Preparation And Properties Of Hydrogenated Nitrile Rubber Based Cation Exchange Membrane

Diffusion dialysis(DD)has been attracting many attentions in recent years because of its advantages,including lower energy consumption,environment-friendly and no secondary pollution.Similar with other membrane separation processes,the most important component of diffusion dialysis is the ion exchange membrane(IEM).Therefore,it is the most important task to choose suitable membrane materials for the alkaline DD possess,which should possess excellent stability as well as favorable ion permeation and selectivity abilities.In this research,hydrogenated nitrile rubber(HNBR),sodium p-styrene sulfonate,azodiisobutyronitrile(AIBN)and divinyl benzene(DVB)are selected as membrane matrix,functioned monomer,initiator and cross-linking agent,respectively,to prepare composite membranes for alkaline diffusion dialysis.The research content is including two parts:In the first part,HNBR,SSS,AIBN and DVB were dissolved in N-dimethylformamide(DMF)and the polymerization was taken at 80 ~oC for 3 hours under vigorous stirring.After that,DCP with different mass ratio(to SSS)was added to the system and the stirring continued for 5 minutes.Then the obtained mixture was evenly cast on a glass surface dish,dried on a heating plate at 60 ~oC until the solvent volatilize completely.The sample was hot-pressed with a flat vulcanizer,and the hot-pressing conditions were controlled to 5 MPa for 5 min.First,the membrane was formed by hot-pressing at 140 ~oC,and then the temperature was raised to 160 ~oC for vulcanization,and finally a series of composite membranes with moderate thickness were obtained.Through testing and characterization of the basic properties and microscopic morphologies of the as-prepared membranes,it was found that the water content(WR)of the membrane was in the range of 92.0-213.2%,and the value increased with the increasing dosage of SSS;The ion exchange capacities(IECs)were in the range of2.02-2.88 mmol/g,and this was accorded with the content of SSS;The ranges of swelling degree(W1)and mass loss rate(W2)obtained by alkali resistance test were in the range of 68.6-204.2%and 8.9-22.8%,respectively;The tensile strength(TS)was between 4.2-8.1 MPa,and the elongation at break(Eb)was between 209.4-1947.2%;SEM pictures of the cross-section of the composite membranes showed well compatibility between the two phases with the increased content of SSS.The Na OH/Na2WO4 mixed system was used to conduct the separation performance of the as-prepared membranes,and the dialysis coefficients of hydroxide ion(UOH)were in the range of 0.0051-0.0158 m/h,while the separation infctors(S)range is 9.9-19.0.The membrane possessed optimal properties while the dosage of DCP was 0.003g,with UOH of 0.0085 m/h and S of 15.8.In the second part,sulfonic acid functionalized mesoporous silica(MS-SO3H)were introduced to the system to prepare a series of organic-inorganic composite membranes.Mesoporous silica was synthesized firstly via sol-gel method andr-mercaptopropyl triethoxy(KH-580)and H2O2 were used as modifier and oxidant,respectively.The obtained MS-SO3H were added to casting solution with the mass ratio of 2%,4%,6%,8%,and 10%(calculated according to the added amount of all the components).A series of composite membranes were obtained after the solvent was completely volatilized and hot-pressed process.The measurement results of basci properties,microscopic structure and separation performance characterization indicated that water content(WR)of the membranes were in the range of 137.4-143.7%,and the ion exchange capacities(IECs)were in the range of 1.47-1.59 mmol/g;The swelling degree and mass loss ratio were in the range of 112.1-148.0%and 17.2-26.4%,respectively;The tensile strength(TS)and elongation at break(Eb)ranged from 3.9-8.2 MPa and 226.9-566.6%,respectively.Diffusion dialysis experiment results showed that the membrane exhibited the optimal separation while the content of MS-SO3H was6%,with UOH of 0.0096 m/h and S of 24.3.The results showed that the introduction of MS-SO3H can effectively improve the dialysis coefficient and separation factor of the membrane,which can be attributed to the selected adsorption abilities of the mesoporous pores for ions and the synergistic effect of the-SO3H group and the-SO3~-group of SSS.Thus,the separation performance of the membranes improved obviously.