Preparation And Properties Of Chlorosulfonated Polyethylene Ion-exchange Membranes

Alkali resistance of membranes was one of the most important roles that affected their application in alkaline diffusion dialysis.In this research,a series of composite ion exchange membranes were prepared by selecting chlorosulfonated polyethylene(CSM)as matrix material and methacrylic acid(MAA)as functional monomer via free radical solution polymerization.Effects of different preparation methods on the alkali resistance,microscopic morphology,mechanical and thermal stability were detected.Separation performance of as-prepared membranes was.investigated by recovering alkali from NaOH/Na2WO4 system via diffusion dialysis process and the relationship between phy-chemical property and separation performance of composite membranes were discussed.The research was stated as follows:In the first part,the CSM/PMAA composite ion exchange membranes were prepared by constructing a semi interpenetrating network(sIPN)network via free radical polymerization in toluene solution.CSM,MAA,azodiisobutyronitrile(AIBN)and divinyl benzene(DVB)were selected as matrix material,functional monomer,initiator and crosslinked agent,respectively.Composite ion-exchange membranes were obtained after casting the solution on the glass plate and then dried in air.Ion exchange capacities(IEC),water uptake(WR),alkali resistance,mechanical and thermal stability of as-prepared membranes were tested and the separation performance was detected by recovering alkali from NaOH/Na2WO4 system via diffusion dialysis.The results indicated that water uptake(WR)of 12.7?34.8%,ion exchange capacities(IECs)of 3.2-4.4 mmol/g,swelling degree of 34.7%?195.4%as well as favorable thermal stability and alkali resistance(almost zero mass loss in hot alkali solution),the tensile strength(TS)between 12.8?27.69 MPa,elongation(Eb)between 132%?688.87%.Dialysis coefficient of OH-(UOH)was 0.004m/h while the separation factor(S)was 12.5.In the second part,a series of composite cationic ion exchange membranes for alkali recovery were prepared by selecting chlorinated polyethylene rubber(CSM)and methacrylic acid(MAA)as framework and functional monomer,respectively.Interpenetrating network(IPN)structure was formed by free radical polymerization and consequent crosslinked reaction by introduction of dipentamethylene thiuram hexasulfide(DPTT).The membranes possessed water uptake(WR)of 5.38%-28.3%and ion exchange capacity(IEC)of 3.57-3.88 mmol/g with initial degradation temperature were in the range of 260-281? and the tensile strength(TS)between 19.3-33.4 MPa,elongation(Eb)between 140.7%-524.9%.The membranes exhibited excellent alkali resistance with weight loss of 0.85%-2.08%after immersing in 65?2mol/L NaOH solution for 60h.The membranes were used for recovering alkali from NaOH/Na2WO4 mixture via diffusion dialysis process successfully:Dialysis coefficient of OH'(UOH)was 0.0034 m/h while separation factors(S)was 16.8.In the third part,cationic exchange membranes for diffusion dialysis(DD)were prepared by selecting chlorosulfonated polyethylene(CSM)and methacrylic acid(MAA)as framework and functional monomer,respectively.An interpenetrating network structure(IPN)was formed by free radical polymerization and consequent crosslinking reaction.The membranes possessed ion exchange capacities(IEC)of 1.98-3.12 mmol/g,water uptake(WR)of 12.7-34.8%,swelling degree of 72.7-170%as well as favorable thermal stability and alkali resistance(almost zero mass loss in hot alkali solution).The membranes were applied for DD process to recover alkali from NaOH/Na2WO4 system at 25? and 65?.Results indicated that coefficients of OH-(UOH)were in the range of 0.0015-0.018 m/h and separation factors(S)were in the range of 9-33 at 25 and 65?,respectively.The composite membrane exhibited optimal separation performance while dosage of DETA was 1.5%:UOH and separation factor were 0.0052 m/s and 19.98 under 65?,respectively.