Protein Transport Properties of PAN Membranes ... - ACS Publications

Subscriber access provided by University of Newcastle, Australia

Article

Protein transport properties of PAN membranes grafted with hyperbranched polyelectrolytes and hyperbranched zwitterions Na Ma, Lianrui Zhao, Xiaoyu Hu, Zhen Yin, Yu-feng Zhang, and Jianqiang Meng Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b03616 • Publication Date (Web): 11 Jan 2017 Downloaded from http://pubs.acs.org on January 17, 2017

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 35

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

Protein transport properties of PAN membranes grafted with hyperbranched polyelectrolytes and hyperbranched zwitterions Na Ma,† Lianrui Zhao,† Xiaoyu Hu,‡ Zhen Yin,† Yufeng Zhang,† Jianqiang Meng∗,†

† State Key Laboratory of Separation Membranes and Membrane Processes, Tianjin Polytechnic University, Tianjin 300387, China

‡ State Key Laboratory of Membrane Materials and Membrane Applications, Tianjin Motimo Membrane Technology Co., Ltd., Tianjin 300042, China

ABSTRACT: A series of charge-modified polyacrylonitrile (PAN) membranes with different surface charge properties and densities have been obtained via firstly grafting with hyperbranched polyethylenimine (PEI) and then ring-opening with 1,4-butane sultone. The obtained PAN-gr-PEI membranes and PAN-gr-PEIS membranes have hyperbranched polycation and hyperbranched zwitterions tethered on the surface respectively. They were characterized in detail by FT-IR, AFM, XPS, SEM, WCA and zeta-potential measurements. Bovine serum albumin (BSA) and lysozyme (Lys) were chosen as model proteins in order to evaluate the separation performance of the modified membranes via dead-end ultrafiltration. The membranes grafted with PEI of different densities have different surface chemical compositions but very similar surface charge properties. PAN and PAN-gr-PEI membranes are highly negatively charged and moderately positively charged. PAN-gr-PEIS membranes show typical amphoteric characteristics. The UF performance is highly dependent on charge

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

properties. The membrane shows high flux and low transmission when membrane and protein have the same charge. At pH of 7 and 10, BSA and Lys are oppositely charged so that PAN-gr-PEIS and PAN membranes show good selectivity. When membrane and protein are oppositely charged, the membrane was fouled severely, including zwitterionic PAN-gr-PEIS membranes, which should be due to the stiffness of the hyperbranched zwitterions.

2


Page 2 of 35

Page 3 of 35

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


1. INTRODUCTION The separation and purification of proteins is an important process in biotechnology, food, biomedical and pharmaceutical industries.1-3 To obtain purified proteins, precipitation, ion-exchange chromatography, ultrafiltration, centrifugation, adsorption, and electrophoretic membrane contactor have been used.2-4 Separation technologies based on membrane have been regarded as very useful methods for biomaterials purification, due to its high separation efficiency, facile implementation, and cost effectiveness, such as protein separation.5-6 Thereinto, ultrafiltration (UF) is widely used for the concentration of various protein products in the present days, such as recombinant therapeutics, industrial enzymes, and various food and beverage products.7-9 However, UF had usually been identified as separation process based on size; it’s hard for separation of similar molecular weight molecules.7, 10 Zydney et al. found that the protein could be separated through electrostatic interactions via the control of solution pH and ionic strength. For instance, the BSA permeation through the poly (ether sulfone) ultrafiltration membrane of 100,000 molecular weight cut-off (MWCO) declined by almost two orders of magnitude along with the salt concentration from 150 to 1.5 mM.11-12 If the ionic strength was low, the raise of electrostatic exclusion between the bovine serum (BSA) and the charged membrane pores would lead to high protein rejection. Moreover, the sieving coefficient of BSA became much lower if the pH value declined because of the strong electrostatic exclusion between the positively charged protein and the membrane pores.13 In general, when membranes and proteins possess the same charge, it is hard for protein 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

to penetrate through the membrane pore due to the electrostatic exclusion. As a result, the permeability of protein reduces greatly. By taking advantage of this, the selectivity of the membrane can be improved greatly. Actually, a sharp enhance in separation selectivity of immunoglobulins (IgG) and BSA has been observed at pH 4.8, which is isoelectric point (pI) of BSA, and a low salt concentrations.14 The enhancement in selectivity was resulted from the electrostatic repulsion between the positively charged IgG and membrane, on the other hand, the uncharged BSA passes through the membrane easily. It has been confirmed by Van Eijndhoven et al.15 that the BSA and hemoglobin proteins can be separated with the high selectivity at pH = 7 because of the electrostatic repulsion between the negatively charged BSA and membrane. Similar result about the separation of BSA-IgG and BSA monomer-dimer has been reported by van Reis et al.16 Hence, the charge-modified and polyelectrolyte-tethered UF membrane have been regarded as one good choice for efficient protein separations.

Since the electrostatic interaction plays a key role on protein transport through UF membrane, many charge-modified and polyelectrolyte-tethered UF membrane have been prepared for efficient protein separations. Meanwhile, the pH value and the salinity of solution were adjusted in order to obtain high protein selectivity. In recent years, zwitterionic UF membranes have attracted intensive attention due to their minimal protein fouling properties. Attracted by their low fouling properties, people also use zwitterionic membranes for protein separation. Bai found that the permeation selectivity of zwitterionic membranes for proteins can be tuned by the electrolyte 4


Page 4 of 35

Page 5 of 35

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


concentration.17 Zydney et al. investigated the protein separation effect with various zwitterionic cellulose UF membranes, which were obtained by a chemical modification process.18

In spite of the extensive synthesis of UF membranes modified with charged or zwitterionic ligands and analysis of their protein transport properties, the tethered ligands are mostly linear molecules. There has been no study of the effects of the architecture of tethered ligands on protein transport properties. Hyperbranched polymer is a special class of macromolecules containing a large number of terminal functional groups. We envisage that surface modification of UF membranes with hyperbranched polyelectrolytes can significantly enhance membrane surface charge density so that high protein selectivity can be expected.

