Enhancement of Plasticizing Effect on Bio-Based Polyurethane Acrylate Solid Polymer Electrolyte

18 Pages·2017·4.51 MB·English

polymers
Article
Enhancement of Plasticizing Effect on Bio-Based
Polyurethane Acrylate Solid Polymer Electrolyte
and Its Properties
TuanSyarifahRossyidahTuan.Naiwi1,MinMinAung1,2,* ,AzizanAhmad3,4,
MarwahRayung2,MohdSukorSu’ait4,NorAzahYusof1andKhineZarWynnLae5
1 DepartmentofChemistry,FacultyofScience,UniversitiPutraMalaysia,UPMSerdang43400,Selangor,Malaysia;
[email protected](T.S.R.T.N.);[email protected](N.A.Y.)
2 HigherEducationCentreofExcellence(HiCoE),InstituteofTropicalForestryandForestProducts,
UniversityPutraMalaysia,UPMSerdang43400,Selangor,Malaysia;[email protected]
3 SchoolofChemicalScienceandFoodTechnology,FacultyofScienceandTechnology,
UniversitiKebangsaanMalaysia,Bangi43600,Selangor,Malaysia;[email protected]
4 SolarEnergyResearchInstitute(SERI),UniversitiKebangsaanMalaysia,
UKMBangi43600,Selangor,Malaysia;[email protected]
5 DepartmentofChemistry,YangonUniversity,Yangon11041,Myanmar;[email protected]
* Correspondence:[email protected][email protected]
(cid:1)(cid:2)(cid:3)(cid:1)(cid:4)(cid:5)(cid:6)(cid:7)(cid:8)(cid:1)
(cid:1)(cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:7)
Received:6September2018;Accepted:9October2018;Published:12October2018
Abstract:Polyurethaneacrylate(PUA)fromvegetableoilhasbeensynthesizedandpreparedforsolid
polymerelectrolyte. Polyolhasbeenend-cappedwithToluene2,4-Diisocyanate(TDI)followedby
hydroxylethylmethylacrylate(HEMA)inaurethanationprocesstoproducePUA.Themixtureswere
curedtomakethinpolymericfilmsunderUVradiationtoproduceexcellentcuredfilmswhichexhibit
goodthermalstabilityandobtainhighionicconductivityvalue. 3to15wt. %ofethylenecarbonate
(EC)mixedwith25wt.%LiClO wasaddedtoPUAtoobtainPUAelectrolytesystems.PUAmodified
4
withplasticizerEC9wt. %achievedthehighestconductivityof7.86×10−4S/cm,andrelatively
improved the linear sweep voltammetry, transference number and dielectric properties. Fourier
TransformInfraredSpectroscopy(FTIR)anddielectricanalysiswerepresented. Thermogravimetric
analysis(TGA)anddifferentialscanningcalorimetry(DSC),followedbyX-rayDiffraction(XRD)
andmorphologyhavebeenstudied. Theadditionofplasticizertothepolyurethaneacrylateshows
significantimprovementintermsoftheconductivityandperformanceofthepolymerelectrolyte.
Keywords: biopolymerelectrolyte;plasticizer;solidpolymer;polyurethaneacrylate;conductivity
1. Introduction
Polyurethaneacrylate(PUA)isacopolymerthatconsistsofurethanelinkage(-NHCOO-)and
the acrylate group in its molecular structure. It was synthesized from polyol and isocyanate with
theadditionofacrylatecompound[1–5]. Commonly,PUAhasbeensynthesizedfrompolyetheror
polyesterpolyolofsyntheticpolymersastheyhavereactivesitestoreactwiththeisocyanategroup.
Thepropertiesofvegetableoilthatcanbemodifiedtopolyolhavebeenstudiedtoproducebio-based
polymerPUA[6–10].
UrethaneacrylateismostlyapplicableforcoatingpurposeswithinsitupolymerizationviaUV
andiscurableinthepresenceofreactivediluentandfreeradicalphotoinitiator. Urethaneacrylate
oligomerhasbeenstudiedspecificallyfortheUVcurablepolymer. Mostofthestudiesonacrylate
polymersarerelatedtotheUVradiationpreparationmethodthathaveveryhighspeedsofcuring
thatleadtohighproductivity,lowerenergyconsumption,reductionofvolatileorganiccompound
Polymers2018,10,1142;doi:10.3390/polym10101142 www.mdpi.com/journal/polymers
Polymers2018,10,1142 2of18
emission,reducingriskoffires,improvingaspectsofoccupationalsafetyandhealthandsoforth[11,12].
Moreover,monomersderivedfromvegetableoilareenvironmentallyfriendlyandlow-costcompared
tothesyntheticpolymerfrompetroleum.
