Enhanced Permeation Performance of Cellulose Acetate Ultrafiltration

Aug 8, 2014 - The performance of the membranes was analyzed on the basis of water ... via distillation-precipitation polymerization and its applicatio...
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Enhanced Permeation Performance of Cellulose Acetate Ultrafiltration Membranes by Incorporation of Sulfonated Poly(1,4phenylene ether ether sulfone) and Poly(styrene-co-maleic anhydride) Seema Shenvi,† A. F. Ismail,‡ and Arun M. Isloor*,† †

Membrane Technology Laboratory, Chemistry Department, National Institute of Technology Karnataka, Surathkal, Mangalore 575 025, India ‡ Advanced Membrane Technology Research Center (AMTEC), UniversitiTeknologi Malaysia, 81310 Skudai, Johor Bahru, Malaysia S Supporting Information *

ABSTRACT: A cellulose acetate (CA)-based ultrafiltration membrane was prepared by incorporation of mechanically strong, sulfonated poly(1,4-phenylene ether ether sulfone) (SPEES) to which hydrolyzed poly(styrene-co-maleic anhydride) (PSMA) was added as a novel additive. The preparation of SPEES was investigated in detail. SPEES having a degree of sulfonation of 21%, was more suitable for the blend. The chemical constitutions of SPEES, PSMA, and the blend membranes were confirmed by attenuated total reflectance fourier transform infrared spectroscopy. The scanning electron microscopy images revealed fingerlike projections in the membrane structure. The performance of the membranes was analyzed on the basis of water content, porosity, flux, and antifouling studies. A membrane comprising 30% SPEES and 2% additive showed superior performance with flux and flux recovery ratio of 228 L/(m2 h) and 91%, respectively. It was concluded that the prepared membranes showed better performance in comparison with neat CA membranes.

1. INTRODUCTION Membrane technology as an efficient separation tool has already been well established. To ensure sustainability, expansion, and progress of this technology by overcoming the existing shortcomings is the need of the hour. Plasma treatment, atomic transfer radical polymerization technique (ATRP), synthesis of tailored polymers, grafting, and electrospinning, are a few of the efforts that have been undertaken in this direction.1−5 Physical or chemical modification of the commercial polymers is one of the simplest, cost-effective, and popular methods to prepare membranes and enhance their performance. Cellulose acetate (CA) is a commonly used low cost ultrafiltration (UF) material that is known for its hydrophilicity and biocompatibility.6,7 However, the low mechanical and thermal resistance of CA has necessitated the use of structurally and mechanically strong polymers to overcome these drawbacks. Blending the CA with suitable functional polymers and additives is a simplest and costeffective methods, since it is known that blending proves to be an efficient way to achieve combined properties of the individual polymers. One of the major problems faced in the field of membrane technology is fouling. Fouling refers to a decline in the membrane performance over a period of time due to formation of cake on the membrane surface resulting from the adsorption of foulants.8,9 It may also result from the blocking of membrane pores. This problem needs to be addressed while designing and suggesting a new membrane. In our current work, with the intention of improving the permeation and antifouling property of the CA membrane, a CA blend with sulfonated poly(phenylene ether ether sulfone) © 2014 American Chemical Society

(SPEES) using hydrolyzed poly(styrene-co-maleic anhydride) (PSMA) as an additive was carried out. SPEES serves as a novel alternative to the commonly used polysulfone, poly(ether ketone), poly(ether imide) having good mechanical, chemical, and thermal stability. The aromatic and ether linkages in the structure of PEES provided the necessary molecular rigidity, strength, and good processability.10 This is a relatively new material to be used in the field of membrane technology. Recently Maheshwari et al. reported UF performance of the blend comprising CA and PEES. However, the hydrophobic nature of this material restricts its wide-scale utilization. In the current study, PEES was chemically modified by a sulfonation reaction to increase the much required hydrophilicity. Moreover, the additive PSMA consisted of an anhydride moiety which on hydrolysis would give a diacid that can serve as a binding site for metal ions in addition to increased hydrophilicity.11 Also the aromatic ring in its backbone gives additional rigidity to the molecule. This paper reports the account of UF performance of a novel blend CA/SPEES using hydrolyzed PSMA. In addition to this, the preparation of sulfonation of PEES and the hydrolysis conditions of PSMA has been investigated in detail. Received: Revised: Accepted: Published: 13820

