Improved Antifouling Property of Poly(ether sulfone) Ultrafiltration

Subscriber access provided by Brought to you by ST ANDREWS UNIVERSITY LIBRARY

Article

Improved Anti-fouling Property of Polyethersulfone Ultrafiltration Membrane Through Blending Polyvinyl alcohol Haikuan Yuan, Yanmei Wang, Liang Cheng, Wangcai Liu, Jie Ren, and Linghao Meng Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie502797k • Publication Date (Web): 10 Nov 2014 Downloaded from http://pubs.acs.org on November 15, 2014

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Industrial & Engineering Chemistry Research

Improved Anti-fouling Property of Polyethersulfone Ultrafiltration Membrane Through Blending Polyvinyl alcohol Haikuan Yuan1*, Yanmei Wang2, Liang Cheng3, Wangcai Liu4, Jie Ren1, Linghao Meng1 1. College of Chemical Engineering, Zhejiang University of Technology, 310014, Hangzhou, China 2. School of Chemical Engineering and Environmental Science, Weifang University of Science and Technology, 262700, Weifang, China 3. Chemical Engineering Research Center, East China University of Science and Technology, 200237, Shanghai, China 4. Key Laboratory for Polymerization Engineering and Technology of Ningbo, Institute of Chemical Engineering, Ningbo University of Technology, 315016, Ningbo, China Abstract: Polyethersulfone-polyvinyl alcohol (PES-PVA) ultrafiltration (UF) membrane was prepared through phase inversion induced by immersion precipitation method. The physicochemical properties, permeation performance and anti-fouling property of membrane were investigated. FT-IR spectra and XRD patterns confirmed that PVA was incorporated in PES membrane and did not wash out during the membrane-forming process. SEM images indicated that the morphology of PES-PVA membrane was influenced considerably by the blending content of PVA. The water contact angle showed that the surface hydrophilicity of membrane was remarkably improved after being blended by PVA. The permeation performance of PES-PVA blending membrane was superior to that of PES membrane. The pure water flux of the blending membrane increased with increasing the blending content of PVA, while the bovine serum albumin (BSA) rejection decreased. When the composition of dope solution was PES/PVA/polyethylene glycol (PEG)/dimethyl sulfoxide (DMSO)=15.2/3.8/5/76 (wt%), the water flux of as-prepared membrane was of 131.5 L m-2 h-1, and the BSA rejection was of 61.2%. In addition, the effect of ethanol additive concentration in dope solution on the morphology and permeation performance of PES-PVA membrane was also investigated. Moreover, PES-PVA membrane showed good anti-fouling properties, which may expand the application fields of PES 1

Corresponding author. E-mail: [email protected]. Tel: 86-571-88320208 1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 24

membrane. Keywords: polyethersulfone membrane, polyvinyl alcohol, anti-fouling property, ultrafiltration, blending, ethanol additive

Introduction Ultraﬁltration (UF) membrane has received intense attentions in purification, concentration, filtration and separation of solutes in pharmaceuticals, dairy, biotechnology industries and wastewater treatments. Polyethersulfone (PES) UF membrane has been applied extensively because of its favorable mechanical strength, excellent chemical resistance and good thermal stability.1 Nevertheless, the inherent hydrophobic characteristics of PES often causes the serious membrane fouling, leading to the deterioration of separation performance. The fouling is one of the most arduous challenges for UF membranes. Development of absolutely non-fouling membrane seems particlularly difficult, but not impossible. The membrane fouling was mainly caused by the following three ways: pore constriction within the membrane pores, pore blocking and cake formation on the membrane surface.2 The irreversible fouling was mainly caused by pore blocking, while the reversible fouling was chiefly due to cake formation. In general, the membrane fouling could be effectively reduced through enhancing hydrophilicity of membrane surface.3 Thus, major efforts focus on improving the hydrophilicity of PES membrane through different methods, including the following four aspects. (i) Surface modification, such as ultraviolet irradiation,4 grafting polymerization5. (ii) Blending with nanoparticles, such as TiO2,6 SiO2,7,8 silica-polyvinylpyrrolidone (PVP) nanocomposites9 and nanotubes10,11. The hydrophilicity of membrane was enhanced because of the blending of those nanoparticles, and the pure water flux and the antifouling property of the hybrid membrane were significantly improved. However, the agglomeration of the particles is one of problems that can not be ignored. (iii) Physical blending with hydrophilic polymer, such as polyethylene glycol (PEG),12 PVP,13 zwitterionic polymers14,15 and other hydrophilic polymers, i.e., polyacrylonitrile (PAN),16 cellulose acetate phthalate

(CAP),17

polyethylenimine-graphene

amphiphilic oxide

methacrylate)-b-poly(methacrylic

copolymer

(HPEI-GO),20

of

block-like

F127,18,19 copolymer

acid)-b-poly(hexafluorobutyl

hyperbranched of

poly(butyl

methacrylate)

(PBMA-b-PMAA-b-PHFBM).21 The surface hydrophilicity and anti-fouling property of modified

