CPVC Blend

Article pubs.acs.org/IECR

Preparation and Performance of Antifouling PVC/CPVC Blend Ultrafiltration Membranes Jiazhen Liu,† Yanlei Su,*,†,‡ Jinming Peng,† Xueting Zhao,† Yan Zhang,† Yanan Dong,† and Zhongyi Jiang† †

Key Laboratory for Green Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China ‡ National Key Laboratory of Biochemical Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, China ABSTRACT: Polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC) were used as membrane materials to fabricate blend ultrafiltration membranes. Polyethylene glycol (PEG2000) and polyethylene oxide-polypropylene oxidepolyethylene oxide triblock copolymer (Pluronic F127) were used as both pore forming agent and surface modifier to improve the permeability. The advantage of amphiphilic Pluronic F127 is that it enables higher −CH2−CH2−O− segment coverage on the membrane surfaces. The increase of CPVC proportion in membrane materials could improve the water fluxes of PVC/CPVC blend membranes with the slight change of protein rejection ratios. All the PVC/CPVC blend membranes with an additive of Pluronic F127 have excellent antifouling property. The blend method is an appropriate way to prepare new antifouling PVC/ CPVC ultrafiltration membranes which have lower cost and better performance.

1. INTRODUCTION Ultrafiltration is a highly efficient and low energy consumption separation technology which has been widely used in the drinking water treatment, environment protection, separation and purification in the textile, pharmaceutical, and food industries.1−5 Good ultrafiltration membrane should have adequate mechanical strength, appropriate pore size and narrow pore size distribution, thermal and chemical resistance, and excellent antifouling property. An ideal membrane process should be able to maintain high permeability, a desired rejection, long operation cycle, and few chemical cleanings during the membrane separation. Polyvinyl chloride (PVC) is one of the most widely used raw materials in plastic production with the virtues of acid and alkali resistance, microbial corrosion resistance, chemical performance stabilization, innocuity, and economical benefits. PVC resin has been used as a promising ultrafiltration and microfiltration membrane material in wastewater treatment.6−10 Due to the hydrophobicity of PVC, the application of PVC membranes has been limited. Polyvinyl butyral (PVB) had been introduced as the second polymer component to improve the hydrophilicity of PVC ultrafiltration membranes.8 It was found that water fluxes and hydrophilicity of the PVC/PVB blend membranes were better than that of the pure PVC membranes. Polyvinyl pyrrolidone (PVP) is a more hydrophilic polymer; PVC/PVP blend ultrafiltration membranes were more hydrophilic and less susceptible to fouling by adsorption of proteins.9 Polyethylene glycol (PEG) with different molecular weights was also used as the additive to fabricate the asymmetric PVC hollow fiber membranes, porosity was increased, and water fluxes were improved due to the additive of PEG.10 Chlorinated polyvinyl chloride (CPVC) resin is a thermoplastic produced by chlorination of PVC resin. CPVC shares most of the features and properties of PVC. In the present study, PVC and CPVC were blended to fabricate ultrafiltration membranes. PVC and CPVC are completely miscible in a wide © 2012 American Chemical Society

concentration range in organic solvent of dimethylacetamide (DMAC) to prepare casting solutions. PEG and polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPOPEO) triblock copolymer Pluronic F127 were selected as additives. PVC/CPVC blend membranes with an additive of Pluronic F127 have better performance than that with PEG2000. The appearance of −CH2−CH2−O− segments on the membrane surfaces would make the PVC/CPVC blend membranes have excellent antifouling property. It is wellknown that PVC and CPVC are lower price polymers than the common membrane materials, such as polysulfone (PS), polyacrylonitrile (PAN), polyethersulfone (PES), and polyvinylidene difluoride (PVDF). Therefore, it is significant to prepare antifouling ultrafiltration membranes with those low cost polymers.