June 18, 2014 August 4, 2014 August 8, 2014 August 8, 2014 dx.doi.org/10.1021/ie502310e | Ind. Eng. Chem. Res. 2014, 53, 13820−13827

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Scheme 1. Schematic Representation of Sulfonation of PEES

2. EXPERIMENTAL SECTION 2.1. Materials. Cellulose acetate (Mw ≈ 50 000 with acetyl content 39.7 wt %), poly(styrene-co-maleic anhydride) cumene terminated (Mw ≈ 1600, Tg = 154 °C), and poly(1,4 phenylene ether ether sulfone) (Tg = 192 °C) were procured from SigmaAldrich. The materials were dried overnight in oven at 50 °C prior to their use. N-Methyl pyrrolidone (NMP) of analytical grade was obtained from Merck, India, and was used without further purification. Bovine Serum Albumin (BSA) (Mw ≈ 69 kDa) used for antifouling study was procured from CDH chemicals. Sulfuric acid and hydrochloric acid was obtained from Merck. 2.2. Sulfonation of PEES. Sulfonation of PEES was carried out by a slightly modified procedure as mentioned by Unveren et al.12,13 A solution of 10 wt % PEES was prepared in concentrated sulfuric acid (95−98%) in a three necked flask and was stirred for a certain period of time ranging from 24 to 120 h. After a determined reaction time, the reaction mass was slowly precipitated in ice cold water to obtain white sulfonated product. The product was initially filtered off and was thereafter repeatedly washed with distilled water until the pH was neutral. The product being hydrophilic in nature showed considerable swelling during water washings. This swollen mass was then dried in a vacuum oven for over 24 h at 60 °C to obtain SPEES. Schematic representation of the reaction and the mechanism is given in Schemes 1 and 2.

The degree of sulfonation (DS) was found out by the titration method. 2.3. Hydrolysis of Poly(styrene-co-maleic anhydride). PSMA was first dissolved in 1 N NaOH for over 1 h to prepare 6 wt % solution (Scheme 3). The dissolved hydrolyzed product Scheme 3. Schematic Representation of Hydrolysis of PSMA

was then reprecipitated by 0.1 N HCl.15 The white solid product was carefully filtered. Also care was taken while giving water washings to the product in order to neutralize the acid. An excess of water washings was avoided. 2.4. Preparation of Membrane. Sixteen wt % of the polymer solution was prepared in NMP with different compositions as mentioned in Table 1. Homogeneous solutions Table 1. Composition of the CA/SPEES Blend Membranes blend composition (16 wt %) code M1 M2 M3 M4 M5 M6 M7 M8 M9

Scheme 2. Schematic Representation of Plausible Mechanism of Generation of Electrophile and Its Subsequent Attack on the PEES Ring during Sulfonation Reaction

CA (wt %) SPEES (wt %) PSMA (wt %) solvent NMP (wt %) 90 80 70 90 80 70 90 80 70

10 20 30 10 20 30 10 20 30

0 0 0 1 1 1 2 2 2

84 84 84 83 83 83 82 82 82

were prepared by the addition of first SPEES and PSMA in the required amount at room temperature. After their dissolution, CA was added in short intervals under constant stirring. On ensuring complete polymer dissolution, the solution was degassed by sonication before casting the membrane. The membrane was prepared by the phase inversion technique in which distilled water was used as nonsolvent in a coagulation bath.16,17 The membranes were stored in 1% formalin solution to prevent microbial attack. The thickness of the membranes was found to be 200 μm.

