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Influence of Polystyrene on PDMS IPNs Blend MembranePerformanceNasrul Fikry Che Pa a , Iqbal Ahmed b , Mohd Ghazali Mohd Nawawi a & Wan Aizan Wan AbdRahman aa Department of Chemical Engineering, Faculty of Chemical and Natural ResourcesEngineering, Universiti Teknologi Malaysia, Skudai, Johor, Malaysiab Department of Gas Engineering, Faculty of Chemical and Natural Resources Engineering,Universiti Malaysia Pahang, Kuantan, Pahang, MalaysiaAccepted author version posted online: 29 Nov 2011.Version of record first published: 21 Feb2012.

To cite this article: Nasrul Fikry Che Pa , Iqbal Ahmed , Mohd Ghazali Mohd Nawawi & Wan Aizan Wan Abd Rahman (2012):Influence of Polystyrene on PDMS IPNs Blend Membrane Performance, Separation Science and Technology, 47:4, 562-576

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Influence of Polystyrene on PDMS IPNs Blend MembranePerformance

Nasrul Fikry Che Pa,1 Iqbal Ahmed,2 Mohd Ghazali Mohd Nawawi,1 andWan Aizan Wan Abd Rahman11Department of Chemical Engineering, Faculty of Chemical and Natural Resources Engineering,Universiti Teknologi Malaysia, Skudai, Johor, Malaysia2Department of Gas Engineering, Faculty of Chemical and Natural Resources Engineering, UniversitiMalaysia Pahang, Kuantan, Pahang, Malaysia

In this work, a series of pervaporation blend membranes withpolydimethylsiloxane (PDMS)/polystyrene (PS) were prepared byusing the sequential interpenetrating polymer network (IPNs) tech-nique with various amount of PS (10–70wt.%). The blend IPNmembranes were supported by Teflon (polytetrafluoroethylene)ultrafiltration membrane. Effect of PS contents in PDMS IPNson crosslinked density, molecular weight, network-chain segmentconcentration, water swelling properties, and tensile properties wereinvestigated. Results revealed that the degree of crosslink densityand tensile strength of the PDMS IPNs blend membrane dependingon wt.% of PS added and scan electron microscope image confirmedthat the PDMS/PSt IPN membranes have continuous microphasestructures. The synthesized IPNs blend membrane was used forethanol recovery from aqueous solution by pervaporation, andexhibited enhanced separation performance compared with PDMSmembranes. The maximum separation factor of IPNs blendmembrane were obtained at 50�C, and the total flux increasedexponentially along with the increase of temperature. ThePDMS/PS membrane synthesized by 50wt.% PS gave the bestpervaporation performance with a selectivity (a) of 7.6, permeationrate of 214 g/m2 h with a 10wt.% ethanol (EtOH) concentration at60�C.

Keywords IPNmembrane; pervaporation; polydimethylsiloxane;polystyrene; water-ethanol mixtures

INTRODUCTION

Over the past twenty years, membrane pervaporationhas gained acceptance by the chemical industry as an effec-tive process tool for the separation and recovery of liquidmixtures. The main field of pervaporation separation isthe dehydration of organic compounds using a hydrophilicmembrane or for the removal of organic solvents from

water using an organophilic membrane (1–3). Desirablemem-brane properties, regardless of the separation process are highflux and selectivity, chemical resistance, and durability.Primarily the membrane material determines flux and selec-tivity. The selection of membrane materials for use in liquidand gas separations has often been made based on either anEdisonian or a common sense approach. For example, mem-brane research efforts focus upon the determination of thepermeability and selectivity of candidate polymers (4).

Recent literature surveys reveal an increasing number ofpolymers, copolymers, and blends that are beingconsidered as potential materials that can be used to mod-ify membrane morphology. As ethanol-permselectivemembranes for the concentration of aqueous ethanol solu-tions, the PDMS and polytrinlethylsilylpropion (PTMSP)are the most interesting and promising membrane materialsfor hydrophobic=organophilic separation that has beeninvestigated extensively (2). However, PDMS has poorcohesive property and mechanical strength (5). Theseproperties have been improved by using crosslinked PDMSblock or graft PDMS with a polymer having excellentfilm-forming and mechanical properties. Saam and Fearon(6) reported the first PDMS=PS block copolymers by poly-merizing hexamethylcyclotrisiloxane with ‘‘living’’ poly-styrene prepared from an alkyllithium and investigated itsmechanical and morphological properties. Miyata (7) andLiang (8) synthesized PDMS=PSt interpenetratingpolymer network (IPN) pervaporation membranes forethanol-water mixtures. The PDMS-PSt IPNs membraneswere prepared via the sequential IPNs technique used thebulk copolymerization of styrene and divinylbenzene inthe PDMS networks. Byun et al. (9) reported the gas sep-aration membranes with polydimethylsiloxane (PDMS)=polystyrene (PSt) were prepared by using the sequentialinterpenetrating polymer network (IPN) method.Turner (10) synthesized PDMS=PMAA interpenetratingpolymer network membranes using the monomer

Received 15 April 2011; accepted 21 September 2011.Address correspondence to Iqbal Ahmed, Department of Gas

Engineering, Faculty of Chemical and Natural Resources Engin-eering, Universiti Malaysia Pahang, Kuantan, Pahang, Malaysia.Tel.: þ605492881; Fax: þ0605492889. E-mail: iqbalmouj@hotmail.com or iqbal@ump.edu.my

Separation Science and Technology, 47: 562–576, 2012

Copyright # Taylor & Francis Group, LLC

ISSN: 0149-6395 print=1520-5754 online

DOI: 10.1080/01496395.2011.626828

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immersion method. Hillerstrom (11) prepared thepolyvinylpyrrolidone (PVP)=PDMS IPN membrane indifferent solvents via a two-step preparation method.

The solvent used during polymerization of the IPNshowed a significant impact on the properties of the PVP=PDMS-IPN. Garg (12) described the preparation and inves-tigation of membranes based on new interpenetrating poly-mer network (IPN) of vinyl terminated poly(dimethylsiloxane) and aromatic polyimide (PI) with respect to theirthermal and pervaporation properties. The modified mem-branes were prepared using simultaneous IPN (SIPN) tech-nique by variation of polyimide loading of 5, 10, and15wt.%, respectively. Regardless of the PDMS content dur-ing modification for membranes preparation, the selectiv-ities and permeabilities were enhanced. Though, they weredecreased with time because of the conformational changesuch as mechanical strength, swelling, and crystallizationof the polymer resulting in more dense and nonpermeablestructure (5). All the PDMS=PSt IPNs membranes had amicrophase-separated structure in which PS domains existin a continuous PDMS phase. The effects of theirmicrophase-separated structures on the permeability andselectivity for aqueous ethanol solutions (7,8) through theirmembranes by pervaporation.