2. EXPERIMENTAL SECTION 2.1. Materials. PVC resin with average polymerization degree 800 was purchased from Dagu Chemical factory (Tianjin, China). CPVC resin with average polymerization degree 800 was obtained from Cangzhou Yuanzhen New Material Co. (Hebei Province, China). PEO-PPO-PEO block copolymer Pluronic F127 with a molecular weight of 12,600 and a PEO content of 70 wt % was purchased from Sigma. PEG with molecular weight of 2000 (PEG2000) was purchased from Damao Chemical Reagent Co. (Tianjin, China). N,NDimethylacetamide (DMAC) was purchased from Kewei Chemicals Co. (Tianjin, China). Bovine serum albumin (BSA, Mw = 67 kDa) was purchased from the Institute of Hematology, Chinese Academic of Medical Sciences (Tianjin, China). Other chemicals were of commercially analytical grade Received: Revised: Accepted: Published: 8308

April 3, 2012 May 29, 2012 June 1, 2012 June 1, 2012 dx.doi.org/10.1021/ie300878f | Ind. Eng. Chem. Res. 2012, 51, 8308−8314

Industrial & Engineering Chemistry Research

Article

⎛ Cp ⎞ ⎟ × 100% R = ⎜⎜1 − Cf ⎟⎠ ⎝

and used without further purification. Water used in all experiments was reverse osmosis water. 2.2. Membrane Preparation. PVC and CPVC were used as membrane materials, hydrophilic PEG and amphiphilic Pluronic F127 were used as additives. PVC/CPVC blend membranes were prepared by a nonsolvent induced phase separation method. The membrane materials and additive were dissolved in DMAC and stirred at 60 °C for about 4 h to ensure the homogeneous mixing and then left for 5 h to allow bubbles to release completely. After having been cooled to room temperature, the solutions were cast on glass plates with a steel knife and then immediately immersed into the coagulation bath of water. The blend membranes with a wet thickness of about 240 μm were peeled off and subsequently rinsed with water to remove the residual solvent and additive. PVC/CPVC blend membranes were kept in water before use. The viscosities of PVC and CPVC casting solutions were measured by a viscometer (Brookfield Viscometer, Model DV-I Prime). Viscosity measurements were performed at a constant shear rate under different temperatures. 2.3. Membrane Characterization. The static water contact angles of PVC/CPVC blend membranes were measured at room temperature with a contact angle goniometer (JC2000C contact angle meter, Powereach Co., Shanghai, China). At least five water contact angles at different locations on one surface were averaged to get a reliable value. The crosssection morphologies of PVC/CPVC blend membranes were observed by scanning electron microscopy (SEM, Philips XL30E scanning microscope). The membranes frozen in liquid nitrogen were broken and sputtered with gold before SEM analysis. The surface chemical compositions of PVC/CPVC blend membranes were analyzed by X-ray photoelectron spectroscopy instrument (XPS, PHI-1600, USA) using Mg Kα as radiation source. The takeoff angle of photoelectron was set to 90°. Surface XPS spectra were collected over a range of 0− 1100 eV. 2.4. Ultrafiltration Experiments. A dead-end stirred cell filtration system connected with a N2 gas cylinder and solution reservoir was designed to evaluate the filtration performance of PVC/CPVC blend membranes. All ultrafiltration experiments were carried out using a filtration test cell (Model 8200, Millipore Co., USA) whose volume capacity was 200 mL. The effective area of the membrane was 28.7 cm2. The operation pressure in the system was maintained by nitrogen gas. All the ultrafiltration experiments were carried out at a stirred speed of 400 rpm and a room temperature of about 20 °C. After fixing the membrane in the cell, the stirred cell and solution reservoir were filled with water. Each membrane was initially compacted for 0.5 h at 150 kPa; then the pressure was lowered to the operating pressure of 100 kPa. Pure water flux (Jw1) was calculated by the following equation

Jw1 =

V AΔt

(2)

where Cp and Cf (mg/mL) are solute concentrations of permeate and feed solutions, respectively. After 40 min protein ultrafiltration, the membrane was cleaned with water for 20 min, and then pure water flux was measured (Jw2) again. In order to evaluate the antifouling property of PVC/CPVC membrane, flux recovery ratio (FRR) was calculated using the following expression ⎛J ⎞ FRR = ⎜⎜ w2 ⎟⎟ × 100% ⎝ Jw1 ⎠

(3)

The higher FRR value means the better antifouling property of the ultrafiltration membrane.