The objective of this study was to examine the protein transport properties of a UF membrane tethered with hyperbranched polyelectrolytes and hyperbranched zwitterions. PEI was at first attached onto PAN membrane via cyanide hydrolysis and amidation reaction to prepare positively charged UF membranes. Then the amine group on the membrane surface was reacted with 1,4-butane sultone to prepare UF membranes grafted with hyperbrached zwitterions. The membranes were thoroughly characterized by FT-IR, AFM, XPS, SEM, WCA and zeta-potential measurements. BSA (pI = 4.8, Mw = 66,000 g/mol) and lysozyme (Lys) (pI = 11.0, Mw = 14,400 g/mol) were regarded as model proteins in order to investigate their protein transport properties.

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

Page 6 of 35

2. EXPERIMENTAL SECTION 2.1. Materials. Polyacrylonitrile (PAN) ultrafiltration membrane (Model number: PA200, USA) was obtained from SePRO corporation (CA, USA). The membrane has the PAN skin layer supported by a polyester nonwoven fabric material and has a MWCO of 100 kDa. The membrane was sliced into round pieces (diameter: 4.5 cm), and sequentially cleaned by ethanol and deionized (DI) water at 40 oC to remove the additives. Then the films were dried under vacuum at 50 oC before use. PEI, (Mn = 10,000 g/mol, Mw / Mn = 2.5), 1,4-butane sultone, ethyl acetate, BSA and Lys were purchased from Sigma-Aldrich. PBS solution (10 mM potassium phosphate buffer, pH = 7.4) was used for protein dissolution. All reagents were used as received without any further purification. Deionized (DI) water was obtained with a Millipore Milli-Q Advantage A 10 water purification system (18.2 MΩ cm-1, Billerica MA USA). 2.2.

Synthesis

of

polyacrylonitrile-g-polyethylenimine

(PAN-gr-PEI)

membrane. The grafting process of PAN membranes was similar to other reported method with slight modifications.19 Briefly: The PAN membrane(4 × 8 cm2) and PEI (1.6 g) were put into an autoclave. And then, 25 mL of DI water was introduced, stirred for 2h. The autoclave was put into an oven and kept at 145 oC for 3, 4 and 5h, respectively. After naturally cooled down to room temperature, the membrane was filtered out and washed repeatedly. Finally, it was dried at 70 oC under vacuum oven over night. The PAN membranes after reacting with PEI for 3 h, 4 h and 5 h were designated as PAN-gr-PEI3, PAN-gr-PEI4 and PAN-gr-PEI5 respectively. 2.3. Preparation of zwitterions-grafted membranes (PAN-gr-PEIS) via 6


Page 7 of 35

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


ring-opening reaction of 1,4-butone sultone with PAN-gr-PEI membrane. The PAN-gr-PEIS membrane was obtained through ring-opening reaction of peripheral amine/amino groups in membrane-tethered PEI molecules with 1,4-butane sultone. At first, the PAN-gr-PEI membrane was soaked in 100 mL of ethyl acetate solution of 0.6 g of 1,4-butane sultone in a conical flask. The flask was kept shaking at 25 oC for 8 h. The membrane was then filtered out and repeatedly washed with DI water. PAN-gr-PEIS membrane was dried in vacuum oven at 45 oC overnight. The PAN-gr-PEIS

membranes

prepared

from

PAN-gr-PEI3,

PAN-gr-PEI4

and

PAN-gr-PEI5 were designated as PAN-gr-PEIS3, PAN-gr-PEIS4 and PAN-gr-PEIS5, respectively. The grafting yield (GY, mg/cm2) was calculated with the Eq (1): GY

(1)

where W0 is the weight of the PAN-gr-PEI membrane; W1 is the weight of PAN-gr-PEIS membrane, and A is the membrane surface area.

Fig. 1. The synthesis route of PAN-gr-PEI and PAN-gr-PEIS membranes. 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

Page 8 of 35

2.4. Characterization. The characterization of surface chemical compositions was conducted using Fourier transform infrared (FT-IR) spectrophotometer (Vector-22, Bruker Co. Ltd, Germany) and X-ray photoelectron spectroscopy (XPS) (K-Aepna, Thermo Fisher Co., Ltd. USA) with a monochromatic Al-Ka X-ray source (1486.6 eV photons). Survey spectra in XPS were operated from 0 eV to 1000 eV. Binding energies were calibrated with the containment carbon (C1s = 284.6 eV). The PAN layer surface of the membrane were observed using field emission scanning electron microscopy (FE-SEM, Hitachi S-4800, Japan). Membrane surface roughness was measured by Atomic Force Microscopy (AFM Agilent technologies 5500 scanning probe microscope, USA) in non-contacting mode. An area of 3 × 3 µm were scanned and five replicates for each sample were tested. The surface roughness parameters, including Ra (arithmetical mean deviation of the profile), Rz (ten point height of irregularities) and Rmax (maximum height of the profile), were obtained following the ISO 4287 standard and calculated as following:

∑ ;

(2)

∑ + ;

(3)

∑ + ;

(4)

All the symbols have their usual meanings.20 The water contact angle (WCA) of dry membrane was measured with a contact angle meter (Kruss CM3250-DS3210, Germany) at room temperature. Water (2 µL) was carefully dropped on the dry membrane with the syringe. Three areas were selected for measuring each membrane. The membrane was dried overnight at 45 oC 8


Page 9 of 35

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


before the measurement. Zeta potential of the membranes were measured by a SurPASS electrokinetic analyzer (Anton-Paar GmbH, Austria). A pair of membranes of 10 mm × 20 mm were fixed on sample holders, and then inserted into the adjustable-gap cell. A gap of 100 µm was set between the membrane surfaces. Before the sample mounting, the membranes were soaked in a 1 × 10-3 mol/L KCl solution for 24 h and rinsed thoroughly with the measuring electrolyte. The measurements were started at pH of 7 in KCl solution (1 × 10-3 mol/L). Then the electrolyte solution was adjusted to other pH values with HCl (0.1 mol/L) and NaOH solutions (0.1 mol/L). The streaming current

was

tested

and

converted

to

the

zeta

potential

with

the

Helmholtz-Smoluchowski model. The zeta potential data were averages of three measurements. 2.5. The pure water permeation and rejection experiment. The pure water flux and rejection experiment of membranes was tested with a stirred filtration cell (Amicon 8010, Millipore) under the pressure of 0.1 MPa. The effective testing area of the membrane is 15.9 cm2. The membranes were immersed in ethanol for 1 min before the test, and then were pressured for 10 min to obtain a stable flux value. The flux was calculated by measuring the permeation volume in 5 min for 3 times. The flux was calculated using Eq. (5):21-23