In this research, an attempt has beenmade to improve themechanical strength, homogeneous microphase structure,and also the selectivity or flux of the PDMS blend mem-brane towards ethanol separation in water by using interpe-netrating polymer networkmethod. Until now, to the best ofour knowledge, the use of two different types of catalystsbeing used as initiator and crosslinker for the preparationof PDMS=PSt blend membrane supported on polytetra-flouroethylene (PTFE) ultrafiltration (UF) membranes hasnever been investigated. Thus, in the present paper, wereport the preparation of PDMS-PSt IPNs membrane usingtwo different catalysts; dibutyltin dilaurate (DBD) 2wt.%for PDMS network, and 5wt.% of dicumyl peroxide(DCP) as the initiator for PSt network and crosslinker forPDMS=PSt IPNs system. Polytetraflouroethylene UF mem-branes were used as a support for PDMS=PSt membrane.The membrane performance was characterized in the selec-tive pervaporation of ethanol from ethanol-water mixtures.The IPNsmembrane can be utilized efficiently in biotechnol-ogy application, especially in the biomedical field, whereantiseptic recycling is one of the major concerns.

EXPERIMENTAL

Materials

The materials used to prepare the PDMS host polymernetwork a,x-dihydroxypolydimethylsiloxane (PDMS) withaverage molecular weight of 50,000 was generously donatedby Wacker-Silicones, Germany. Reagent grade styrenemonomer, tetraethylorthosilicate (TEOS), dibutyltin

dilaurate, divinylbenzene (DVB), and sodium hydroxide(99.9%) were procured from Sigma-Aldrich Chemie GmbH,Germany. Dicumyl peroxide (DCP) was obtained fromAldrich Chemical Company Inc., USA. Solvents (Ethanol,methanol, chloroform, and toluene) were of reagent gradepurities and were purchased from Merck Germany. Ultra-filtration membranes made from PTFE with an averagemolecular weight cut-off of more than 10,000 supplied fromDonaldson Filtration (Asia Pacific) Pvt Ltd., was used as asupport. The purification of styrene, DVB, and DCP hasalready been reported in our earlier communication (13).

Preparation of Crosslinked PDMS Supported Membranes

A pre-weight of PDMS was mixed with 16wt.% of TEOSwhich act as crosslinking agent and 2wt.% of DBD whichact as catalyst in the reaction before being dissolved in afixed volume of toluene to produce PDMS network sol-ution. The solution was then stirred until it became suffi-ciently viscous (about 30 minutes). It was then poured onthe surface of PTFE membrane inside a stainless steel plateby an area of 15 cm� 15 cm with 3 cm height. Aluminumfoil with small holes was used to cover the stainless steelplate preventing rapid evaporation. A fixed volume of100mL total membrane solution was used for every mem-branes fabricated to control the membrane range thicknessover the PTFE membrane support surface area.

Preparation of PDMS/PS IPN Supported Membranes

The compositions of casting solutions used to preparePDMS=PSt IPNs layers are summarized in Table 1. Mixedsolutions of PDMS, styrene monomer, crosslinking agent,as well as initiator were stirred for 30 minutes until itbecame sufficiently viscous. The solution was then pouredon the surface of PTFE membrane. In order to preventthe evaporation of styrene and DVB, the system was cov-ered with a glass dish. The system was left in an ambienttemperature for 2 hours for the preliminary formation ofPDMS network as the reaction for PDMS networks startat room temperature. It was then introduced into an ovenat 80�C for 6 hours to complete the crosslinking of PDMSand for the polymerization of styrene monomer to begin.The system was again introduced into the oven at 100�Cto complete the polymerization and crosslinking of poly-styrene network. All the supported membrane would besubjected to drying in ambient temperature for 24 hoursbefore used in pervaporation (14).

MEMBRANE CHARACTERIZATION

Fourier Transform Infrared (FTIR) Spectroscopy

The infrared absorption through Fourier TransformInfrared (FTIR) spectroscopy technique was employed,to identify the presence of styrene and siloxanes groups

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in the polymer samples. In the present study, FTIR spectraobtained from Nicolet (Magna-IR 560) spectrometerequipped with attenuated total reflection having a Gespherical crystal. The spectra measured in transmittancemode over a wave number range of 4000–600 cm�1.

Field Emission Scanning Electron Microscope (FESEM)

The morphology of the PDMS=PSt IPNs supportedmembranes was determined by Carls Zeiss Supra 35 vari-able pressure field emission scanning electron microscope(FESEM). Membranes samples for the FESEM were pre-pared by freeze-fractured in liquid nitrogen and mountedon the aluminum stub. The specimens were coated with athin layer of gold to improve the macroscopic image. Themembranes were examined to determine if there were anydefects in term of existing visible holes or flaws in themembrane through the surface and cross section SEMmicrograph. Besides that, SEM micrographs were alsoused to show the existing layer inside the membrane.

Tensile Testing

Tensile strength-elongation test of PDMS=PStsupported membrane were performed according to thestandard method (ASTM D638-58T) using a Lloyduniversal testing machine (model Lloyds EZ50, LloydsInstruments Ltd., Fareham, UK). The test specimens werecut into strips 9.53mm long and 3.18mm wide (fixed valueon specimen mold), and the thickness of each strip(approximately 400 mm) was measured with digital verniercaliper. First, the membrane specimens were cut intodumbbell shape. The dumb bell shaped specimens werecut into different directions of grains of each IPNs mem-brane sheets, so as overall tensile property can be studied.Each end of the membrane specimens were taped withmasking tape to prevent it from being torn when it wasplaced in the grips of the testing instrument. Once themembrane specimen was properly placed in the testinginstrument, the grip was tightened evenly and firmly toprevent slippage of the specimen during test. The crosshead

speed of the instrument was fixed to 10mm=min at roomtemperature. The minimum number of specimens neededfor each sample was five and the average value was takenfor the respective data.

Determination of IPN Membrane Density

Density of the membrane was determined using digitalelectronic balance with a precision �1.5� 10�5 g (modelAT-201, Mettler Toledo, Switzerland). Prior to themeasurement of the membranes, the samples were firstweighed in air, then were immersed in distilled water andthe weights in distilled water were determined. The densityof the specimens had been calculated using the followingequation:

q ¼ A

A� B� q0 ð1Þ

Where q is the density of the solid specimen, A is the weightof the solid specimen in air; B is the weight of the solidspecimen in distilled water, and q0 is the density of distilledwater at a given temperature.

Density and Degree of Crosslinking

Crosslink density can be determined by the two meth-ods, modulus and swelling measurements. Values of thenetwork-chain segment concentrations, n obtained canused to calculate Young’s Modulus, E using the relation-ship in Eq. (2):

E ¼ 3nRT ð2Þ

Where E is the Young Modulus, n is the number of theeffective crosslink per unit volume, R being the gas con-stant, and T is the temperature. The modulus will give adirect measurement of stiffness, which is directly pro-portional to the crosslink density.