In the method mentioned, concentrated sulfuric acid served as the solvent as well as reagent for the sulfonation reaction. The effect of chlorosulfonic acid as the sulfonating reagent, was studied by performing another reaction, where concentrated sulfuric acid served as solvent only. In this procedure, 1 g of PEES was dissolved in conc. sulfuric acid as mentioned above for a period of 24 h. After its dissolution, 2 mL chlorosulfonic acid was added dropwise to the reaction mass at less than 10 °C. The reaction was maintained in this condition for a period of 2 h, after which it was precipitated in ice cold water. The white sulfonated mass was separated and given water washings until the filtrate was neutral.14

3. CHARACTERIZATION 3.1. Degree of Sulfonation of SPEES. The DS was calculated by the titration method as mentioned in the literature.18 Briefly, dry SPEES was stirred with 10 mL of dimethylformamide (DMF) overnight. The amount of liberated H+ ions was titrated with a standard NaOH solution using phenolphthalein as an indicator. The DS was calculated as 13821

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Industrial & Engineering Chemistry Research DS =

Research Note

0.324 × C NaOH × VNaOH W − 0.08(C NaOH × VNaOH)

precompressed membranes at room temperature, a transmembrane pressure of 1.5 bar, and at a stirring speed of 300 rpm. The pure water flux (PWF) Jw (L/(m2 h)) was determined by the use of following equation

where W is the weight of the sample, CNaOH is the molarity of the standard NaOH solution, VNaOH is the amount of NaOH solution consumed, 324 is the molecular weight of the repeating unit of PEES, and 80 is the difference in molecular mass of SPEES and PEES. 3.2. NMR Spectral Measurement. The occurrence of sulfonation reaction of PEES was confirmed by recording the 1 H NMR spectrum on a Varian NMR-400 instrument. The samples were dissolved in deuterated dimethyl sulfoxide (d6DMSO). Chemical shift was measured against tetramethylsilane (TMS) as the internal standard. 3.3. FTIR Analysis. The confirmation of the homogeneous blend formation and its chemical constitution was done by recording the FTIR spectra between the working range of 4000−650 cm−1 on JASCO 4200 instrument. The sulfonation of PEES and the hydrolysis of PSMA were also confirmed, and the spectra were compared with the unmodified polymers. 3.4. Water Content. The presence of different hydrophilic functional groups such as −SO3H, −COOH, and −OH makes it interesting to study the increase in water uptake of the prepared membranes in comparison with that of the neat membrane.19 In general, the swelling study aids in knowing the bulk hydrophilicity of the membranes. It was calculated as follows

Jw =

where Q is the volume of water (L) permeated through the membrane having area A (m2) in time Δt (h). The antifouling property of the membranes was tested using 1000 mg/L of BSA solution. For this study, the pure water flux was first determined for 30 min and noted as Jw1. The feed solution tank was then replaced by the BSA solution and its flux was recorded for 40 min by the above equation as Jp. The BSA fouled membranes were first flushed and then mechanically washed with distilled water to remove the loosely adhering BSA molecules from the membrane surface, after which again the pure water flux for 30 min was recorded as Jw2. From the recorded flux values, the flux recovery ratio is calculated from the equation

Jw2

FRR(%) =

Jw1

100

The extent of membrane fouling was assessed in terms of reversible Rrev and irreversible Rirr fouling ratio R rev(%) =

⎛ W − Wd ⎞ %water content = ⎜ w ⎟100 ⎝ Ww ⎠

(Jw2 − Jp ) Jw1

100

⎛J − J ⎞ w2 ⎟⎟ R irr(%) = ⎜⎜ w1 J ⎝ ⎠ w1

where Ww and Wd are the weight of wet and dry membrane samples, respectively. 3.5. Porosity. Porosity of the membranes was determined as mentioned in the literature.20 Porosity is defined as the ratio of pore volume to the geometrical volume of membrane. In this study, the wet weight of the membrane was recorded after it was carefully mopped to remove the surface adhering water. This was followed by drying the membrane sample for about 48 h in an oven at 50 °C whose weight was noted as Md. Porosity was obtained by the equation ε(%) =

