Preparation and Recovery Properties of HomogeneousModified Polysulfone Plate Affinity MembraneChromatography with Thiohydroxy as Chelating Groups. I.Synthesis and Preparation of Plate Matrix Membrane

Bing Wang,1,2 Wenqiang Huang,1 Xinlin Yang1

1State Key Laboratory of Functional Polymer Materials for Adsorption and Separation, Institute of Polymer Chemistry,Nankai University, Tianjin 300071, China2School of Materials Science and Chemical Engineering, Tianjin Polytechnic University, Tianjin 300160, China

Received 20 November 2003; accepted 28 June 2004DOI 10.1002/app.21135Published online in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: A chloromethylation polysulfone (CMPSF),having good properties of membrane formation, spinnability,and reactive groups, was synthesized with Friedel–Crafts re-action, which could be used as reactivity matrix membranematerials. The effects of ZnCl2 quantity, monochloro methylether quantity, reaction time, and reaction temperature on thechlorinity of CMPSF were investigated. The CMPSF plate ma-trix membranes were prepared with phase inversion by use ofthe CMPSF/additive/N,N�-dimethylacetamide (DMAc) cast-ing solution and CMPSF as membrane materials. The focus ofthis study was primarily concerned with the relationshipamong such factors as species and contents of additives,CMPSF content in casting solutions, and temperature of solu-tions, and the morphological structure of the membrane, pore

size, porosity, and water flux of the membrane. It was con-cluded that these factors had obvious effects on the structureand the performance of the CMPSF matrix plate membrane,which could be improved within a wide range by changing thethermodynamic conditions of the casting solution. The effectsof coagulation conditions on the microstructure and perfor-mance of CMPSF plate matrix membrane were also studied. Itwas found that the water flux of the CMPSF plate matrixmembrane was at a maximum value by use of 10% DMACsolution as coagulation bath. © 2005 Wiley Periodicals, Inc. J ApplPolym Sci 96: 2117–2131, 2005

Key words: chromatography; matrix; membranes; separa-tion techniques; Friedel–Crafts reaction

INTRODUCTION

Chelating affinity membrane chromatography is con-veniently used to treat industrial wastewater and re-cover metal ions because it integrates the advantagesof both modern membrane techniques and affinitychromatography techniques.1–6

The chelating resin with N and S coordinationatoms has good adsorptive capacity for Hg2� be-cause Hg2� is a kind of soft acid or middle acid,whereas the organic S and N chemical compoundshave the properties of a soft alkaline or mid-alkaline. According to the soft and hard acid– basetheory, they easily form a chelating complex that ismore stable. There are numerous reports concerning

the synthesis of thiohydroxy chelating resin. Most of theunderlying studies used polystyrene (PS) or poly(methylmethacrylate) (PMMA) as the macromolecule carrierbringing into chelating groups with S and N throughmacromolecular reactions. The main chains of thesemacromolecule carriers are all carbon–carbon bonds.The adsorption of the resin for valuable and heavy metalions is determined by the functions of chelating groupswith lateral chains.

In our previous works,7 the high quality heteroge-neous polysulfone (PSF) affinity plate filter mem-branes with chelating groups were prepared withphase separation by using blends of the chelating resinand polysulfone as materials.

In this study, we used PSF as the original materialto synthesize chloromethyl polysulfone (CMPSF)with Friedel–Crafts reaction and produced a CMPSFmembrane using the phase-inversion method. TheCMPSF matrix membrane was reacted with sulfo-carbamide and hydrolysis under alkaline condi-tions, the homogeneous thiohydroxy modified poly-sulfone chelating affinity plate membrane chroma-tography was obtained, and its adsorptionproperties for Fe2�, Cu2�, Hg2�, and Zn2� were alsoinvestigated.

Correspondence to: B. Wang (hxl_009@sina.com).Contract grant sponsor: Science and Technical Develop-

ment Foundation of Colleges and Universities, Tianjin; con-tract grant number: 20030409. China Postdoctoral ScienceFoundation; Contract grant number: 2003034314. EmphasisItem of Science and Technical Research Ministry of Educa-tion, China; contract grant number: 20511.

Journal of Applied Polymer Science, Vol. 96, 2117–2131 (2005)© 2005 Wiley Periodicals, Inc.

EXPERIMENTAL

Materials and reagents

Dichloromethane and 1,2-dichloroethane, analyti-cally pure, were supplied by Tianjin Chemical Re-agent Plant (China); monochloro-methyl ether wassupplied by Nankai University Chemical Plant (Chi-na); zinc chloride, analytically pure, was suppliedby Chemical Reagent Plant (China); sodium rhodan-ate, analytically pure, was supplied by Tianjin Yao-hua Chemical Plant (China); ferriammonium sul-fate, analytical pure, was supplied by Tianjin Nan-kai Chemical Plant (China); and nitrobenzene andpolyethylene glycol were supplied by Tianjin Chem-ical Reagent Plant.

Main apparatuses

A Vector 22 Fourier infrared spectrometer (with ARTappendix) was made by Bruker (Darmstadt, Germa-ny); S450 scanning electron microscope was made byHitachi (Osaka, Japan).

