K.H.Shobana, K.S.Radha, D.Mohan / International Journal of Engineering Research and                  Applications (IJERA) ...
K.H.Shobana, K.S.Radha, D.Mohan / International Journal of Engineering Research and                     Applications (IJER...
K.H.Shobana, K.S.Radha, D.Mohan / International Journal of Engineering Research and                  Applications (IJERA) ...
K.H.Shobana, K.S.Radha, D.Mohan / International Journal of Engineering Research and                  Applications (IJERA) ...
K.H.Shobana, K.S.Radha, D.Mohan / International Journal of Engineering Research and                                       ...
K.H.Shobana, K.S.Radha, D.Mohan / International Journal of Engineering Research and                Applications (IJERA) IS...
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  1. 1. K.H.Shobana, K.S.Radha, D.Mohan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.605-610Preparation, Characterization and Application Studies of PVDF- PS Ultrafiltration Membranes K.H.Shobanaa, K.S.Radhab, D.Mohanc, a) SIES-Graduate School of Technology, Nerul, NaviMumbai – 400706, India b) R.M.D. Engineering College, Kavaraipettai, Chennai - 601206, India. c) Membrane Laboratory, Dept. of Chemical Engg., A.C.College of Technology, Anna University Chennai, ChennaiAbstract Polyvinyledenefluoride–polystyrene many acids and alkalis. This polymer is widely used(PVDF/PS) blend ultrafiltration membranes in food and medicine field for ultrafiltration [3].were prepared using phase inversion technique.Casting solutions were prepared with different These properties make PVDF as an attractivecompositions of polyvinylidene fluoride (PVDF) membrane material [4]. Its crystalline phaseand polystyrene (PS) both in the presence and provides thermal stability while the amorphousabsence of the additive, polyvinylpyrolidone phase provides the desired membrane flexibility.(PVP) using di- methylacetamide as solvent. The However, the crystallinity in PVDF has aeffects of compositions of PS and detrimental effect on the final membrane transportconcentrations of PVP on shrinkage ratio, pure properties by decreasing both the free volume andwater flux, percentage of water content and amorphous region available for species transport.[5].porosity of the blend ultrafiltration membranes Being a hydrophobic polymer PVDF has a highwere studied and results are discussed. It was shrinkage ratio which would affect the porosity offound that with the increase in PS and PVP in the membrane which in turn would reduce the purethe blend, the shrinkage ratio decreased while water flux.the pure water flux, water content and porosityof the membrane increased. The morphology of To over come the defects of the PVDF membranes,the blend membranes were obtained by scanning it requires modification. Blending of polymers inelectron microscope . Further, the application of the membrane casting solution is an usefulthe PVDF/PS blend membranes in separation of technique for modifying the properties of thetoxic heavy metal ions from aqueous streams prepared membrane and considerable a cost-were also attempted and the results are effective method. In the present investigationdiscussed. commercially available polystyrene was blended with PVDF in the presence of additiveKeyword: Polyvinylidene fluoride, polyvinylpyrolidone (PVP). PS was chosen due topolyvinylpyrolidone, polystyrene, ultrafiltration their high mechanical, thermal and chemicalmembranes ,shrinkage ratio, metal ions. resistance properties[6]. It is an amorphous polymer having wide variety of application in fuel cells,1. INTRODUCTION pervaporation and gas separation applications. There is an increasing demand fordeveloping ultrafiltration(UF) membranes with high 2 MATERIALS AND METHODSperformance to price ratio for various Industrial 2.1 MATERIALSapplications. Generally the best and extensively Polyvinylidene fluoride (Kynar gradeused method for preparation of the UF asymmetric 760, Mw 444,000) was obtained from ARKEMA,membrane is based on the finding of Loeb Singapore. Polystyrene was procured from SupremeSourirajan’s method [1]. The polymer–solvent Petrochemicals Private Limited, India. The solvent,interactions, solvent–nonsolvent interactions and Dimethylacetamide (DMAc) and the surfactant,interfacial stability play key role in the membrane Sodium Lauryl Sulphate (SLS) of AR grade wereperformance. Thus, the material selection such as purchased from M/s. Sisco Research Laboratoriespolymers, solvents, and nonsolvents is very Private Limited, India. Acetone andimportant for the fabrication of asymmetric Polyvinylpyrolidone (PVP) (Mw 40,000) weremembranes, according to its applications [2]. supplied by Hi-Pure Pvt Ltd India.Polyvinylidene fluoride (PVDF) is a polymer with 2.2. MEMBRANE PREPARATIONincreasing scientific attention and industrial The UF membranes were prepared by theimportance because of its, durability and phase inversion method using immersionbiocompatibility and high chemical resistance to precipitation technique. The blends of PVDF and 605 | P a g e
  2. 2. K.H.Shobana, K.S.Radha, D.Mohan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.605-610PS polymers were prepared by dissolving two Q - quantity of permeate collected, lpolymers at different compositions in DMAc as JW - the pure water flux, lm-2h-1solvent by thoroughly mixing for 4h at roomtemperature both in the presence and absence of t - Sampling time, hPVP at various concentrations as pore former. Thedetailed description of the preparation of the A - Area of the membrane, m2.membranes are explained elsewhere [7]. The 2.6 METAL-ION REJECTION STUDIESmembranes were prepared by casting this blend Aqueous solutions of Zn2+ and Cu2+ withsolution on a glass plate followed by evaporation an approximate 1000 ppm concentration werefor definite time in a non-solvent water bath which prepared in 1 wt% solution of Polyvinylalcoholwas kept at 10o C. (PVA) in deionized water. The pH of these aqueous solutions were adjusted to 6.25 by adding small2.3 SHRINKAGE RATIO amount of either 0.1M HCl or 0.1M NaOH. A piece of wet membrane immersed in the Solutions containing PVA and individual metal ionsglycerin solution was cut into square shape. The or metal chelates were thoroughly mixed and leftlength and width were measured with a square standing for 5 days for complete binding [10,11].caliper and the average value was obtained aftermeasuring the dimension three times. The The chelate-metal ion containing solutions weremembrane was dried at 750C for 3 h. [8] .The filled in the feed reservoir. For each run, the firstshrinkage ratio was calculated using the formula as few ml of the permeate was discarded. The permeatefollows: flux was measured by collecting the permeate at a pressure of 345 kPa. The concentration of eachShrinkage ratio (%) = [1 – ( ab/ ao bo )]x 100 metal ion in feed and permeate was measured by using Atomic Absorption Spectrophotometer where ao and bo are the length and breath of the (Perkin Elmer-2380). The pH of feed and permeatewet membrane, cm were measured with Elico pH meter. a and b are the length and breath of the The % metal ion rejection (%SR) was evaluateddry membrane, cm from the concentrations of the feed and permeate using equation2.4 WATER CONTENT The membranes were soaked in distilled  Cp water for 24h.. The soaked membranes were % SR  1   X 100mopped with the blotting paper and weighed with  C an electronic balance with 0.0001g accuracy. The  f wet membrane samples were placed in the dryer at75oCfor 48h and cooled it to room temperature in where,the desiccators and then the dry weights were Cp - Concentration of metal ion inmeasured [9] The percentage water content was permeatedetermined as follows Cf - Concentration of metal ion in feed (W1W2)% Water Content = ----------------- x 100 3. RESULTS AND DISCUSSION W1 3.1 EFFECT OF POLYMER BLENDwhere, COMPOSITION AND ADDITIVEW1 - Wet membrane weight (g) CONCENTRATION ON THE W2 - Dry membrane weight (g) SHRINKAGE RATIO OF THE MEMBRANES.2,5 PURE WATER FLUX (PWF) Shrinkage ratio plays a vital role on the porosity of the membrane. Above 30% shrinkageMembranes after compaction, were subjected to will bring much negative effect on porosity andpure water flux at a trans-membrane pressure of 345 mean pore size of membranes[8]. Higher shrinkagekPa. The permeate was measured under steady state tendency will result in tension in the membrane andflow. Pure water flux was calculated from the this has the strong influence on the structure [12].equation The casting solution was prepared from PVDF and PS polymers at a total polymer concentration of 17.5 wt%. The composition of polystyrene in the casting Jw = Q/(A t) solution was varied and its effect on the shrinkageWhere ratio was studied. It can be seen from the Fig 1 that the pure PVDF has the highest shrinkage ratio of 606 | P a g e
