Preparation And Application Of Solvent-Resistant Membrane Materials Based On Poly(aryl Ether Ketone)s

Traditional polymer membrane materials will be swelling or even dissolution in organic solvents,which limits the application of membrane separation technology in organic solvent systems.Poly(aryl ether ketone)s(PAEKs)have excellent mechanical strength,chemical stability,thermal stability and solvent resistance.However,the semi-crystalline PAEKs has poor processability and is almost insoluble in all common organic solvents,so it is difficult to process it into membranes by conventional methods.The methods for preparing PAEKs into membranes include dissolving in strong acid such as concentrated sulfuric acid or using a modified amorphous PAEKs to prepare them into membranes.However,these methods all lead to irreversible changes in own structure of PAEKs,which eventually lead to the loss of solvent resistance.In this paper,amination-crosslinking and chemically induced crystallization was used to prepare solvent-resistant membrane materials based on PAEKs.Performance as an organic solvent nanofiltration membrane was explored.In addition,the application of PAEK solvent-resistant membrane materials in the preparation of lithium battery separators is also expanded.The details are as follows:1.A hydrazide-containing diphenol monomer(PPH-NH2)was prepared from low-cost industrial raw materials phenolphthalein and hydrazine hydrate.Theoretical calculations and experimental results show that the phenolic hydroxyl groups in PPHNH2 have higher activities than amino groups.A high molecular weight aminocontaining Cardo Poly(ether ketone)(PEK-NH2)was prepared by nucleophilic polycondensation.PEK-NH2 has good solubility,mechanical strength,thermal stability and hydrophilicity,and is a promising novel membrane material.In addition,the amino groups in the polymer can react with aldehydes for further cross-linking.Characterization of various chemical structures demonstrated the occurrence of crosslinking within PEK-NH2.The results showed that the PEK-NH2 membranes crosslinked by glutaraldehyde have good solvent resistance.2.Thin film composite(TFC)membranes with amino group-containing polyether ketone as support layer and amino-containing polyester as separation layer were prepared by an interfacial polymerization reaction with PEK-NH2 ultrafiltration membrane as the support layer,PPH-NH2 as the water phase monomer,and trimesoyl chloride as the organic phase monomer.Then the prepared TFC membrane was crosslinked with glutaraldehyde.Characterization results demonstrate that crosslinking occurs both within and between the support and separation layers.The separation performance of the multi-crosslinked composite membrane was adjusted by controlling the interfacial polymerization time.The C-TFC-30 membrane with better performance had a molecular weight cutoff of about 321 g mol-1 and a methanol permeance of 10.41 L m-2 h-1 bar-1.The prepared multi-crosslinked composite membranes can operate stably in common organic solvents(over 12 days in methanol),and show interfacial polymerization resistance even to polar aprotic solvents.3.A novel method for preparing poly(ether ether ketone)(PEEK)membranes by chemical-induced crystallization was developed,as follows.The carbonyl group in the monomer 4,4’-difluorobenzophenone was modified with aniline,and a PEEK precursor polymer containing a ketimine structure was prepared by a polycondensation reaction.The prepared polymer had a high molecular weight and was soluble in polar aprotic solvents.After the precursor polymer was prepared into an asymmetric membrane by a non-solvent-induced phase inversion method,the membrane was soaked in hydrochloric acid for treatment,and the ketimine structure was hydrolyzed into carbonyl groups.Various characterization results demonstrate that the chemical structure of the polymer is converted to PEEK after acid treatment,and the aggregated state is converted to a semi-crystalline state.The separation performance of the prepared PEEK asymmetric membrane was optimized by adjusting the membrane production process and adopting a solvent activation method.The prepared PEEK membrane has good solvent resistance and pressure resistance.4.PEK nanofiber membranes were prepared by a similar chemically induced crystallization strategy.Firstly,the ketone of the monomer was converted into ketal,and the soluble PEK precursor polymer was prepared.This polymer was prepared into a nanofiber membrane by electrospinning and underwent an acid treatment.Finally a PEK nanofibrous membrane was obtained.The prepared PEK nanofiber membrane has good solvent resistance,excellent mechanical properties and heat resistance,high porosity and narrow pore size distribution.We choose the lithium-oxygen battery system as the verification of PEK nanofiber membrane used as lithium battery separator.Compared with lithium-oxygen batteries assembled with commercial separators,the batteries assembled with the PEK separator have a longer battery life due to the fact that the nanofibrous structure of the PEK separator promotes the uniform transport of Li+and the hydrophobicity of the PEK separator has a protective effect on the lithium anode.