2


Page 3 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


PES membranes were significantly improved. (iv) Surface coating with hydrophilic polymers, i.e., PVA.22 PVA, a highly hydrophilic polymer with good thermal and chemical stabilities and excellent mechanical strength,23 adsorbed spontaneously on the hydrophobic PES membrane surface to improve surface hydrophilicity.24 Subsequently, the irreversible fouling was decreased. Compared with other methods, physical blending is a simple and effective way to prepare the membrane with a new high performance, which may achieve the useful combinations of different materials. PVA is easily accessible and inexpensive, so it is very convenient to choose PVA as the blending polymer to modify PES membrane. PES-PVA blending UF membrane was prepared through phase inversion process induced by immersion precipitation. The physicochemical properties of PES-PVA membrane were characterized by SEM, FT-IR, XRD and static contact angle. The permeation property and the anti-fouling performance of membrane were also discussed.

2 Experimental 2.1 Chemicals and instrumentals Polyethersulphone (PES) (E6020P, MW=58,000 g mol-1, porous flake) was purchased from BASF Chemical Company (China); polyvinyl alcohol (PVA) with polymerization degree of 1750±50 and alcoholysis degree of 98% was provided by Shanghai Chemical Reagent Co., Ltd. (China); polyethylene glycol (MW=1000) was obtained from Chemical Reagent Co., Ltd. (Sinopham Group, China); dimethyl sulfoxide (DMSO), A.R., was obtained from Wuxi Haishuo Bio Co., Ltd. (China); bovine serum albumin (BSA) (Mw=67000) was from Shanghai Lanji Science Development Co., Ltd. (China); the commercial milk was from Bright Diary & Food Co., Ltd. (China); twice-distilled water was employed for all experiments. Cup-like

filter

was

self-processed

for

evaluating

the

permeation

performance.

Ultraviolet-visible spectrophotometer (Ultrospec2100 pro, GE (China) Co., Ltd.) was used for measuring the absorbances of the feed BSA solution and the permeate.

2.2 Preparation of PES-PVA membrane The compositions of dope solution for preparing PES-PVA blending flat membrane are listed in Table 1. A certain amount of polymers, additives and solvent were added in flask, stirring hermetically at 90°C for 5 h, then being degassed. The dope solution was scraped uniformly on a

3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

glass plate using a casting knife, immersed immediately into the coagulation bath of water at room temperature. After peeling off from the glass plate, the as-prepared membranes were stored in distilled water for at least 24 h before use, which allowed the residual solvent and water soluble components in membrane to be separated out. Table 1

2.3 Characterizations of membrane 2.3.1 Scanning electron microscopy (SEM) The morphology of membrane was observed by scanning electron microscopy (SEM, Hitachi S-4700, Japan). In order to reduce the surface tension effect and minimize destruction of pores during membrane drying, the membrane stored in water was transferred and immersed into 10% of glycerol solution for 24 h and dried under ambient atmosphere. The cross-section of membrane was viewed after the sample was frozen and fractured in liquid nitrogen. Before being viewed, all samples were sputtered with gold. 2.3.2 Fourier transform infrared spectroscopy (FT-IR) Infrared spectra of PES-PVA membrane were recorded using Fourier transform infrared spectrometer equipped with attenuated total reflection crystals (ATR-FTIR, Nicolet 6700, America). 2.3.3 X-ray diffraction (XRD) X-ray diffractometer (X’Pert PRO, PANalytical, Holland) equipped with graphite monochromated Cu Kα radiation (λ=0.154056 nm) operating at 40 mA and 40 kV from 10 to 50º was used to record the XRD patterns of PES-PVA membranes. 2.3.4 Static contact angle The surface hydrophilicity of PES-PVA membrane was evaluated by measuring the water contact angle using a goniometer (JC2000D3, Shanghai Zhongchen Digital Equipment Co., Ltd., China). 1 µL of deionized water was carefully dropped on the membrane surface and then the water contact angle was measured at the 5th second. To minimize the experimental error, the contact angle was measured at five random locations for each membrane and the average value was taken. Before measurement for each sample, it was dried by placing it between two sheets of filter paper for 24 h at room temperature. 2.3.5 Porosity and mean pore size calculations 4


Page 4 of 24

Page 5 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Overall porosity (ε) can be determined by the gravimetric method. The membrane stored in distilled water was weighted after wiping excessive water on the surface with filter paper (w1). Then the membrane was dried in a vacuum oven at 60°C for 24 h and was also weighted (w2). The overall porosity (ε) is calculated as follows:25

ε=

w1 − w2 A ⋅ l ⋅ ρW

(1)

Where w1 and w2 are the weights of the wet and the dry membranes (g), respectively, A is the effective membrane area (m2), l is the membrane thickness (m) and ρW is the water density (0.998 g cm-3). The mean pore radius (rm) of membrane is determined according to the pure water flux and the porosity data, which is calculated by the Guerout-Elford-Ferry equation:26

rm =

(2.9 − 1.75ε ) ⋅ (8ηlQ ) ε ⋅ A ⋅ ∆P

(2)

Where η is the water viscosity (8.9×10-4 Pa s), Q is the volume of the permeate of pure water per unit time (m3 s-1) and △P is the operation pressure difference (0.1 MPa).