Synthesis of CMPSF

A given amount of dried PSF was weighed and dis-solved in dichloromethane (or 1,2-dichloroethane), towhich mixture the complex of anhydrous zinc chlori-ode/monochloro methyl ether was added dropwise;the reaction temperature was slowly increased to 40°Cand the reaction lasted for 6 h. After the circumfluousreaction was finished, the solution was cooled to roomtemperature and the solution was slowly added tomethanol with vigorous stirring, yielding CMPSF as alump precipitate. It was repeatedly washed by hotdistilled water until bubbling ceased. The precipitatewas dried at a temperature between 60 and 70°C, afterwhich the rough CMPSF was prepared. The roughCMPSF was sheared into small pieces, dissolved inDMAc, poured into distilled water maintained at 70–80°C, and stirred, after which the white stripe or flocwas separated out. The refined CMPSF was preparedby filtering the precipitate, washing it three times withdistilled water, and drying the precipitate at 60–70°C.

Determination of CMPFS chlorinity

Determination of CMPSF chlorinity was carried out byusing the Woolhad method.8

Preparation of CMPSF matrix plate membrane

The matrix plate membranes were prepared by thephase-invertion method.9 Using CMPSF as themembrane material, PEG as the additive, and DMAcas the solvent, the three ingredients were mixedtogether in a certain ratio and heated to dissolve the

constituents, after which the casting solution wasobtained after vacuum defoaming. The casting so-lution was poured onto a clear and smooth glassplate at a predetermined temperature. After evapo-rating in the air for seconds, the solution was castinto a thin film using a blade, and the glass platewas saturated in a DMAc water solution at a certaintemperature to let it solidify into a membrane. Bychanging the casting solution temperature, evapo-rating time, and temperature and concentration ofthe coagulation bath, different test samples of platemembrane were produced at different ratios andconditions. The test samples of membrane were pre-served in a 50% glycerin solution.

IR spectra of PSF and CMPSF

The PSF and CMPSF plate membranes were dried at50–70°C. The dried membrane plates were placed di-rectly on the ART crystal and firmly fastened by clips.The metal peg must be firmly screwed when fasten-ing, and the ART annex must be securely fastenedwith the membrane plate onto Vector 22 Fourier in-frared spectrometer.

SEM analysis of CMPSF matrix membrane

The CMPSF matrix membrane was soaked in glyc-erol (50 vol % ratio) for 24 h, after which the mem-brane was removed and the glycerol wiped from itssurfaces. After stepwise dehydration, through themass fraction of 50, 70, 90, and 100% EtOH in se-quence, membrane samples were snapped by freez-ing them in liquid nitrogen; they were then fastenedonto the sample table and the film were coated byion sputtering. Thickness of the samples was about20 nm. The morphological structure of the surfacesand cross section of the matrix membrane wereobserved by an S450 scanning electron microscopeto determine the pore size with respect to membranedistributions.

Water flux measurement

The water flux was determined using equipment thatwas specially designed to evaluate the properties ofultrafiltration membranes (made in Tianjin Polytech-nic University, China). The pressure was 0.1 MPa andthe medium was ultrapure water. From the measuredvolume V of transmission liquid and ultrafiltrationtime t, the water flux Q was calculated from the fol-lowing equation:

Q �VSt (1)

2118 WANG, HUANG AND YANG

where S is the effective surface area of the membrane.

Porosity measurement

The membrane porosity was determined by means ofthe gravimetry method.10 We used glycerol as satu-rant, sheared a prescribed area of wet membrane,wiped the glycerol from the membrane surface, andweighed the wet membrane (Ww). Then the wet mem-brane was placed in a vacuum dry box to dry until itsweigh was constant. Last, we weighed the dry mem-brane (Wd). Percentage porosity of the membrane Pr

was calculated from the following equation:

Pr �Ww � Wd

Sd�� 100% (2)

where d is the average thickness of membrane and � isthe density of glycerol.

Membrane pore size measurement

The membrane pore size was determined by means ofthe filtering velocity method.10 The membrane porediameter rf was calculated from the following equa-tion:

rf � �8 � �2.90 � 1.75Pr��LQPr�PS (3)

where Pr is the porosity, L is the thickness of themembrane, � is the viscosity of the transmission liq-uid, Q is the flux, �P is the pressure, and S is thefiltering area.

RESULTS AND DISCUSSION

Synthesis of CMPSF

In this study, CMPSF was obtained by the Friedel–Craftselectrophilic substitution reaction under anhydrous con-ditions using PSF as the original material, dichlorometh-ane as the solvent, monochloro methyl ether as the chlo-romethyl reagent, and anhydrous ZnCl2 as the catalyst.The specific reactions are expressed as

The effects of ZnCl2 quantity on the chlorinity ofCMPSF are shown in Table I. PSF (20 g) was dissolvedin 200 mL of dichloromethane, and a prescribed quan-tity of ZnCl2 was dissolved in 20 g of chloromethylether to form a compound. The reaction lasted for 5 hat 40°C. From Table I one can observe that the quantityof ZnCl2 has substantial effects on the chloromethyl ofPSF. The chlorinity of CMPSF increased quickly withincreasing ZnCl2 quantity, although the productswould be easy to freeze if the ZnCl2 quantity were insufficiently large excess. The effects of the quantity of

monochloro methyl ether on the chlorinity of CMPSFare shown in Table II. PSF (20 g) was dissolved in 200

TABLE IEffect of ZnCl2 Quantity on CMPSF Chlorinity

PSF(g)

CH2Cl2(mL)

CH3OCH2Cl(g)

ZnCl2(g)

CMPSF chlorinity(%)

