research article characterization of functionalized...

Research ArticleCharacterization of Functionalized PolyurethaneFoam for Lead Ion Removal from Water

Subhashini Gunashekar and Nidal Abu-Zahra

Materials Science and Engineering Department University of Wisconsin-Milwaukee 3200 N Cramer StreetMilwaukee WI 53201 USA

Correspondence should be addressed to Subhashini Gunashekar gunashe2uwmedu

Received 14 October 2013 Accepted 28 January 2014 Published 10 March 2014

Academic Editor Harald W Ade

Copyright copy 2014 S Gunashekar and N Abu-Zahra This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Polyurethane foams functionalized with sulfonic acid groups are used in this study to exchange lead (Pb2+) ions from aqueoussolutions Toluene-2 4-diisocyanate 26-diisocyanate (TDI) was reactedwith Polypropylene glycol 1200 (PPG) in 2 1molar ratio toform a linear prepolymer The linear prepolymer was further polymerized using NN-bis(2-hydroxyethyl)-2-aminoethanesulfonicacid (BES) which acts both as a chain extender and an ion-exchanger for Pb2+ ions The functionalized polyurethane foamwas characterized by Fourier transform infrared spectroscopy (FTIR) gel permeation chromatography (GPC) scanning electronmicroscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) The Pb2+ ion exchange capacity was determined using anInductively Coupled PlasmaMass Spectrometer (ICP-MS)Themaximum Pb2+ ion exchange capacity of the foam was found to be51 ppbg from a 100 ppb Pb2+ solution over a period of two hours In addition pH analysis was carried out on the foam compositionwith the best Pb2+ ion removal capacityThe pH results based on two-hour exposures showed that the functionalized polyurethanefoam performed better at lower pH levels

1 Introduction

Polyurethane foams are considered to be one of the bestcommercially available insulation materials They possessgood thermal insulating properties low moisture-vapor per-meability high resistance to water absorption and a relativelyhigh specific strength Another advantage of polyurethanefoam systems is that the synthesis can be tailored to variousspecific applicationsThemajor components of polyurethanefoams are an isocyanate and a polyol (or amixture of polyols)A blowing agent and a catalyst are used to accelerate the foamformation The foams can be synthesized as open-cell foamsor as closed-cell foams based on the initial raw materialsconcentration Recently the cellular form of this polymer hasintrigued researchers to explore other novel applications forthis material

Open cell polyurethane foams have been shown to exhibita reasonable amount of ion exchange capacity and henceare being considered as suitable ion exchange media forheavy metal ions removal [1] Braun and Farag [2] showedthat open-pore polyurethanemicrospheres exhibit low cation

exchange capacity Their research on foams prepared bychemical bonding of specific functional groups (ndashSH) wasused to adsorb mercury ions from mercury (II) chloride andmethyl mercury (II) chloride in the range of 04 to 400 ppbThis also led researchers to consider the functionalizationof polyurethane foams as another effective technique toeliminate heavy metal ions either by adsorption or pre-concentration mechanisms Functional groups like hydroxylketone and carboxylic acids have been found to adjustthe surface energy and improve the hydrogen binding inpolymers [3] This property is the basis for functionaliza-tion of polyurethane foams either by surface or structuralmodification Yeon et al [4] developed a continuous elec-trodeionization medium to deionize aqueous media to ahigh level without the need for chemical regeneration usingfunctionalized polyurethane foam A chain extender wasused during synthesis to functionalize the prepolymer Thisled to the bulk functionalization of polyurethane foam withan increase in ion exchange capacity as the number of sulfonicacid groups increased

Hindawi Publishing CorporationInternational Journal of Polymer ScienceVolume 2014 Article ID 570309 7 pageshttpdxdoiorg1011552014570309

2 International Journal of Polymer Science

Functionalization of polyurethane foams by surfacemod-ification has led to systems capable of adsorbing heavy metaland tracemetal ions Surfacemodification of the foamusuallyinvolves the coupling of a sorbent to the polyurethane foamthrough an AZO group [5ndash8] Fournier et al [9] have used acopper catalyst to aid the cycloaddition of various azide com-pounds to modify the alkyne groups along the polyurethanebackbone to obtain a side-chain functionalized cross linkedpolyurethane by means of click chemistry Researches ongraft and composite foam systems have established theirefficiency to treat heavy metal ions [10ndash12] Polyurethanefoams modified by grafting acrylonitrile and acrylic acidby gamma irradiation method reported by Meligi [10] haveshown that the adsorption of heavy metal ions like Zn(II)Fe(II) Ca(II) Ni(II) Cu(II) and Pb(II) was affected by pHatomic weight and initial contaminant concentration