  3. 3. K.H.Shobana, K.S.Radha, D.Mohan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.605-61020.8% which attributes to its hydrophobic decreases the mean addition between the twonature[13]. The possible mechanism would be the components which further advances the repulsioncontraction of the polymer-rich phase after phase between the polymer leading to larger pores andseparation, which tends to pull the polymer together subsequently increases the water content of thetoward the bulk, like gel syneresis [14] membrane [15]. The addition of of PVP increases the ratio of non solvent inflow to solvent outflow byHowever, the addition of PS in the blend reduces the increasing the viscosity of the casting solution,shrinkage ratio sharply . Thus, the addition of both which according to the theory proposed by YoungPS and PVP to the blend decreases the shrinkage and Chen [16], results in more porous membranesratio. This could be explained on the basis that the resulting in higher water content with increase incast solution containing polymer in its concentrated PVP.form leads to entanglement among themacromolecular chains due to their molecular 3.3 EFFECT OF POLYMER BLENDinteractions. When the cast membrane is dipped in COMPOSITION AND ADDITIVEthe nonsolvent bath the flow of nonsolvent tends to CONCENTRATION ON PURE WATERalign the sections of chains between the coupling FLUX OF THE MEMBRANEpoints. Hence elastic energy will be stored in the The effect of blend composition on puresection of chains between entanglements. The water flux is shown in the Fig. 3.The pure PVDFenergy will be released after certain times when the membrane in the absence of PS and the additiveflow stops [13]. The membrane formation is so short exhibited the lowest flux of 7.39 lm-2h-1. Thethat there is hardly time for the release of energy. addition of 5wt% of PS to the blend, increased theHence much stress is fixed between the flux to 8.87 lm-2h-1 and at 25wt% of PSentanglements in the cast films. The stress will be concentration in the blend the flux further increasedreleased when the temperature rises during drying to 14.79 lm-2h-1. Thus, the increase in flux is a directprocess, thus resulting in the shrinkage of the consequence of the presence of PS in the blend.membrane. However, due to high glass transitiontemperature of PS (80oC) the macromolecular chain This might be due to the fact that with the increasebecomes less flexible at room temperature due to the in the PS content in the blend the nucleationglassy nature of PS. It implies that the PS chain decreases drastically. This indicated that PS additionsegment could not change their position freely at reduces the energy to form critical size nucleus ofroom temperature. Due to this reason PS acts as PVDF [17] which is expected to reduce thereinforcement in the blend membrane which crystalline nature of PVDF resulting in the improvedprevents the blend from shrinking and hence the flux. Hence, PS forms a dispersed phase inobserved results [8]. However, the existence of the continuous matrix of PVDF. Further the weakhigh supersaturation degree between the casting interactions between PVDF and PS chains also leadsolution and nonsolvent results in comparative high to larger distance between the two kinds of chainsshrinkage ratio in the absence of the additive. The and resulting in increase in the pore size and hencesupersaturation degree decreases with the addition increase in the pure water flux of the system [8].of PVP to the casting solution which is due to the Moreover, there is a high interaction between thehydrophilic nature of the PVP[12]. Which explains additive PVP and PVDF [18]. Hence, the thoroughthe low shrinkage ratio with thw addition of PVP to mixing between PVDF and amorphous PVP therethe blend. by further reducing the crystalline nature of the PVDF which has also aided in the increase of flux 