Studies on cellulose acetate and sulfonated poly(ether ether ketone) blend ultrafiltration membranes

European Polymer Journal 40 (2004) 751–762

www.elsevier.com/locate/europolj

Studies on cellulose acetate and sulfonatedpoly(ether ether ketone) blend ultrafiltration membranes

G. Arthanareeswaran, K. Srinivasan, R. Mahendran, D. Mohan *,M. Rajendran, V. Mohan

Membrane Laboratory, Department of Chemical Engineering, A.C. College of Technology, Anna University, Chennai 600 025, India

Received 10 September 2003; received in revised form 26 November 2003; accepted 28 November 2003

Abstract

New ultrafiltration membranes based on chemically and thermally stable arylene main-chain polymers have been

prepared by blending the sulfonated poly(ether ether ketone) with cellulose acetate in various compositions in N,N0-

dimethylformamide as solvent by phase inversion technique. Prepared membranes have been subjected to ultrafiltration

characterizations such as compaction, pure water flux, water content, and membrane hydraulic resistance. The pore

statistics and molecular weight cut-off (MWCO) of the membranes have been estimated using proteins such as trypsin,

pepsin, egg albumin and bovine serum albumin. The pore size increased with increasing concentrations of sulfonated

poly(ether ether ketone) in the casting solution. Similarly, the MWCOs of the membranes ranged from 20 to 69 kDa,

depending on the various polymer compositions. Surface and cross-sectional morphologies of membranes were ana-

lyzed using scanning electron microscopy. The effects of polymer compositions on the above parameters were analyzed

and the results are compared and discussed with those of pure cellulose acetate membranes.

� 2003 Elsevier Ltd. All rights reserved.

Keywords: Poly(ether ether ketone); Sulfonation; Blend membranes; Ultrafiltration; Protein rejection

1. Introduction

Cellulose acetate (CA) was one of the first membrane

polymers that has been used for aqueous based separa-

tions and used as both reverse osmosis (RO) and

ultrafiltration (UF) membranes [1]. The requirement of

more aggressive cleaning and sanitizing agents and more

chemical and mechanical resistant membranes, led to the

necessity of modifying cellulose acetate based mem-

branes [2]. The hydrophilic/hydrophobic balance as well

as the physico-chemical properties of a membrane can

easily be changed if the membrane is prepared from

multicomponent polymer mixture/blends [3]. Cellulose

acetate has been blended with polyurethane in different

* Corresponding author. Tel.: +91-4422203530; fax: 91-44-

2350240/2642.

E-mail address: [email protected] (D. Mohan).

0014-3057/$ - see front matter � 2003 Elsevier Ltd. All rights reserv

doi:10.1016/j.eurpolymj.2003.11.023

compositions, using N,N0-dimethyl formamide (DMF)

to yield membranes applied for the rejection of proteins

and metal ions [4]. Further, CA has been found to be

successful blend component with polysulfone (PS), sul-

fonated polysulfone (SPS), and epoxy resin (DGEBA) in

preparing ultrafiltration membranes [5–7]. Similarly,

poly (ether ether ketone) (PEEK) is being used as a

successful blend material in sulfonated form due to its

superior qualities.

PEEK is a highly crystalline polymer (Tg ¼ 143 �C)having very good thermal, chemical and mechanical

stability. Due to the strong intermolecular interaction

among the polymeric chains, they are practically insol-

uble in most of the solvents. As a consequence, PEEKs

are not easily modified through the common reactions of

organic chemistry and they are not able to form mem-

branes by phase inversion process [8].

However their hydrophilicity and permeability may

be increased by sulfonation [9]. Generally, sulfuric acid

ed.

mail to: [email protected]

752 G. Arthanareeswaran et al. / European Polymer Journal 40 (2004) 751–762

is used for sulfonation since it avoids degradation and

cross-linking reactions [8]. The synthesized hydrophilic

polymer is able to form a membrane with cellulose

acetate by the phase inversion process and optimum

membrane performance can be achieved in terms of

better flux and solute rejection. Further, separation of

proteins is found to be advantageous due to the non-

destructive nature and limited denaturation of proteins

[10]. As the sulfonated PEEK (SPEEK) is hydrophilic in

nature, the blending of SPEEK with CA would sub-

stantially reduce the fouling behavior of the resulting

membranes. Earlier studies have shown that the increase

in hydrophilicity will reduce the fouling behavior and

increase the flux [11,12].