In a study published by Jang et al [11] hydroxyapatite-(HAP-) polyurethane foams were synthesized for Pb2+ ionadsorption A maximum adsorption capacity was deter-mined to be 150mgg for the composite with 50wt HAPThe study also concluded that higher HAP concentrationexhibited higher Pb2+ ion adsorption capacity Less uniformdispersion of HAP in the foam led to slower adsorptionand adsorption was dominant at higher pH levels Anothertype of polyurethane composite foam containing alginatewas synthesized by Sone et al [12] which had a structuresimilar to a weak cation exchanger Results from this studyshowed that Pb2+ adsorption was sensitive to lower pH andcompeting cations and the Pb2+ ion adsorption using thisfoam ranged from 20 ppb to sim100 ppb in 2 hrs

However the research summary described above doesnot address bulk functionalization of polyurethane foamsfor selective elimination of heavy metal ions To addressthis we focused our research work on the development of abulk functionalized polyurethane foam system using a chainextender Chain extenders are low-molecularmultifunctionalspecies They can be used to balance the backbone structureof polymers [13] This makes them suitable for selectiveelimination of heavy metal ions In this paper we discuss themodified synthesis process formulated by Yeon et al [4] usingNN-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES)chain extender to eliminate Pb2+ ions from aqueous mediaIn addition we will present a broad range of characterizationof the functionalized foam in order to better understand thecapabilities and limitations of the foam to remove Pb2+ ionsfrom water

2 Experimental Work

21 Materials Polypropylene glycol 1200 (PPG SigmaAldrich Co LLC) was dried in a vacuum oven at 70∘C for 24hours Toluene diisocyanate (TDI 24ndash80 and 26ndash20Alfa Aesar) Dimethyl Sulfoxide (DMSO Alfa Aesar 999pure) NN-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid(BES Alfa Aesar 99 pure) Dibutyltin dilaurate (DBTLSigma Aldrich 95 pure) Polysiloxane surfactant (SigmaAldrich) and Nitrogen gas (Airgas O

2free UHP) were used

22 Synthesis of Functionalized Polyurethane Foam Theexperimental set up consists of a 3-neck round bottom reac-tion flask placed in an oil bath fitted with a mechanical stirrerand a condenser at the center neck nitrogen gas inlet andoutlet at the right neck and a drop funnel at the left neckThereaction was carried out at 65ndash70∘C in an inert atmosphereThe 3-neck flask was initially charged with TDI and allowedto stabilize at 70∘C in a saturated nitrogen atmosphere A dropfunnel was filled with a preweighted amount of PPG whichwas added drop wise and allowed to react with TDI for 3-4hours until an initial isocyanate content of 11-12was reachedas described in ASTM D5155 procedure

A preweighted amount of BES dissolved in DMSO(amount of DMSO used was based on the solubility limitof BES in DMSO) at 70∘C was added drop wise into thereaction flask The reaction was allowed to proceed until afinal isocyanate content of 7-8 was reached The tin catalystwas added at the end and the prepolymer was decanted into aglass mold Based on the amount of PPG used a preweightedamount of distilled water was added as a blowing agent alongwith the surfactant The mixture was then mixed using amechanical stirrer at 2500ndash3000 rpm for 10ndash15 seconds Thisinitiates the reaction of water with the remaining isocyanategroups forming an intermediate compound and eventuallyreleasing CO

2gas to form the cellular structure [14]

In order to determine the optimum (1) chain extender(BES) content (2) molar ratio of PPG and TDI and (3) chainextender reaction time (CERT) a set of experiments weredesigned as discussed below The objective of these experi-ments was to characterize the effect of these parameters onthe physical properties and performance (ie ion exchangecapacity) of the foam Table 1 shows a detailed list of thecompositions used to prepare the foam samples SamplesA1 to A4 were prepared with different BESDMSO contentswhile other parameters are maintained constant SamplesB5 to B7 were prepared with different PPGTDI ratioswhereas samples C8 toC10were preparedwith different chainextender reaction times (CERT) SamplesA3 B6 andC8havethe same composition but they are used to study differentdesign variables

23 Fourier Transform Infrared (FTIR) Spectroscopy Thefunctionalized polyurethane foam samples were character-ized by a BRUKER vector 22 FTIR with a DTGS (deuteratedtriglycine sulfate) detector and a PIKE 3ndash12 multibounceZn-Se variable angle ATR The incidence angle was set to80 during characterization The foam samples were cut intostrips of 310158401015840 times 110158401015840 times 0510158401015840 and were washed in distilled waterand dried in a vacuum oven before testing The IR spectrumwasmeasured from400 to 4000 cmminus1 to confirm the presenceof sulfonic groups in the polymer structure

24 Gel Permeation Chromatography (GPC) The polyure-thane foam samples were analyzed using a Varian ProStarHPLC system using a PLgel 5mm mixed C column HPLCgrade dimethyl formamide (DMF) was used as the eluentwith a flow rate of 1mLmin The UV detector was set todetect sample at a wavelength of 569 nm Foam samples weredissolved in DMF to get a 05wv concentration and 25 120583L

International Journal of Polymer Science 3

Table 1 Foam composition based on various processing variables

Variable Sample PPG (g) TDI (g) BES (g) DMSO (g) DBTL (g) Surfactant (g) Water (g) CERT (min)