20 200 20 0.5 5.0520 200 20 1.5 7.5820 200 20 2.3 6.46

TABLE IIEffect of CH3OCH2Cl Quantity on CMPSF Chlorinity

PSF(g)

CH2Cl2(mL)

CH3OCH2Cl(g)

ZnCl2(g)

CMPSF chlorinity(%)

20 200 10 1.5 5.0720 200 20 1.5 7.5820 200 40 1.5 10.24

TABLE IIIEffect of Chemical Reaction Time on CMPSF Chlorinity

Reactiontime (h)

PSF(g)

CH2Cl2(mL)

CH3OCH2Cl(g)

ZnCl2(g)

CMPSFchlorinity

(%)

4 20 200 20 1.5 3.285 20 200 20 1.5 5.62

CHELATING AFFINITY MEMBRANE CHROMATOGRAPHY. I 2119

mL of dichloromethane to form a solution. The com-plexes with different concentrations were added to thesolution, and the reaction lasted for 5 h at the reactiontemperature of about 40°C. The chlorinity of CMPSFincreased with increasing content of monochloromethyl ether. The effects of reaction time on the chlo-rinity of CMPSF are shown in Table III. PSF (20 g) wasdissolved in 200 mL of dichloromethane, and 20 mL ofcomplex was added to the solution. Different samplesreacted for different times when the reaction temper-ature was 40°C. The chlorinity of CMPSF increasedwith increasing time span of the reaction. At the initialstage of the reaction, the chlorinity of CMPSF in-creased sharply, and the rate of chlorinity increasedecreased after 5 h. The reaction temperature shouldbe controlled so that the circumfluence of monochloromethyl ether could occur when the chloromethyl re-action of polysulfone was in progress. If 1,2-dichloro-ethane were used as the solvent, the reacting systemwould not have to undergo circumfluence, and thetemperature could be controlled at 40–45°C becausethe rate of chloromethyl would be only slight whenthe reaction temperature was too low and the mono-chloro methyl ether would easily dissipate when thereaction temperature was too high.

IR analysis of CMPSF matrix membrane

The IR spectra of polysulfone and CMPSF are shownin Figure 1 and Figure 2, respectively. ComparingFigure 1 with Figure 2, there was a strong singleabsorption peak in Figure 2, whereas Figure 1 had twoabsorption peaks at the vicinity of 1500 cm�1. Theexistence of –CH2Cl was verified after PSF went

through the Friedel–Crafts reaction combined with thechlorinity test of CMSPF with the Woolhad method.

Effects of CMPSF concentrations in original castingsolution on the matrix membrane structure

The structure and property of the membrane weredetermined not only by the nature of the membranematerials and membrane-forming process conditionsbut also by the thermodynamic conditions of castingsolutions, such as concentration of polymer, type, andamount of additive and temperature of casting solu-tions. SEM micrographs of the cross section and sur-face morphological structure of matrix membranewith different CMPSF concentrations in original cast-ing solutions are shown in Figures 3 and 4. Figure 3shows that the membrane support layers graduallychanged from a finger-shape structure to a sponge-shape structure with increasing CMPSF concentra-tions. From Figure 4 it can be seen that the pore size ofthe membrane dense layer changed from large tosmall and the dense layers gradually became denserwith increasing CMPSF concentration; thus the waterflux of the matrix membrane decreased continually.

Table IV shows the relationship between CMPSFconcentration and properties of the matrix membrane.From Table IV it could be seen that water flux, poresize, and porosity of CMPSF matrix membrane alldecreased with decreasing CMPSF concentration. Poresize and porosity of membrane decreased with in-creasing CMPSF content in the original casting solu-tions. As CMPSF content in the original casting solu-tion increased, the net structure of the original solu-tion became compact and thus the pore size and

Figure 1 IR spectrum of PSF membrane.

2120 WANG, HUANG AND YANG

porosity of the membrane were decreased. Mean-while, as the CMPSF content increased, the viscosityof the casting solution increased, which caused thedouble diffusion rate between solvent and coagulatingagent to decrease when the phase-inversion rate andcoagulating rate gradually decreased. The finger-shape structure gradually transformed to a spongestructure, and water flux, pore size, and porosity ofthe matrix membrane decreased.

Effects of additive type on the structure of CMPSFmatrix membrane

Table V shows the effects of additive types on CMPSFmatrix membrane. The usual casting solution was aternary system composed of polymers, solvent, andadditive. After certain membrane materials and corre-sponding solvent were selected, according to the com-ponent to be separated, the additive was an activefactor that could affect the morphological structure ofthe casting solution, and could determine both struc-ture and function of the terminal membrane withother casting conditions: it is thus crucial for the cast-ing process to choose the additives and to control thethermodynamical conditions of casting solution effec-tively. The additive played an important role in theprocess of forming the CMPSF matrix membrane byphase inversion. A Millipore filter membrane and ul-trafiltration membrane could be obtained by eitheradding solvent to the coagulating bath or addingproper additives to the casting solution such as highpolymer, solid inorganic salt or its dilute water solu-tion, and organic agent. Different additives promotesignificant changes in both the structure and the prop-erties of CMPSF matrix membrane. Figure 5 is the