Q ΔtA

4. RESULTS AND DISCUSSION 4.1. Sulfonation of PEES. Literature suggests that a sulfonation reaction carried out by use of chlorosulfonic acid Table 2. Variation in Degree of Sulfonation with Time

M w − Md 100 Alρ

where Mw and Md are the weights of wet and dry membrane samples, respectively, A is the area of the sample (cm2), l is the thickness (cm), and ρ is the density of water (0.998 g/cm3). 3.6. Scanning Electron Microscopy. The morphology of membranes was studied by taking their SEM images. The SEM images were analyzed on JEOL 6380LA analytical SEM instrument. The samples were initially sputtered with gold for conductivity. To achieve a clean cut, the membrane samples were fractured cryogenically for 1 min before recording the cross section morphology. The surface image of the membrane samples was not taken due to the shrinking property of the CA membrane. The resulting rough surface was not very ideal to study the surface morphology. 3.7. Permeation Study. The filtration performance of the membrane was tested on a dead end filtration setup having a membrane holder with an effective diameter of 5 cm. The filtration setup was connected to a nitrogen cylinder. The membranes were initially subjected to compaction at 2 bar for 30 min. All the filtration experiments were carried out on the

time (h)

degree of substitution (%)

24 36 60 100 120

14 21 55 67 79

and 100% concentrated sulfuric acid as sulfonating agents leads to partial degradation of the polymer as well as other side or cross-linking reactions.21 Moreover the sulfonated product obtained by chlorosulfonic acid showed excessive swelling and was soluble in water to a greater extent. Hence it was decided to bring about the sulfonation in which sulfuric acid (95−98%) acted as solvent as well as a reagent. The sulfonation reaction is an electrophilic substitution reaction. The electrophile is generated as shown in Scheme 2. The electron-rich benzene ring, then reacts with the electrophile to give the sulfonated product. In the structure of PEES, three aromatic rings are present each having different chemical reactivity. Out of the many positions where substitution may possibly occur, the one shown in Scheme 2 seems to be the most plausible one. The substitution at the middle aromatic ring seems most probable since it is ortho to the electron 13822

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Figure 3. Water uptake capacity of the membranes.

Figure 1. ATR-FTIR spectra of (a) M2, (b) M5, and (c) M8.

Figure 4. SEM images of (a) neat CA, (b) M7, (c) M8, and (d) M9.

Figure 2. Porosity study of the blend membranes.

donating ether group on one side of the benzene ring and meta to the electron withdrawing sulfonyl group on the opposite side of the benzene ring, thereby generating a partial negative charge at that position; hence, for the sulfonation reaction, the specified position is the most preferable. Since the chemical reactivity of both ortho positions toward the electrophile is the same, a substitution may occur in either one of the positions or both of the positions. Sulfonation of PEES was confirmed by proton NMR analysis (Figure S1, Supporting Information). Figure S1A represents the proton NMR spectrum of PEES. Since PEES is a symmetric molecule, six protons were observed in the aromatic region. However, after the substitution reaction, a significant change in the pattern was witnessed in the aromatic region. In Figure S1B, the aromatic region showcased 11 protons which justified change in the chemical environment of the protons after substitution. Moreover, it also suggested that, the only monosubstitution took place at one ortho position and not both of the positions as suggested above. The OH proton from

Figure 5. Water flux measurement of the blend membranes at 1.5 bar.

−SO3H was merged with the residual deuterated water (HOD) peak of the DMSO solvent. The DS was strongly influenced by the reaction time which has been summarized in Table 2. 13823

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Table 3. Comparison of the Prepared Membranes with Other CA UF Membranes membrane CA26 CA/Pluronic F12727 CA/PEES10 CA/PSf28 CA/cPSf29 CA/SPEES

additive PVP (3%) PEG (2.5%) SPEEK (15%) hydrolyzed PSMA

flux (L/(m2 h))

water content (%)