BESDMSO

A1

50 183

0 0

2 025 6 40A2 34 78A3 67 157A4 101 235

PPGTDIB5

5091

67 157 2 025 6 40B6 183B7 274

CERTC9

50 183 67 157 2 025 660

C8 40C10 90

of the sample was injected into the column [15] The mainpurpose of this analysis was to determine the effect of thechain extender (BES) and the solvent (DMSO) on the foamstructure during synthesis

25 Sample Preparation for ICP-MS Analysis An InductivelyCoupled Plasma Mass Spectrometer (ICP-MS) was usedfor trace metal analysis at ppb levels The demolded func-tionalized foam was cut into one gram cubes maintaininga constant volume Polyurethane foam requires homoge-neous rearrangement of its polymeric bonds for effectiveion exchange as the foam does not experience stress-freeconditions after synthesis [4] The foam cubes were washedin distilled water and conditioned in 2N NaCl solution forfour hours to ensure rearrangement of the polymeric bonds

Standard Pb2+ solutions of 100 ppb were prepared from astock solution of 1 part per million (ppm) The conditionedfoams were soaked in 25mL of Pb2+ solution in a beakerwith a magnet The beaker was then covered to avoidcontamination and placed on a stirrer Foam cubes weresubmersed in the Pb2+ solution for various time periods10mL of each sample was filtered into 15mL centrifuge tubesNitric acid was added to stabilize the Pb2+ ions in the sampleduring storage and for ICP-MS analysis

3 Results and Discussion

The study samples were prepared according to Table 1 shownearlier The physical characteristics of the foam such as itscolor odor pore size and structure depend primarily onthe DMSO (solvent) content Foam samples A1 A2 and A3whichwere preparedwith lower amounts ofDMSOand lowerCERTs had a similar pale yellow color and were odorlessFoam samples which were prepared with higher amounts ofDMSO andor CERTs were much darker (brownish) and hada strong odor Similarly the flexibility of the foam seemedto increase with increasing DMSO content and CERT as wasobserved with samples A3 A4 C9 and C10 This may be dueto the cleavage of the polymeric bonds connecting the hardsegments in the foam formed by DMSO since it is a strongorganic solvent capable of dissolving the polyurethane foamonprolonged exposuresOn the other hand the rigidity of thefoam increased with increasing TDI content (eg B7) due to

the excess hard segments formed by the quasiprepolymer inthe foam [16] Lower amounts of TDI in sample B5 did notfavor foam formation leading us to the conclusion that theratio of soft and hard segments (polyol isocyanate) shouldbe higher than 1 1 to form an isocyanate terminated trueprepolymer [16]

31 Fourier Transform Infrared (FTIR) Spectroscopy TheFTIR spectrum of the foam samples A1 to A4 with varyingBESDMSO content is shown in Figure 1 Sample A1 showsa clear CndashOndashC peak at 1100 cmminus1 as it does not contain anychain extenders with the sulfonic groups The OndashSndashO peaksstart to appear at sim1060 cmminus1 in other samples and this peakpartially overlaps with the CndashOndashC bandThe asymmetricallystretched S=O peak appears at 1350 cmminus1 The urethanecarbonyl peaks appear at 1700 cmminus1TheNHband andHndashNHband appear at 3000 cmminus1 [4]These indicate that the sulfonicacid functional groups were successfully integrated into thepolyurethane backbone The ndashCH stretching vibrations fromthe polyol appear at 2850ndash3000 cmminus1 followed by the ndashOHand ndashNH stretching that can be seen at 3200ndash3300 cmminus1[17] The ndashCH bending vibrations due to substitution groupsin alkenes and aromatics are usually seen between 850ndash950 cmminus1 [18] The gradual appearance of a peak in thisregion as the BES content and CERT is increased confirmsthe incorporation of the BES chain extender into the polymerbackbone

Sung and Schneider [19] have reported that the ureamicrodomains in polyurethane foams are known to possessbidentate hydrogen bonding which is associated with a1640 cmminus1absorbance observed via FTIR The presence ofhydrogen bonding also leads to the hard segments packingin an organized manner In another study Aneja and Wilkes[20] compared the isomers of TDI and determined that the1640 cmminus1 absorbance was found to decrease as the 24 TDIisomer content increased and suggested that the symmetryof the isocyanate moiety had a considerable impact on thepacking behavior of the urea hard segments FromFigure 2 itis clearly evident that samplesA3 (B6C8) andB7 do not showany significant peaks at 1640 cmminus1 This may be due to thefoam composition since the samples differ only by an excessof 05 moles of TDI in each case whichmay not be significant


500100015002000250030003500Wavenumbers

Abso

rban

ce

A4

A3

A2

A1

Figure 1 FTIR spectrum of samples A1ndashA4

5001000150020002500300035004000Wavenumbers

Abso

rban

ce

C10

C9

C8B6

B7

Figure 2 FTIR spectrum of samples B7ndashC10

to show any changes in absorbance The effect of CERT canbe observed in the absorbance spectrums for samples A3 C9and C10 The CndashOndashC and OndashSndashO peaks start to overlap at1100 cmminus1 as the CERT increases they seem to merge to forma single peak