×

(5)

where Jw is the pure water flux (L/m2h), V is the volume of water (L), A is the membrane area (m2), and t is the time (h). The rejection experiment was tested with 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

Page 10 of 35

dextran (Mw=20,000, 40,000, 70,000, 100,000, respectively), whose concentration was 0.50 g/L. The concentration of the feed solution and permeate solution was tested by total organic carbon (TOC) with the TOC-VCPH instrument from Shimadzu, Japan. The dextran rejection was calculated by the Eq. (6):

R 1−

#$ #%

& × 100

(6)

where CF is the dextran concentration in the feed solution (mg/L) and CP is its concentration in the permeate solution (mg/L). MWCO was determined by the molecular weight of dextran showing rejection of 90% on the rejection vs. molecular weight curve. 2.6. Protein ultrafiltration. UF experiments were conducted at room temperature in an Amicon 8010 cell with a stirring speed of 600 rpm to evaluate the protein transmission by filtrating 1 g/L protein solution at different pH values. All protein solutions were filtered through 0.22 µm cellulose esters membrane in vacuum filter holder immediately prior to use. The protein solution flux was obtained as Eq. (7) and (8):

() ×

(7)

*+, ×

(8)

where JBSA is BSA permeation flux (L/m2 h), JLys is Lys permeation flux (L/m2 h), V is permeation volume (L), A is the effective membrane area (m2), t is the filtration time (h). At first, the membranes were immersed in the BSA or Lys solution at predetermined pH for 24 h before ultrafiltration to ensure equilibrium adsorption. 10


Page 11 of 35

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


Then, 500 mL of BSA or Lys (1 g/L) solution with a certain pH value was filled into the fluid reservoir which is connected to the UF cell, in order to keep constant the concentration of feed protein solution during the UF experiment process. The pH of the feed solution was adjusted by with NaOH and HCl. The membrane was then returned to the stirred cell and the cell was sealed and pressurized at 0.1 MPa to perform the UF experiment for 60 min until the membrane permeation flux became steady. The concentration of BSA or Lys was determined with a UV–Vis spectrophotometer Cary 50 at 280 nm, The observed transmission of protein (τObs) through the membranes was determined using Eq. (9):21, 24-25 #

τ./, #0

(9)

1

where Cf is the protein (BSA or Lys) concentration in the feed solution (mg/L) and CP is the protein concentration in the permeate solution (mg/L). The separation factor (SF) of membranes towards Lys versus BSA was calculated by Eq. (10): >

Separation factor SF >?@A B

(10)

?@A C

where (τObs)i and (τObs)j are the observed transmission values of Lys and BSA. As for the long-term protein UF experiments, the membrane performance was regenerated after the protein solution was filtrated for 60 min. Then, the membrane was cleaned with PBS for 30 min, 0.1 mol/L NaOH solution (25 °C) for 15 min and 1 mol/L NaCl solution (60 °C) for 15 min. After the rinsing in turn, the fluxes (L/m2 h) of pure water and protein solution were tested again. The relative flux recovery (RFRi, %) was calculated by Eq.(11):

D %

FG,B FG

× 100 I 1, 2, 3

(11) 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

Page 12 of 35

where Jw,i is the pure water flux during the cycle filtration (L/m2 h). The observed transmission of protein (τobs,i) in each cycle was calculated by Eq.(12):

LM/,,

#0,B

(12)

#1

where Cf is the protein concentration in the feed solution (g/L) and Cp,i is the protein concentration in the permeate solution after ith cycle filtration (g/L). The same filtration set-up was used to assess the separation performance of the grafted membranes via cross-flow filtration of the mixed protein solution at different pH values. The protein solution of BSA (1 g/L) and Lys (1 g/L) were mixed with the volume ratio of 1:1 and filtered through the as-prepared membrane at room temperature (25 ± 1 oC). The pH of protein solution can be adjusted according to the reported procedure.2 The BSA and Lys concentration in the mixtures were analyzed with the SDS-PAGE method.26 3. RESULT AND DISCUSSION Previous work shows that the electrostatic interaction plays a key role on protein transport through UF membrane. The PEI molecules possess abundant amino groups at the periphery, which can easily change the electrical properties of the PAN membrane surface after the grafting reaction. And then, the 1,4-butane sultone can react with peripheral amine/amino groups in membrane-tethered PEI molecules by ring-opening reaction, which introduces sulfonic acid group as negative charge forming zwitterions. We note here that 1,4-butane sultone rather 1,3-propane sultone was used upon consideration of cost effectiveness. However, a mass loss was observed after the PEI grafting process. Hence, the corresponding grafting yield in the 12


Page 13 of 35

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


first grafting step cannot be calculated due to the possible extraction of organic additives from the membrane by PEI molecules.27 As for the ring-opening reaction, it was found that higher sultone concentration lead to higher GY values, which reached a plateau when the sultone concentration is over 0.044 mol/L. Successive sultone was added so that the plateau GY values of 0.74 mg/cm2, 1.78 mg/cm2 and 0.44 mg/cm2 were obtained for the PAN-gr-PEIS3, PAN-gr-PEIS4 and PAN-gr-PEIS5 membranes, respectively. 3.1. Membrane surface characterization 3.1.1. Membrane surface composition. The membrane surface chemical compositions before and after PEI grafting and zwitterionization were characterized by FT-IR. Fig. 2 shows the FT-IR spectra of PAN membrane, PAN-gr-PEI membranes and PAN-gr-PEIS membranes. Compared to the PAN membrane, the PAN-gr-PEI membranes show new absorptions at 1563 cm-1 and 1651 cm-1, which belong to the C=O stretching of amide groups. The new peak centered at 1394 cm-1 can be assigned to the typical C=O symmetric stretching vibration from carboxylate (COO-). Furthermore, the obvious C=O asymmetric stretching from COO- could be distinguished at 1563 cm-1, which overlapped with C-N stretching and N-H deformation vibrations.19 This observation indicated that the hydrolysis of nitrile groups would happen firstly in basic conditions, and then part of them react with the amino groups in PEI. The COO- group could be formed because of the acid-base neutralization reaction between residual carboxylic acid groups and amino groups of PEI moieties, which could be confirmed by the existence of the broad band resulted 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