Network-chain segment concentration, n, mol per cm3

was calculated by using the Flory-Rehner’s equation for

TABLE 1Design of experiment for PDMS=PS IPNs supported membrane solution composition

�PDMS network PSt networkDCP (Wt. %)

Membrane �PSt (Wt. %) in IPN PDMS (g) �TEOS (g) �DBD (g) �S (g) �DVB (g) �DCP (g) PS network

PDMS 0% 28.0 5.460 0.686 0 0 0 0%90=10 10% 25.2 4.914 0.617 2.8 0.283 0.063 5%70=30 30% 19.6 3.822 0.480 8.4 0.848 0.189 5%50=50 50% 14.0 2.730 0.343 14.0 1.414 0.315 5%30=70 70% 8.4 1.638 0.206 19.6 1.980 0.441 5%

�PDMS¼Polydimethylsiloxane, PSt¼Polystyrene, S¼ Styrene monomer, TEOS¼Tetraethylorthosilicate, DVB¼Divinylbenzene,DCP¼Dicumyl Peroxide, DBD¼Dibutyltin dilaurate, IPN¼ Interpenetrating polymer network.

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crosslinked polymers (15).

n ¼ � ½lnð1� v2Þ þ v2 þ v12 v22�V1½v1=32 � v2=2�

ð3Þ

Where, v2 is the volume fraction of the polymer in the swol-len areas, V1 is the molar volume of solvent; toluene takenas 106.8 cm3=mol and X12 is the Flory-Huggins polymer-polymer interaction parameter (16).

The degree of swelling (q) can be related to the volumefraction of the polymer in the gel v2, by the followingequation.

v2 ¼ � w1=q1w1=q1 þ w2=q2

ð4Þ

Where,w1 is the weight of the polymer in gm. q1 is the densityof the polymer, gm=cm3, w2 is the weight of the solvent ina swollen sample in gm, and q2 is the density of solvent,gm=cm3.

The Flory–Huggins v12 parameter has been one of themost widely used quantities, characterizing a variety ofpolymer-solvent and polymer-polymer interactions. It is aunitless number. While the original theory proposed thatv1 be concentration independent, many polymer-solventsystems exhibit increases of v1 with polymer concentration(15,16). The polymer-solvent interaction parameter v12 forthe system was calculated by using the following equation(15,16),

v12 ¼ bþ V1ðd1 � d2Þ2

RT; ð5Þ

While b, sometimes called the lattice constant of theentropic origin,

v12 ¼V1ðd1 � d2Þ2

RTð6Þ

Where V1 is the molar volume of the solvent, d1 and d2 arethe solubility parameters of the solvent and polymer, R isthe universal gas constant, and T the absolute temperature.However, for a polymer-polymer system as in IPN, thefollowing calculations were assumed for the interactionbetween PDMS-toluene and PS-toluene:

v12 ¼V1ðdtol � dPDMSÞ2

RT; v12 ¼

V1ðdtol � dPSÞ2

RTð7Þ

The v12 parameter, also called Flory’s v12 parameter orFlory–Huggins v12 parameter, and v12 is also called vblendblend is a dimensionless interaction parameter defined as(15–17),

v12 ¼Xi;j

ci;jvi;j ð8Þ

where the coefficients cij are functions of the copolymercompositions, with 0� cij� 1.

From the values of n, the molecular weight betweencrosslink Mc is determined as follows:

n ¼ q=Mc ð9Þ

Mc ¼ q=F ð10Þ

Where F is the network-chain segment concentration, q isthe density of the IPN polymer, and Mc is the molecularweight between crosslinks.

Subsequently, values of E, Young’s Modulus can bedetermined using values of n found from Eq. (3).Network-chain segment concentrations, F also can bedetermined via the relationship in Eq. (2). Thus, two valuesof Mc can be determined using the relationship statedabove, that is, via swelling methods and mechanical testing.The crosslink density is then calculated by the followingequation:

qCx¼ q=2Mc ð11Þ

Where qCxis the crosslink density, q is the density of the

IPN polymer, and Mc is the molecular weight betweencrosslinks.

Determination of Membrane Swelling Behavior

A known weight of the each samples, 1� 1 cm wasplaced in a stopper bottle of a freshly distilled toluene,chloroform, ethanol, and water for a period of 7 days.The samples were re-weighted every day until a constantweight had been achieved indicating that equilibrium swell-ing has taken place. The equilibrium swellings of each sam-ple were obtained using the expression (18):

%Swelling ¼ Ws�Wd

Wd� 100 ð12Þ

MEMBRANE EVALUATION

Membrane Performance Test – Pervaporation

Figure 1 shows the schematic representation of the per-vaporation apparatus. The feed mixtures enter the cellthrough the inlet opening and leave the cell through theoutlet opening on the opposite site. The feed mixture wasthen circulated through the cell by a circulation pump,which was controlled using the control valve. The oper-ation of this unit was in batch mode since the feed was con-tinuously recycled back to the feed tank and the vaporpermeated through the membrane was removed from the

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lower part of the cell, which was kept under vacuum press-ure and condensed in a cold trap that was immersed in theliquid nitrogen.

Downstream pressure was controlled directly by adjust-ing the control panels, which connected to the pressureprobe in the membrane outlet cell. The system was directlyattached with a vacuum pump to control its operation. Avacuum pump will stop operating once the desired pressureis achieved and start to operate again when the pressurefalls and vice versa. Similarly, the feed temperature wascontrolled by using the same method with the temperatureprobe inside the feed tank. The feed tank used a jacketedheating system to increase the temperature of the feed. Ifcompared to direct heating system where heat is supplieddirectly, the jacketed heating system is much safer. Oncethe feed achieved the desired temperature, the jacketedheating system will be stopped and vice versa.

The pervaporation system was run for at least 1 hour forthe startup process until the permeation flow reached steadystate. The permeate sample can only be collected after thepermeation flow reached steady state. The permeate samplewas removed from the system and left to warm up to ambi-ent temperature before being weighed and analyzed for thecomposition. The composition of the permeate was ana-lyzed using the refractive index and compared with the pre-pared standard curve for pure ethanol. The composition ofthe feed mixture in the feed tank was also measured to verifyconsistency of the mixture. However, it is safe to assumethat the feed composition remains constant during the dur-ation of the experiment due to the fact that, the weight ofthe permeate collected was less than 1% of the total feedweight placed into the tank.

