required.Therefore,several approaches have been adopted to modify the polymeric membrane to improve the performance of polyaromatic-type PEMs.Nanocrystal cellulose(NCC)has been gaining increasing interest because of its biodegradability,renewability,hydrophilicity,and excellent mechanical properties,which is ideal filler for high performance composite material.The hydroxyl groups on the surface of NCC can be modified,which endow it with more high performance.In this study,sNCC was preparated by acid hydrolysis of MCC,and introduced to prepare the composite PEMs as an attempt to further enhance the performance of membranes.In this study,fluorene-containing poly(ether ether ketone ketone)(FPEEKK)was synthesized were synthesized by polycondensation with 1,4-bis(4-fluorobenzoyl)benzene and 4,4-(9-fluorenylidene)-diphenol,firstly.Sulfonated fluorene-containing poly(ether ether ketone ketone)(SFPEEKK)was obtained by post-sulfonated.Using the solution blending method,sulfonated nanocrystal cellulose(sNCC)-enhanced SFPEEKK composites(SFPEEKK/sNCC)were successfully prepared for investigation as proton exchange membranes.The properties of the composite membranes,including thermal stability,mechanical properties,water uptake,swelling ratio,and proton conductivity were thoroughly evaluated.Results indicated that the insertion of sNCC could contribute to water management and improve the mechanical performance of the membranes.Notably,the proton conductivity of SFPEEKK5/sNCC-5 was as high as 0.242 S cm–1 at 80 °C.In order to further improve the mechanical property of the composite proton exchange membrane,some composites were prepared from sNCC and sulfophenylated poly(ether ether ketone ketone)(Ph-SPEEKK).The proton conductivity of the sNCC/Ph-SPEEKK composite membrane with 4 wt% sNCC content could reach 0.115 S cm-1 at 80 °C,which was much higher than that of pure Ph-SPEEKK(0.078 S cm-1).In addition,the mechanical properties of the composite membranes were much improved compared with pure Ph-SPEEKK membrane.When the sNCC ratio was 4 wt%,the tensile strength and strain of dry composite membranes were 19% and 213% higher than that of pristine membrane,respectively.To further improve the comprehensive performance of the composite membranes,a functionalized nanocrystal cellulose bearing amino,silane,and sulfonic acid groups(Am-sNCC)was prepared through a two-step chemical modification of microcrystal cellulose powders,first by sulfonic acid and then by a 3-trimethoxysilyl propyl ethylenediamine.The uniform and flexible composite membranes composed of the Ph-SPEEKK matrix and the Am-NCC additive were successfully prepared by a solution casting method.The composite membranes containing Am-sNCC,which serves as a performance-enhancing component to form covalent-ionic interaction networks with the Ph-SPEEKK matrix,exhibited improved dimensional stability,higher water absorption and retention capacities,higher proton conductivity,and better mechanical properties than the Ph-SPEEKK membrane.The results show that the composite proton exchange membrane containing Am-sNCC exhibits excellent comprehensive performance,and it has broad potential applications.