32 Gel Permeation Chromatography (GPC) BES is a chainextender which links the isocyanate groups in the linear poly-mer chains through its hydroxyl groups thereby increasingthe molecular weight of polyurethane DMSO is a strongorganic solvent that dissolves polyurethane as well as BESSince BES is insoluble in other organic solvents the use ofDMSOcannot be eliminated from the foam synthesis processHence both BES and DMSO have an opposite effect on themolecular weight of the resulting polyurethane system

GPC analysis shows that the retention time needed toelute higher molecular weight or larger molecules decreasesas the DMSO content and CERT increase during synthesisThis can be seen in Figure 3 for samples A1ndashA4 SampleA1 has no DMSO and it elutes at 114 minutes As theamount of DMSO increases in samples A2ndashA4 we can seelarger molecules eluting earlier than 114 minutes followed by

Table 2 Retention times of foam samples

Sample Peak retention time (mins)A1 114A2 95 113A3 86 111 116A4 77 110 117 137 146B7 92 114C9 94 110 114 139C10 94 97 106 117 153

(mAU

)(m

AU)

(mAU

)(m

AU)

5 10 15 20 25(min)

40

20

0

100500

minus50

100

50

0

minus50

minus100

200

100

0

minus100

A1

A4

A2

A3

114

7211

131

113

20

953

1

770

1

110

5911

780

137

4414

693

864

3

143

84

116

24

Figure 3 High and low molecular weight compounds of function-alized polyurethane foam samples based on BESDMSO content

smaller molecules after 114 minutesThis can be attributed tothe cleavage of polyurethane chains forming in samples withhigher DMSO content The peak retention times for all thetested samples are summarized in Table 2

Samples A2 and B7 seem to show a similar elution trendA2 has a lower amount of DMSO and B7 has a higherTDI content in its composition This provides additionalisocyanate groups for functionalization therefore loweringthe ability of DMSO to break the polymer chains duringsynthesis Hence increasing the TDI content in the foamcomposition without affecting the structural integrity of thefoam may be a way to reduce the cleaving effect of DMSO

Similarly Figure 4 shows GPC analysis for samples B7ndashC10 It is evident that increasing CERT has the same effectin samples C9 and C10 Larger molecules start to elute after94 minutes and with reasonable amounts of DMSO higherCERT seems to cleave polymer chains to a greater extentresulting in a large molecular weight distribution in the foamsampleThis is confirmed by the higher number of molecularsegments that are seen to elute at 94 97 106 117 and 153minutes respectively in sample C10 which was prepared withthe highest CERT These factors influence the distributionof the functional group in the foam and affect the Pb2+ ionremoval capacity of the foam


C9

B7

C10C10

B7

C9

5 10 15 20

(min)

50

0

minus50

7550250

minus25minus50minus75

50

25

0

minus25

minus50

minus75

(mAU

)(m

AU)

(mAU

)

944

8

119

7511

491

139

95

114

00

924

09

488

977

310

696

117

89

153

60

Figure 4 High and low molecular weight compounds of function-alized polyurethane foam

33 Scanning Electron Microscopy and Energy DispersiveX-Ray Analysis (SEMEDX) Foam samples were analyzedusing a Topcon SM-300 SEMEDX instrument The sampleswere coated using a sputter coater before analysis Figure 5confirms the open cell structure of an unconditioned foamsample with A3 composition Elemental analysis by EDXperformed on the foam sample after soaking in 100 ppbstandard Pb2+ solution for 2 hours shows the presence ofPb2+ in the bulk of the foam sample along with sulfur andvarious other elements as shown in Figure 6 This confirmsthe Pb2+ ion exchange with sulfonic acid groups in thefunctionalized polyurethane foam

34 Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) ICP-MS is a powerful analytical technique that allowsdetection of trace elements at parts per billion and parts pertrillion levels Lead ion exchange capacity of the synthesizedfoam was measured using ICP-MS

The synthesized foam samples were cut into symmetricalcubes weighing about 1 gram and were conditioned in 2NNaCl solution for 4 hours before soaking in a 100 ppb leadsolution for a period of 2 hours The lead solution wasfiltered and analyzed by ICP-MS to determine the final leadconcentration in the solutionThe experiments were repeatedwith two grams of foam samples The results of this analysisare shown in Figure 7

Foam samples A1 (0 moles BES) showed some Pb2+removal in the absence of sulfonic functional groups whichconfirms that the mechanism of lead ion removal is not onlyby ion exchange but may also be due to surface adhesion orabsorption [21] The lead removal capacity steadily increasesas the chain extender (BES) content increases in samples A2(002 moles BES) and A3 (003 moles BES) However sampleA4 (005 moles BES) exhibited lower Pb2+ removal This maybe a result of uneven distribution of functional groups inthe bulk of the foam due to the disintegration of polymer

Figure 5 SEM image of polyurethane foam at 50x magnification

248

186

124

62

Spectrum 1

Cou

nts

000 128 256 384 512 640 768 896 1024

X-ray energy (keV)