Pore statistics, molecular weight cut-off (MWCO)

and morphological studies are the structural properties

of membranes that are essential for the applications of

membrane processes for the desired permeate quality

[13]. It has been found that a broad variety of mor-

phologically different polymeric membranes can be

prepared by changing the parameters such as composi-

tion, concentrations of polymer, solvent and additive in

the casting solutions [14,15]. The determination of

morphological characteristics is playing an important

role in evaluating the performance of the membranes.

The membrane usually consists of cylindrical pores

perpendicular to the membrane surface, whose sizes are

represented by pore size distribution. Only solute mo-

lecules smaller than membrane pore diameters are al-

lowed to transport through the membrane [16]. Most of

the commercially available membranes are specified by

the pore size or molecular weight cut-off (MWCO) value

[17], and has been found to be an important parameter,

which affects the separation characteristics of the ultra-

filtration membranes [18]. Hence, in the present inves-

tigation, CA is blended with SPEEK in polar medium

and the membrane compaction, pure water flux, water

content, membrane resistance (Rm) and protein rejection

have been determined. Solute rejection method and

scanning electron microscopy (SEM) have been used for

determining pore statistics, MWCO and morphology

and results are discussed.

2. Materials and methods

2.1. Materials

Cellulose acetate (CA) was procured from Mysore

Acetate & Chemical Co. Ltd., India; PEEK polymer was

procured from Victrex Inc. Ltd. Sulfuric acid (97–99%),

DMF and sodium lauryl sulfate (SLS) were obtained

from Qualigens Fine Chemicals, Glaxo India Ltd.,

India, which were of analytical grade. DMF was sieved

through molecular sieves (Type-4 A�) to remove mois-

ture and stored in dried conditions prior to use. Acetone

(AR) procured from Sisco Research Laboratories Pvt.

Ltd., India. Sodium monobasic-phosphate anhydrous

and sodium dibasicphosphate heptahydrate were pro-

cured from CDH Chemicals Ltd., India and used for the

preparation of phosphate buffer solutions in protein

analysis. Proteins viz., bovine serum albumin (BSA),

Mw ¼ 69 kDa, pepsin, Mw ¼ 35 kDa, and trypsin,

Mw ¼ 20 kDa were purchased from SRL Chemicals

Ltd., India. Egg albumin (EA), Mw ¼ 45 kDa was ob-

tained from Council of Scientific and Industrial Re-

search (CSIR), Bio-Chemical Center, New Delhi, India.

Deionized and distilled water was employed for the

washing of SPEEK polymers, preparation of protein

solutions and also used for the preparation of gelation

bath.

2.2. Preparation of SPEEK polymer

2.2.1. Sulfonation of PEEK

Twenty-five grams of PEEK powder was carefully

added to the 500 ml of concentrated sulfuric acid (98%).

The reaction mixture was magnetically stirred for 5 h at

50 �C. The mixture was then added to a large excess of

crushed ice where precipitation occurred. The precipi-

tated SPEEK was recovered and washed with deionized

water many times to remove the excess acid. Finally the

polymer was dried around 70 �C, and stored in a deci-

cator [8]. The ion exchange capacity (IEC) of prepared

SPEEK polymer was measured by the Fisher’s back

titration method [19] at room temperature. 1–2 g of

SPEEK was kept in 0.1 N aqueous NaOH for 24 h. The

solution was then back titrated with 0.1 N HCl using

phenolphthalein indicator. The IEC is expressed as meq.

of sulfonic groups/g of dry polymer.

2.2.2. Thermo gravimetric analysis (TGA)

The TGA was carried out using a STA 409PC ther-

mal analysis instrument. A sample of 27.4 mg of SPEEK

was dried at 200 �C to remove moisture for 30 min, and

then programmed from 20 to 900 �C at a rate of 10 �C/min under the nitrogen atmosphere.