cross-sectional SEM micrograph of CMPSF matrixplate membrane when the inorganic agent NH4Cl andthe organic agent ethanediol, respectively, were usedas additive. From Figure 5 it can be seen that supportlayers of the CMPSF matrix membrane appeared as aloose finger-shape structure when the inorganic agentwas used as additive, whereas support layers of theCMPSF matrix membrane appeared as a dense spongestructure when the organic agent was used as addi-tive. The addition of dilute inorganic water solutionchanged the acting force between solute and solvent,and caused entanglement of CMPSF macromoleculesinto a large net structure, thus causing the microporeto enlarge. The solid inorganic salt NH4Cl had addi-tional effects that could produce pores when the solidinorganic salt was removed from the casting solution.The organic agent ethanediol as additive was a poorsolvent to CMPSF, but was good for formation of netmicropores on surfaces of the CMPSF matrix mem-brane such that pore size of the membrane was en-larged; however, it decreased the phase-transfer rate,and formed a sponge-shape support layer, which de-creased both porosity and water circumfluence. Highpolymer additive PEG (MW 10000) was incompatiblewith CMPSF and left micropores in the membranematerial when it was wiped away after casting.

Effect of inorganic additive on the structure ofCMPSF matrix membrane

Changes in structure of the CMPSF plate membranewith inorganic additive content are shown in Table VI.From Table VI it can be seen that water flux, averagepore size, and porosity of CMPSF membrane all in-creased with increase of additive NH4Cl, and reached

Figure 2 IR spectrum of CMPSF membrane.

CHELATING AFFINITY MEMBRANE CHROMATOGRAPHY. I 2121

their maximum value when the additive NH4Cl con-tent was 6%, concomitantly with the relationship be-tween additive content and viscosity of the originalcasting solution. With increasing additive content, vis-cosity of the casting solution decreased continually;the double diffusion rate between solvent and coagu-lating agent increased; and pore size, porosity, andwater flux of CMPSF matrix membrane all increased.When the additive content increased to over 6%, vis-cosity of the casting solution, which was related togelation of the original solution, increased suddenly,the rate of double diffution decreased, and a densemembrane structure formed.

Effects of polymer additive on the structure ofCMPSF matrix membrane

Table VII shows the effect of polymer additive PEG(MW 10000) content on the CMPSF matrix membrane

structure. It can be seen from Table VII, that waterflux, pore size, and porosity of the CMPSF matrixmembrane all increased with increasing content ofhigh polymer additive (percentage of entire solidamount) in the casting solution.

Figure 6 and Figure 7 show SEM micrographs, re-spectively, of the cross section and surface of theCMPSF matrix membrane with different contents ofpolymer additive PEG (MW 10000). From Figure 6, itcan be seen that with increasing polymer additive, thecross-sectional structure of the membrane graduallychanged from dense to loose, the pore size of themembrane changed from small to large, and the struc-ture gradually changed from compact to loose. TheSEM micrograph of the membrane surface revealedthat the pore size of the membrane increased slightlywith increasing polymer additive content. From TableVII it can be seen that the water flux obviously in-

Figure 3 SEM micrographs of cross section of matrix membrane with different CMPSF contents: (a) 10%; (b) 12%; (c) 14%;(d) 16%.

2122 WANG, HUANG AND YANG

creased with increasing additive content, which sug-gests that the increase of water flux was determinednot only by the increase of pore size but also by theextent of contact between the membrane pores. The

formation process of the micropore membrane was aliquid–liquid phase-inversion process. Membranestructure was mainly determined by composition of

Figure 4 SEM micrographs of surface section of matrix membrane with different CMPSF contents: (a) 10%; (b) 12%; (c) 14%;(d) 16%.

TABLE IVRelationship Between CMPSF Concentration and

Properties of Membranea

CMPSF content(%)

Water flux(L m�2 h�1)

Pore diameter(nm)

Porosity(%)

10 64.2 38.5 61.312 51.8 31.2 52.414 45.3 27.1 48.416 40.7 23.2 45.718 37.6 22.1 43.220 34.3 20.6 42.6

a Additive content: 0%; casting solution temperature:25°C; coagulating bath temperature: 25°C; ultrafiltrationpressure: 0.1 MPa; effective area of membrane: 26.22 cm2.

TABLE VEffect of Various Additives on Structure of

Matrix Membranea

AdditiveWater flux

(L m�2 h�1)

Porediameter

(nm)Porosity

(%)

Nonadditive 41.2 24.0 46.3High polymer (PEG) 180.4 37.2 61.3Dilute inorganic salt (NH4Cl) 94.7 31.5 58.2Solid inorganic salt (NH4Cl) 101.5 34.8 60.1Organic reagent

(CH2OH CH2OH) 80.4 32.9 59.4

a Casting solution temperature: 25°C; coagulating bathtemperature: 25°C; ultrafiltration pressure: 0.1 MPa; effec-tive area of membrane: 26.22 cm2.

CHELATING AFFINITY MEMBRANE CHROMATOGRAPHY. I 2123

the local field in the casting solution during phaseinversion. After phase inversion of the casting solu-tion, the rich phase of CMPSF was continuous andgelled, after which it solidified into membrane contin-uous phase and formed the micropores of the CMPSFmembrane; on the other hand, as the solvent (DMAc)and additive (PEG) dispersed in the polymer as thepoor phase was being washed away, the poor phasegrew increasingly larger and then intercrossed into theaggregations among micropores during casting. Theprecondition for the continuous growth of the poorphase was that the surrounding environment couldcontinuously provide solvent for the poor phase be-fore solidification of the rich phase.