65 95 255.5 132 116 228

83 84.3 88 81.63 88.06

It was observed that with an increase in DS, the sulfonated product exhibited excessive swelling as well as partial dissolution in water. This was one of the primary reasons for the higher solubility of SPEES prepared from chlorosulfonic acid. Chlorosulfonic acid being a stronger sulfonating reagent resulted in higher DS than sulfuric acid. The product was completely soluble in hot water when DS was more than 60%. These observations indicated that SPEES with higher DS was not suitable for membrane-based separation applications. For further studies, SPEES with 21% of DS was used to prepare blend membranes with CA. Noticeable changes in the physical and chemical properties are known to occur by the introduction of the sulfonic acid group in the polymer. The sulfonation reaction is known to reduce the crystallinity of the polymers, thereby increasing its solubility in different solvents.22 The solubility of PEES in organic solvents differs considerably than SPEES which has been tabulated in Table S1, Supporting Information. 4.2. Hydrolysis of PSMA. The hydrolysis of PSMA was carried out before its incorporation in the polymer blend unlike that performed in the literature. Padaki et al. reported a blend comprising PSf and poly(isobutylene-alt-maleic anhydride) (PIAM) and studied its permeation performance before and after alkali treatment.15 In this work PIAM was first incorporated in the polymer blend after which hydrolysis of the composite membrane was carried out to bring about the conversion of anhydride to diacid. The addition of PSMA into the blend and then bringing about the hydrolysis of the membrane would have resulted in the hydrolysis of cellulose acetate as well. To avoid the disintegration of the membrane matrix, it was first decided to bring about the hydrolysis of

Figure 7. Flux recovery ratio and fouling resistance of the prepared membranes.

PSMA by base treatment and then assimilate this product in the blend solution as an hydrophilic additive. The concentration of PSMA in the blend was restricted up to 2 wt % since above this level, excessive leaching of the material into the coagulation bath was observed. This is due to the higher affinity of PSMA toward water and its partial water solubility. 4.3. FTIR Analysis. Figure S2A, Supporting Information represents the IR spectra of PEES and SPEES. In addition to the peaks of PEES, a new broad peak corresponding to the −OH of −SO3H was observed in Figure S2Ab of SPEES at 3500 cm−1. The presence of this peak in the SPEES spectrum confirms the successful modification of PEES. The other significant peaks common to both PEES and SPEES have been mentioned in Table S2, Supporting Information. The IR spectra of PSMA and its hydrolysis have been demonstrated in Figure S2B, Supporting Information. It is evident from the spectra that there is a disappearance of the anhydride peak in hydrolyzed PSMA. The shoulder peak of anhydride functionality appearing at 1840 and 1758 cm−1 in PSMA has been substituted by a single peak at 1705 cm−1 corresponding to the carbonyl stretching frequency of diacid featured in the hydrolyzed product. Moreover, a new broad peak at 3391 cm−1 was ascribed to the −OH stretch of

Figure 6. Effect of change in concentration of (a) SPEES and (b) PSMA on the fouling behavior of the membranes. 13824