Throughout the experiment, low concentration ofethanol (10wt.%) was used, as the purpose of this experi-ment was to allow only ethanol to permeate through themembrane while retaining water in the feed stream toachieve a high separation process. Each type of membraneswere tested with a fixed composition of feed mixture at fourdifferent temperatures, namely 30, 40, 50, and 60 degreeCelsius. The upstream pressure of the pervaporator wasat atmospheric pressure, while the downstream pressurewas maintained at 0.07 bar with vacuum pump. The flowrate of the feed mixture circulating system was fixed at3.5 liter per minute. Every permeate sample collected wasrun at least 3 times before the data for the permeation fluxand the separation factor can be obtained to validaterepeatability. The permeation flux of the membrane wascalculated with Eq. 13 where the membrane area, A(m2)¼ 6.36� 10�3m2. The permeation rate (J) at steadystate was calculated using the expression (7,8):

Jt ¼ w

ADtð13Þ

Where, w is the total amount of permeate at steady stateduring the experimental permeation time (h) Dt and A isthe effective membrane surface area. The permselectivityof the membrane was expressed via the separation factor(a) defined as (7,8)

aij ¼Yi=Yj

Xi=Xjð14Þ

Subscript Yi and Yj are the weight fraction of component iand j in the permeate, respectively. Whereas, Xi and Xj arethe feed phase weight fraction of component i and j.Component i is a more preferentially permeating compo-nent in the i and j mixture.

RESULTS AND DISCUSSION

Infrared Study Using Fourier Transform InfraredSpectroscopy (FTIR)

In order to classify the occurrence of PDMS and PSgroup in PDMS=PSt IPNs supported membranes, FourierTransform Infrared (FTIR) spectroscopy used in thepresent study. A sample spectrum of IPN membrane isused to verify the presence of PDMS and PS group in thesystem as the rest of the spectrum shows similar absorptionpeak wavelength with different intensity.

Figure 2 shows the FTIR spectrum 4000–600 cm�1ofpure PDMS membrane and Fig. 3 shows the FTIR spec-trum of 50=50 (PDMS=PSt) IPNs supported membranewith 5wt.% of DCP content. Figure 2 shows the absorptionpeak at 2963 cm�1 and 2905 cm�1 can be assigned to the C-H methyl group due to symmetric stretching vibration ofCH3. It also displayed three new absorbance signals at

FIG. 1. Schematic representation of the pervaporation experimental

setup. (Color figure available online)

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850–730 cm�1 (CH3 out-of-plane bending and Si–C stretch-ing), 1066 cm�1 (Si–OH stretching), and 863 cm�1 (Si–OHangle bending vibration), respectively. The silicon–methylbond (Si-CH3) at 1259 cm

�1, and the broad PDMS back-bone absorption band between 1130 -1000 cm�1 are found(19–21). The ring CH2 and C-H group in a monoalkylcy-clopropane ring absorb in the region of 3003 cm�1,2984 cm�1 and 2964 cm�1, respectively. Generally speakingin IPNs blend membrane the main material is PDMS,– (Si(CH3)2–O)n–. This compound has a very simple IRspectrum, in the spectrum (Fig. 3) featuring threedistinctive band due to the methylene stretchingvibrations at 1281 cm�1, 1259.94 cm�1 and 1236 cm�1,respectively (symmetric CH3 deformation of the CH3–Si–CH3 group), 1071–1017 cm�1 (Si–O–Si and Si–O–C), and

869–850 cm�1 (Si–CH3) as shown in Fig. 3. It alsoshowed five new absorbance signals at 842–750 cm�1

(CH3 out-of-plane bending and Si�C stretching). Theasymmetric CH3 deformation of CH3�Si�CH3 and appearas weak bands at 1414 cm�1. However, the antisymmetricstretching vibrations, in which the oxygen atom motionoccurs in the Si�O�Si plane and parallel to a line joiningthe two silicon atoms, are responsible for the strongestabsorption, near 1080–1087 cm�1. It is attributed that asthe constant concentration of DCP, the 1081–1071 cm�1

peak area were distributed in several peaks, as seen in theFig. 3, corresponding to Si-O-C bonds. This leads to theconclusion that at fixed concentration of DCP, it increasesthe amount of silane that occurs during cross linkingbetween PDMS and PSt, because the peaks at 1081 to

FIG. 3. FTIR spectrum 4000–600 cm�1 of 50=50 (PDMS=PSt) IPNs supported membrane with 5wt.% of DCP content. (Color figure available online)

FIG. 2. FTIR spectrum 4000–600 cm�1 of pure PDMS membrane. (Color figure available online)

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1071 cm�1 are assigned to the functional group Si=OCH(20). The higher frequency band at 3647 cm�1, 3618 cm�1,3367 cm�1, and 3265 cm�1, respectively is attributed to sila-nol (SiOH). The absorption peak at 1651 cm�1, 759 cm�1,and 765 cm�1, respectively can be assigned to the aromaticskeletal vibration of PS and the peak at 655.80 cm�1,632 cm�1, and 625 cm�1, to the aromatic C-H out of planedeformation vibration. These characteristic absorptionsshowed that PS was incorporated and presence in PDMSmatrix during IPN synthesis (20–22).

Membrane Morphology

Morphology of Crosslinked PDMS Supported Membranes

The properties presented by the IPNs can be clarifiedbased on the phase morphology recognized during syn-thesis. Figure 4(a–e) shows field emission scanning electronmicroscope (FESEM) for the cross section at 500X of thePDMS IPNs blend membranes with and without PS con-tents. In Fig. 4a, it was observed that there is a robustboundary amongst the PDMS layer and the PTFE layer.As confirmed in the SEM image, there is a clear boundary

between the PTFE support upper layer and the PDMSlower layer with DBTDL as catalyst to cure the crosslinkof PDMS. SEM observations show that the type ofDBTDL catalyst used in synthesis produced a homo-geneous and defect-free structure of PDMS membrane.The lower PDMS layer, functioning as the basis of perms-electivity, had a nonporous and constricted structure. Thethickness of the top skin layer of the supported membranewas determined to be 40.26 mm by means of SEMphotographs.

Figure 4(b–e) shows the FESEM micrographs graphsimage for the cross section of IPNs membranes with vari-ous contents of PS. When the effect of the blend ratiowas compared, it was found that as the PS contentincreases the PS phase becomes more and more compactand continuous. This is clear from Fig. 4(b–d). In these fig-ures the SEM micrograph of PDMS IPNs membranes con-tains, 10–50wt.% PS illustrations are specified.

In PDMS, the IPNs membrane contains 10–50wt.% ofPSt are crosslinked expressively with PDMS in the presenceof dicumyl peroxide (DCP). As a result homeomorphismnetworks are formed which is clear from Fig. 4(b–d). Asdemonstrated in the SEM photograph of PDMS=PSt(Figs. 4b–d), there is no boundary between the PDMSand PS layer which showed a molecular level mixing andhomogenous dispersion of PSt into PDMS matrix beforeits crosslinking at high temperature. It is also clear inFig. 4(b–d) has a non-porous, tight, and dense structureand there is no fractured structure, connected pores orcrack, which is important for the practical application.However, in Fig. 4(e) IPNs membrane contains 70wt.%of PSt shows that dual phase continuity is observed. InPDMS=PSt IPNs membrane the PSt (70wt.%) phase is pre-dominant due to the fact that a higher amount of the phasedistribution is uneven and seems to have a disintegratedstructural form. Thus, it is attributed that, due to higheramount of PSt content the crosslinking of IPNs membraneis low. So the PSt (70wt.%) phase shows a tendency toagglomerate. This will lead to brittleness and thus poorelongation break performance. It was expected thatincreasing the amount (50=50wt.%) of PSt in the PDMSnetwork will eventually increase the chances of interpene-trating on the molecular level structure; where the rigidPSt molecule will interpenetrate and reinforce the rubberymolecule of the PDMS structure, thus forming a homogen-ous hydrophobic moiety and dense matrix structure.