2.4 UF experiment Fig. 1 UF experimental set-up was presented in Fig. 1. The flat membrane was installed in a cup-like filter and compacted tightly. The effective membrane area was of 28.26 cm2. The membrane was pre-pressurized with pure water through constant-flow pump at 0.1 MPa for 30 min, then the pure water flux (JW) was measured at pressure difference of 0.1 MPa. The pure water flux is calculated as follows.

JW =

V A×t

(3)

Where V is the volume of the permeate liquid (L), A is the effective membrane area (m2), t is the time interval of permeation (h). In order to measure the rejection of membrane, the filtration medium was changed into 3 mg L-1 of BSA aqueous solution after 30 min of pure water filtration for the same membrane. The BSA concentrations in the feed and the permeate were measured by ultraviolet-visible spectrophotometer. The BSA rejection of membrane is calculated as follows. 5



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

R % = (1 −

Page 6 of 24

CP ) × 100% CF

(4)

Where CP and CF are the concentrations of BSA solution in the permeate and the feed, respectively.

2.5 Anti-fouling property evaluation BSA aqueous solution was chosen as a model filtration medium. Firstly, the membrane was pre-pressurized using distilled water at 0.1 MPa for 30 min, then the pure water flux was obtained (JW). The filtration medium was replaced by 3 mg L-1 of BSA solution, after filtering for 10 min, the flux (JBSA) was measured. The total filtering time for BSA solution was of 30 min. After that, the membrane was backwashed with pure water for 1 h under stirring, and the pure water flux was ' measured ( J W ).

The recovery ratio of water flux for evaluating the antifouling property of membrane is calculated by the following equation:

RF =

J W' × 100% JW

(5)

The diluted commercial milk (1/10 times diluted (mass ratio)) was chosen as another filtration medium. The experimental process was same to the above one, and the recovery ratio of water flux was also obtained.

3 Results and discussions 3.1 Compatibility between PES and PVA Fig. 2 The compatibility between PES and PVA could be evaluated by the mixing enthalpy (△HM) reported by Schneier27 as follows. 1

2 2     x2 ∆H M =  x1M 1ρ1 (δ1 − δ 2 ) 2      (1 − x2 ) M 2 ρ 2 + (1 − x1 ) M 1ρ1  

(6)

Where △HM is the mixing enthalpy of polymers, xi is the mass fraction of polymer i, ρ is the polymer density, M is the molecular weight of an average monomer unit, δ is the solubility parameter of component i, which is from Ref28.

6


Page 7 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The values of △HM vs. entire mass fraction of blending polymers (x) are shown in Fig. 2. Although slight differences are observed depending on which polymer is selected as component 1, △HM of 10×10-3 cal mol-1 (the critical one is of 1×10-3 cal mol-1 for some systems) is considered as the critical value for evaluating the compatibility of polymers.27 If △HM values are lower than the critical value, the blending systems are considered compatible. If △HM values are intersectant with the critical one, the systems are partially compatible, in which the compatibility is related with the blending compositions. As shown in Fig. 2, for PES/PVA blending system in this study, the values of △HM are smaller than the critical one of 10×10-3 cal mol-1, indicating that PES and PVA are compatible. Even if the critical one is of 1×10-3 cal mol-1, the blending system of PES and PVA is also considered compatible when PVA concentration is less than 0.4. Therefore, PES and PVA are compatible under the proportions shown in Table 1.

3.2 Characterizations of PES-PVA membrane 3.2.1 FT-IR analysis Fig. 3 Fig. 3 shows FT-IR spectra of PES-PVA membranes. As shown in Fig. 3, peaks at 1105 and 1300 cm-1 are attributed to the sulfone groups (-SO2-) of PES, peak at 1245 cm-1 is due to the stretching vibration of aromatic ether (-C-O-C-), and peaks at 1488 and 1580 cm-1 are owing to the aromatic benzene ring, which are the characteristic bonds for PES.29 In addition, with increasing PVA content in dope solution (from M1 to M5 membranes), the peak intensity at 3400-3500 cm-1 becomes stronger. It is attributed to the stretching vibration of hydroxyl groups in PVA, which indicates that more PVA was incorporated in PES matrix. Consequently, more hydroxyl groups (–OH) existed on the membrane surface, enhancing the hydrophilicity of membrane. That is to say, PVA did not wash out during the membrane-forming process although the membrane was prepared by wet phase inversion method. 3.2.2 XRD analysis Fig. 4 The XRD patterns of PES-PVA membranes are shown in Fig. 4. The results reveal the change in dominant crystal phase of PES membrane due to blending of PVA. Except for a large peak of 2θ at 18°, a new peak at 22.5° in PES-PVA membrane appears obviously in Fig. 4, and this peak intensity becomes stronger with increasing PVA content in dope solution. As is known that PVA 7