In the casting system that used water as gel agent,the diffusion rate of solvent toward water was greaterthan that of water immersed into the casting solution.The further the casting solution composition divergedfrom cloud point composition, the later the phaseinversion and the more the solvent (DMAc) over-flowed. When the additive PEG content was low, thecomposition of the casting solution was diverged sub-stantially from that of the cloud point. The overflow-ing amount of solvent and the CMPSF concentration

before phase inversion were both significant, thus pro-ducing a dense top-layer structure and small pore size.The dense layers hindered the solvent DMAc fromfurther interchanging with water, which successfullypromoted formation of finger-shape micropores. Withincreasing PEG additive content in the casting solu-tion, the composition of the solution approached thatof the cloud point. The rate of phase inversion in-creased and the solvent overflowed less before phaseinversion. The excessive amount of solvent providedgood conditions for poor phase growth. The contactamong membrane micropores increased, thus induc-ing formation of a loose top layer. The hindrance ofthe loose top layer from contacting the next layersdecreased, thus favoring an intercrossed finger-shapestructure. Although there was little change amongpore sizes, their finger-shape contacts were good, os-mosis resistance decreased, and flux of the membraneclearly increased.

Table VIII shows the effects of polymer additivePEG molecular weight on the structure of the CMPSFmatrix membrane. From Table VIII it can be seen thatwater flux, pore size, and porosity of the CMPSF ma-

TABLE VIRelationship Between Additive (Inorganic Salt) and

Properties of CMPSF Membranea

Additive content(%)

Water flux(L m�2 h�1)

Pore diameter(nm)

Porosity(%)

0 41.2 24.1 46.32 101.5 34.8 60.14 140.7 41.2 65.76 187.5 44.3 69.18 39.0 23.1 45.4

a Additive: NH4Cl; casting solution temperature: 25°C;coagulating bath temperature: 25°C; ultrafiltration pressure:0.1 MPa; effective area of membrane: 26.22 cm2.

TABLE VIIRelationship Between Additive (High Polymer) and

Properties of CMPSF Membranea

Additive content(%)

Water flux(L m�2 h�1)

Pore diameter(nm)

Porosity(%)

0 41.2 24.0 46.32 170.1 34.8 60.14 180.4 37.2 61.36 194.5 38.4 62.78 201.1 40.1 65.7

10 208.4 42.1 67.8

a Additive: PEG(10000); casting solution temperature:25°C; coagulating bath temperature: 25°C; ultrafiltrationpressure: 0.1 MPa; effective area of membrane: 26.22 cm2.

Figure 5 Effect of additives on structure of CMPSF membrane: (a) inorganic reagent; (b) organic reagent.

2124 WANG, HUANG AND YANG

Figure 6 SEM micrographs of cross section of CMPSF matrix membrane in casting solution with different polymer additivecontents: (a) 0%; (b) 2%; (c) 4%; (d) 6%; (e) 8%; (f) 10%.

CHELATING AFFINITY MEMBRANE CHROMATOGRAPHY. I 2125

Figure 7 SEM micrographs of surface section of CMPSF matrix membrane in casting solution with different polymeradditive contents: (a) 0%; (b) 2%; (c) 4%; (d) 6%; (e) 8%; (f) 10%.

2126 WANG, HUANG AND YANG

trix membrane all increased with increasing PEG mo-lecular weight, attributed to the fact that PEG was notcompatible with CMPSF and took up a certain volumein the casting solution. Through phase inversion, themicropores were produced after PEG was removed bydissolution in the coagulating agent. Obviously, thelarger the PEG molecular weight, the larger the micro-pores on the membrane. With increasing PEG molec-ular weight, the number of micropores on the mem-brane dense layer increased. Thus the loose layer fa-vored an increase of the double diffusion rate betweensolvent and coagulating agent when support layers ofthe membrane were forming, which would acceleratecoagulation of the loose layer, causing the membranestructure to become looser. Besides, the additive mol-ecules dispersed into the macromolecule chains anddestroyed the binding force among them, and thus therelatively loose net structure was formed. With in-creasing additive PEG molecular weight, the bindingforce among the molecules of polymer CMPSF becameweak. The amount of crosslinked points decreased,which caused the casting solution structure to becomelooser and the double diffusion rate between solventand coagulation to increase. With increasing coagulat-ing rate, the water flux, pore size, and porosity of theCMPSF membrane all decreased.

Effects of casting solution temperature on thestructure of CMPSF matrix membrane

Table IX shows the relationship between the structureof the matrix membrane and temperature of the cast-ing solution. It can been seen from Table IX that waterflux, pore size, and porosity of CMPSF matrix mem-brane gradually decreased with increasing casting so-lution temperature, but when the temperature of thecasting solution reached 45°C, water flux, pore size,and porosity of CMPSF matrix membrane notablyincreased afterward. The diffusion rate of solvent to-ward the coagulating bath increased with increasingcasting solution temperature. Because of the rapidoutflow of solvent, the local concentration of CMPSFon the membrane surface was too great; the dense skin

layer formed, and thus water flux, pore size, andporosity of the matrix membrane all showed a de-creasing trend. Meanwhile, according to characteris-tics of the polymer dilute solution, the intrinsic viscos-ity [�] of the solution decreased with increasing tem-perature of the casting solution. Because of thedecrease of casting solution viscosity and increase offluidity of casting solution, the thickness of the mem-brane decreased, the flowing resistence was reduced,and the water flux increased under the same castingconditions. With increasing casting solution tempera-ture, viscosity of the casting solution decreased con-tinuously, and thus the double diffusion rate betweenthe solvent and coagulating agent accelerated. The fastspeed of coagulation caused the matrix membranestructure to become looser, thus causing the increasingtrend of pore size, porosity, and water flux of themembrane: when the temperature of the casting solu-tion reached 45°C, this trend was dominant. Withfurther increases of temperature of the casting solu-tion, the water flux, pore size, and porosity of matrixmembrane all increased.