3. RESULTS AND DISCUSSION 3.1. Preparation of PVC/CPVC Blend Ultrafiltration Membranes. PVC has been used as the main membrane material to fabricate ultrafiltration and microfiltration membranes.6−10 CPVC resin is the chlorinated product of PVC resin with the increased chlorine content to 65−70%. Compared with PVC, many characters of CPVC, such as solubility in organic polar solvent, thermal and chemical stability, are enhanced due to chlorination. Vicat softening temperature of CPVC resin is also up to 90−125 °C, while PVC is only 72−82 °C. Therefore, CPVC is a novel engineering plastic with wide application prospect. Blending is a very interesting way of producing polymer materials with improved bulk properties. In the present study, PVC and CPVC were blended as membrane materials to prepare ultrafiltration membranes. PVC and CPVC are completely miscible in wide concentration range in a polar organic solvent of DMAC to fabricate casting solutions. Figure 1 showed the influence of membrane material compositions of PVC/CPVC blend casting solutions on the viscosity−temperature curves (membrane material concentration is fixed at 18 wt %). The viscosities of PVC/CPVC blend casting solutions are increased with a decrease of temperature. At the same temperature, pure PVC solution has the highest viscosity,

(1)

where V is the volume of permeated water (L), A is the membrane area (m2), and Δt is the permeation time (h). The cell and solution reservoir were emptied and refilled rapidly with 1.0 mg/mL BSA in 0.1 M phosphate buffer solution at pH 7.0. The flux of protein solution (Jp) was recorded. In order to probe the pore size of the blend membrane, the rejection ratio of BSA was calculated by the following equation

Figure 1. The influence of temperature on the viscosity values of casting solutions with different membrane material compositions in casting solutions. 8309

dx.doi.org/10.1021/ie300878f | Ind. Eng. Chem. Res. 2012, 51, 8308−8314


Article

Figure 2. Cross-sectional SEM morphologies of PVC/CPVC blend ultrafiltration membranes, 1# membrane (a), 4# membrane (b), 10# membrane (c), and 14# membrane (d).

membranes.10 Pluronic F127 is an amphiphilic triblock copolymer with hydrophilic PEO segments and hydrophobic PPO segments. Pluronic F127 has been thought of as both a pore forming agent and a surface modifier for preparing antifouling PES ultrafiltration membranes.11−14 PEG2000 and Pluronic F127 were used as additives to fabricate PVC/CPVC blend membranes. Figure 3 shown the time-dependent fluxes of PVC/CPVC blend membranes (membrane material concentration is fixed at 18 wt %, PVC/CPVC weight ratio is fixed at 6:4, and additive/membrane material weight ratio is fixed at 20% in casting solution) during protein ultrafiltration operation. Pure water flux of the PVC/CPVC blend membrane is increased to 138.7 ± 2.6 L/(m2·h) for an additive of PEG2000 and 166.3 ± 3.4 L/(m2·h) for an additive of Plutonic F127. Although PEG2000 as a low molecular weight additive could improve the permeability of PVC/CPVC blend membranes, Pluronic F127 is more significant and effective as a pore forming agent to increase permeability of PVC/CPVC blend membranes. In Figure 3, the fluxes of protein solutions (Jp) for PVC/ CPVC blend membranes are lower than that of pure water (Jw1). The probable reasons are protein adsorption and deposition on the membrane surfaces and concentration polarization phenomenon occurring,1−5,15−19 leading to an abrupt drop in flux in the first few minutes of operation. Protein deposition and back diffusion toward bulk may reach equilibrium in the boundary layer on the membrane surfaces, so that relatively steady fluxes (Jp) were reached in the final operation of ultrafiltration. After 40 min of protein ultra-