Real time 618Live time 600

Figure 6 EDX elemental analysis

0

10

20

30

40

50

60

Experiment

0BE

S

002

BES

003

BES

005

BES

CERT

60

CERT

90

Pb2+

ions

rem

oved

(ppb

)

1 3

PPG

TD

I

ppb2gppb1g

Figure 7 Lead removal capacity based on foam weight

chains by excess DMSO used to dissolve higher amounts ofBES This is supported by a similar behavior observed withincreasing the CERT in experiment C10 Foam samples withcomposition A3 exhibited the best lead removal capacity

An increase in lead removal capacity for all the foamsamples was observed when 2 grams of the foam was soaked


0

10

20

30

40

50

60

1 2 24 48

Lead

rem

oved

(ppb

)

Time (hrs)

pH 65pH 85

Figure 8 pH analysis of functionalized polyurethane foam

in Pb2+ solutionThis is clearly due to the availability of addi-tional functional groups for ion exchangewhich increased thePb2+ ion removal capacity from 48 ppbg to 53 ppb2g of A3foam

35 pH Analysis Based on the above results A3 foam sam-ples were analyzed at 65 and 85 pH levels over a period of 1 to48 hours as shown in Figure 8 Since the foam is consideredfor drinking water applications it was not tested at higheror lower pH levels The lead removal capacity of the foamseemed to be higher at a pH of 65 with a maximum leadremoval capacity of 51 ppbg after soaking the foam in leadsolution for 2 hrs

The lead removal capacity of the foam seemed to taperdown and saturate after 2 hrs Lead removal capacity of thefoam also seemed to decrease as the pH of the solutionincreases to 85 This may be due to the neutralizationof the sulfonic acid groups at higher pH levels which inturn diminishes the availability of functional groups for ionexchange [21] The foam seems to have a better lead removalcapacity at lower pH values for the same reason

4 Summary and Conclusions

Polyurethane foam made of PPG and TDI segments withsulfonic functional groups was synthesized using BES chainextender dissolved inDMSO for Pb2+ ion removal fromaque-ous solutions Various parameters such as PPGTDI ratioBESDMSO content and CERT were studied by designinga set of ten experiments The outcome of each experiment(ie combination) was recorded to analyze the physicalcharacteristics of the functionalized foam The foams wereconditioned in 2NNaCl solution to improve the ion exchangecapacity and to realign the polymeric bonds

FTIR characterization of the foam samples confirmed thepresence of sulfonic groups in the polyurethane backboneGPC characterization confirmed polymer chain disintegra-tion due to higher DMSO content and increased CERT Thiswas further confirmed by ICP-MS analysis showing the leadremoval capacity of the foams Foam samples containing

higher DMSO exhibit lower Pb2+ removal rate since thefunctional groups were not available uniformly throughoutthe bulk of the foam EDX analysis confirmed the presenceof Pb2+ in the foam samples soaked in a standard leadsolution Foam samples synthesized with 1 2 mole ratio ofPPG TDI and 06 4 moles of BES DMSO (based on molesof TDI) exhibited the best performance of lead removal Themeasured lead removal capacity of the foam was 48 ppbgand 51 ppb2g pH analysis of the foam showed reductionin its lead removal capacity at higher pH levels due toneutralization of sulfonic acid groups which lowered thenumber of functional sites available for ion exchange

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Theauthorswould like to thank themembers ofWater Equip-ment Policies (WEP) and Industry-University cooperativeresearch program (IUCRC) for their support through thecourse of this research work The authors would also like toextend their gratitude to Susan Krezoski from the Depart-ment of Chemistry and Biochemistry UW-Milwaukee forscheduling and coordinating the use of ICP-MS and DrXiangyang Liu and Dr Marianna Orlova of the UW-Milwaukee biotech facility for training and coordinating theuse of GPC

References

[1] R L MacBrayer D C Wysocki Polyurethane Foams Formula-tion and Manufacture Program Division Technomic Publish-ing Company Incorporated 347 pages 1998

[2] T Braun and A B Farag ldquoPolyurethane foams and micro-spheres in analytical chemistry Improved liquid-solid gas-solidand liquid-liquid contact via a new geometry of the solid phaserdquoAnalytica Chimica Acta vol 99 no 1 pp 1ndash36 1978

[3] J G A Terlingen ldquoIntroduction of functional groups at poly-mer surfaces by Glow discharge techniquesrdquo Tech Paper Euro-plasma 1993

[4] K H Yeon JW Lee J S Lee and S HMoon ldquoPreparation andcharacterization of cation-exchange media based on flexiblepolyurethane foamsrdquo Journal of Applied Polymer Science vol 86no 7 pp 1773ndash1781 2002

[5] V A Lemos L N Santos A P O Alves and G T DavidldquoChromotropic acid-functionalized polyurethane foam a newsorbent for on-line preconcentration and determination ofcobalt and nickel in lettuce samplesrdquo Journal of SeparationScience vol 29 no 9 pp 1197ndash1204 2006