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the solvent and nonsolvent in the coagulation bath. It is the result of this morphology that has resulted in enhanced water uptake, porosity, and flux. The variation in concentration of SPEES did not have a significant effect on the morphology of membranes. However, for M9, having 30% SPEES and 2 wt % PSMA, the walls of the projections seem to be diminishing with a great number of big voids. This indicates that beyond this limit, the assembly may not be suitable for efficient separation. 4.6. Membrane Permeability. Inclusion of SPEES and PSMA increased the flux of blend membranes due to two factors. First, both the materials contained functional groups which were responsible to enhance the membrane hydrophilicity. Second, it affected the membrane morphology in a positive way leading to formation of finger-like projections and more porous structure. The flux of neat CA membrane was found to be 60 L/(m2 h). With the addition of SPEES, the flux increased as expected (Figure 5). Without the presence of additive, the increase in PWF was from 85 L/(m2 h) to 103 L/ (m2 h) from M1 to M3. A similar trend was observed in other membranes; at a given concentration of PSMA, flux increased with an increase in the content of SPEES in the composition. One of the possible explanations for the increase in flux with SPEES can be attributed to the amorphous nature of SPEES which helps in increasing the pore size of the membrane due to the extended segmental gap between the polymer chains. An upward trend was observed in PWF with an increase in the amount of PSMA too. At higher percentage, more amount of PSMA along with NMP leached out of the membrane, which resulted in an enhancement in the membrane porosity and pore size. The simultaneous increase of SPEES and PSMA may cause the polymer segments to repel each other; in addition the leach ability of PSMA may lead to more void formations in the membrane structure, which explains the increase in PWF. Table 3 compares the performance of prepared CA/SPEES blend membranes with a few of the reported CA UF membranes. 4.7. Antifouling Study. Fouling mechanisms such as hydrophobic or electrostatic interaction and protein properties such as size or aggregation behavior determine the ultrafiltration performance of membranes in terms of flux and rejection.23 The antifouling property of the membrane is an indication of the membrane resistance toward fouling which encompasses the self-cleaning property of the membranes.30 The hydrophilicity of the prepared membranes is evident from the preceding sections in which increased flux, water uptake, and porosity has been observed in membranes having higher composition of SPEES and PSMA. All the blend membranes exhibited higher flux recovery than neat CA membranes (CA had 52% FRR, 38% Rrev, and 47.6% Rirr) suggesting that the addition of SPEES and PSMA improved the antifouling property of the membrane as observed from Figure 7. The presence of carboxylic, hydroxyl, and sulfonic acid groups on the membrane surface facilitated adsorption of incoming water molecules to form a hydrated layer on the active surface. The interaction between the protein molecules and the membrane surface is significantly reduced because of this hydrated layer. The sudden dip in the protein flux value (Figure 6) indicated that the protein molecules formed a film on the membrane surface within the first few seconds of BSA filtration. However, because of the presence of the hydrated layer, the BSA molecules adhered loosely to the membrane surface which allowed recovery of PWF by simple hydraulic cleaning. This reflected the self-cleaning property of the prepared membranes.

carboxylic group in the modified product. In addition to this, a common peak at 1195 cm−1 was attributed to the C−O stretch of the carboxyl group. Peaks which are obtained at 3400, 1736, and 1035 cm−1 corresponding to −OH, carbonyl of acetyl group, and that of a cyclic ether group of CA and 1301, 1148, and 1228 cm−1 corresponding to symmetric and the asymmetric stretch of −SO2 and aromatic ether of SPEES are seen to be present in the blend with a slight shift in their values indicating interactions between CA and SPEES in the blend in Figure 1. The cyclic ether peak in the membrane is seen to be shifted to 1053 cm−1, whereas the aromatic ether peak is shifted to 1239 cm−1. Also, there is a change in peak of −OH to 3487 cm−1 which includes the −OH stretch of the sulfonated product and hydrolyzed PSMA. An increase in intensity of peak at 1736 and 1228 cm−1 has been observed from panels a to c in Figure 1 which has been attributed to a successive increase in concentration of the additive. 4.4. Porosity and Water Content. Figure 2 indicates an increase in the porosity with an increase in concentration of PSMA. PSMA being partially water-soluble behaves like other water-soluble additives such as PEG and PVP. It plays a dual role: a hydrophilic additive as well as a pore former. When the membrane was dipped in coagulation bath, PSMA partially leached out of the membrane and pores were formed in its place. With the increase in concentration of PSMA, this effect was more pronounced, which explains the increase in porosity. However, beyond 2 wt %, excessive leaching was observed because of which the concentration of PSMA was restricted up to 2 wt %. Increase in porosity of the membrane subsequently increased the water uptake capacity of the membranes. The hydrophobic interaction between the membrane surface and macromolecules which gives rise to the fouling of a membrane surface is greatly reduced if the membranes are hydrophilic in nature.23 The abundant presence of different functional groups such as −SO3H, −COOH, and −OH enhanced the porosity and hence the water content of the blend membranes as evidenced from Figures 2 and 3. At a given concentration of PSMA, water content of the membrane increased with an increase in the SPEES content as anticipated. As discussed earlier, PSMA served as a pore former, and at a higher concentration the diffusion of PSMA from the membrane matrix to the gelation bath was relatively faster giving rise to fingerlike structures. This morphology enabled the membranes to hold more water and hence the increase in the water uptake. The results were in accordance with the literature.24 4.5. Cross Sectional Morphology of the Membranes. The cross section morphology of the membranes is shown in Figure 4. All the membranes depict typical asymmetric membrane structure which is characterized by a dense layer at the top followed by a porous sublayer. It is observed that neat CA membrane did not possess noticeable fingerlike projections as the other membranes. It demonstrated a porous structure resulting from the interaction of solvent and water during the coagulation process.25 However, with the addition of SPEES and PSMA, the projections were more pronounced as evident from SEM images of M7, M8, and M9. The presence of this morphology is a direct result of the concentration of SPEES and PSMA. It is evident from SEM images that membranes M7, M8, and M9 have well-defined fingerlike morphology and wall structure extending to the sub-base layer. The rise of this morphology reflects instantaneous demixing of 13825