2.2.3. Differential scanning calorimetry (DSC)

DSC measurement of PEEK and its sulfonated form

was carried out using a DSC 200PC differential scanning

calorimeter at a heating rate of 10 �C/min under nitro-

gen atmosphere. The weight of sample taken for PEEK

and SPEEK were 2.3 and 2.6 mg respectively. The glass

transition temperature Tg, was calculated at the inter-

section of the tangents to the corresponding DSC curve.

2.2.4. 1H-NMR

The 1H-NMR spectra were recorded on a JEOL

(Model GSX 400) spectrometer at a resonance fre-

quency of 399.65 MHz. For analysis, 2–5 wt.% of

SPEEK solution was prepared in DMSO-d6 solvent.

G. Arthanareeswaran et al. / European Polymer Journal 40 (2004) 751–762 753

NMR data were acquired for 32 scans at a temperature

of 23 �C. The degree of sulfonation was determined by

integration of distinct aromatic signals [20].

2.3. Preparation and characterization of polymers

The casting solution was prepared by blending CA

and SPEEK at different compositions as shown in Table

1 in the presence of DMF solvent under constant

mechanical stirring in a three necked round bottom flask

at 40–45 �C. The blend polymer compositions were

formulated on the basis of preliminary membrane

studies. The conditions maintained in casting and gela-

tion of the polymeric films are given in Table 2. The

homogeneous solution obtained was allowed to stand

for 1/2 h in order to eliminate the air bubbles. The

casting environment, viz. relative humidity and tem-

perature were standardized for the preparation of

membranes with better physical properties such as

homogeneity, thickness and smoothness. Prior to cast-

ing, a gelation bath of 2 l consists of 2.5% (v/v) DMF

and 0.2 wt.% SLS, in distilled water (non-solvent), was

prepared and kept at 20 �C [5]. Similar casting and

gelation conditions were maintained for the blend sys-

tems and for pure CA, since the thermodynamic con-

ditions would largely affect the performance of resulting

membranes [21]. The membranes were prepared by

casting using doctor blade on the glass plate and

maintaining the desired thickness by adjusting the height

of the doctor blade and fixing an oil sheet paper at both

ends of the doctor blade. After casting, the solvent

Table 1

Membrane formulations

Membrane no. Polymer (wt.%) CA (wt.%)

1 17.5 100

2 17.5 95

3 17.5 90

4 17.5 85

5 17.5 80

6 17.5 75

7 17.5 70

8 17.5 65

Table 2

Film casting conditions

Conditions

Temperature of casting solutions (�C)Temperature of casting atmosphere (�C)Humidity of casting atmosphere (�C)Period of casting (s)

Solvent evaporation time (s)

Temperature of gelation bath (�C)Period of leaching membranes in gelation bath (h)

Thickness of film on glass plate (mm)

present in the cast film was allowed to evaporate for

30± 5 s, and the cast film along with glass plate was

gently immersed into the gelation bath. The membranes

were removed from the gelation bath and washed

thoroughly with distilled water to remove all DMF and

surfactant from membranes. The thickness of prepared

membranes was measured using a micrometer (Mityu-

toyo, Japan) at various parts of the membranes. The

thickness of the membrane was maintained at 0.22 ±

0.02 mm as followed in earlier studies [4,22]. The

membranes were subsequently stored in 0.1% of for-

malin solution to prevent microbial growth.

The UF experiments were carried out in a batch type,

dead end cell (UF cell-S76-400-Model, Spectrum, USA)

with a diameter of 76 mm, fitted with a Teflon coated

magnetic paddle.

2.3.1. Compaction

The prepared membranes were cut into desired size

needed for fixing it up in the ultrafiltration kit of

38.5 cm2 area and initially pressurized with distilled

water at 414 kPa for 6 h. The water flux was measured at

every one hour. The flux generally declines initially and

attained steady state after 4–5 h of compaction. The pre-

pressurized membranes were used in subsequent ultra-

filtration experiments at 345 kPa [1].