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

owns a semi-crystalline polymer with a large diffraction peak of 2θ at around 20°.30 However, their locations in PES-PVA membranes are shifted right slightly compared with that of PVA. Moreover, the characteristic peak of PES shifts left gradually with increasing PVA content, indicating the existence of the stronger combining force between PES and PVA. The XRD results also reveal that PVA remained in the PES-PVA membrane during the membrane-forming process, although PVA was strongly hydrophilic in the coagulation bath of water. 3.2.3 Surface hydrophilicity Fig. 5 Surface hydrophilicity is very important for evaluating anti-fouling property and permeation performance of UF membrane. The lower water contact angle means the stronger hydrophilicity. Fig. 5 shows effect of PVA content on water contact angle for PES-PVA membrane. The PES membrane possesses the highest water contact angle of about 79°, representing the lowest surface hydrophilicity of membrane. With increasing PVA content in dope solution, the water contact angle decreases gradually. That is, the membrane is more hydrophilic, which is attributed to the hydrophilic character of hydroxyl groups in PVA. 3.2.4 Porosity and mean pore size Table 2 The overall porosities and mean pore sizes of PES-PVA membranes are listed in Table 2. With increasing PVA content in dope solution, the porosity and the respective mean pore size of PES-PVA membrane both increase. Especially, for PES-PVA membrane with higher PVA content (M5), the porosity and mean pore size increase sharply compared with other PES-PVA membranes. This phenomenon indicates that PVA in dope solution accelerated phase separation in membrane-forming process and formed the larger pores.

3.3

Permeation performance of PES-PVA membrane

3.3.1 Influence of PES/PVA mass ratio Fig. 6 As a pore-forming reagent, PEG is oftern used for preparation of UF membrane, which promotes the formation and growth of many finger-like pores (shown in Fig. 6 (M1)). In addition, PEG would be washed out in coagulation bath through the double diffusions between solvent and coagulant during membrane-forming process and the storage period in water. Thus the primmary 8


Page 8 of 24

Page 9 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


positions of PEG in membrane would form the pores. The membrane prepared from PES without PVA (M1) exhibits the asymmetric structure of membrane consisting of a dense skin layer, a porous sub-layer composed by the closed cells and finger-like macrovoids. When the dope solution is immersed in coagulation bath, the phase inversion occurs with the instaneous demixing, and the dense skin surface of membrane firstly forms. According to the hypothesis of Mckelvey et al31, finger-like macrovoids are initiated by nucleation of polymer-lean phase just beneath the skin layer, and its growth lies on the rate difference between the diffusion rate of nonsolvent into the dope solution and the diffusion rate of the solvent into the coagulation bath. This rate difference induces a nonsolvent concentration gradient in dope solution, forming a driving force to cause the macrovoids growth. As shown in Fig. 6, the effect of PVA content on the size and shape of finger-like macrovoids and sub-layer morphology is obvious. With increasing PVA content in dope solution, the finger-like pores degenerate, collapse, or even disappeare, and more irregular macrovoids form in sub-layer of membrane. The morphology of M5 membrane is absolutely different to those of other membranes, which can be explained by the miscibility and the interaction effect (affinity force) between PVA and coagulant of water.32 When coagulant of water diffuses into dope solution, PVA would inhibit the phase inversion rate of PES, causing the formation of larger macrovoids. Furthermore, the introduction of PVA enhances thermodynamic instability of dope solution and accelerates the diffusion rate of solvent into the coagulant bath, consequently, the thickness of skin layer significantly decreases, even if this layer nearly disappears (shown in Fig. 5 (M5)). Fig.7 Fig.7 shows magnification of cross-section images of PES-PVA membranes with different PVA contents. As mentioned above, the addition of PVA to the dope solution enhances the porosity of PES-PVA membrane. Moreover, with increasing PVA content, the pore density in cross-section of PES-PVA membrane decreases, which is shown in Fig. 7. That is to say, the pore size in the sub-layer of membrane enlarges and the connectivity between pores improves. Fig. 8 Not only does PVA affect the sub-layer structure of PES-PVA membrane, but also the skin surface. Fig. 8 shows the outer surface SEM images of PES-PVA membranes. With increasing PVA content in dope solution, the number and size of pores on the outer surface of membrane 9



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

increase. When PVA content in dope solution increases up to 30wt%, a membrane surface with defects is formed (shown in Fig. 8 (M5)). The increase of surface pores with introduction of PVA may be caused by increasingly large affinity forces between PVA and water (coagulation bath), and the enhanced exchange rate between solvent and non-solvent, especially at high concentration of PVA in dope solution. Moreover, some PVA molecules segregate the polymer/water interfaces because of the presence of hydrophilic groups during the precipitation process, thus forming more pores on the skin surface. Therefore, the introduction of PVA are prone to form the thinner thickness of skin layer and the skin surface with more pores, which means a higher pure water flux. Fig. 9 The permeation performance is consistent with membrane structure, especially the surface pore size and the skin layer thickness. As shown in Fig. 9, with increasing PVA content in dope solution, the pure water flux increases, while the BSA rejection of membrane decreases. The flux enhancement and the BSA rejection reduction are owing to the macrovoids in the sub-layer and the more pores on the skin surface of membrane. In addition, the hydrophilicity of membrane improved remarkably by introduction of PVA, which could attract water molecules and promote them to pass through membrane. Consequently, the permeability enhances, while the BSA rejection reduces.33 In a word, the introduction of PVA in PES dope solution has two main influeces on the membrane preparation: one is the changes in the membrane surface and sub-layer morphology, another is an enhancement of membrane hydrophilicity. It is also can be said that PVA is an excellent pore-forming agent in this study. 3.3.2