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This was further proven by the reduction in irreversible fouling as observed in Figure 7. As the percentage of SPEES and PSMA increased, the extent of irreversible fouling reduced to 8.33% for M9 membrane.

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CONCLUSION The novel ultrafiltration membrane was prepared by a phase inversion technique using cellulose acetate and sulfonated poly(1,4-phenylene ether ether sulfone) as base polymers and hydrolyzed poly(styrene-co-maleic anhydride) as an additive. Sulfonation of PEES was successfully carried out, and after a detailed investigation, SPEES prepared using concentrated sulfuric acid as the sulfonating reagent and having DS equal to 21% was incorporated in the membrane matrix. SPEES with a higher degree of sulfonation was not suitable for membrane preparation because of its higher water solubility. Hydrolyzed PSMA served as an additive which enhanced the water content, porosity, and permeation property of the membrane. It was concluded that M9 membrane with 70:30 composition of CA/ SPEES and 2% PSMA showed best performance among all the membranes with flux, FRR, and porosity of 228 L/(m2 h), 91.46% and 82.24%, respectively. The cross sectional SEM analysis revealed the change in morphology of blends with inclusion of SPEES and PSMA. Thus, from the studies, it was concluded that CA membranes prepared by sulfonation of PEES and hydrolyzed PSMA proved to be a very efficient ultrafiltration membrane with high flux and flux recovery ratio.

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

1

H NMR spectra of PEES and SPEES; characteristic peaks, and solubility of PEES and SPEES in different solvents. This material is available free of charge via the Internet at http:// pubs.acs.org.

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PSMA = poly(styrene-co-maleic anhydride) PVP = polyvinylpyrrolidone PWF = pure water flux Rrev = reversible fouling Rirr = irreversible fouling SEM = scanning electron microscopy SPEEK = sulfonated poly(ether ether ketone) SPEES = sulfonated poly(1,4-phenylene ether ether sulfone) Tg = glass transition temperature TMS = tetramethylsilane UF = ultrafiltration ε = porosity

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: 91 824 2474033. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS A.M.I. thanks Prof. Swapan Bhattacharya, Director, National Institute of Technology Karnataka, Surathkal, India, for providing the research facilities and encouragement.

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LIST OF ABBRREVIATIONS ATR-FTIR = attenuated total reflectance Fourier transform infrared spectroscopy ATRP = atomic transfer radical polymerization BSA = Bovine Serum Albumin CA = cellulose acetate cPSf = carboxylated polysulfone DMF = dimethylformamide DMSO = dimethyl sulfoxide DS = degree of sulfonation FRR = flux recovery ratio Mw = average molecular weight NMP = N-methyl pyrrolidone NMR = nuclear magnetic resonance PEG = poly(ethylene glycol) PEES = poly(1,4-phenylene ether ether sulfone) 13826

dx.doi.org/10.1021/ie502310e | Ind. Eng. Chem. Res. 2014, 53, 13820−13827

Industrial & Engineering Chemistry Research

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dx.doi.org/10.1021/ie502310e | Ind. Eng. Chem. Res. 2014, 53, 13820−13827