Effects of nonsolvent additive on dynamics factorDe of membrane formation

Strathmann et al.11 used optical microscopy to recordchanges of forward peak displacement D2 with time t,when the ternary phase equilibria of the polymer/additive/solvent penetrated into the coagulating bathto precipitate. It was found that D2–t showed a goodlinear relation. Kang et al.12 simply described the for-mula as

D � 2�De,t�1/2

where D is the forward peak displacement in thephase separation; De is the dynamics factor (mm s�1)of membrane formation; and t (s) is the time immersedin the coagulating bath. In the practical gel process,the composition of the precipitant changed with the

TABLE IXRelationship Between Casting Solution Temperature and

Properties of CMPSF Membranea

Temperature(°C)

Water flux(L m�2 h�1)

Pore diameter(nm)

Porosity(%)

20 140.6 41.3 65.825 135.2 40.1 64.830 130.6 39.4 63.435 122.4 38.6 62.340 118.9 37.5 61.145 121.5 37.9 61.750 135.7 40.7 65.1

a Additive: PEG(10000); content 4%; coagulating bath tem-perature: 25°C; ultrafiltration pressure: 0.1 MPa; effectivearea of membrane: 26.22 cm2.

TABLE VIIIRelationship Between Additive Molecular Weight and

Properties of CMPSF Membranea

Molecular weight(PEG)

Water flux(L m�2 h�1)

Pore diameter(nm)

Porosity(%)

400 76.3 28.4 51.9600 81.5 30.1 57.4

10000 180.4 37.2 61.320000 201.3 43.6 68.5

a Additive: PEG 4%; casting solution temperature: 25°C;coagulating bath temperature: 25°C; ultrafiltration pressure:0.1 MPa; effective area of membrane: 26.22 cm2.

CHELATING AFFINITY MEMBRANE CHROMATOGRAPHY. I 2127

continuous overflow of solvent, and thus the linearrelation between D2 and t was changed. Sun13 pointedout that every segment of the gel rate curve wascomposed of several sections of segments with differ-ent rate constant ki values and the rate constant ofevery segment corresponded to different structurelayers on the membrane cross section. The property ofthe asymmetric membrane was mainly determined bythe skin layer structure of the membrane. The skinlayer structure of the matrix membrane also deter-mined the gel behavior of the subsequent layer duringmembrane formation, and thus the study of mem-brane layer gel dynamics behavior is important forunderstanding the properties and phase-inversionprocess of the membrane. Table X shows the effects ofPEG concentration in casting solution, which con-sisted of CMPSF � 15% on the membrane structure. Itcan be seen from Table X that pure water flux firstincreased and then decreased with increasing ratio ofPEG/CMPSF. When PEG/CMPSF � 2/3, water flux,pore size, and porosity of the matrix membrane allreached their maximum value. On one hand, the ex-istence of polymer additive PEG changed the phase-equilibrium relation of the casting solution and in-creased the homogeneous internal space of the solu-tion, which in turn increased the required amount ofnonsolvent during the phase inversion; moreover, theexistence of PEG increased the viscosity of the castingsolution and hampered the movement of the macro-molecular chain in the casting solution. These twoaspects both delayed the occurrence of phase inver-

sion. On the other hand, PEG was a kind of hydro-philic polymer that could be dissolved in water, andthus the immersing rate of the nonsolvent could beaccelerated to promote phase inversion by increasingthe affinity between the casting solution and the pre-cipitant. Because of resistances and competition be-tween the two aspects, when PEG/CMPSF was at aratio of 2/3, the two aspects achieved equilibrium, theDe value reached to a maximum value, the phase-inversion rate was the largest, and the asymmetrymembrane with high porosity was readily formed.These phenomena proved that nonsolvent additivePEG changed the casting solution system with respectto the thermodynamic equilibrium relation and thedynamics rate of membrane formation. Such changingtrends of De had important effects on the ultimatestructure and separating properties of the matrixmembrane.

Effects of water content in casting solution ondynamics factor De of CMPSF matrix membrane

Table XI shows the effects of water content in theCMPSF/PEG/DMAc/H2O casting solution on thestructure of the matrix membrane. It can be seen fromTable XI that water flux, pore size, and porosity ofmatrix membrane all increased with increasing watercontent in the casting solution. When a given amountof water (less than the water content at cloud point)was added into the casting solution, the compositionof the casting solution approached the phase-inver-

TABLE XEffect of PEG Concentration on the Structure of CMPSF Membranea

Casting solution composition (%) Water flux(L m�2 h�1)

Pore diameter(nm)

Porosity(%)CMPSF PEG DMAC PEG/CMPSF

15 0 85 0 41.2 24.0 46.315 5 80 1/3 189.2 40.2 61.215 10 75 2/3 208.4 42.0 67.815 15 70 1/1 178.3 37.1 57.4

a Additive: PEG(10000); coagulating bath temperature: 25°C; ultrafiltration pressure: 0.1 MPa; effective area of membrane:26.22 cm2.