Influence of ethanol additive Fig. 10

Fig. 10 shows the cross-section SEM images of PES-PVA membranes with different concentrations of ethanol additive in dope solution. The morphology of membrane changes significantly after adding ethanol additive. With increasing ethanol concentration in dope solution, more macrovoids form in the membrane and the pore size in sub-layer becomes larger, moreover, the thickness of skin layer also decreases. When ethanol concentration is above 5wt%, the finger-like macrovoids even disappear and change into irregular ones with better connectivity between pores. The appropriate amount of non-solvent additives accelerated the diffusion rate of 10


Page 10 of 24

Page 11 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


dope solution into coagulation bath and offered the condition for growth of polymer-lean phase, which was prone to form the macrovoids.34-36 Furthermore, the higher opposite diffusion rates between solvent and non-solvent resulted in the membrane with the higher porosity in sub-layer and the larger pore size on the outer skin layer. Fig. 11 shows outer surface images of PES-PVA membrane affected by ethanol additive. As shown in Fig. 11, with increasing ethanol concentration in dope solution, the more and larger pores form on the outer skin surface of membrane, which is also due to the faster diffusion rate of solvent to the coagulation bath and the rapid breakthrough rate of solvent before formation of outer skin layer. Fig. 11 Fig. 12 Fig. 12 shows effect of ethanol concentration in dope solution on permeation performance of PES-PVA membrane. With increasing ethanol concentration, the pure water flux increases while the BSA rejection decreases. That is because the pore size on the surface increases and the skin layer thickness decreases.

3.4

Anti-fouling property of membrane

3.4.1 BSA aqueous solution as filter solution During UF process, the membrane fouling is caused by the protein adsorption or deposition (cake formation) on the surface or inside the membrane pores, and the reversible fouling could be eliminated through hydraulic cleaning. The more hydrophilic of membrane surface, the easier to reduce the reversible fouling.37 The hydrophilic surface prevents the hydrophobic materials, such as proteins, to form filtration cake layer on the membrane surface. Fig. 13 shows comparison of anti-fouling properties for M1 and M4 membranes when filtering BSA aqueous solution. As shown in Fig. 13, the RFs of PES-PVA and PES membranes are of 92.6% and 52.0%, respectively. The higher flux recovery ratio (RF) value means the better anti-fouling property of membrane. BSA molecules could easily adsorb onto the hydrophobic surface or inside membrane pores for PES membrane when filtering BSA solution, causing the more irreversible fouling. However, after introduction of PVA in PES membrane, the higher hydrophilicity of PES-PVA membrane would avoid proteins adsorption or deposition on the membrane, and the adsorption sites of proteins on the membrane surface would substantially decline.38 Moreover, the interactions between membrane with higher hydrophilicity and proteins were expected to be lower because of the 11



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

inhibition of non-specific binding.39 It is also can be said that PVA significantly improved the cohesion free energy between foulants and membrane surface.40 Based on these reasons, the foulants on PES-PVA membrane are more efficient to remove upon backwashing by water (hydraulic cleaning) for comparison with that of PES membrane. Fig. 13 3.4.2 Milk aqueous solution as filter solution Fig. 14 The diluted commercial pasteurized and homogenized milk (per 100 mL) with about 3.1g of protein, 3.6 g of fat, 5.0 g of carbohydrate and more than 8.5% of solids-not-fat was used as another feed solution for membrane fouling evalution, and the diluted mass ratio by distilled water was of 1/10. More than 95% of milk fat is in the globule form ranging in size from 0.1 to 15 µm in diameter, mainly causing the pore blocking or internal adsorption (probably irreversible fouling). The decline in flux and the increase in total resistance with time were probably thanks to the decreasing transmission of fat and small soluble compounds through the membrane, as well as adsorption or deposition on the membrane surface or pores. As shown in Fig. 14, the RFs of PES-PVA and PES membranes after backwashing are of 52.3% and 35.6%, respectively. Although they are lower individually compared with those for filtering BSA aqueous solution, they still indicated that PES-PVA membrane had better anti-fouling property than PES membrane. The improved anti-fouling property of PES-PVA blending UF membrane is the distinguishing feature of this study, which is also desired for practical application in the future.