Homogeneously hydrophobic moieties are attributed tothe fact that the incidence of the catalyst as a crosslinkingagent the PDMS backbone support better mixing and pro-mote homogeneous structure and under the functions ofthe dicumyl peroxide (DCP), will promote the balancemembrane structure due to a joint network between thePDMS and PSt. Rao el al (23) also reported that the pres-ence of a functional crosslinking agent along the PDMS

FIG. 4. Micrograph image of cross sectional area PDMS IPNs sup-

ported membrane with various concentration of PS; (a) 0% (b) 10%; (c)

30%, (d) 50%, (e) 70%.

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backbone did indeed promote better mixing of the organicphase and the inorganic phase, that is, under the functionsof the crosslinking agent, covalent bonding and mutualnetwork between the organic phase and the inorganicphase occurred. A high value of the network chain segmentconcentration, F with a low value of molecular weightbetween crosslink Mc was a clear sign of a compact anddense network structure for the respective membrane.

PDMS/PSt IPNs Blend Membranes Study on SwellingBehavior in Various Solvents

The measure of swelling characteristic of IPNs mem-branes will reveal several interesting features. Swelling inIPNs membrane depends on the glassy or rubbery natureof the polymer pairs, chemical crosslinks and physicalentanglements in the IPNs system itself. The swelling testgave values for the swelling ratios, percentage of swelling,network–chain segment concentration, F (mol=cm3), cross-link density, Cx, and the molecular weight between thecrosslink, by measuring their equilibrium swelling beha-vior. An increase in crosslinking density (CLD) for theIPNs membranes samples was observed and the value willobviously affect the selectivity for the separation process. Ahigher degree of crosslinking will tighten the network andusually would increase the selectivity but inversely decreasethe flux of the separation.

Figure 5 shows the relationship between percentages ofswelling with various concentration of PSt for IPNs blendmembranes in various solvents (H2O, toluene, ethanol, andchloroform). In IPNs consisting of both hydrophobic poly-mers, the swelling capability of the IPNs in water and etha-nol is a result of the hydrophobic component. Resultsshows that the swelling degree of PDMS membrane inwater was a little higher than that of PDMS IPNs mem-brane contain 10wt.% PSt, but much lower than that of

IPNs membranes which contain 50–70wt.% of PSt. Besidesthat, a similar observation was observed in ethanol exceptIPNs membranes contain 10wt.% and 50wt.% of PSt. But,as shown in Fig. 5, nearly all of the IPNs swelled in tolueneand chloroform and reached equilibrium swelling. How-ever, it was observed that the PDMS=PSt IPNs supportedmembranes have lower value of swelling compared tocrosslinked PDMS supported membrane in all solvents.This was due to the interpenetration between both mole-cules into the PDMS=PSt matrix which leads to a compactand dense membrane structure and thus suppresses swell-ing. The effects of swelling due to PSt content were similarto the density effect of the same membranes compositionsbut in an opposite direction. The results thus, consistentwith the theory which stated that, increase of crosslinkingin the IPN will result in increase of density and suppressswelling. Similar types of results have also been reportedby other researchers (24,25).

Density Study on PDMS/PS IPN Supported Membranes

Density measurement was done carefully for the resultwill be used to determine crosslink density of each mem-brane. Table 2 illustrates the value of density obtainedfor both crosslink PDMS membranes and PDMS=PStIPNs membrane samples with a fixed amount of DCP.An increase in the value of density was examined for allIPNs membrane samples compared to PDMS crosslinkedsample. Results revealed that the density for each IPNsmembrane linearly increased with the increased amountof PSt in the membrane composition. These trends ofincreasing IPNs density is a consequence of interpen-etration between two networks filling the comparativelyloose and amorphous molecular structure and the forma-tion of a more compact structure. Kujawski et al. (25) alsoreported that if the cross-linking density is high smallmicrophases are formed, while at low cross-linking densitylarge microphases or loose structure are formed. The effectof increasing density was observed in PDMS=PSt IPNssupported membrane with respect to PSt composition. Thiswas attributed to the increased number of crosslinksbecause of the interpenetrating forming a more compactstructure whereby the rigid PSt phase reinforces the moreelastic PDMS matrix.

Tensile Strength Study IPNs Blend Membranes

Figure 6 shows the results of stress and elongation breakmeasurements of PDMS IPNs by variation of PSt loadingof 0, 10, 30, 50, and 70wt.%, respectively, in the dry state.Results revealed that, in contrast with unmodified PDMS,the moduli of all IPNs increased with the integration of PStin the PDMS network. However, except for the 70wt.%concentration, their elongation at break point decreasedas compared to 30wt.% and 50wt.% PSt. The increasedtensile strength and elongation of the PDMS=PSt IPNs

FIG. 5. Percentage of swelling in versus various concentration of PSt

(wt.%) in IPNs for PDMS=PSt IPNs supported membrane.

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compared with the pure PDMS was due to stiffening of thePDMS network from increased PSt content, respectively.The observations of SEM micrographs figures are in goodagreement to support the tensile strength. The tensilestrength of PDMS=PSt IPNs supported membranesincreases following the increase of PSt content in the sys-tem. The tensile strengths of the PDMS=PSt IPNs mem-branes were almost 62% higher than that of the PDMSmembrane except 10wt.% of PSt content in IPNs mem-brane. Simultaneously the elongation breaks (see Fig. 6)of the PDMS=PSt IPNs membrane were almost 29–114%higher than the PDMS membrane. This indicates that theinterpenetration of PSt in the PDMS networks canefficiently improve mechanical properties of the PDMSmembranes. The maximum tensile strength and elongationbreak were observed for 50wt.% PSt content in PDMS=PStIPNs membranes. This was attributed to the fact that rigidPSt phase reinforce and interpenetrate with the more elas-tic and rubbery PDMS matrix transforming it into a tight

and dense network thus increasing its strength towardscreed and flow as reported by Mathew et al. (26).