3.2 EFFECT OF POLYMER BLEND with the increase of additive concentration.COMPOSITION AND ADDITIVECONCENTRATION ON WATER CONTENT 3.4 METAL ION REJECTION STUDIESOF THE MEMBRANE Ultrafiltration processes cannot be directly Effect of water content of the membrane is applied for ionic level rejection owing to the largershown in the Fig2. The water content of pure PVDF pore size of the membranes . Hence to apply thiswas found to be 59.9% in the absence of both PS membrane in metal ion rejection, the size of theand additive PVP. Since PVDF is a polar polymer it metal ions need to be enlarged there by enhancingis possible that the electrostatic repulsion will the rejection of the metal ions. In this study, a waterimpede the bundling of the polymer which could soluble chelating polymer, PVA, was used as thegive rise to larger pores or interconnected pores as complexing agent for the metal ions Cu2+ and Zn2+observed by Bowen et al [15]. However, with the and were subsequently rejected individually fromincrease in the content of PS from 5 to 25 wt% in the aqueous stream by using PVDF/PS blendthe blend, the water content also increased from ultrafiltration membranes at 345 kPa.60.6% to 82.1%. This increase in the water contentis due to the poor miscibility between the twopolymer which substantially and systematically 607 | P a g e
  4. 4. K.H.Shobana, K.S.Radha, D.Mohan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.605-6103.4.1 ROLE OF POLYMER BLEND AND FigureADDITIVE CONCENTRATION 1. Shrinkage Ratio of PVDF/ PS blendCOMPOSITION membranes The rejection of the metal ions usingPVDF/PS blend membranes in the absence of the 25additive, was carried out individually after the metalions were complexed by PVA and the results areshown in the Figs 7 and 8. 20Thus, the pure PVDF membrane in the absence of Shrinkage ratio (%)additive yielded a highest separation of 99.6% forZn2+ and 99.4% for Cu2+. It was observed that in the 15case of PVDF/PS blend membranes, the separationof Zn2+ remained constant at 99.6% when the PScontent was increased from 5 to 25 wt% in the blendin the absence of additive. Similarly the rejection for 10Cu2+ also remained constant at 99.4% with theincrease of PS in the blend from 5 to 25wt%.Moreover, there was no significant change in the 5percentage of rejection with the addition of PVP to PVP 0 wt% PVP 2.5wt% PVP 5wt%the blend. As explained already the addition of PS inthe blend decreases the shrinkage ratio. Decrease inthe shrinkage has high impact on the porosity of the 0membrane. With the increase in the PS in the 0 5 10 15 20 25 30polymer blend the pure water flux increases whilethere is no effect on the rejection of the metal ion. Polystyrene (wt % )Thus from the rejection behavior of the membrane,it could be concluded that the porosity of the Fig 1 Effect of PS and PVP on the shrinkagemembrane has increased with the increase in PS in ratio of– PVDF/PS blend membranesthe blend. Moreover, the polystyrene being nonadsorptive to electrolyte [19] the presence of PS in 2. Water Content PVDF/ PS blendthe membrane will not aid the passage of metal ion membranesresulting in higher percentage of rejection. 100/04. CONCLUSION : 79 95/5 Ultrafiltration membranes are widely used 85/15in the chemical process industries for separation and 76 75/25removal of wide variety of chemicals due to its highefficiency, low energy requirements and its compact 73 Water Content (%)nature. The ultrafiltration membranes were preparedusing PVDF and PS blend membranes in absence 70and presence of additive PVP in the solvent DMAc.By adding certain amount of PS into PVDF , the 67flux of membranes increased greatly whilemaintaining the retention ratio nearly unchanged. 64The shrinkage ratio is high in the case of pure PVDFmembrane and an addition of PS in the blend 61enhances the flux of the membrane and decreasesthe shrinkage ratio of the membrane which 58establishes that an addition of PS in the blend not 0 1 2 3 4 5 6only decreases the shrinkage ratio but also enhancesthe flux of the membrane by increasing the porosity PVP (wt%)of the membrane . Fig 2. Effect of PVP on the water content of– PVDF/PS blend membranes 3. Pure water flux (PWF) PVDF/ PS blend membranes 608 | P a g e