from the characteristic of NH3+ symmetric stretching vibration in the range of 2000 3000 cm-1.19 In addition, the vibration of NH3+ asymmetric stretching could be observed at ~3072 cm-1, overlapping partially with the new broad band located at ~3290 cm-1 , which could be attributed to the N-H stretching vibration for primary, secondary amine and amide groups of PEI moieties. These observations indicate the PEI polymer chains were successfully anchored on the membrane surface via grafting. Moreover, for the PAN-gr-PEI membranes with different grafting yields, there were the obvious absorption peak of the C≡N stretching at 2242 cm-1, suggesting that only some nitrile groups of PAN involved in the reaction. With the grafting time increasing, the FT-IR absorption intensities of the amides, amines and carboxylates increased dramatically. It should be noted that the spikes at 2842 cm-1 and 2935 cm-1 are the typical C-H stretching vibrations resulted from alkane groups, existing in both FT-IR spectra of PAN membrane and PAN-gr-PEI membranes. Compared to the PAN-gr-PEI membrane, the PAN-gr-PEIS membranes have the absorption from 1340 cm-1 to 1385 cm-1, which belongs to the -SO3H asymmetric stretching vibration and symmetric stretching vibration respectively. The new peak from 570 cm-1 to 705 cm-1 is the typical C-S stretching vibration of R-SO3H. In addition, the intense S-O asymmetric stretching can also be found from 700 cm-1 to 810 cm-1. These observations indicate the successful anchoring of -SO3H onto the membrane surface via the ring-opening reaction.

14


Page 14 of 35

Page 15 of 35

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. ATR-FTIR spectra of PAN, PAN-gr-PEI and PAN-gr-PEIS membranes.

The surface chemical composition of the PAN, PAN-gr-PEI and PAN-gr-PEIS membrane was further ascertained by XPS analysis. Fig.3 (a) shows the wide spectra of the membranes. The peaks located at about 284.5 eV, 532.2 eV and 399.8 eV can be attributed to C 1s O 1s and N 1s, respectively. Table 1 shows the corresponding results. The existence of the O 1s peak should be resulted from the oxygen containing additive, which might be introduced in the production process of membrane.19 In comparison with the PAN membrane, the O content of PAN-gr-PEI membranes increase dramatically after grafting of PEI. The C content decrease and the O content increase should be due to the introduction of carboxylate group upon hydrolysis, which corresponds well with the FT-IR results. In comparison with the spectra of the PAN and PAN-gr-PEI4 membranes, the S 2p peak appeared at 168.2 eV in the spectrum of PAN-gr-PEIS membranes can be attributed to the sulfonate group grafted on the membrane surface. The O/N atomic ratio of PAN-gr-PEI5 membrane is the highest, followed by PAN-gr-PEI4, PAN-gr-PEI3 and PAN. The S/N atomic ratio of PAN-gr-PEIS membrane is in the range of 0.04 to 0.06, with that of PAN-gr-PEIS4 membrane as the highest and that of PAN-gr-PEIS5 as the lowest, which is consistent with the grafting yield values. 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

Page 16 of 35

Fig. 3. XPS survey spectra of (a) PAN, (b) PAN-gr-PEI4 and (c) PAN-gr-PEIS4 membranes. Table 1. Elemental surface compositions of PAN, PAN-gr-PEI and PAN-gr-PEIS membranes determined by XPS. Element (atom %)

Membrane PAN PAN-gr-PEI3 PAN-gr-PEI4 PAN-gr-PEI5 PAN-gr-PEIS3 PAN-gr-PEIS4 PAN-gr-PEIS5

C

N

O

S

79.20 74.12 72.25 72.19 73.62 70.87 69.37

16.97 18.74 18.39 18.05 17.89 17.95 18.31

3.82 7.14 9.36 9.76 7.55 10.04 11.53

0 0 0 0 0.94 1.14 0.97

O/N

S/N

0.23 0.38 0.51 0.54 0.05 0.06 0.04

3.1.2. Membrane surface morphology. SEM was used to observe the surfaces morphology of membrane. Fig. 4 shows the SEM images of the membranes surface area. The surface roughness of the top layer seems to increase with the grafting reaction time, which may be related to the increased PEI grafting amount with the extension of reaction time. In order to verify this observation, the membrane surfaces were measured with AFM. The surface roughness data were shown in Table 2. We see that all the roughness parameters, including Ra, Rz and Rmax, increased with the grafting reaction time.

16


Page 17 of 35

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. Surface SEM images of (A) PAN, (B) PAN-gr-PEI3, (C) PAN-gr-PEI4, (D) PAN-gr-PEI5, (E) PAN-gr-PEIS3, (F) PAN-gr-PEIS4, and (G) PAN-gr-PEIS5.

Table 2. Surface roughness of the virgin and modified membranes. Membranes

Ra (µm)

Rz (µm)

Rmax (µm)

PAN PAN-gr-PEI3 PAN-gr-PEI4

0.0708 0.110 0.273

0.444 0.864 1.430

0.892 1.735 2.731

PAN-gr-PEI5

0.378

1.840

2.984

PAN-gr-PEIS3 PAN-gr-PEIS4 PAN-gr-PEIS5

0.125 0.285 0.385

1.150 1.520 1.610

2.353 2.917 3.215

3.1.3. Membrane surface zeta potential. The surface charge property of membranes has great influence on the filtration process and fouling phenomenon.28-29

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

The protein separation efficiency of the membrane can be controlled through the interaction between membrane surface and protein via electro kinetic characteristics. Zeta potential is the primary parameter characterizing surface charge properties. In solution, an electric double layer was induced by the surface charge of membrane or protein. There is a shear plane between the fixed layer and the diffusive layer. The electric potential resulted from the ions movement at the shear plane is defined as the zeta potential (ζ).30 The zeta potential values of the membranes surface at varied pH are listed in Fig. 5. Interestingly, the zeta potential values are negative over the entire studied pH range for PAN membrane. We did not expect that the PAN membrane is negatively charged since it has no ionizable groups. However, there are quite a few articles reporting the same result and ascribing it to the specific adsorption of electrolyte anions onto the surface.31-32 All the PAN-gr-PEI membranes have positive ζ values from the acidic to neutral pH range. The pI value of PAN-gr-PEI membranes were around pH = 9, which fall at the pKa range of primary, secondary and tertiary amine groups in PEI molecules, confirming that the membrane surface is fully covered by the grafted PEI molecules. There is an obvious shift of membrane surface potential upon grafting of PEI, which should be ascribed to the high positive charge density of hyperbranched PEI molecules. The introduction of the sulfonate group via reaction of amine with 1,4-butane sultone again shifts the zeta potential profile to the negative direction. As a result, the sulfonate group should form zwitterions with the adjacent amine groups. The PAN-gr-PEIS membranes show typical amphoteric charge properties with pI value at about 6.5. In spite of significant variation of surface 18


Page 18 of 35

Page 19 of 35

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


composition for membranes grafted with PEI of different densities, the PAN-gr-PEI membranes have very similar charge properties, as is the same case for PAN-gr-PEIS membranes.