2.3.2. Pure water flux

Membranes after compaction were subjected to pure

water flux at transmembrane pressure of 345 kPa. The

SPEEK (wt.%) Solvent (wt.%)

0 82.5

5 82.5

10 82.5

15 82.5

20 82.5

25 82.5

30 82.5

35 82.5

Range

28± 2

24± 1

55± 2

3–6

30± 5

12± 2

1–3

0.22± 0.02


flux was measured under steady state flow i.e., after

every 1 h for 4 h. The pure water flux was determined

using an Eq. (1).

Jw ¼ QA � DT ð1Þ

where, Jw is the water flux (lm�2 h�1), Q is the quantity

of permeate (l), A is the membrane area (m2) and DT is

the sampling time (h).

2.3.3. Water content

Water content of the membranes was measured as

follows [23]. The membranes were soaked in water for

24 h and weighed after mopping with blotting paper.

These wet membranes were placed in a drier at 80–100

�C for 48 h and the dry weights were determined. From

the two values the percent water content was derived by

Eq. (2).

%Water content ¼ Ww � Wd � 100

Ww

ð2Þ

where Ww is the wet sample weight and Wd is the dry

sample weight.

2.3.4. Membrane hydraulic resistance (Rm)

Membrane hydraulic resistance is an important

parameter, which decides the productivity of the mem-

branes at a given pressure [24]. This would be of more

useful to apply the membrane for a particular environ-

ment and to identify the suitability of the membranes

for a particular membrane process. Membrane hydrau-

lic resistance (Rm), was evaluated by measuring pure

water flux at different transmembrane pressures such

as 69, 138, 207, 276 and 345 kPa after compaction.

The resistance of the membrane was evaluated from

the slope obtained by plotting the transmembrane

pressure difference (DP ) vs. water flux (Jw) using the

Eq. (3).

Rm ¼ DPJw

ð3Þ

2.3.5. Molecular weight cut-off (MWCO)

Molecular weight cut-off of the membrane was

determined by identifying an inert solute, which has the

lowest molecular weight and has solute rejection of 80–

100%, in steady state UF experiments [25]. Thus, the

proteins of different molecular weights such as, bovine

serum albumin (69 kDa), egg albumin (45 kDa), pepsin

(35 kDa) and trypsin (20 kDa) were taken for rejection

studies for the membranes with 100/0%, 90/10%, 80/

20%, 70/30%, 65/35% of CA/SPEEK compositions. The

permeate concentrations were analyzed using UV–visi-

ble spectrophotometer (Shimadzu, Model UV-160A), at

kmax ¼ 280 nm.

2.4. Application studies

2.4.1. Protein rejection

After mounting the membrane in the UF cell, the

chamber was filled with individual protein solution and

immediately pressurized under nitrogen atmosphere to

the desired level (345 kPa) and maintained constant

throughout the run. Proteins such as BSA, EA, pepsin

and trypsin were dissolved (0.1 wt.%) in phosphate

buffer (0.5 M, pH 7.2) and used as standard feed solu-

tions. For all experiments, the concentration of feed

solution was kept constant. Permeate was collected over

measured time intervals in graduated tubes and the tube

contents were analyzed for protein content by UV–

visible spectrophotometer (Shimadzu, Model UV-160A)

at kmax 280.0 nm. The percent protein separation was

calculated from the concentration of feed and permeates

[25] using Eq. (4)

%SR ¼ 1� Cp

Cf

� �� 100 ð4Þ

where Cp and Cf are concentrations of permeate and

feed, respectively.

Upon, completion of run, the ultrafiltration cell was

emptied, the membrane was removed and washed gently

with pure water to remove adherent protein solution,

and then re-inserted in the clean cell for re-measurement

of its pure water flux.

2.5. Morphological studies

Scanning electron microscopy (SEM) (LEICA Ste-

reoscan, Cambridge, UK) analyzed the morphology of

the blend membranes with different compositions. The

membranes were cut into pieces of various sizes and

mopped with filter paper. These pieces were immersed in

liquid nitrogen for 20–30 s and were frozen. Frozen bits

of the membranes were broken and kept in a desiccator.

These membrane samples were used for SEM studies

[26]. Various SEM images were taken for top surface

and cross-sectional views of the membranes of 100%,

95%, 85%, 75% and 65% of CA.