  5. 5. K.H.Shobana, K.S.Radha, D.Mohan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.605-610 100 100 90 80 99.5 h -1 -2 70 Pure Water Flux, lm 99 60 Rejection, % 50 98.5 40 98 30 20 97.5 100/0 w t% 95/5 w t% 10 85/15 w t% 75/25 w t% 97 100/0 95/5 85/15 75/25 0 0 1 2 3 4 5 6 96.5 Time, h 0 1 2 3 4 5 6 PVP Concentration, % Fig 3 Effect of PVP on the PWF of– PVDF/PS blend membranes Fig 5 Effect of PVP concentration on rejection of Cu2+ metal ions 4. Zn2+ ion rejection PVDF/ PS blend PVDF/PS blend membranes membranes Reference 99.8 [1]. G.S. Loeb, S. Sourirajan, Sea water demineralization by means of an osmotic 99.6 membrane, Adv. Chem. Ser. 38 (1963) 117. 99.4 [2]. P. Van de Witte, P.J. Dijkstra, J.W.A. Van den Berg, B.J. Feijen, Phase separation processes in polymer solutions in relationRejection, % 99.2 to membrane formation, J. Membr. Sci. 117 (1996) 1. 99 [3]. Zhihong Xu, Lei Li, Fawen Wu, Shujuan Tan and Zhibing Zhang (2005), ‘The 98.8 application of the modified PVDF ultrafiltration membranes in further 98.6 purification of Ginkgo biloba extraction’,J. 100/0 95/5 85/15 75/25 Membr. Sci., 255 (2005)125.. 98.4 [4]. Deshmukh S.P. and Li K., ‘Effect of 0 1 2 3 4 5 6 ethanol composition in water coagulation PVP Concentration, % bath on morphology of PVDF hollow fibre membranes’, J. Membr. Sci., 150 (1998) 75. Fig 4 Effect of PVP concentration on rejection of [5]. Recent advances in the formation of phase Zn2+ metal ions inversion membrane from amorphous or PVDF/PS blend membranes semi-crystalline polymers, J. Membr. Sci. 113 (1996) 361 5. Cu2+ ion rejection PVDF/ PS blend [6]. M. E. Chiriac, V. Chiriac, C. Vasilea, M. membranes Pascub*Asymmetric membranes from polystyrene/polyolefin blends Journal of Optoelectronics and Advanced Materials. 7,(2005), 2895. [7]. Malaisamy.R, Mahendran.R, Mohan.D, Rajendran.M, Mohan.V, Cellulose acetate and Sulfonated Polysulfone blend ultrafiltration membranes. I. preparation 609 | P a g e
  6. 6. K.H.Shobana, K.S.Radha, D.Mohan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.605-610 and characterization, Journal of Membrane HFP/PS polymer blends’, J. Electrochem. Science, 86 (2002) 1749. Soc.148 (2001) 279.[8]. Lishun Wu, Junfen Sun, Qingrui Wang, Poly(vinylidene fluoride)/polyethersulfone blend membranes: Effects of solvent sort, polyethersulfone and polyvinylpyrrolidone concentration on their properties and morphology. J. Membr. Sci. 113 (1996) 361.[9]. Qing-Zhu Zheng, Peng Wang, Ya-nan Yang, De-Jie Cui, The relationship between porosity and kinetics parameter of membrane formation in PSF ultrafiltration membrane J.Membr Sci 286 (2006) 7.[10]. Jarvis N.V and Wagener J.M.,Mechanical study of metal ion binding to water soluble polymers using potentiometry, Talanta 12 (1995) 219.[11]. Kobayashi S., HiroishiK., Tokunoh M. and saegusa T., Chelating properties of linear and branched poly(ethyleneimines), Macromolecules 20 (1987) 1496.[12]. Susanto H. and Ulbricht M., ‘Charecterisation performance and stability of PES ultrafiltration membrane prepared by phase separation method using different macromolecular additive’, J. Membr. Sci., 327 (2009) 125.[13]. P. Menut, Y.S. Su, W. Chinpa, C. Pochat- Bohatier, A. Deratani, D.M. Wang, P. Huguet, C.Y. Kuo, J.Y. Lai, C. Dupuy, A top surface liquid layer during embraneformation using vapour-induced phase separation (VIPS)—evidence and mechanism of formation, J. membr. Sci. 310 (2008) 278.[14]. T.A. Tweddle, O. Kutowy, W.L. Thayer, S. Sourirajan, Polysulfone ultrafiltration membranes, Ind. Eng. Chem. Prod. Res. Dev. 22 (1983) 320.[15]. W. Richard Bowen, Shu Ying Cheng, Teodora A. Doneva and Darren L. Oatley,’ Manufacture and characterisation of polyetherimide/sulfonated poly(ether ether ketone) blend membranes, J.Membr.Sci 250 (2005) 1.[16]. Young T.H. and Chen L.W. ‘A diffusion- controlled model for wet-casting membrane formation’, J. Membr. Sci., 59 (1991) 169.[17]. Del Rio C. and Acosta J.L., ‘Microstructure and Compatibility of PVDF/PS Blends in the Presence of PVA’, Polym. Inter., 34, (1994) 417.[18]. Ningping Chen and Liang Hong, ‘Surface morphology and the composition of casting film of PVDF-PVP blend’, Polymer, 43, (2002) 1429.[19]. Hitao Huang and Wunderz S.L., ‘Ionic conductivity of Microporous PVDF- 610 | P a g e