Fig. 5. Outer surface zeta potential of PAN, PAN-gr-PEI and PAN-gr-PEIS membranes at different pH.

3.1.4. Membrane surface hydrophilicity. The hydrophilicity of the membrane surface has significant impact on non-specific protein adsorptions and was usually characterized by static WCA measurements. WCA is one efficient method to determine the wettability properties of membrane and to investigate the interaction energy between the membrane surface and the solution.33 The WCA of membrane surface depends upon many factors including surface hydrophilicity, roughness, porosity, pore size and its distribution etc..34 The obtained values are presented in Fig. 6. The highest value (72˚) was obtained for the PAN membrane. The WCA value decreases distinctly after grafting PEI due to the introduction of a large amount of amine groups. There is a weak correlation of the WCA value with the O/N ratio determined by XPS. The PAN-gr-PEI membrane surface having higher nitrogen 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

content or lower O/N ratio exhibits lower WCA value and better hydrophilicity. Interestingly, after introduction of sulfonate groups, the WCA value increases. We ascribe this result to the more neutral surface for PAN-gr-PEIS leading to decreased electrostatic interaction with water molecules. The lowest WCA value (26 ˚) was obtained for membrane PAN-gr-PEI, which correlated with its lowest O/N ratio.

Fig. 6. The WCA values for the PAN, PAN-gr-PEI and PAN-gr-PEIS membranes.

3.2. Membrane permeability. The pure water flux (Jw) of PAN, PAN-gr-PEI and PAN-gr-PEIS membranes were tested for evaluation of the influence of membrane surface grafting on the membrane permeability. As shown in Table 3. It can be seen that both PEI grafting and covalent attachment of sulfonate groups cause flux decline. In addition, the Jw value gradually decreases with the PEI grafting time, which can be correlated with the grafting layer thickness demonstrated by the SEM. The Jw value for PAN membrane was found to be 550 L/m2 h, which is higher than all the other membranes. In spite of the highly “crosslinked” structure of hyperbranched polymers, hyperbranched grafting still brings about dramatic flux decline, which may be due to the high MW and high grafting density of PEI. The introduction of sulfonate group 20


Page 20 of 35

Page 21 of 35

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


appears to further promote the hydrogel swelling leading to even lower membrane flux. The rejection curves were obtained with plotting the values of rejection versus dextran molecular weight to evaluate the selectivity of membrane and the MWCO values were also shown in Table 3. The MWCO of the PAN membrane is100 kDa while those of the grafted membranes gradually decreased to 65-75 kDa with the grafting time. The rejection curves became steeper after grafting, indicating narrower pore size distribution upon grafting of hyperbranched polymers. The PAN-gr-PEIS4 and PAN-gr-PEIS5 membranes show MWCO values at 65-75 kDa, which is approaching the molecular weight of BSA (Mw = 66.2 kDa). Since Lys has a Mw of 14.4kDa, it is expected that the PAN-gr-PEIS membrane show marked steric hindrance to BSA but minimal sieving effect to Lys.

Fig. 7. Rejection curves of various membranes.

Table 3. The water flux and dextran MWCO of various membranes. Membranes

Jw(L/m2 h)

MWCO(kDa)

PAN PAN-gr-PEI3 PAN-gr-PEI4 PAN-gr-PEI5 PAN-gr-PEIS3 PAN-gr-PEIS4

549.4 465.8 406.1 310.5 274.7 215.0

100 90-100 80-90 80-90 80-90 65-75 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

PAN-gr-PEIS5

167.2

65-75

3.3. Protein ultrafiltration. It is well known that concentration polarization close to the membrane surface can be dramatically reduced by rigorous stirring during the UF process of protein solution.35 In the present work, all filtration experiments of protein solutions were performed at 600 rpm stirring speed and an applied transmembrane pressure of 0.1 MPa. Since the protein solution flux values (JBSA and JLys) at different solution pH values are shown in Fig. 8. Interestingly, in spite of the complicated architecture of the tethered hyperbranched polymers, the protein solution flux values are still highly dependent on the electrostatic interaction between protein and membrane surface, which corresponds well with the zeta potential results. In order to correlate the protein transport property with membrane and protein charge properties, the surface charge characteristics are marked in Fig. 5. When the charge property was marked as “0”, it means a nearly neutral surface having minimal charge. We see when the surface charge on membrane and protein are opposite or both protein and membrane are approaching their PI values (Lys / PAN-gr-PEI4 at pH = 10), the membrane tends to have low flux. When the membrane and protein are both negatively or positively charged, the membrane tends to have a high protein flux. We attribute the low flux phenomena to the rapid protein deposition on membrane surface forming a thick layer leading to severe membrane fouling. We used SEM to observe the membrane surface morphology after protein ultrafiltration. The corresponding SEM images are shown in Fig. 9. There is a good correlation between membrane flux and membrane surface morphology. The membranes showing low flux happen to have rougher surfaces. There appears to be a deposited protein layer on these membrane 22