3. Results and discussion

3.1. Sulfonation of PEEK

The introduction of –SO3H groups per repeating unit

in the PEEK chain leads to a large modification of its

solubility. The physical and chemical properties of

SPEEK depend on the concentration of –SO3H group

and the nature of counter ions. Sulfonation modifies the

chemical character of PEEK, reduces the crystallinity

and consequently affects solubility.


The thermal stability of sulfonated and pure PEEK

was investigated by TGA. The experiment was run from

20 to 900 �C at a heating rate of 10 �C/min under

nitrogen atmosphere. The TGA and DTG curves of

PEEK and SPEEK are shown in Fig. 1. It is seen that

three-weight loss steps are observed for SPEEK, which

is reflected by three broad peaks in the DTG curve in

three separate temperature ranges. The second weight

loss peak in SPEEK is believed to be due to splitting-off

sulfuric acid groups. A similar observation was also

made for sulfonated polysulfone [27]. The maximum of

third peak for SPEEK sample shifted to 530 from 600 �Cfor PEEK [20]. The sulfonic acid decomposition was

found to be at 355 �C in the TGA/DTG for the sulfo-

nated sample.

From the DSC analysis of PEEK and SPEEK are

reported Fig. 2 it is easy to indicate that the introduction

of –SO3H groups into PEEK significantly decreases its

Fig. 1. TGA curve of (a) PE

thermal stability, probably due to acid-catalyzed deg-

radation. It is found that the onset weight loss temper-

ature of SPEEK strongly decreases as the degree of

sulfonation is increased. Similar behavior has been ob-

served for sulfonated polysulfone [27–29].

3.1.1. Determination of degree of sulfonation

From Fisher’s back titration method [19], the ion-

exchange capacity of SPEEK polymer measured at

room temperature. The degree of sulfonation was

determined quantitatively by H1-NMR spectra using the

method described in [20] for SPEEK polymers. Fig. 3

shows that the presence of sulfonic acid groups causes a

significant 0.25 ppm down-field shift of the hydrogen HE

compared with HC, HD in the hydroquinone ring. The

nomenclatures of the aromatic protons for the SPEEK

repeat unit is given in Fig. 4. The presence of each

–SO3H group results in a distinct signal for the protons

EK and (b) SPEEK.

Fig. 2. DSC thermogram of (a) PEEK and (b) SPEEK.


at the E position. The intensity of this HE signal yields

the estimation of HE content which is equivalent to the

–SO3H group content [20]. The 1H-NMR signal for the

–SO3H group is less easily recordable directly because

this proton is labile. The ratio between the peak area of

the distinct HE signal, (AHE) and the integrated peak

area of the signals corresponding to all the other aro-

matic hydrogens (AHA;A0 ;B;B0 ;C;D), is expressed as

nð12� 2nÞ ¼

AHEPAHA;A0 ;B;B0 ;C;D

ð06 n6 1Þ ð5Þ

where n is the number of HE per repeat unit. An estimate

of the degree of sulfonation is obtained as n� 100%.

3.2. Characterization of the blend membranes

The blend membranes were found to be compatible

up to a composition of 65/35% of CA/SPEEK in DMF.

These membranes were subjected to the characterization

and solute rejection studies and the results have been

discussed with respect to the effect of polymer blend

composition.

3.2.1. Membrane compaction

At constant operating pressure (414 kPa), the pure

water flux of CA/SPEEK blend membranes upon com-

paction was measured for every one hour. During

compaction, the water flux was found to be high initially

and declines gradually and reaches a steady state after 4

h of compaction, for all membranes as shown in Fig. 5.

This initial decline in flux may be due to the fact that the

membrane pores are being compacted leading to uni-

form pore size and steady state water flux.

3.2.2. Pure water flux

Membranes after compaction were subjected to a

pressure of 345 kPa for the measurement of pure water

flux. The flux was measured under steady state flow [30].

Fig. 4. Nomenclature of the aromatic protons for the SPEEK.

Fig. 3. 1H-NMR spectrum of SPEEK.