4 Conclusions PES membrane was blended with hydrophilic PVA for improving the resistant fouling ability, and phase inversion induced by immersion precipatation method was used. The stable residence of PVA in PES matrix during membrane-forming process was validated by FT-IR spectra and XRD patterns. The hydrophilicity of PES-PVA membrane was improved significantly compared with PES membrane. The SEM images showed that the blending amount of PVA had obvious influence on the microstructure of PES-PVA membrane. With increaseing PVA content in dope solution, the pure water flux increased, while the BSA rejection decreased. The effect of ethanol additive on the membrane morphology and permeation properties was also investigated. In addition, the

12


Page 12 of 24

Page 13 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


anti-fouling properties of PES-PVA and PES membranes were investigated and compared through measuring the flux recovery ratio for filtering BSA and milk solutions, respectively. PES-PVA blending membrane exhibited the improved anti-fouling property due to the higher hydrophilicity, which is quite benefical for practical applications. Acknowledgements The financial support from National Natural Science Foundation of China (No. 21206146) is gratefully acknowledged. References (1) Marchese, J.; Ponce, M.; Ochoa, N. A.; Prádanos, P.; Palacio, L.; Hernández, A. Fouling behaviour of polyethersulfone UF membranes made with different PVP. J. Membr. Sci. 2003, 211, 1-11. (2) Katsoufidou, K.; Yiantsios, S. G.; Karabelas, A. J. A study of ultrafiltration membrane fouling by humic acids and flux recovery by backwashing: Experiments and modeling. J. Membr. Sci. 2005, 266, 40-50. (3) Arahman, N.; Maruyama, T.; Sotani, T.; Matsuyama, H. Fouling reduction of a poly(ether sulfone) hollow-fiber membrane with a hydrophilic surfactant prepared via non-solvent-induced phase separation. J. Appl. Polym. Sci. 2009, 111, 1653-1658. (4) Rahimpour, A. UV photo-grafting of hydrophilic monomers onto the surface of nano-porous PES membranes for improving surface properties. Desalination 2011, 265, 93-101. (5) Yune, P. S.; Kilduff, J. E.; Belfort, G. Fouling-resistant properties of a surface-modified poly(ether sulfone) ultrafiltration membrane grafted with poly(ethylene glycol)-amide binary monomers. J. Membr. Sci. 2011, 377, 159-166. (6) Razmjou, A.; Mansouri, J. Chen, Vicki. The effects of mechanical and chemical modification of TiO2 nanoparticles on the surface chemistry, structure and fouling performance of PES ultrafiltration membranes. J. Membr. Sci. 2011, 378, 73-84. (7) Huang, J.; Zhang, K. S.; Wang, K.; Xie Z. L.; Ladewig, B.; Wang, H. T. Fabrication of polyethersulfone-mesoporous silica nanocomposite ultrafiltration membranes with antifouling properties. J. Membr. Sci. 2012, 423-424, 362-370. (8) Yu, H. X.; Zhang, X. F.; Zhang, Y. T.; Liu, J. D.; Zhang, H. Q. Development of a hydrophilic PES ultrafiltration membrane containing SiO2@N-Halamine nanoparticles with both organic 13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

antifouling and antibacterial properties. Desalination 2013, 326, 69-76. (9) Sun, M. P.; Su, Y. L.; Mu, C. X.; Jiang, Z. Y. Improved antifouling property of PES ultrafiltration membranes using additive of silica-PVP nanocomposite. Ind. Eng. Chem. Res. 2010, 49, 790-796. (10) Rahimpour, A.; Jahanshahi, M.; Khalili, S.; Mollahosseini, A.; Zirepour, A.; Rajaeian, B. Novel functionalized carbon nanotubes for improving the surface properties and performance of polyethersulfone (PES) membrane. Desalination 2012, 286, 99-107. (11) Zhang, J. Y.; Zhang, Y. T.; Chen, Y. F.; Du, L.; Zhang, B.; Zhang, H. Q. Liu, J. D.; Wang, K. J. Preparation and characterization of novel polyethersulfone hybrid ultrafiltration membranes blending with modified halloysite nanotubes loaded with silver nanoparticles. Ind. Eng. Chem. Res. 2012, 51, 3081-3090. (12) Susanto, H.; Ulbricht, M. Characteristics, performance and stability of polyethersulfone ultrafiltration membranes prepared by phase separation method using different macromolecular additives. J. Membr. Sci. 2009, 327, 125-135. (13) Zhou, C.; Hou, Z. C.; Lu, X. F.; Liu Z. Y.; Bian, X. K.; Shi, L. Q.; Li, L. Effect of polyethersulfone molecular weight on structure and performance of ultrafiltration membranes. Ind. Eng. Chem. Res. 2010, 49, 9988-9991. (14) Jiang, S. Y.; Cao, Z. Q. Ultralow-fouling, functionalizable, and hydrolyzable zwitterionic materials and their derivatives for biological applications. Adv. Mater. 2009, 22, 920-932. (15) Shi, Q.; Su, Y. L., Zhao, W.; Li, C.; Hu, Y. H.; Jiang, Z. Y.; Zhu, S. P. Zwitterionic polyethersulfone ultrafiltration membrane with superior antifouling property. J. Membr. Sci. 2008, 319, 271-278. (16) Amirilargani. M.; Sabetghadam, A.; Mohammadi, T. Polyethersulfone/polyacrylonitrile blend ultrafiltration membranes with different molecular weight of polyethylene glycol: preparation, morphology and antifouling properties. Polym. Adv. Technol. 2012, 23, 398-407. (17) Rahimpour, A.; Madaeni, S. S. Polyethersulfone (PES)/cellulose acetate phthalate (CAP) blend ultrafiltration membranes: Preparation, morphology, performance and antifouling properties. J. Membr. Sci. 2007, 305, 299-312. (18) Zhao, W.; Su, Y. L.; Li, C.; Shi, Q.; Ning, X.; Jiang, Z. Y. Fabrication of antifouling polyethersulfone ultrafiltration membranes using Pluronic F127 as both surface modifier and 14