Page 22 of 35

Page 23 of 35

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


surfaces, which confirms the occurrence of severe membrane fouling. It should be noted that the change in protein charge will also influence the diffusion coefficient of protein, which will in turn affect the mass transfer coefficient and the degree of concentration polarization.36 In this context, BSA should be more charged at pH of 10 corresponding to higher diffusion coefficient with slighter concentration polarization and higher flux as a result, which is the same case for Lys at pH of 4. Apparently, we can hardly see this tendency, presumable due to the diffusion effects overwhelmed by the electrostatic interactions between the proteins and the membrane. In addition, the zwitterions grafted membranes PAN-gr-PEIS were heavily fouled by Lys at pH of 7 and 10, which is different from the previous observation by Zydney et. al..37 They found that the zwitterionic membranes showed minimal protein adsorption over a broad range of conditions with various proteins, even at the condition that membrane and protein are oppositely charged. Since both studies investigated UF operations under very similar conditions, the different fouling behavior should be related to membrane structure. We attribute the fouling of PAN-gr-PEIS membrane to the stiffness of grafted hyperbranched zwitterions.38-39 Although zwitterions forms upon ring-opening of 1,4-sultone by the amine group, the sulfonate groups concentrated at membrane surface are more prone than ammonium groups to contact with the positively charged Lys. It appears that hyperbranched zwitterions do not show any advantage on fouling resistance over small molecular or linear polymeric ones, although their concentration may be higher. We note here that 1,4-butane sultone was used leading to zwitterionic side groups with larger spacer length (four carbons), 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

which may be less fouling resistant than that derivatized from 1,3-propane sultone (three carbons).40 But with the consideration of the zeta potential and filtration results in this work, we believe that the influence from the spacer length is minimal. The hyperbranched structure and the charge properties should account for the less than expected antifouling properties of the membranes.

Fig. 8. The (a) BSA and (b) Lys protein solution flux of PAN, PAN-gr-PEI4 and PAN-gr-PEIS4 membranes at different pH values. ( x / y : “ x ” is the charge of protein; “ y ” is the charge of membrane. “ + ” : positive charged; “ - ” : negative charged; “ 0 ” : uncharged )

Fig. 9. SEM images of the upper surface of (A, D) PAN, (B, E) PAN-gr-PEI4 and (C, F)PAN-gr-PEIS4 after filtration of 1 g/L BSA solution (A-C) or 1 g/L Lys solution (D-F) at different pH.

The observed transmission (τObs) values were calculated by Eq. (9) and were shown 24


Page 24 of 35

Page 25 of 35

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


in Fig.10. We see there is good correlation of membrane flux with protein transmission. The high flux membranes show low protein transmission, which is due to the electrostatic repulsive force between membrane and protein showing the same charge. On the contrary, when the protein and membrane were oppositely charged, the protein transmission was high. BSA shows net negative charge at pH = 7 and pH = 10 while Lys shows net positive charge at pH = 4 and pH = 7. Therefore, it is possible to obtain good selectivity at pH of 7 and 10 where BSA and Lys are oppositely charged using a charged membrane. As shown in Fig. 10, the results are the same as what we expected. The negatively charged PAN and PAN-gr-PEIS membranes show very different transmissions for BSA and Lys at both pH = 7 and pH = 10. At the same time, the transmission of BSA and Lys also differ for positively charged PAN-gr-PEI membrane at pH of 7. According to the MWCO results of the grafted membranes, the smaller pore size of the PAN-gr-PEIS4 membrane than the PAN-gr-PEI4 may also account for the significant drop of the transmission of BSA upon grafting of the zwitterions.

Fig. 10. Observed transmission (τObs) for: (a) BSA and (b) Lys (1 g/L each) through the membranes at varied pH and 0.1 MPa applied transmembrane pressure. ( x / y : “ x ” is the charge 25



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

of protein; “ y ” is the charge of membrane. “ + ” : positive charged; “ - ” : negative charged; “ 0 ” : uncharged )

The separation factor (SF) values were estimated by Eq. (10), shown in Fig.11. As expected, the charge properties of protein and membrane play a key role on protein separation performance. At pH = 7 and pH = 10, BSA and Lys are oppositely charged. High SF values are obtained for highly charged membranes, including PAN and PAN-gr-PEIS membranes. We can expect that high selectivity can be obtained for BSA and Lys at pH of 7 and 10 with positively charged membranes. But the PAN-gr-PEI membrane only showed low charge density at these pH values. Therefore, SF values of close to one were obtained for the PAN-gr-PEI membrane. Because the PAN membrane showed the highest charge density, the highest SF value 13.3 was obtained at pH of 7. As for the PAN-gr-PEIS membrane, switchable protein selectivity was obtained because the membrane surface charge can be reversed via pH adjustment due to its amphoteric charge property.14

Fig. 11. Ultrafiltration separation selectivity of PAN, PAN-gr-PEI4 and PAN-gr-PEIS4 membranes for Lys vs. BSA (1:1 mixture, 1 g/L) at different pH. ( L B / y : L is the charge of Lys, B is the 26


Page 26 of 35

Page 27 of 35

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


charge of BSA; y is the charge of membrane. “ + ” : positive charged; “ – ” : negative charged; “ 0 ” : uncharged )

3.4. UF performance regeneration. As discussed above, a thick layer could usually formed on the membranes surface due to the severe fouling after filtration process, resulting in decline of protein solution flux. To investigate the rinsing and regeneration properties of the membranes, the PAN-gr-PEIS4 was selected for long-term filtration because of its zwitterionc surface nature. As shown in Fig. 12 (a, b), the filtration flux of both proteins displayed gradual decrease during each cycle. However, after the washing process, the RFRi (%) values for both BSA and Lys reach above 90 % in different pH environments (Table 4), indicating robust protein filtration performance of the grafted membrane under routine rinsing conditions. The transmission behaviors of BSA and Lys through PAN-gr-PEIS4 at different pH environment were shown in Fig. 12 (a’, b’). Whether for BSA or Lys, the observed transmission was quite stable after three cycles, even with the different pH value, indicating good transmission stability of the membranes.

27



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 28 of 35

Fig. 12. Filtration flux (a, b) and observed transmission (a’, b’) of 1 g/L BSA solution or Lys solution through PAN-gr-PEIS4 at different pH in three cycles.

