Preparation And Properties Of Nanocellulose/sulfonated Poly (Arylene Ether Ketone) Containingcarboxylic Acid Groups Composite Membrane

Poly?arylene ether ketone??PAEK?is a kind of material with low cost and excellent performance.It could be used as proton exchange membrane after sulfonation treatment.Highly sulfonated SPAEK membrane shows high proton conductivity,but high sulfonation degree causes deteriorated dimensional stability and mechanical strength.Thus,it is necessary to design structure of SPAEK or prepare reinforced composites to improve its application.Nanocellulose?NCC?,a rigid rod-like nanoscale material with high strength,high aspect ratio,can be put into polymer matrix for a wide utilization in different fields.In this thesis,NCC was obtained by the acid hydrolysis of microcrystalline cellulose?MCC?.Then two series of PAEK-CN10 and PAEK-CN30 were initially synthesized by the polycondensation from 4,4'-difluorobenzophenone,?4-cyano?phenylhydroquinone and2-phenylhydroquinone.CN10 and CN30 represented the mole percentage of?4-cyano?phenylhydroquinone in the polymerization to be 10%and 30%,respectively.And then the sulfonic groups?-SO₃H?and carboxylic acid groups?-COOH?were simultaneously introduced into the side chain of the prepared polymer by site-specific post-sulfonation approach and hydrolysis reactions of cyano groups?-CN?to obtain the polymer SPAEK-COOH-10 and SPAEK-COOH-30?The oretical molar content of carboxylic acid groups were 10%and 30%respectively?.The prepared NCC was incorporated into SPAEK matrix to fabricate nanocomposite membrane with different ratio via solution casting as proton exchange membrane.The result indicated that all composite membranes displayed higher proton conductivity,improved dimensional stability and mechanical properties than the respective pristine membrane,which were mainly attributed to the toughness of NCC and hydrogen network among hydroxyl groups,sulfonic groups and carboxylic acid groups.When the content of NCC reached up to 5%,the enhanced performance of membrane materials was more evident.The SPAEK-COOH-10/NCC5 nanocomposite membrane showed maximum proton conductivity of 0.272 S cm^-1 at 80 ^oC,tensile strength was 28 MPa.The conductivity of SPAEK-COOH-30/NCC5 was 0.239 S cm^-1 at 100 ^oC,tensile strength was 47 MPa.Electrospinning is a fascinating way to produce continuous fibers with high-surface area and diameters in the nanometer range from polymer solution,which has a significant effect on proton conductivity.Herein,the polymer?SPAEK-COOH-10?was mixed with different content of NCC to obtain blend solution.Nanocomposite fibrous membranes had been fabricated by the electrospinning of NCC-loaded SPAEK-COOH-10 mixtures.A method was used to fabricate the electrospun nanofiber mats into dense proton exchange membrane by filling the gap voids between the fibers with inert polymer.The surface and freeze-fractured cross-section SEM images of the obtained membrane indicated that the polymer was successfully filled in composite nanofibers to achieve void-free structure in the membrane material.After measurement,a dense composite proton exchange membrane containing electrospun nanofibers NF-NCC2 showed good strength performance,and high proton conductivity(0.29 S cm^-1)compared with that of casting membrane.Thus,during the electrospinning process,the orientated acid groups and ordered nanocellulose constructed a three-dimensional network structure to the enhancement of proton conduction and mechanical properties.The results exhibited that composite membranes with nanocellulose possess good performance.