Page 14 of 24

Page 15 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


pore-forming agent. J. Membr. Sci. 2008, 318, 405-412. (19) Peng, J. M.; Su, Y. L.; Chen, W. J.; Shi, Q.; Jiang, Z. Y. Effects of coagulation bath temperature on the separation performance and antifouling property of poly(ether sulfone) ultrafiltration membranes. Ind. Eng. Chem. Res. 2010, 49, 4858-4864. (20) Yu, L.; Zhang, Y. T.; Zhang, B.; Liu, J. D.; Zhang, H. Q.; Song, C. H. Preparation and characterization of HPEI-GO/PES ultrafiltration membrane with antifouling and antibacterial properties. J. Membr Sci. 2013, 447, 452-462. (21) Zhao, X. T.; Su, Y. L.; Chen, W. J.; Peng, J. M.; Jiang, Z. Y. pH-responsive and fouling-release properties of PES ultrafiltration membranes modified by multi-functional block-like copolymers. J. Membr. Sci. 2011, 382, 222-230. (22) Gholap, S. G.; Badiger, M. V. Gopinath, C. S. Molecular origins of wettability of hydrophobic poly(vinylidene fluoride) microporous membranes on poly(vinyl alcohol) adsorption: Surface and interface analysis by XPS. J. Phys. Chem. B 2005, 109, 13941-13947. (23) Li, N.; Liu, Z. Z.; Xu, S. G. Dynamically formed poly (vinyl alcohol) ultrafiltration membranes with good anti-fouling characteristics. J. Membr. Sci. 2000, 169, 17-28. (24) Ma, X. L.; Su, Y. L.; Sun, Q.; Wang, Y. Q.; Jiang, Z. Y. Enhancing the antifouling property of polyethersulfone ultrafiltration membranes through surface adsorption-crosslinking of poly(vinyl alcohol). J. Membr. Sci. 2007, 300, 71-78. (25) Li, J. F.; Xu, Z. L.; Yang, H.; Yu, L. Y.; Liu, M. Effect of TiO2 nanoparticles on the surface morphology and performance of microporous PES membrane. Appl. Surf. Sci. 2009, 255, 4725-4732. (26) Feng, C. S.; Shi, B. L.; Li, G. M.; Wu, Y. L. Preparation and properties of microporous membrane from poly(vinylidene fluoride-co-tetrafluoroethylene) (F2.4) for membrane distillation. J. Membr. Sci. 2004, 237, 15-24. (27) Bemard, S. Polymer compatiblitiy. J. Appl. Polym. Sci. 1973, 17, 3175-3185. (28) Brandrup, J.; Immergut, E. H.; Grulke, E. A. (Editors). Polymer Handbook (Fourth Edition). John Wiley & Sons. Inc. 1999, New York. (29) Han, J. Y.; Lee, W. S.; Choi, J. M.; Patel, R.; Min, B. R. Characterization of polyethersulfone/polyimide blend membranes prepared by a dry/wet phase inversion: Precipitation kinetics, morphology and gas separation. J. Membr. Sci. 2010, 351, 141-148. 15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(30) Nam, S. Y.; Chun, H. J.; Lee, Y. M. Pervaporation separation of water–isopropanol mixture using carboxymethylated poly(vinyl alcohol) composite membranes. J. Appl. Polym. Sci. 1999, 72, 241-249. (31) McKelvey, A. S.; Koros, J. W. Phase separation, vitrification, and the manifestation of macrovoids in polymeric asymmetric membranes. J. Membr. Sci. 1996, 112, 29-39. (32) Wang, D. M.; Lin, F. C.; Wu, T. T.; Lai, J. Y. Formation mechanism of the macrovoids induced by surfactant additives. J. Membr. Sci. 1998, 142, 191-204. (33) Liao, C. J.; Yu, P.; Zhao, J. Q.; Wang, L. M.; Luo, Y. B. Preparation and characterization of NaY/PVDF hybrid ultrafiltration membranes containing silver ions as antibacterial materials. Desalination 2011, 272, 59-65. (34) Smolders, C. A.; Reuvers, A. J.; Boom, R. M.; Wienk, I. M. Microstructures in phase-inversion membranes. Part 1. Formation of macrovoids. J. Membr. Sci. 1992, 73, 259-275. (35) Torrestiana-Sanchez, B.; Ortiz-Basurto, R. I.; Brito-De, E. Effect of nonsolvents on properties of spinning solutions and polyethersulfone hollow fiber ultrafiltration membranes. J. Membr. Sci. 1999, 152, 19-28. (36) Xu, Z. L.; Qusay, F. A. Polyethersulfone (PES) hollow fiber ultrafiltration membranes prepared by PES/non-solvent/NMP solution. J. Membr. Sci. 2004, 233, 101-111. (37) Celik, E.; Park, H.; Choi, H. Carbon nanotube blended polyethersulfone membranes for fouling control in water treatment. Water Res. 2011, 45, 274-282. (38) Cheryan, M. Ultrafiltration and Microfiltration Handbook (2nd ed.). Technomic Publishing Ltd. 1998, Lancaster. (39) Vatanpour, V.; Madaeni, S. S.; Moradian, R.; Zinadini, S.; Astinchap, B. Fabrication and characterization of novel antifouling nanofiltration membrane prepared from oxidized multiwalled carbon nanotube/polyethersulfone nanocomposite. J. Membr. Sci. 2011, 375, 284-294. (40) Zhang, J.; Wang, Q. Y.; Wang, Z. W.; Zhu, C. W.; Wu, Z. C. Modification of poly(vinylidene fluoride)/polyethersulfone blend membrane with polyvinyl alcohol for improving antifouling ability. J. Membr. Sci. 2014, 466, 293-301.