while pure CPVC solution has the smallest viscosity. The viscosity values of all the blended systems are above 1000 mPa·s which are suitable for production of membranes by the phase inversion method,10 but the pure PVC casting solution is not easy to cast on glass plates with a steel knife at lower temperature due to its higher viscosity. PVC/CPVC blend membranes were prepared by nonsolvent induced phase separation method. During the phase separation process, a one-phase casting solution was converted into a twophase system consisting of a solid phase (polymer rich phase) that forms the membrane structure and a liquid phase (polymer poor phase) that forms the pores in the final membrane. The cross-sectional morphologies of the PVC/CPVC blend membranes were shown in Figure 2. All of the prepared membranes exhibit the typical asymmetric structure with a skin layer on top and fingerlike porous sublayer and fully developed macro-void at the bottom. The composition of membrane material, the incorporation of an additive, and the concentration of membrane material in casting solutions have no dramatic influence on the microscale morphologies of PVC/ CPVC blend membranes. 3.2. The Role of an Additive. The permeability of PVC/ CPVC blend membrane was measured by a dead-end stirred filtration cell. The pre-experiments showed that PVC/CPVC blend membrane without a pore forming agent has lower water flux (1# PVC/CPVC blend membrane). It is necessary to add a pore forming agent in casting solutions to enhance permeability. PEG is a hydrophilic polymer which has been used as an additive to enhance porosity and permeation fluxes of PVC 8310



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the XPS spectra of PVC/CPVC blend membranes with an additive of PEG2000 or Pluronic F127, respectively. The atomic percentages of C, O, and Cl elements are 72.0, 10.3, and 17.7 at% for the PVC/CPVC membrane with an additive of PEG2000. The atomic percentages of C, O, and Cl elements are 71.1, 21.3, and 7.6 at% for the PVC/CPVC membrane with an additive of Pluronic F127. PEG2000 or Pluronic F127 is the only source of O element of PVC/CPVC blend membranes. XPS measurement gave valuable information to confirm the appearance of −CH2−CH2−O− segments on the membrane surfaces. The additive of PEG2000 or Pluronic F127 takes both roles as pore-forming agent and surface modifier, simultaneously. Based on atomic percentages of the O element, there is a significantly higher −CH2−CH2−O− segment near-surface coverage on the PVC/CPVC membrane surface with an additive of Pluronic F127 than that with an additive of PEG2000. The probable reason is that Pluronic F127 is an amphiphilic block copolymer, and the interactions between the hydrophobic PPO block with PVC or CPVC render more Pluronic F127 molecules to retain on the membrane surfaces.11−14 The appearance of more hydrophilic −CH2− CH2−O− segments on the membrane surfaces would enhance the antifouling property of ultrafiltration membranes.1−5,20 This is consistent with the experiment results during the protein ultrafiltration process. 3.3. Pluronic F127 Contents in Casting Solutions. Since Pluronic F127 is a good pore forming agent and surface modifier, the influence of Pluronic F127 contents in casting solutions on the membrane performance was further studied. A series of PVC/CPVC blend membranes with different Pluronic F127/membrane material weight ratios were prepared (1−5# PVC/CPVC blend membranes, the concentration of membrane material is fixed at 18 wt %, PVC/CPVC weight ratio is fixed at 6:4 in casting solutions). Water contact angles of PVC/ CPVC blend membranes with different Pluronic F127/ membrane material weight ratios were measured and given in Table 1. The wetting angle of PVC/CPVC blend membrane without an additive is 63.7 ± 1.8°. When Pluronic F127/ membrane material weight ratios in casting solutions are increased, the wetting angles of PVC/CPVC blend membranes are decreased to 55.8 ± 1.4°; this means that the hydrophilic property of PVC/CPVC blend membranes is improved at higher Pluronic contents in casting solutions. Figure 5 presented the influence of Pluronic F127/ membrane material weight ratios in casting solutions on the time-dependent fluxes of PVC/CPVC blend membranes during protein ultrafiltration operation. Water fluxes of the PVC/ CPVC blend membranes are 38.5 ± 0.4, 150.6 ± 2.8, 163.2 ± 4.5, 170.6 ± 2.1, and 209.0 ± 1.9 L/(m2·h) at an operation pressure of 100 kPa with Pluronic F127/membrane material weight ratios of 0, 10, 20, 30, and 40% in casting solutions, respectively. Water fluxes of PVC/CPVC blend ultrafiltration membranes are usually increased with an increase of pore forming agent contents in casting solutions.10,12 The pore sizes were evaluated by using BSA as molecular probe. The BSA rejection ratios of PVC/CPVC blend membranes were also shown in Table 1. It was observed that 81.3, 83.0, 84.6, 81.4, and 76.2% of BSA molecules are rejected by PVC/CPVC blend membranes with Pluronic F127/membrane material weight ratios from 0 to 40% in casting solutions, respectively. The pore sizes of PVC/CPVC blend membranes are enlarged at higher Pluronic F127/membrane material weight ratio of 40% in casting solution.