[6] R J Krupadam M S Khan and S Das ldquoAdsorption of fluor-ide from water by surface-functionalized polyurethane foamrdquoWater Science and Technology vol 62 no 4 pp 759ndash765 2010

[7] E A Moawed M A A Zaid and M F El-Shahat ldquoAnalyticalapplication of polyurethane foam functionalized with quinolin-8-ol for preconcentration and determination of tracemetal ionsin wastewaterrdquo Journal of Analytical Chemistry vol 61 no 5 pp458ndash464 2006


[8] E A Moawed M A Zaid and M F El-Shahat ldquoPreparationcharacterization and applications of polyurethane foam func-tionalized with resorcinol for quantitative separation and deter-mination of silver(I) andmercury(II) from tap and wastewaterrdquoInternational Journal of Environmental Analytical Chemistryvol 84 no 12 pp 935ndash946 2004

[9] D Fournier B G de Geest and F E du Prez ldquoOn-demand clickfunctionalization of polyurethane films and foamsrdquo Polymervol 50 no 23 pp 5362ndash5367 2009

[10] G A Meligi ldquoRemoval of some heavy metal ions using graftedpolyurethane foamrdquo Polymer vol 47 no 1 pp 106ndash113 2008

[11] S H Jang B G Min Y G Jeong W S Lyoo and S C LeeldquoRemoval of lead ions in aqueous solution by hydroxyapatitepolyurethane composite foamsrdquo Journal of Hazardous Materi-als vol 152 no 3 pp 1285ndash1292 2008

[12] H Sone B Fugetsu and S Tanaka ldquoSelective eliminationof lead(II) ions by alginatepolyurethane composite foamsrdquoJournal of Hazardous Materials vol 162 no 1 pp 423ndash4292009

[13] ldquoUnderstanding Chain Extenders and CrosslinkersrdquoSpecialChem 2004 httpwwwspecialchem4polymerscomresourcesarticlesarticleaspxid=1777

[14] M Szycher SzycherrsquoS Handbook of PolyurethaneS CRC PressNew York NY USA 1999

[15] G Saunders and B MacCreath Application Note MaterialsTesting and Research Polymers 2013 httpwwwchemagilentcomLibrarybrochures5990-7994-GPCorganics-Apr11-9lopdf

[16] MChanda and SK RoyPlastics TechnologyHandbook chapter2 CRC Press New York NY USA 3rs edition 1998

[17] J Hansen Characteristic IR Absorption Frequencies of OrganicFunctional Groups 2006 httpwww2upsedufacultyhan-sonSpectroscopyIRIRfrequencieshtml

[18] P Beauchamp Spectroscopy Data Tables 2010 httpwwwcsupomonaedusimpsbeauchamppdf424 spectra tablespdf

[19] C S P Sung and N S Schneider ldquoInfrared studies of hydrogenbonding in toluene diisocyanate based polyurethanesrdquo Macro-molecules vol 8 no 1 pp 68ndash73 1975

[20] A Aneja and G L Wilkes ldquoOn the issue of urea phase connec-tivity in formulations based on molded flexible polyurethanefoamsrdquo Journal of Applied Polymer Science vol 85 no 14 pp2956ndash2967 2002

[21] C E Harland Ion ExchangeTheory and Practice Royal Societyof Chemistry 2nd edition 1994

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


Functionalization of polyurethane foams by surfacemod-ification has led to systems capable of adsorbing heavy metaland tracemetal ions Surfacemodification of the foamusuallyinvolves the coupling of a sorbent to the polyurethane foamthrough an AZO group [5ndash8] Fournier et al [9] have used acopper catalyst to aid the cycloaddition of various azide com-pounds to modify the alkyne groups along the polyurethanebackbone to obtain a side-chain functionalized cross linkedpolyurethane by means of click chemistry Researches ongraft and composite foam systems have established theirefficiency to treat heavy metal ions [10ndash12] Polyurethanefoams modified by grafting acrylonitrile and acrylic acidby gamma irradiation method reported by Meligi [10] haveshown that the adsorption of heavy metal ions like Zn(II)Fe(II) Ca(II) Ni(II) Cu(II) and Pb(II) was affected by pHatomic weight and initial contaminant concentration

In a study published by Jang et al [11] hydroxyapatite-(HAP-) polyurethane foams were synthesized for Pb2+ ionadsorption A maximum adsorption capacity was deter-mined to be 150mgg for the composite with 50wt HAPThe study also concluded that higher HAP concentrationexhibited higher Pb2+ ion adsorption capacity Less uniformdispersion of HAP in the foam led to slower adsorptionand adsorption was dominant at higher pH levels Anothertype of polyurethane composite foam containing alginatewas synthesized by Sone et al [12] which had a structuresimilar to a weak cation exchanger Results from this studyshowed that Pb2+ adsorption was sensitive to lower pH andcompeting cations and the Pb2+ ion adsorption using thisfoam ranged from 20 ppb to sim100 ppb in 2 hrs