Network Chain Segment Concentration, n and Value ofCrosslink Density on Blended PDMS/PS IPN SupportedMembranes

Applying the Flory-Rehner equation for crosslinkedpolymers, Eq. (3), the values of n were calculated bothfor crosslinked PDMS and PDMS=PSt IPNs supportedmembrane samples from their equilibrium swelling results.The polymer-solvent interaction parameter v12 for the sys-tem was calculated using Eq. (5) where the following valueswere used (16);

V1 ¼ 106:29 cm3=mol; dToluene ¼ 8:9ðcal=cm3Þ1=2;

dPDMS ¼ 7:5ðcal=cm3Þ1=2; R ¼ 1:9872 cal=mol at

Ko and T ¼ 300:15Ko

:

The interaction between PSt and toluene was then taken asusing Eq. (5), where the following values were used (16):

V1 ¼ 106:29 cm3=mol; dToluene ¼ 8:9ðcal=cm3Þ1=2;dPS ¼ 9:1ðcal=cm3Þ1=2; R ¼ 1:9872 cal=mol �Ko

and T ¼ 300:15Ko:

Subsequently the interaction parameter v12 was calculatedusing Eq. (7):

This value of v12 was then substituted into theFlory-Rehner Eq. (3) to give values of the network chainsegment concentration, g (mol=cm3) which is tabulated inTable 2; where nTensile represented the values calculatedusing the tensile strength result, and nswell represented thevalues calculated from their equilibrium swelling behavior.

The values of n were also determined from the relation-ship of E¼ 3 n RT, thus giving the experimental value of

TABLE 2Values of network chain segment concentration (n), molecular weight (Mc), density (q) and crosslink density (qCx)

obtained from swelling test and tensile strength test for 5% DCP PDMS=PS IPNs supported membrane with variouscomposition of PS

Network-chain segmentconcentration Molecular weight Crosslinked Density

Membrane compositionPS=PDMS

Densityq, gm=cm3

gswell� 10�4,mol=cm3

gtensile,g mol=cm3

Mcswilling,g=mol

Mctensile,g=mol

qCxswilling� 10�4,g mol=cm3

qCxtensile� 10�4,g mol=cm3

0% 0.9987 3.71 14.00 2688.45 0.071 1.86 7.0010% 1.0022 5.37 21.19 1867.52 0.047 2.68 10.6030% 1.0159 5.46 28.14 1859.28 0.036 2.73 14.0750% 1.0202 4.97 29.92 2054.61 0.034 2.48 14.9670% 1.0365 4.91 29.96 2113.02 0.035 2.45 14.95

FIG. 6. Tensile strength for various composition of PSt (wt%) in IPNs

for PDMS=PS IPNs supported membrane.

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n using tensile strength tests. A bar graph comparing thetwo values of n calculated using both methods is tabulatedin Table 2. The values calculated from the tensile strengthresults were more than 4–6 times higher as compared to theswelling test. This indicates that the level of physical entan-glements is more than two times higher than the chemicalcrosslink, which is true for most IPNs (27).

From Table 2, it is shown that higher degrees of networkchain segment concentration, g (gswell and gtensile) wereobtained when the PSt is increased for IPNs composition.Both of the values for the network chain segment concen-tration, g obtained by tensile test and swelling test showingsimilar trend with a different ratio. All of the PDMS=PStIPNs blend membranes showed an increase in the networkchain segment concentration, g compared with the cross-linked PDMS supportedmembrane. The effect of PSt content(70=30wt.%) in each respective IPNs supported membranescomposition showed an increase in the value of the networkchain segment concentration, gswell and gtensile. It was shownthat for the composition of 30wt.% PSt and 70wt.% of PStcontent in IPNs system gave the highest value for gswell5.45mol=cm3 and gtensile 29.96 gmol=cm3.

The results of SEM photographs, tensile strength, and %of swilling are in good agreement to support the results ofthe network chain segment. Increasing PSt content eventu-ally privileged the value for network chain segment concen-tration, g and lowered the molecular weight of the PDMS=PSt IPNs membrane. Thus, increment in PSt compositionwithin IPNs supported membrane highly influence the ten-sile strength and swelling resistance whereas a rigid poly-mer, PSt reinforce tensile strength and swelling resistantnot only by network chain segment concentration valuebut also physical entanglement between molecules whichleads to a higher degree of network chain segment concen-tration. Liang and Ruckenstein (8) also reported that theproperties of crosslinked PDMS membrane are improvedby the PDMS-PS IPN membranes.

Table 2 also represents the crosslink density of eachof the relevant membranes composition using both valueof qCxswilling and qCxTensile. It was found that the trend ofcrosslink density was parallel to the network chain segmentconcentration, g as the value of network-chain segmentconcentration value was used to calculate the crosslinkdensity, as well as the molecular weight between the cross-link or chain molecular weight,Mc. These phenomena wereexpected as IPNs blend membrane at a molecular levelshows a dense and close structure due to a high degree ofcrosslink density for the respective membranes. The smallvalue of the molecular weight between crosslink Mc indi-cated a short chain between the molecular structure thusproving the existence of a dense and close structure ofthe respective membranes.

Moreover, experimental result shows that the trend formolecular weight between the crosslink, Mc were opposite

with the trend of the crosslink density for the respectivemembranes. The molecular weight between the crosslink,Mc, shows lower value compared to the crosslink densityfor the respective membranes which indicated that the dis-tance between crosslink networks is small, indicative of acompact chain structure. On a molecular level, a shorterchain=length between crosslink networks with a highdegree of crosslink density obtained both the from chemi-cal crosslink and the physical entanglement leads to a denseand close membrane structure. Sperling (15) reported thatthe presence of crosslinks may indeed cause smallerdomains with larger interphases and therefore more mix-ing. Dense membrane structure with a close networkbetween the crosslink leads to suppress swelling in themembrane and lowered flux for separation. On the con-trary, the effects of the dense membrane although resultedin lower flux for separation usually will produce a highermembrane selectivity which depends on the affinity of themembrane.

PERVAPORATION (PV) STUDIES

The pervaporation studies of a membrane is evaluatedin terms of two main factors specifically, flux (g m �m�2 �hr�1), and selectivity (a) towards the water=EtOH (90=10wt.%) permeated element. The flux standards are usuallycontrolled with respect to thickness of the membrane.Membranes were examined for water flux and selectivityfor the entire range of water=ethanol feed compositions.In addition the other parameter such as temperature (�C)against flux and selectivity of individual membranes hasbeen taken into account. Feed concentration was set to aconstant of 10wt.% ethanol in water and has been moni-tored for consistency. The effective surface area of theresulting membranes in contact with the feed mixture was63.62 cm2.