TABLE XIEffect of Water Content on the Structure of CMPSF Membranea

Casting solution composition (%) Water flux(L m�2 h�1)

Pore diameter(nm)

Porosity(%)CMPSF PEG DMAC H2O

15 10 85 0 208.4 42.1 67.815 10 72 3.0 227.4 47.7 69.315 10 71 4.0 257.3 54.6 75.415 10 70 5.0 268.7 59.2 79.815 10 69 6.0 291.0 61.1 81.6

a Additive: PEG(10000); coagulating bath temperature: 25°C; ultrafiltration pressure: 0.1 MPa; effective area of membrane:26.22 cm2.

2128 WANG, HUANG AND YANG

sion curve, the water amount needed in phase inver-sion was reduced, and the forward peak displacementrate of phase inversion was accelerated. When the Devalue increased, the casting solution had a swift sep-aration; the polymer concentration at the phase-inver-sion point decreased; and pore size, porosity, andwater flux of the matrix membrane all increased.

Effects of evaporating time on the structure ofCMPSF matrix membrane

The quality of affinity membrane chromatographywas determined by membrane materials and mem-brane-forming conditions. When the membrane mate-rial was fixed, the structure of casting solution anddesolvating speed could finally affect both the struc-ture and the properties of CMPSF matrix membrane.Table XII shows the effects of evaporating time on thestructure of CMPSF matrix membrane. It can be seenfrom Table XII that water flux, pore size, and porosityof CMPSF matrix membrane all reached their maxi-mum value when the evaporating time was 120 s. Boththe volatilization effect and the hygroscopic effect ofDMAc controlled the evaporating process. The hygro-scopic effect of the solvent was substantial when theevaporating time was short. On one hand, with in-creasing evaporating time, the CMPSF macromole-cules gathered from the homogeneous scattering netstructure to form a macromolecular aggregate, andthus water flux, pore size, and porosity of the matrixmembrane all increased. On the other hand, with in-creasing evaporating time, the solvent concentrationdecreased, the casting solution viscosity increased,and the DMAc hygroscopic speed decreased sharply.When evaporating time reached 120 s, the volatiliza-tion of the solvent was relatively significant. Withincreasing evaporating time, the binding forces amongthe CMPSF macromolecules increased, which causedCMPSF macromolecules to shrink upon desolvating,and thus a relatively dense structure was formed. Thepore size on the membrane skin layer and porosity

inside matrix membrane decreased and thus the waterflux of the matrix membrane decreased.

Effects of coagulating bath concentration on thestructure of CMPSF matrix membrane

Changes in structure of the CMPSF matrix membrane,with different NaCl concentrations in the coagulatingbath, are shown in Table XIII. The coagulating valuewas the necessary flocculant volume (coagulation me-dium) to cause a certain polymer to begin to produceprecipitation in its dilute solution. The coagulatingvalue can represent the relationship between the co-agulating speed and the structure of the matrix mem-brane. The greater the coagulating value, the slowerthe desolvating speed; then the membrane having acompact structure was readily formed. It can be seenfrom Table XIII that the coagulating value of the mem-brane reached its maximum value, and water flux,pore size, and porosity of the membrane reached theirminimum value when 10% NaCl solution was used asthe coagulating bath. When the concentration of NaClsolution was less than 10%, the desolvating speed wasfast, the coagulation was severe, and the membrane ofloose structure was readily formed with increasingconcentration of coagulating bath, whereas when theconcentration of NaCl was above 10%, with furtherincreases of the concentration of coagulating bath, thecoagulating value decreased, the desolvating speedbecame fast, and the membrane structure becameloose instead.

Effects of coagulating medium on the structure ofCMPSF matrix membrane

Table XIV shows the effects of the different coagulat-ing media (H2O, NaCl solution, DMAc water solution)on the structure of CMPSF matrix membrane. It can beseen from Table XIV that the different coagulating

TABLE XIIIRelationship Between Coagulating Bath Concentration

and Properties of CMPSF Membranea

Concentration(%)

Coagulatingquantity

(mL)Water flux

(L m�2 h�1)

Porediameter

(nm)Porosity

(%)

4 3.43 180.8 36.6 56.68 3.50 166.7 31.7 54.8

10 3.56 150.3 28.3 51.712 5.51 160.2 29.8 53.714 3.14 184.1 37.1 58.818 2.01 186.2 37.3 58.120 1.86 194.5 38.4 62.7

a Evaporation time: 10 s; additive: PEG(10000) 6%; castingsolution temperature: 25°C; coagulating bath temperature:25°C; ultrafiltration pressure: 0.1 MPa; effective area ofmembrane: 26.22 cm2.

TABLE XIIRelationship Between Evaporation Time and Properties

of CMPSF Membranea

Evaporation time(s)

Water flux(L m�2 h�1)

Pore diameter(nm)

Porosity(%)

20 140.1 32.1 43.240 148.4 33.2 45.860 160.2 35.8 47.680 168.4 37.5 52.3

120 194.5 38.4 62.7140 170.3 37.3 53.6160 162.5 36.4 49.2

a Additive: PEG (10000) 6%; casting solution temperature:25°C; coagulating bath temperature: 25°C; ultrafiltrationpressure: 0.1 MPa; effective area of membrane: 26.22 cm2.