However the research summary described above doesnot address bulk functionalization of polyurethane foamsfor selective elimination of heavy metal ions To addressthis we focused our research work on the development of abulk functionalized polyurethane foam system using a chainextender Chain extenders are low-molecularmultifunctionalspecies They can be used to balance the backbone structureof polymers [13] This makes them suitable for selectiveelimination of heavy metal ions In this paper we discuss themodified synthesis process formulated by Yeon et al [4] usingNN-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES)chain extender to eliminate Pb2+ ions from aqueous mediaIn addition we will present a broad range of characterizationof the functionalized foam in order to better understand thecapabilities and limitations of the foam to remove Pb2+ ionsfrom water

2 Experimental Work

21 Materials Polypropylene glycol 1200 (PPG SigmaAldrich Co LLC) was dried in a vacuum oven at 70∘C for 24hours Toluene diisocyanate (TDI 24ndash80 and 26ndash20Alfa Aesar) Dimethyl Sulfoxide (DMSO Alfa Aesar 999pure) NN-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid(BES Alfa Aesar 99 pure) Dibutyltin dilaurate (DBTLSigma Aldrich 95 pure) Polysiloxane surfactant (SigmaAldrich) and Nitrogen gas (Airgas O

2free UHP) were used

22 Synthesis of Functionalized Polyurethane Foam Theexperimental set up consists of a 3-neck round bottom reac-tion flask placed in an oil bath fitted with a mechanical stirrerand a condenser at the center neck nitrogen gas inlet andoutlet at the right neck and a drop funnel at the left neckThereaction was carried out at 65ndash70∘C in an inert atmosphereThe 3-neck flask was initially charged with TDI and allowedto stabilize at 70∘C in a saturated nitrogen atmosphere A dropfunnel was filled with a preweighted amount of PPG whichwas added drop wise and allowed to react with TDI for 3-4hours until an initial isocyanate content of 11-12was reachedas described in ASTM D5155 procedure

A preweighted amount of BES dissolved in DMSO(amount of DMSO used was based on the solubility limitof BES in DMSO) at 70∘C was added drop wise into thereaction flask The reaction was allowed to proceed until afinal isocyanate content of 7-8 was reached The tin catalystwas added at the end and the prepolymer was decanted into aglass mold Based on the amount of PPG used a preweightedamount of distilled water was added as a blowing agent alongwith the surfactant The mixture was then mixed using amechanical stirrer at 2500ndash3000 rpm for 10ndash15 seconds Thisinitiates the reaction of water with the remaining isocyanategroups forming an intermediate compound and eventuallyreleasing CO

2gas to form the cellular structure [14]

In order to determine the optimum (1) chain extender(BES) content (2) molar ratio of PPG and TDI and (3) chainextender reaction time (CERT) a set of experiments weredesigned as discussed below The objective of these experi-ments was to characterize the effect of these parameters onthe physical properties and performance (ie ion exchangecapacity) of the foam Table 1 shows a detailed list of thecompositions used to prepare the foam samples SamplesA1 to A4 were prepared with different BESDMSO contentswhile other parameters are maintained constant SamplesB5 to B7 were prepared with different PPGTDI ratioswhereas samples C8 toC10were preparedwith different chainextender reaction times (CERT) SamplesA3 B6 andC8havethe same composition but they are used to study differentdesign variables

23 Fourier Transform Infrared (FTIR) Spectroscopy Thefunctionalized polyurethane foam samples were character-ized by a BRUKER vector 22 FTIR with a DTGS (deuteratedtriglycine sulfate) detector and a PIKE 3ndash12 multibounceZn-Se variable angle ATR The incidence angle was set to80 during characterization The foam samples were cut intostrips of 310158401015840 times 110158401015840 times 0510158401015840 and were washed in distilled waterand dried in a vacuum oven before testing The IR spectrumwasmeasured from400 to 4000 cmminus1 to confirm the presenceof sulfonic groups in the polymer structure

24 Gel Permeation Chromatography (GPC) The polyure-thane foam samples were analyzed using a Varian ProStarHPLC system using a PLgel 5mm mixed C column HPLCgrade dimethyl formamide (DMF) was used as the eluentwith a flow rate of 1mLmin The UV detector was set todetect sample at a wavelength of 569 nm Foam samples weredissolved in DMF to get a 05wv concentration and 25 120583L




BESDMSO

A1

50 183

0 0

2 025 6 40A2 34 78A3 67 157A4 101 235

PPGTDIB5

5091

67 157 2 025 6 40B6 183B7 274

CERTC9

50 183 67 157 2 025 660

C8 40C10 90










500100015002000250030003500Wavenumbers

Abso

rban

ce

A4

A3

A2

A1


5001000150020002500300035004000Wavenumbers

Abso

rban

ce

C10

C9

C8B6

B7







(mAU

)(m

AU)

(mAU

)(m

AU)

5 10 15 20 25(min)

40

20

0

100500

minus50

100

50

0

minus50

minus100

200

100

0

minus100

A1

A4

A2

A3

114

7211

131

113

20

953

1

770

1

110

5911

780

137

4414

693

864

3

143

84

116

24






C9

B7

C10C10

B7

C9

5 10 15 20

(min)