Influence of PSt Content on IPNs Supported MembranePerformance

The effect of PSt content on IPNs blend supportedmembrane performance in the presence of two differentcatalysts (DBD and DCP) is presented in Fig. 7. The per-vaporation experiments were conducted at 60�C. The totalflux of various IPNs blend membranes simultaneously byvariation of PSt loading of 10, 30, 50, and 70wt.%, respect-ively, and the separation factors followed the same order.The results revealed that the permeation rate and selectivityfor H2O=EtOH solution is significantly affected by PStcontents (wt.%) added to IPNs blend membrane. PDMSmembrane without PSt exhibits a permeation rate of163 gm �m�2 � hr�1 and a separation factor of 2.23.Addition of PSt contents in the blended IPNs supportedmembrane loaded with 10wt.%, 30wt.%, and 70wt.% ofPSt, respectively, showed (see Fig. 7) a reduced permeationrate but increased selectivity as compared to cross-linked

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PDMS membrane. Though, IPNs blend membrane contain50wt.% of PSt showed a much higher total flux and a sel-ectivity than pure PDMS membrane and other IPNs blendmembranes which may result from its significantcross-linking density and sufficient swelling resistance andefficient tensile properties. Moreover, the results suggestthat the balanced hydrophobic moieties of PDMS=PStblend loaded by 50wt.% of PSt in the presence of a catalystseems to well integrate the cross-linking of the bond net-work. The SEM micrograph image of IPNs blend mem-brane contains 50wt.% PSt is in good agreement toconfirm these results. Apparently, the results indicated thatthe hydrophobicity of the membrane increases withincreasing amount of PSt content. Liang, Miyata, andco-workers (7,8) have also reported similar results and thisconclusion is in agreement with the observed effects ofmembrane SEM micrographs image, minimum swelling,efficient tensile properties, network chain segment, andcrosslink density, respectively, on water=EtOH mixture.In addition, the membrane solute-solvent blend interactionhad an excessive consequence on the transport process ofsorption and diffusion. The effect of transport is relatedto not only the polymer properties, such as free volume,chain mobility, degree of cross-linking, etc., but also theproperties of the permeating components, molecular size,molecular shape, temperature, and concentration of thepermeating component (12).

Influence of Feed Temperature and PS Content on BlendedIPN Supported Membrane Performance

Pervaporation performance is influenced by tempera-ture, and thus, promoting feed mixing near the membranesurface seems to be an efficient way of reducing thetemperature drop. Therefore, temperature was an impor-tant process variable affecting the membrane performances

in terms of the permeation flux and selectivity (28). Theconsequence of the temperature on the permeation rateand separation factor for a H2O=EtOH mixture containing10wt.% EtOH is presented in Figs. 8 and 9, respectively. Itcan be seen that higher flux and the selectivity rate areobtained at higher operating temperature of PDMS mem-brane without PSt. However, it was observed that the IPNsblend membranes loaded by 10, 30, 50, and 70wt.% PSt,respectively, shows a similar trend in flux at temperaturesbetween 30–60�C (see Fig. 8). It can be seen that theincrement of fluxes rate of IPNs blend membrane contains30–50wt.% PSt almost shows monotonically; however,70wt.% PSt showed linear flux. The increment of the fluxrate with respect to temperature is attributed to the factthat the motion of permeating molecules are enhanced bythe temperature, and continuous thermal fluctuations ofpolymers leads to a temperature gradient in the directionof permeate flow. Thus, when the feed temperature is high,the diffusion rates of associated permeating moleculesbetween ethanol and water are high. Thus, this enables per-meant molecules to permeate through, which in turnincrease flux. One of the reasons for the performance wasdue to an increased of PSt in the PDMS network. Workdone by Uragami (1996) (29) stated that the PS membraneshows water-permselective in spite of the hydrophobic nat-ure of PSt. Therefore, increasing the composition of PS upto 50=50wt.% in the PDMS network will decrease the totalmembrane degree of water-permselectivity and thus thehigher the value of flux.

Moreover, the increase of the selectivity of IPNs blendmembranes (see Fig. 9) with respect to temperature is poss-ibly due to the decreased intermolecular forces of hydrogenbonding between water and ethanol molecules withincreasing temperature, less water is therefore stimulated

FIG. 8. Flux rate versus various feed temperature (�C) of PDMS=PSt

IPNs supported membrane at various concentration of PSt (wt.%) in

IPNs. EtOH, 10wt%.

FIG. 7. Flux rate and selectivity versus various concentration of PS

(wt.%) in IPNs for PDMS=PSt IPNs supported membrane at temperature

60�C. EtOH, 10wt.%.

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to permeate the membrane which is more selectively swol-len by ethanol. Yeom et al. (5) and Young et al. (18) alsoreported similar results. The increase of reasonable valuesof flux and selectivity with respect to temperature at thebeginning of the separation process verify the effects ofthe swelling nature of PSt in H2O=EtOH. However, athigher temperature (60�C), flux, and selectivity increasedmore rapidly, indicating that the dependency feed concen-tration on the PSt content of IPNs blend membranes. It isattributed that the movement of the permeating moleculesis boosted both by the temperature and by the higher flexi-bility of the polymer chain due to thermal motions insidethe aqueous solution (5). Besides that, with increasing tem-perature it was suspected that the vibration between thedense and close chain molecular structure of crosslinkedpolymer increase.

From Fig. 9, it was noted that the selectivity shows over-all tremendous increment trends between 90=10–70=30wt.% and 30=70wt.% at various temperature as com-pared to cross linked PDMS membrane. However, the sel-ectivity of IPNs blend membrane contain 10wt.% PStshows variance drift at temperature between 30-40�C.Nevertheless, the results revealed that with increasing tem-perature, the selectivity of cross link PDMS and IPNsblend membranes increases for water=EtOH. One of thereasons for the behavior was due to a loaded amount ofPSt in the PDMS network. Work done by Liang (8) statedthat PSt membrane shows EtOH-permselective in spite ofthe hydrophobic nature of both polymers. Therefore,increasing the composition of PSt in the PDMSnetwork will increase the total membrane degree ofEtOH-permselectivity, thus the higher the value ofselectivity and flux (see Figs. 8, 9) at higher temperatureduring separation. On the contrary, with selectivity and

flux, for the composition of 50=50 (PDMS=PSt) IPNsblend membrane shows increasing value with temperature.Although IPNs blend membrane of 50=50wt.% (PDMS=PSt) shows overall significant trend in selectivity and fluxcompared to PDMS, 90=10–70=30wt.% and 30=70wt.%.As PSt is well known for hydrophobic superiority in nat-ure, highly interpenetrated supported membrane with70wt.% of PSt in composition will eventually increase thedegree of hydrophobicity. Hence the restrained water aswell as the ethanol molecule from passing through themembrane therefore lowered the flux and selectivity valuesas compared to 50=50wt.% (PDMS=PSt) of IPNs mem-branes. The analyses of the swelling test are in good agree-ment to justify the results. Overall, the experiments weobserved that the pervaporation performance of IPNsblend membrane contain 50wt.% of PSt, as shown inFigs. 8 and 9, increased efficiently with increasing tempera-ture of feed. It is attributed that at 5wt.% of DCP (catalyst)the network interlocking between two hydrophobic poly-mers is quiet stable and significant. Thus, IPNs blend mem-brane at 50wt.% PSt shows a balanced hydrophobicstructure among both polymers and it can clearly beobserved in Fig. 4.