0

50

100

150

200

250

300

0 1 2 3 4 5 6 7Time, h

Pure

wat

erflu

x,lm

-2h-1

SPEEK (0%) SPEEK (5%)SPEEK (10%) SPEEK (15%)SPEEK (20%) SPEEK (25%)SPEEK (30%) SPEEK (35%)

Fig. 5. Effect of compaction time on pure water flux of CA/SPEEK blend membranes.


88

90

92

94

cont

ent,

%


The values of pure water flux are presented in the Fig. 5.

The value shows that in the blend membranes, as the

concentration of the SPEEK increases from 5% to 35%

in the increment of 5%, the water flux also increases

from 34.28 to 157.91 lm�2 h�1. This linear trend due to

the increase in SPEEK content in the blend may be due

to the hydrophilic nature of the –SO3H group present in

the membrane.

80

82

84

86

60 65 70 75 80 85 90 95 100Composition of CA, %

Wat

er

Fig. 6. Effect of water content on composition of CA in CA/

SPEEK membranes.

3.2.3. Water content

Water content is considered to be an important

parameter for membrane characterization, since the

pure water flux of the membrane can be predicted

qualitatively based on these results. Variation in the

concentration of SPEEK from 5 to 35 wt.% in the blend

membranes resulted in an increase in the water content

of the membranes from 84.9% to 93% as shown in Fig.

6. This increase in percent water content may be due to

the hydrophilic nature of the membranes due to the

presence of –SO3H group of SPEEK, as compared with

pure cellulose acetate membrane.

3.2.4. Membrane hydraulic resistance (Rm)

Resistance of the membrane was calculated from the

slope of the plot of transmembrane pressure vs. water

flux as shown in Fig. 7. The effects of concentration of

SPEEK on Rm values are given Table 3. From the values

it is obvious that as the concentration of the SPEEK in

the blend system is increased, the membrane resistance

decreased. This may be due to the fact that and increase

in SPEEK content in blend increases the void volume

0

20

40

60

80

100

120

140

160

180

0 100 200Transmembra

Pure

wat

erflu

x,lm

-2h-1

100/0 % 95/5%

90/10 % 85/15 %

80/20 % 75/25 %

70/30 % 65/35 %

Fig. 7. Effect of transmembrane pressure on pure

due to large segregated distances between polymer

chains. Further, the values are inversely proportional to

the water flux of the respective membranes.

3.2.5. Molecular weight cut-off

Based on the rejection values of the globular proteins

and the procedure followed by Sarbolouki [25], the

MWCO of the CA/SPEEK membranes has been deter-

mined and is reported in Table 3. It is seen that pure CA

membrane (100/0%), has the lowest MWCO value of 20

kDa, as the membrane has yielded 82% rejection for

300 400 500ne pressure,kPa

water flux of CA/SPEEK blend membranes.

130

180

230

280

Perm

eate

flux,

lm-2

h-1

TrypsinPepsinEgg albuminBSA

Table 3

Characteristics of CA/SPEEK blend membranes

Polymer blend composition (17.5 wt.%) Pure water flux

(lm�2 h�1) 345 kPa

Water content (wt%) Rm (kPa/lm�2 h�1) MWCO (kDa)

CA % SPEEK %

100 0 20.78 81.98 18.762 20

95 5 34.28 84.89 10.846 –

90 10 70.65 86.78 5.479 35

85 15 101.81 88.95 4.045 –

80 20 114.28 89.70 3.498 45

75 25 128.32 90.88 3.160 –

70 30 139.21 91.97 2.907 69

65 35 157.91 93.00 2.567 >69


trypsin (20 kDa). The MWCO value has increased upon

an increase of SPEEK content in the blend and thus, at

35% SPEEK content, the MWCO was found to be >69

kDa. This increase in MWCO value may be due to

formation of a segmental gap, due to the partial phase

separation upon proportionately increasing the concen-

tration of SPEEK in the blend. Similar results have been

observed for CA and epoxy resin blend membranes,

with various blend compositions and found successful in

protein rejection applications [7].

30

80

60 65 70 75 80 85 90 95 100Composition of CA, %

Fig. 8. Effect of permeate flux of protein solutions on various

compositions of CA in CA/SPEEK membranes.