List of Figures 16


Page 16 of 24

Page 17 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 1 Schematic presentation of UF experimental set-up Fig. 2 Relationship of △HM and x in PES/PVA blending system Fig. 3 FT-IR spectra of PES-PVA membranes Fig. 4 XRD patterns of PES-PVA membranes Fig. 5 Effect of PVA content on surface hydrophilicity of PES-PVA membrane Fig. 6 Cross-section SEM images of PES-PVA membranes with different PVA contents Fig.7 Magnification of cross-section images of PES-PVA membranes with different PVA contents Fig. 8 Outer surface SEM images of PES-PVA membranes Fig. 9 Effect of PVA content on permeation performance of PES-PVA membrane Fig. 10 Cross-section images of PES-PVA membrane affected by ethanol additive Fig. 11 Outer surface images of PES-PVA membrane affected by ethanol additive Fig. 12 Effect of ethanol concentration on the permeation performance of PES-PVA membrane Fig. 13 Comparison of anti-fouling properties for M1 and M4 membranes when filtering BSA aqueous solution Fig. 14 Comparison of anti-fouling properties for M1 and M4 membranes when filtering milk aqueous solution

Fig. 1 Schematic presentation of UF experimental set-up

17



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 2 Relationship of △HM and x in PES/PVA blending system

Fig. 3 FT-IR spectra of PES-PVA membranes

18


Page 18 of 24

Page 19 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 4 XRD patterns of PES-PVA membranes

Fig. 5 Effect of PVA content on surface hydrophilicity of PES-PVA membrane

19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 6 Cross-section SEM images of PES-PVA membranes with different PVA contents

Fig.7 Magnification of cross-section images of PES-PVA membranes with different PVA contents

20


Page 20 of 24

Page 21 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 8 Outer surface SEM images of PES-PVA membranes

Fig. 9 Effect of PVA content on permeation performance of PES-PVA membrane

21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 10 Cross-section images of PES-PVA membrane affected by ethanol additive

Fig. 11 Outer surface images of PES-PVA membrane affected by ethanol additive

22


Page 22 of 24

Page 23 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 12 Effect of ethanol concentration on the permeation performance of PES-PVA membrane

Fig. 13 Comparison of anti-fouling properties for M1 and M4 membranes when filtering BSA aqueous solution

Fig. 14 Comparison of anti-fouling properties for M1 and M4 membranes when filtering milk aqueous solution

23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 24

List of Tables Table 1 Component proportion for preparation of PES-PVA UF membrane Table 2 Overall porosity and mean pore size of PES-PVA membranes

Table 1 Component proportion for preparation of PES-PVA UF membrane Membrane No.

PES (g)

PVA (g)

mPVA (wt%) mPES + mPVA

PEG (g)

DMSO (g)

EtOH (g)

M1 M2 M3 M4 M5 M6 M7 M8 M9

19 18.05 17.1 15.2 13.3 15.2 15.2 15.2 15.2

0 0.95 1.9 3.8 5.7 3.8 3.8 3.8 3.8

0 5 10 20 30 20 20 20 20

5 5 5 5 5 5 5 5 5

76 76 76 76 76 75 73 71 69

0 0 0 0 0 1 3 5 7

Table 2 Overall porosity and mean pore size of PES-PVA membranes Membrane No.

l (µm)

ε (%)

rm (nm)

M1 M2 M3 M4 M5

143.5 146.5 126.0 175.0 153.0

54.21 56.13 58.31 65.54 73.07

11.2 15.3 27.7 34.9 80.9

24


Improved Antifouling Property of Poly(ether sulfone) Ultrafiltration

Recommend Documents