According to the solution-diffusion model, the transportof molecule i through crosslinked PDMS and IPNs blendmembrane can be expressed as the following simplifiedequation (30):

Ji ¼JpudT

ð15Þ

where u is the amount of ethanol in water; dT the thicknessof the membrane, and Jp the permeability of ethanol.

FIG. 9. Selectivity versus various feed temperature (�C) of PDMS=PSt

IPNs supported membrane at various concentration of PSt (wt.%) in

IPNs. EtOH, 10wt%.

FIG. 10. Arrhenius plots for the total permeation rate over supported

PDMS=PSt membranes versus temperature, for 10wt.% ethanol. (Color

figure available online)

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Nevertheless, the experimental data of temperature depen-dence of both total and partial permeation fluxes generallyexhibit a linear relationship between the exponential of fluxversus reciprocal temperature (30). Thus, flux hasan Arrhenius relationship with operating temperature asfollows,

Jp ¼ Jp0 ln � Ep

RT

� �ð16Þ

where Ep has been considered to be the activation energyfor permeation. Equation (16) has been commonly usedin pervaporation to calculate the activation energy of per-meation from in Jt vs. 1=T plot. In the Arrhenius plotsshown in Fig. 8, the slope of each curve stands for the per-meation activation energy, Eu. Generally, in a membranetesting system having diffusion-rate determining step, theactivation energy is related with both the interface amongpermeant molecules and the plasticization action of thepermeants on the membrane material. The interaction isa positive factor and the plasticization action is a negativefactor on the permeation activation energy (5). Figure 10shows the activation energy of PDMS and PDMS IPNsblend membrane for PV of ethanol=water mixtures.

It can be seen that the activation energy (Ep) of crosslinked PDMS membrane for water=EtOH is somewhatgreater than that of IPNs blend membrane. The differencebetween cross linked PDMS and IPNs blend membrane ofEp values in Fig. 10 is not a significant difference whichshows that neither water nor ethanol affects the surfacedue to both the polymer and the hydrophobicity. It mightbe explained in terms of the competitive effects of thepolarity action of the permeant and the desorption resist-ance on the Ep, with membrane hydrophobicity. Thesetwo factors can compete to influence the Ep value in anopposite way; the desorption resistance increases Ep whilethe polarity action of permeants decreases Eu by enhancing

membrane mobility. However, the activation energy ofIPNs blend membrane decreased with increasing cross-linked PSt content up to 10–30wt.% of PSt, because fora lower crosslinking between PDMS and PSt. Thus, loweractive energy of IPNs blend membrane (10–30wt.%) ascompared to cross linked PDMS and IPNs blend mem-brane contains 50–70wt.% of PSt shows the lower thermalmobility of the polymer surface. While IPNs blend mem-brane contains 50wt.% of PSt revealed balanced hydro-phobic moieties and due to this significant desorptionresistance the surface membrane shows moderate thermalmobility. For comparison reasons, the PV performancesof PDMS=PSt IPNs blend membranes reported by otherresearchers are summarized in Table 3. It was observedthat the PDMS-PS IPN supported membrane has a rela-tively high permeation rate, activation energy, and anacceptable selectivity for the separation of ethanol fromethanol-water mixtures.

CONCLUSIONS

The conclusions that can be made from the presentstudy are:

1. PS has been proven to reinforce the physical propertiesof PDMS supported membrane. From their tensile test-ing as well as swelling testing, it was confirmed thatPDMS=PSt IPNs supported membrane showed anincrease in the tensile strength and at the same time sup-press the swelling effect towards toluene.

2. The highest value for flux and selectivity at 60�C for thepervaporation process to separate 10wt.% ethanol inwater using IPNs blend membrane in this study was214 g �m�2 � h�1 and 7.6, respectively. These values wereachieved using the membrane composition of50=50wt.% PDMS=PSt with 5% DCP having approxi-mate average total thickness off 600 mm with pervapora-tion feed temperature of 60�C and operating system

TABLE 3Pervaporation performances of PDMS=PSt IPNs blends membranes

PDMS blend membrane Catalyst cross linked Permeation (g=m2h) Selectivity aEP

(kJ=mol) Ref.

PDMS-PS graftcopolymer

– 130 (Water=EtOH) 6.2 – 25

PDMS=PSt BP, DVB 419=159 (O2=N2) 2.62 (O2=N2) – 26PDMS=PSt TEOS, BPO 1000 – – 7Natural Rubber –PSt IPNs

DCP, BPO, AIBNand DVB

Aromatic solventseparation

– – 27

PDMS-PSt IPNs DVB, AIBN, TEOS 160 (Water=EtOH) 5.5 4.6–7.2 8PDMS-PSt IPNs TEOS, DVB, DCP, DBD 31–326 (Water=EtOH) 0.36–7.6 8.3–14.5 this study

IPNs¼ Interpenetrating polymer network, TEOS¼Tetraethylorthosilicate, DVB¼Divinylbenzene, DCP¼Dicumyl Peroxide,DBD¼Dibutyltin dilaurate, AIBN¼ azobisisobutyronitrile, BPO¼Benzoyl peroxide.

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vacuum pressure of under 0.07 bar. The highest total fluxand selectivity was found in the requirement of the mem-branes for use in cost-competitive fermentation-perva-poration processes, assuming that the thermodynamiceffects of the other component in the fermentation brothon activity coefficients and coupling effects will notseverely affect the pervaporation performance.

ACKNOWLEDGEMENTS

The authors would like to acknowledge the support andfunding opportunities provided by the UniversityTechnology Malaysia in assistance with the MalaysianGovernment. Finally, we would like to thank theUniversity Malaysia Pahang for technical support.

LIST OF SYMBOLS

A Membrane surface area (m�2)Ad Weight of the solid specimen in air (g m)Bw Weight of solid specimen in distilled waterqs Density of the solid specimen (g m=cm3)qo density of distilled water (g m=cm3)E Young’s modulus (MPa)n Number of effective crosslink per unit volume

(Kg �mol=m3)R Gas constantT Absolute temperature (�C)nswell Network-chain segment concentration (mol=cm3)ntensile Network-chain segment concentration (mol=cm3)v2 Volume fraction of polymer in the swollen areasV1 Molar volume of solvent (cm3=mol)X12 Flory-Huggins polymer-polymer interaction

parameterd1 Solubility parameters of solventd2 Solubility parameters of polymerMc Molecular weight (g=g mol)qCx

Crosslink density (g mol=cm3)Ws Weight of wet membrane (g m)Wd Weight of dry membrane (g m)w The total amount of permeate at steady

state (cm�3)a Separation factorYi, Yj Weight fraction of component i and j in the

permeateXi, Xj Feed phase weight fraction of component i and jv1 Volume fraction of solventv2 Volume fraction of polymerds Solubility parameters of the solvent and polymerq Density of polymerDt Permeation timer Tensile stresse Tensile straing Number of effective crosslink per unit volume or

Network chain segment concentration

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