0

20

40

60

80

100

60 70 80 90 100Composition of CA, wt %

Rej

ectio

n, %

TrypsinPepsinEgg albuminBSA

Fig. 9. Effect of percentage rejection of proteins on various

compositions of CA in CA/SPEEK membranes.

3.3. Protein rejection studies

The rejection of proteins viz., BSA, EA, pepsin and

trypsin has been carried out using CA/SPEEK (100/0%,

90/10%, 80/20%, 70/30% and 65/35%) membranes. The

pH of the feed solution was kept constant at 7.2, since,

the change in pH may increase the adsorptive fouling of

the membrane [31]. Further, intermolecular forces be-

tween protein molecules and membranes will predomi-

nate and affect the efficiency of membranes if pH of the

solution changes [32].

The permeate flux of proteins such as BSA, EA,

pepsin and trypsin by 100/0%, 90/10%, 80/20%, 70/30%

and 65/35% CA/SPEEK blend membranes are shown in

Fig. 8. From the figure, it is obvious that when the

SPEEK content in the blend is increased, the flux of the

all the proteins is also increased. This is because mem-

branes with SPEEK can absorb more water on feed side

of the membrane, the transport driving force of water is,

thus, increased. Thus trypsin has shown higher flux of

297.52 lm�2 s�1 at 65/35 of CA/SPEEK compared to

other proteins in view of its low molecular weight and

smaller solute radius.

When pure CA membrane (100%) was subjected to

separation of proteins, it exhibited a higher separation

of 90%, 85.5%, 84% and 82% of BSA, EA, pepsin and

trypsin respectively as shown in Fig. 9. For CA/SPEEK

blend membranes, as the CA content decreased, the

separation also decreased for all proteins. Thus for


90/10% CA/SPEEK blend membranes, BSA exhibited a

higher rejection of 82% and reduced to 66% for 65/35%

blend membrane compared to other proteins in order to

its higher molecular weight. Similar trend was observed

for other proteins.

Fig. 10. SEM micrographs of top surface of CA/SPEEK membranes

(d) 75/25; (e) 65/35 wt.% of CA/SPEEK blend membranes (5000· ma

3.4. Morphological studies

Morphology of the blend membranes were analyzed

by SEM with different polymer compositions and the

results are depicted in Figs. 10 and 11. At 100 wt.% of

with different blend compositions (a) 100/0; (b) 95/5; (c) 85/15;

gnification).

Fig. 11. SEM micrographs of cross-section of CA/SPEEK membranes with different blend compositions (a) 100/0; (b) 95/5; (c) 85/15;

(d) 75/25; (e) 65/35 wt.% of CA/SPEEK blend membranes (250· magnification).


CA, membrane exhibit smaller pores distributed evenly.

As, the SPEEK composition increased in the casting

solution, the pore size increased proportionally. The

cross-section of membrane confirms the asymmetry in

the ultrastructure of the membrane. The addition of

SPEEK to CA greatly reduced the formation of mac-

rovoids. At the base CA content, increasing SPEEK

content gives substantial and systematic increases in the

membrane permeability.

4. Conclusion

A new type of polymeric blend membrane material

based on cellulose acetate and SPEEK has been devel-

oped. Sulfonation studies prove that sulfonation of

PEEK occurred in sulfuric acid at room temperature.

Thermal analysis of SPEEK shows that the stability is

almost same to that observed for the parent PEEK. DSC

analysis proves that SPEEK does not reach the glass


transition temperature before its decomposition. The

extent of blend compatibility with various polymer

compositions using DMF as solvent has been determined

to be 65/35% of CA/SPEEK. The membranes prepared

have been characterized for their compaction, pure water

flux, water content, membrane resistance, and molecular

weight cut-off. The membrane showed higher pure water

flux and good resistance toward hydraulic pressure as

compared with pure CA membranes. These blend

ultrafiltration membranes with different compositions

were subjected to the separation of proteins such as BSA,

EA, pepsin and trypsin. SEM analysis shows that in the

blend membranes, the pore size increases with an in-

crease of sulfonated PEEK concentration.

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Studies on cellulose acetate and sulfonated poly(ether ether ketone) blend ultrafiltration membranes

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