Figure 3. Time-dependent fluxes of PVC/CPVC blend membranes without and with the additives of PEG2000 and Pluronic F127 during protein ultrafiltration operation. PVC/CPVC blend membranes were prepared with 18 wt % membrane material in casting solution. The weight ratio of additive/membrane material is 20%. The ultrafiltration process includes four steps: pure water flux measurement from 0 to 20 min, BSA solution ultrafiltration from 20 to 60 min, water cleaning at 60 min, and pure water flux measurement of the cleaned membranes from 60 to 80 min.

filtration, PVC/CPVC blend membranes were directly cleaned with stirred water in the filtration cell, and the fluxes of the cleaned membranes (Jw2) were measured again. FRR values were calculated to study the antifouling ability of the ultrafiltration membranes. The PVC/CPVC blend membrane with an additive of PEG2000 has a flux recovery of only 83.3%, while the membrane with an additive of Pluronic F127 has a flux recovery of 97.6%. The above data clearly demonstrated that the PVC/CPVC ultrafiltration membrane with an additive of Pluronic F127 has a better antifouling property than that with an additive of PEG2000. The surface compositions of PVC/CPVC blend membranes were carefully characterized by XPS analysis. Figure 4 presented

Figure 4. XPS spectrum of PVC/CPVC blend membranes. PVC/ CPVC blend membranes were prepared with membrane material concentration of 18 wt % in casting solution. The weight ratio of additive/membrane material is fixed at 20%. 8311



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Table 1. Influence of Pluronic F127/Membrane Material Weight Ratios on the Property of PVC/CPVC Blend Ultrafiltration Membranesa membrane 1 2 3 4 5 a

# # # # #

Pluronic F127/membrane material (w/w %) 0 10 20 30 40

water contact angle (deg) 63.7 62.3 61.7 60.1 55.8

± ± ± ± ±

pure water flux (L/m2·h)

1.8 1.1 1.0 1.5 1.4

38.5 150.6 163.2 170.6 209.0

± ± ± ± ±

BSA rejection (%)

flux recovery ratio (%)

81.3 83.0 84.6 81.4 76.2

100 95.5 100 96.4 100

0.4 2.8 4.5 2.1 1.9

Membrane material concentration is fixed at 18 wt %; PVC/CPVC weight ratio is fixed at 6:4 in casting solutions.

Figure 6. Time-dependent fluxes of PVC/CPVC blend membranes with different membrane material compositions in casting solutions during protein ultrafiltration operation (6−10# PVC/CPVC blend membranes in Table 2). The ultrafiltration process includes four steps: pure water flux measurement from 0 to 20 min, BSA solution ultrafiltration from 20 to 60 min, water cleaning at 60 min, and pure water flux measurement of the cleaned membranes from 60 to 80 min.