CHELATING AFFINITY MEMBRANE CHROMATOGRAPHY. I 2129

media had significantly different effects on the coag-ulating value and the structure of the membrane.When 10% NaCl solution was used as the coagulatingbath, the coagulation value increased and the desol-vating speed was relatively slow, so the structure onthe membrane surface and inside the membrane washomogeneous and compact, which caused water flux,pore size, and porosity of CMPSF matrix membrane todecrease.

Effects of coagulating bath temperature on thestructure of CMPSF matrix membrane

Table XV shows the effects of coagulating bath tem-perature on the structure of CMPSF matrix membrane.Changes of coagulating bath temperature had com-plex effects on the structure of CMPSF membrane.Experimental results showed that, at a range of 25–45°C, with increasing coagulating bath temperature,the diffusion rate of the coagulating agent in the cast-ing solution increased, which caused a loose mem-brane structure at the initial stage of increasing tem-perature; therefore, water flux, pore size, and porosityof CMPSF matrix membrane all increased. With thefurther increase of the coagulating bath temperature,the pores on the membrane surfaces shrunk, and thewater flux, pore size, and porosity of CMPSF matrixmembrane all decreased. When the temperature was

above 45°C, but did not reach the casting solutiontemperature (because the temperature difference be-came increasingly small), pore size on the membranesurface increased and the water flux increased as well.When the coagulating bath temperature was above55°C, the temperature difference became greater, sothe structure inside the membrane became loose, theporosity increased, and water flux and pore size con-tinued to increase.

CONCLUSIONS

High-quality CMPSF matrix plate membranes,which were synthesized by Friedel–Crafts electro-philic substitution reaction under anhydrous condi-tion using PSF as the original material, dichlo-romethane as solvent, monochloro methyl ether aschloromethyl reagent, and anhydrous ZnCl2 as cat-alyst, were prepared by phase inversion. The struc-ture and properties of CMPSF matrix plate mem-brane were determined not only by the nature of themembrane materials and the membrane-formingprocess conditions but also by the thermodynamicconditions of casting solutions, such as the concen-tration of polymer, the type and amount of additive,and the temperature of the casting solutions. It wascrucial for the casting process to choose the addi-tives with care and to control effectively the ther-modynamic conditions of casting solution. Nonsol-vent additive PEG changed the casting solution sys-tem with respect to both the thermodynamicequilibrium relationship and dynamics rate of mem-brane formation. The changing trend of De and de-solvating speed, which was controlled by such fac-tors as coagulating bath temperature, different co-agulating bath media, and coagulating bathconcentration, could influence the ultimate struc-ture and separating properties of CMPSF matrixplate membrane.

References

1. Beeskow, T. C.; Kusharyoto, K.; Anspach, F. B. J Chromatogr A1995, 715, 49.

TABLE XIVRelationship Between Coagulating Medium and Properties of CMPSF Membranea

Coagulatingmedium

Coagulating quantity(mL)

Water flux(L m�2 h�1)

Pore diameter(nm)

Porosity(%)

H2O 3.49 165.4 30.8 54.110% NaCl solution 3.56 150.3 28.3 51.710% DMAC solution 3.43 180.8 36.6 62.4

a Evaporation time: 10 s; additive: PEG(10000) 6%; casting solution temperature: 25°C; coagulating bath temperature: 25°C;ultrafiltration pressure: 0.1 MPa; effective area of membrane: 26.22 cm2.

TABLE XVRelationship Between Coagulating Temperature and

Properties of CMPSF Membranea

Coagulatingtemperature

(°C)Water flux

(L m�2 h�1)Pore diameter

(nm)Porosity

(%)

25 183.2 34.8 56.735 190.4 38.1 61.845 181.4 33.6 55.255 184.7 35.7 57.465 187.6 36.4 59.3

a Evaporation time: 10 s; additive: PEG(10000) 6%; castingsolution temperature: 25°C; coagulating medium: H2O; ul-trafiltration pressure: 0.1 MPa; effective area of membrane:26.22 cm2.

2130 WANG, HUANG AND YANG

2. Serfica, G. C.; Pimbley, J.; Belfort, G. J Membr Sci 1994, 88,292.

3. Reif, O. W.; Volker, N.; Bahr, U. J Chromatogr A 1993, 654,29.

4. Petsch, D.; Beeskow, T. C.; Anspach, F. B. J Chromatogr B 1997,693, 79.

5. Li, J.; Chen, H.-L.; Chai, H. Chem J Chin Univ 1999, 20, 1322.6. Bao, S.-X.; Shi, G.-J.; Jiang, W. J Chem Ind Eng (China) 1995, 46,

15.7. Wang, B.; Cui, Y.-F.; Du, Q. J Appl Polym Sci 2003, 87, 908.

8. Wuhan University. Analytical Chemistry; Higher EducationPress: Beijing, 1997; p 146.

9. Osada, Y.; Nakagawa, T. Membrane Science and Technology;Marcel Dekker: New York, 1992; p 8.

10. Gao, Y.-X.; Ye, L.-B. Membrane Separation Technology Base;Science Press: Beijing, 1989; p 173.

11. Strathmann, H.; Kock, K.; Amar, P.; Baker, R. W. Desalination1975, 16, 179.

12. Kang, Y. S.; Kim, H. J.; Kim, U. Y. J Membr Sci 1991, 60, 219.13. Sun, B.-H. Technol Water Treat (China) 1993, 19, 308.

CHELATING AFFINITY MEMBRANE CHROMATOGRAPHY. I 2131