Table 4. The flux recovery values for BSA and Lys with different pH values. RFRi (i=1,2,3) (%) pH 4 7 10

BSA

Lys

1st

2nd

3rd

1st

2nd

3rd

93.3 94.7 91.6

98.0 98.9 98.5

98.4 97.9 97.4

95.4 94.9 91.3

98.1 99.0 98.3

98.5 99.0 98.9

3.5. Separation of BSA and Lys from a binary mixture model solution. The SDS-PAGE marker was shown in Fig.13. The band at 66.2 kDa was BSA and the band at 14.4 kDa was Lys in the SDS-PAGE patterns. The result corresponds well with the obtained SF values. For the PAN membrane, the permeate mixture at pH = 7 and pH = 10 displayed the thinnest band of BSA and thickest band of Lys respectively. For PAN-gr-PEI4 membrane, the permeate mixture at pH = 4 and pH = 7 revealed the thickest band of BSA and the thinnest band of Lys respectively. As for PAN-gr-PEIS4 28


Page 29 of 35

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


membrane, the thickest band of BSA and the thinnest band of Lys was found in the permeate mixture at pH = 4, while the opposite result was observed in the permeate mixture at pH = 10.

Fig. 13. SDS-PAGE pattern of the permeate mixture of PAN, PAN-gr-PEI4 and PAN-gr-PEIS4 membranes at different pH.

4. CONCLUSIONS A series of charge-modified PAN membranes with different surface charge properties were obtained successfully via firstly grafting with PEI and subsequent ring-opening reaction with sultone. The protein transmission properties of the charge-modified membranes grafted with hyperbranched polycations and hyperbranched zwitterions were investigated. Although the hyperbranched molecules are rigid and “crosslinked”, hyperbranched grafting still leads to dramatic flux decline, with hyperbranched zwitterions showing higher swelling and more severe flux drop. In spite of the complicated structure of hyperbranched molecules, the protein transmission properties are still highly dependent on surface charge properties. The zeta potential measurement can be a powerfully tool predicting the membrane performance for protein separation. When the protein and membrane are oppositely charged, the 29



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

membrane shows low flux and high protein transmission and vice versa. The low flux of the membrane was attributed to membrane fouling. The zwitterionic PAN-gr-PEIS membrane was also severely fouled when the membrane and protein surface was oppositely charged, which is different from previous observation. We attribute this result to the rigid structure of hyperbranched PEIS molecules. High protein selectivity can be obtained with highly charged membranes, either positively or negatively charged, by adjusting solution pH so that the proteins are oppositely charged.

AUTHOR INFORMATION

Corresponding Author *Tel.: 86-22-83955386. Fax: 86-22-83955055. E-mail: [email protected]. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS

We gratefully acknowledge support from the National Natural Science Foundation of China (Grant No. 21574100), the National Basic Research Program of China (2014CB660813), the National Natural Science Foundation of China (Grant No. 21274108) and the Program for Chang-jiang Scholars and Innovative Research Team in University of Ministry of Education of China (Grant No. IRT13084). Prof MJQ thanks Mr Yao Wang and Prof. Zhi Wang for zeta potential measurements.

REFERENCES

(1) Kumar, M.; Ulbricht, M. Low fouling negatively charged hybrid ultrafiltration membranes for protein separation from sulfonated poly(arylene ether sulfone) block copolymer and functionalized multiwalled carbon nanotubes. Sep. Purif. Tech. 2014, 127, 181-191. (2) Li, Q.; Bi, Q. Y.; Lin, H. H.; Bian, L. X.; Wang, X. L. A novel ultrafiltration (UF) membrane with 30


Page 30 of 35

Page 31 of 35

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


controllable selectivity for protein separation. J. Membr. Sci. 2013, 427, 155-167. (3) Orr, V.; Zhong, L.; Moo-Young, M.; Chou, C. P. Recent advances in bioprocessing application of membrane chromatography. Biotechnol. Adv. 2013, 31, 450-465. (4) Sarvi, M. N.; Bee, T. B.; Gooi, C. K.; Woonton, B. W.; Gee, M. L.; O’Connor, A. J. Development of functionalized mesoporous silica for adsorption and separation of dairy proteins. Chem. Eng. J. 2014, 235, 244-251. (5) Barbosa, E. F.; Silva, L. P. Nanoscale characterization of synthetic polymeric porous membranes: Scrutinizing their stiffness, roughness, and chemical composition. J. Membr. Sci. 2012, 407–408, 128-135. (6) Wu, Q.-Y.; Wan, L.-S.; Xu, Z.-K. Structure and performance of polyacrylonitrile membranes prepared via thermally induced phase separation. J. Membr. Sci. 2012, 409–410, 355-364. (7) Peeva, P. D.; Million, N.; Ulbricht, M. Factors affecting the sieving behavior of anti-fouling thin-layer cross-linked hydrogel polyethersulfone composite ultrafiltration membranes. J. Membr. Sci. 2012, 390, 99-112. (8) Susanto, H.; Stahra, N.; Ulbricht, M. High performance polyethersulfone microfiltration membranes having high flux and stable hydrophilic property. J. Membr. Sci. 2009, 342, 153-164. (9) Zhang, M.; Zhang, L.; Cheng, L.-H.; Xu, K.; Xu, Q.-P.; Chen, H.-L.; Lai, J.-Y.; Tung, K.-L. Extracorporeal endotoxin removal by novel l-serine grafted PVDF membrane modules. J. Membr. Sci. 2012, 405, 104-112. (10) Tomicki, F.; Krix, D.; Nienhaus, H.; Ulbricht, M. Stimuli–responsive track-etched membranes via surface-initiated controlled radical polymerization: Influence of grafting density and pore size. J. Membr. Sci. 2011, 377, 124-133. (11) Burns, D. B.; Zydney, A. L. Contributions to electrostatic interactions on protein transport in membrane systems. AIChE J. 2001, 47, 1101-1114. (12) Pujar, N. S.; Zydney, A. L. Electrostatic and Electrokinetic Interactions during Protein Transport through Narrow Pore Membranes. Ind. Eng. Chem. Res. 1994, 33, 2473-2482. (13) Burns, D. B.; Zydney, A. L. Effect of solution pH on protein transport through ultrafiltration membranes. Biotechnol. Bioeng. 1999, 64, 27-37. (14) Saksena, S.; Zydney, A. L. Effect of solution pH and ionic strength on the separation of albumin from immunoglobulins (IgG) by selective filtration. Biotechnol. Bioeng. 1994, 43, 960-968. 31