Figure 5. Time-dependent fluxes of PVC/CPVC blend membranes with different Pluronic F127 contents in casting solutions during protein ultrafiltration operation (2−5# PVC/CPVC blend membranes in Table 1). The ultrafiltration process includes four steps: pure water flux measurement from 0 to 20 min, BSA solution ultrafiltration from 20 to 60 min, water cleaning at 60 min, and pure water flux measurement of the cleaned membranes from 60 to 80 min.

Table 2. Influence of Membrane Material Compositions on the Property of PVC/CPVC Blend Ultrafiltration Membranesa

3.4. Membrane Material Compositions in Casting Solutions. The membrane material compositions in casting solutions also have an influence on the permeability of PVC/ CPVC blend membranes. A series of PVC/CPVC blend membranes with different CPVC proportions in membrane materials were fabricated (6−11# PVC/CPVC blend membranes, membrane material concentration is fixed at 18%, and Pluronic F127/membrane material weight ratio is fixed at 20% in casting solutions). Figure 6 presented the influence of membrane material compositions in casting solutions on the time-dependent fluxes of PVC/CPVC blend membranes during protein ultrafiltration operation. Table 2 showed the performance of PVC/CPVC blend membranes of different membrane material compositions. The hydrophilicity of PVC/CPVC blend membranes was improved with an increase of CPVC proportions in membrane materials. With the increase of the proportions of CPVC in membrane materials from 0 to 100%, the wetting angles of membranes are gradually decreased from 64.2 ± 1.2° to 52.3 ± 1.3°, and the water fluxes of PVC/CPVC blend membranes are gradually increased from 142.5 ± 2.4 to 292.3 ± 6.5 L/(m2·h). The increased water fluxes of PVC/ CPVC blend membranes with an increase of CPVC proportions in membrane materials may be due to enhanced hydrophilic property. In Table 2, it was seen that there are slight changes of BSA rejection ratios, meaning that PVC/ CPVC blend membranes with different membrane material compositions have nearly similar pore sizes. 3.5. Membrane Material Concentrations in Casting Solutions. The membrane permeability is also affected by

membrane

PVC/ CPVC weight ratio

water contact angle (deg)

6# 7# 8# 9# 10 # 11 #

1:0 0.8:0.2 0.6:0.4 0.4:0.6 0.2:0.8 0:1

64.2 63.0 61.8 61.0 56.2 52.3

± ± ± ± ± ±

1.2 1.0 1.4 0.9 1.1 1.3

pure water flux (L/m2·h) 142.5 162.8 179.0 201.8 243.6 292.3

± ± ± ± ± ±

2.4 4.5 2.0 2.6 4.7 6.5

BSA rejection (%)


82.3 82.6 84.6 81.7 82.6 80.5

100 95.5 100 96.4 97.5 100

Membrane material concentration is fixed at 18 wt %; Pluronic F127/ membrane material weight ratio is fixed at 20% in casting solutions.

a

membrane material concentrations in casting solutions. A series of PVC/CPVC blend membranes with different membrane material concentrations in casting solutions were fabricated (12−15# PVC/CPVC blend membranes, Pluronic F127/ membrane material weight ratio is fixed at 20%, PVC/CPVC weight ratio is fixed at 6:4 in casting solutions). The influence of membrane material concentrations in casting solutions on the time-dependent fluxes of PVC/CPVC blend membranes during protein ultrafiltration operation were given in Figure 7, and the results of water fluxes and BSA rejection ratios were given in Table 3. With the increase of membrane material concentrations in casting solutions, pure water fluxes of PVC/ CPVC blend ultrafiltration membranes are decreased rapidly. The porosity in the skin layer of PVC/CPVC blend membranes 8312