50

0

minus50

7550250


50

25

0

minus25

minus50

minus75

(mAU

)(m

AU)

(mAU

)

944

8

119

7511

491

139

95

114

00

924

09

488

977

310

696

117

89

153

60







248

186

124

62

Spectrum 1

Cou

nts

000 128 256 384 512 640 768 896 1024

X-ray energy (keV)



0

10

20

30

40

50

60

Experiment

0BE

S

002

BES

003

BES

005

BES

CERT

60

CERT

90

Pb2+

ions

rem

oved

(ppb

)

1 3

PPG

TD

I

ppb2gppb1g





0

10

20

30

40

50

60

1 2 24 48

Lead

rem

oved

(ppb

)

Time (hrs)

pH 65pH 85











Acknowledgments


References






























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






BESDMSO

A1

50 183

0 0

2 025 6 40A2 34 78A3 67 157A4 101 235

PPGTDIB5

5091

67 157 2 025 6 40B6 183B7 274

CERTC9

50 183 67 157 2 025 660

C8 40C10 90










500100015002000250030003500Wavenumbers

Abso

rban

ce

A4

A3

A2

A1


5001000150020002500300035004000Wavenumbers

Abso

rban

ce

C10

C9

C8B6

B7







(mAU

)(m

AU)

(mAU

)(m

AU)

5 10 15 20 25(min)

40

20

0

100500

minus50

100

50

0

minus50

minus100

200

100

0

minus100

A1

A4

A2

A3

114

7211

131

113

20

953

1

770

1

110

5911

780

137

4414

693

864

3

143

84

116

24






C9

B7

C10C10

B7

C9

5 10 15 20

(min)

50

0

minus50

7550250


50

25

0

minus25

minus50

minus75

(mAU

)(m

AU)

(mAU

)

944

8

119

7511

491

139

95

114

00

924

09

488

977

310

696

117

89

153

60







248

186

124

62

Spectrum 1

Cou

nts

000 128 256 384 512 640 768 896 1024

X-ray energy (keV)



0

10

20

30

40

50

60

Experiment

0BE

S

002

BES

003

BES

005

BES

CERT

60

CERT

90

Pb2+

ions

rem

oved

(ppb

)

1 3

PPG

TD

I

ppb2gppb1g





0

10

20

30

40

50

60

1 2 24 48

Lead

rem

oved

(ppb

)

Time (hrs)

pH 65pH 85











Acknowledgments


References






























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




500100015002000250030003500Wavenumbers

Abso

rban

ce

A4

A3

A2

A1


5001000150020002500300035004000Wavenumbers

Abso

rban

ce

C10

C9

C8B6

B7







(mAU

)(m

AU)

(mAU

)(m

AU)

5 10 15 20 25(min)

40

20

0

100500

minus50

100

50

0

minus50

minus100

200

100

0

minus100

A1

A4

A2

A3

114

7211

131

113

20

953

1

770

1

110

5911

780

137

4414

693

864

3

143

84

116

24






C9

B7

C10C10

B7

C9

5 10 15 20

(min)

50

0

minus50

7550250


50

25

0

minus25

minus50

minus75

(mAU

)(m

AU)

(mAU

)

944

8

119

7511

491

139

95

114

00

924

09

488

977

310

696

117

89

153

60







248

186

124

62

Spectrum 1

Cou

nts

000 128 256 384 512 640 768 896 1024

X-ray energy (keV)



0

10

20

30

40

50

60

Experiment

0BE

S

002

BES

003

BES

005

BES

CERT

60

CERT

90

Pb2+

ions

rem

oved

(ppb

)

1 3

PPG

TD

I

ppb2gppb1g





0

10

20

30

40

50

60

1 2 24 48

Lead

rem

oved

(ppb

)

Time (hrs)

pH 65pH 85











Acknowledgments


References






























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




C9

B7

C10C10

B7

C9

5 10 15 20

(min)

50

0

minus50

7550250


50

25

0

minus25

minus50

minus75

(mAU

)(m

AU)

(mAU

)

944

8

119

7511

491

139

95

114

00

924

09

488

977

310

696

117

89

153

60







248

186

124

62

Spectrum 1

Cou

nts

000 128 256 384 512 640 768 896 1024

X-ray energy (keV)



0

10

20

30

40

50

60

Experiment

0BE

S

002

BES

003

BES

005

BES

CERT

60

CERT

90

Pb2+

ions

rem

oved

(ppb

)

1 3

PPG

TD

I

ppb2gppb1g





0

10

20

30

40

50

60

1 2 24 48

Lead

rem

oved

(ppb

)

Time (hrs)

pH 65pH 85











Acknowledgments


References






























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0

10

20

30

40

50

60

1 2 24 48

Lead

rem

oved

(ppb

)

Time (hrs)

pH 65pH 85











Acknowledgments


References






























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials

























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



research article characterization of functionalized...

Documents