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

(15) van Eijndhoven, R. H.; Saksena, S.; Zydney, A. L. Protein fractionation using electrostatic interactions in membranel filtration. Biotechnol. Bioeng. 1995, 48, 406-414. (16) van Reis, R.; Gadam, S.; Frautschy, L. N.; Orlando, S.; Goodrich, E. M.; Saksena, S.; Kuriyel, R.; Simpson, C. M.; Pearl, S.; Zydney, A. L. High performance tangential flow filtration. Biotechnol. Bioeng. 1997, 56, 71-82. (17) Zhao, Y.-H.; Wee, K.-H.; Bai, R. A Novel Electrolyte-Responsive Membrane with Tunable Permeation Selectivity for Protein Purification. ACS Appl. Mater. Interfaces 2010, 2, 203-211. (18) Rohani, M. M.; Zydney, A. L. Protein transport through zwitterionic ultrafiltration membranes. J. Membr. Sci. 2012, 397, 1-8. (19) Wang, M.-L.; Jiang, T.-T.; Lu, Y.; Liu, H.-J.; Chen, Y. Gold nanoparticles immobilized in hyperbranched polyethylenimine modified polyacrylonitrile fiber as highly efficient and recyclable heterogeneous catalysts for the reduction of 4-nitrophenol. J. Mater. Chem. A 2013, 1, 5923-5933. (20) Haq, S.; Srivastava, R. Measuring the influence of materials composition on nano scale roughness for wood plastic composites by AFM. Measurement 2016, 91, 541-547. (21) Kumar, M.; McGlade, D.; Lawler, J. Functionalized chitosan derived novel positively charged organic–inorganic hybrid ultrafiltration membranes for protein separation. RSC Adv. 2014, 4, 21699-21711. (22) Zhao, H. Y.; Wu, L. G.; Zhou, Z. J.; Zhang, L.; Chen, H. L. Improving the antifouling property of polysulfone ultrafiltration membrane by incorporation of isocyanate-treated graphene oxide. Phys. Chem. Chem. Phys. 2013, 15, 9084-9092. (23) Eren, E.; Sarihan, A.; Eren, B.; Gumus, H.; Kocak, F. O. Preparation, characterization and performance enhancement of polysulfone ultrafiltration membrane using PBI as hydrophilic modifier. J. Membr. Sci. 2015, 475, 1-8. (24) Kumar, M.; Ulbricht, M. Novel antifouling positively charged hybrid ultrafiltration membranes for protein separation based on blends of carboxylated carbon nanotubes and aminated poly (arylene ether sulfone). J. Membr. Sci. 2013, 448, 62-73. (25) Ghosh, R.; Cui, Z. Fractionation of BSA and lysozyme using ultrafiltration: effect of pH and membrane pretreatment. J. Membr. Sci. 1998, 139, 17-28. (26) Xing, L.; Wu, W.; Zhou, B.; Lin, Z. Streamlined protein expression and purification using 32


Page 32 of 35

Page 33 of 35

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


cleavable self-aggregating tags. Microb. Cell Fact. 2011, 10, 42. (27) Meng, J.; Cao, J.; Xu, R.; Wang, Z.; Sun, R. Hyperbranched grafting enabling simultaneous enhancement of the boric acid uptake and the adsorption rate of a complexing membrane. J. Mater. Chem. A 2016, 4, 11656-11665. (28) Huisman, I. H.; Vellenga, E.; Trägårdh, G.; Trägårdh, C. The influence of the membrane zeta potential on the critical flux for crossflow microfiltration of particle suspensions. J. Membr. Sci. 1999, 156, 153-158. (29) Kim, K.; Fane, A.; Nystrom, M.; Pihlajamaki, A.; Bowen, W.; Mukhtar, H. Evaluation of electroosmosis and streaming potential for measurement of electric charges of polymeric membranes. J. Membr. Sci. 1996, 116, 149-159. (30) Wilbert, M. C.; Delagah, S.; Pellegrino, J. Variance of streaming potential measurements. J. Membr. Sci. 1999, 161, 247-261. (31) Jimbo, T.; Tanioka, A.; Minoura, N. Pore-surface characterization of poly(acrylonitrile) membrane having amphoteric charge groups by means of zeta potential measurement. Colloids Surf. A 1999, 159, 459-466. (32) Jimbo, T.; Tanioka, A.; Minoura, N. Characterization of an Amphoteric-Charged Layer Grafted to the Pore Surface of a Porous Membrane. Langmuir 1998, 14, 7112-7118. (33) Nabe, A.; Staude, E.; Belfort, G. Surface modification of polysulfone ultrafiltration membranes and fouling by BSA solutions. J. Membr. Sci. 1997, 133, 57-72. (34) Rana, D.; Matsuura, T. Surface modifications for antifouling membranes. Chem. Rev. 2010, 110, 2448-2471. (35) Wang, T.; Wang, Y.-Q.; Su, Y.-L.; Jiang, Z.-Y. Antifouling ultrafiltration membrane composed of polyethersulfone and sulfobetaine copolymer. J. Membr. Sci. 2006, 280, 343-350. (36) Gaigalas, A. K.; Hubbard, J. B.; McCurley, M.; Woo, S. Diffusion of bovine serum albumin in aqueous solutions. The Journal of Physical Chemistry 1992, 96, 2355-2359. (37) Hadidi, M.; Zydney, A. L. Fouling behavior of zwitterionic membranes: Impact of electrostatic and hydrophobic interactions. J. Membr. Sci. 2014, 452, 97-103. (38) Gao, C.; Yan, D. Hyperbranched polymers: from synthesis to applications. Prog. Polym. Sci. 2004, 29, 183-275. (39) Connolly, R.; Bellesia, G.; Timoshenko, E. G.; Kuznetsov, Y. A.; Elli, S.; Ganazzoli, F. "Intrinsic" 33



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

and "topological" stiffness in branched polymers. Macromolecules 2005, 38, 5288-5299. (40) Shao, Q.; Jiang, S. Effect of Carbon Spacer Length on Zwitterionic Carboxybetaines. J. Phys. Chem. B 2013, 117, 1357-1366.

34


Page 34 of 35

Page 35 of 35

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


Table of Contents Protein

transport

properties

of

PAN

membranes

grafted

hyperbranched polyelectrolytes and hyperbranched zwitterions

35


with

Protein Transport Properties of PAN Membranes ... - ACS Publications

Recommend Documents