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In this report, hydrophilic PEO segments were incorporated in PVC/CPVC blend membrane surfaces by the blending method with an additive of Pluronic F127. BSA was used as both probe of pore size and model foulant to evaluate the antifouling property of PVC/CPVC blend ultrafiltration membranes. Based on the experimental results shown in Tables 1, 2, and 3, it can be clearly found that the flux recovery ratios of all prepared PVC/CPVC blend membranes with an additive of Pluronic F127 are above 95%. The most deposited protein molecules on the membrane surfaces were washed out without chemical cleaning. Due to excellent antifouling property, lower cost, and better performance, PVC/CPVC blend membranes with an additive of Pluronic F127 have potential applications in wastewater treatment and bioseparation. Figure 7. Time-dependent fluxes of PVC/CPVC blend membranes with different membrane material concentrations in casting solutions during protein ultrafiltration operation (12−15# PVC/CPVC blend membranes in Table 3). The ultrafiltration process includes four steps: pure water flux measurement from 0 to 20 min, BSA solution ultrafiltration from 20 to 60 min, water cleaning at 60 min, and pure water flux measurement of the cleaned membranes from 60 to 80 min.

4. CONCLUSIONS PVC/CPVC blend membranes with an additive of Pluronic F127 can be used as new antifouling ultrafiltration membranes. Pluronic F127 takes both roles of appropriate pore forming agent and surface modifier in the fabrication of PVC/CPVC blend membranes. Water fluxes of PVC/CPVC blend membranes are increased at higher Pluronic F127/membrane material weight ratio, higher CPVC proportion in membrane material, and lower membrane material concentration in casting solutions. Since the surfaces are covered with hydrophilic −CH2−CH2−O− segments, PVC/CPVC blend membranes with an additive of Pluronic F127 have excellent antifouling properties.

Table 3. Influence of Membrane Material Concentrations in a Casting Solution on the Property of PVC/CPVC Blend Ultrafiltration Membranesa membrane 12 13 14 15

# # # #

casting solution

water contact angle (deg)

16 wt % 18 wt % 20 wt % 22 wt %

61.7 62.0 61.5 61.8

± ± ± ±

1.0 1.2 2.1 1.3

pure water flux (L/m2·h) 212.4 167.2 120.5 118.3

± ± ± ±

4.2 5.5 4.5 5.4

BSA rejection (%)


84.4 84.3 84.6 84.5

97.6 100 100 99.4

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AUTHOR INFORMATION

Corresponding Author

*Fax: 86-22-27890882. E-mail: [email protected].

Pluronic F127/membrane material weight ratio is fixed at 20%; PVC/ CPVC weight ratio is fixed at 6:4 in casting solutions. a

Notes

The authors declare no competing financial interest.

■

is largely dependent on the membrane material concentrations in the casting solutions. The PVC/CPVC blend membrane prepared from a lower concentration of membrane material in a casting solution has a greater porosity in its skin layer. Water flux of PVC/CPVC blend membrane with membrane material concentration of 16 wt % in a casting solution is 212.4 ± 4.2 L/ (m2·h), while PVC/CPVC blend membrane with membrane material concentration of 22 wt % in a casting solution is only 118.3 ± 5.4 L/(m2·h). According to the results in Table 3, BSA rejection ratios of PVC/CPVC blend membranes with different membrane material concentrations are in the range from 84.3 to 84.6%. The membrane material concentrations in casting solutions have almost no dramatic influence on the pore sizes in the skin layers of PVC/CPVC blend ultrafiltration membranes. 3.6. Excellent Antifouling Property. Despite ultrafiltration being technologically relevant with a wide range of applications, one of its limitations is flux decline due to membrane fouling. Membrane fouling is caused by foulant adsorption and desorption, which further leads to pore blocking and filter cake formation.15−19 The surface properties of ultrafiltration membranes such as high hydrophilicity and low roughness are the dominant factors in reducing the membrane fouling.1−5 PEO is a biocompatible, highly hydrophilic, and antifouling polymer. Modifying surfaces with PEO is an effective method to resist protein adsorption. A highly hydrated and dense −CH2−CH2−O− segment layer on the membrane surfaces can strongly resist protein adsorption and deposition.11−14,20

ACKNOWLEDGMENTS This research is supported by Open Funding Project of the National Key Laboratory of Biochemical Engineering and the Program of Introducing Talents of Discipline to Universities (NO: B06006).

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REFERENCES

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