Theenhancementinionicconductivityofpolymerelectrolytecanbeachievedbytheadditionof
eitherorganicorinorganicfillerintoelectrolytesystemssuchasTiO ,SiO ,Al O ,ethylenecarbonate
2 2 2 3
(EC),andpropylenecarbonate.[13,14]. Inorganicfillerpromotesmorefreelithiumionsandproduces
moreamorphousregionsintheelectrolyteforthetransferofchargecarriers. Meanwhile,organicfiller
actsasaplasticizertoreducetheglasstransitiontemperature,T ,ofpolymer,whichhelpstoincrease
g
thesegmentalmotionofthepolymerbackboneandgeneratefreevolume. Therefore, theionscan
easilymigratethroughthevoid,resultinginabetterionicconductivity[15]. Plasticizerswithhigh
electricconstantandlowviscositybehaviorenablethemtobeincorporatedwithapolymerhostto
facilitatetheformationofdissociatedions[16]. Incorporationofaplasticizerintoapolymersystemis
alsoawaytoreducecrystallinityandincreasetheamorphousphaseofapolymerelectrolyte,thereby
increasing the mobilityofions, andgeneratinghigherionicconductivity[17]. Theadditionof EC
increasesthedegreeofsaltdissociationandionicmobility[18].
Astheconcentrationofplasticizerincreases,theamorphousnatureoftheelectrolyteincreases,
thusimprovingtheionicconductivityofthepolymerelectrolyte. Plasticizersofpoly(ethyleneglycol)
(PEG)withdifferentmolecularweight,PEG ,PEG ,andPEG showedthattheconductivity
200 400 600,
ofapolymerelectrolytedecreasesasmolecularweightofplasticizerincreases[19]. PEG hasthe
200
largestconcentrationoffreeionsassociatedonlywiththeanti-symmetricstretchingmodeinthematrix
polymer. Alongerchainlengthcontributestomoreoxygen,implyingthatlithiumionsandfewions
are available for ionic conduction, hence lower the ionic conductivity in the system. The smooth
surface of the polymer electrolyte also observed for polymer with the highest conductivity in the
presentofEC.P(GMA-co-MMA)matrixhasgoodflexibilityofpolymerchainswithinclusionofEC
andconsequentlyimprovedtheionicconductivity[20].
Inthisresearch,biopolymerpolyurethaneacrylateelectrolytewassynthesizedfrompolyolof
JatrophaoilinthepresenceofTDIandHEMA.Theeffectofplasticizingonconductivityandthermal
stabilityofbiopolymerelectrolytewerestudied. PUAmodifiedwithplasticizerEC9%hasthehighest
conductivityof7.86×10−4S/cmandthedielectricanalysiswasstudied. ThesynthesizedPUAwas
confirmedbyFourierTransformInfraredSpectroscopy(FTIR).Thethermalbehaviorofthebiopolymer
electrolytewasstudiedbythermogravimetricanalysis(TGA)anddifferentialscanningcalorimetry
(DSC)andfollowedbyX-rayDiffraction(XRD)andmorphologystudy.
2. Experimental
2.1. Material
JatrophaoilwasobtainedfromBiofuelBionas,KualaLumpur,Malaysiaandtheoilwasusedas
received. Hydrogenperoxide30%(H O )andN,N-dimethylformamide(DMF)(98%)werepurchased
2 2
formR&Mchemicals,PetalingJaya,Malaysia. Formicacid(98%)andtolulene2,4-diisocyanate(TDI)
(98%) were purchased from Acros Organic, New Jersey, US). EC, 2-Hydroxyethylmethyl acrylate
(HEMA)(99%),1,6-Hexanedioldiacrylate(HDDA),2-methylpropiopropanone(Darocure)andlithium
perchlorate(LiClO )wasobtainedfromSigmaAldrich,St.Louis,Missouri,USA.Allchemicalswere
4
usedasreceivedwithoutfurtherpurification.
2.2. PreparationofPUAOligomer
ThePUAoligomerwaspreparedbyreactionoftheJatrophaoil-polyolwithTDIinafour-necked
round-bottomflaskequippedwithamechanicalstirrer,athermometer,andarefluxcondenserunder
nitrogenatmosphere. DMFwasusedassolvent. TheTDIwasaddedinadropwisemannerat60◦C
andthereactionwascontinuedfortwohourstocompletetheNCO-terminatedpre-polymerafter
confirmationbyFTIR[21]. Afterthat,thereactionwascooleddownto40◦CandHEMAwasadded
Polymers2018,10,1142 3of18
Polymers 2018, 10, x FOR PEER REVIEW 3 of 18
inadropwisemanner. AftercompleteaddingofHEMA,thetemperaturewasraisedto60◦Cand
thereraecatcitoino nwwasa scocnotnintiunouuosulys lystisrtrierdre dfofro ornoen heohuoru. rF.rFormo mtimtiem teo ttoimtiem, eD,MDFM wFaws aasdaddedde tdo tcooncotrnotlr othlet he
visvciossciotysitoyf othf ethme imxtiuxrteursein sciencDeM DFMsFo lsvoelvnetnbto biloinilginpgo pinotinwt awsahsi ghhig,ha,s aws awsacso cnotnrotrloflo rfours uasgaeg[e2 1[2]1.]I.n Inth is
stutdhiys, tshtuedmyo, ltahrer amtioolaorf rpaotiloy oolft opoTlDyoIla ntod THDEIM aAndu HseEdMisA1 :u1s:1e.dT ihse 1r:e1s:1u. ltTinhge PreUsuAltwinags PtrUaAns pwaarse nt
andtrayneslploawreinsht ainndc oyleollro.wish in color.
2.32..P3.r Pepraepraatriaotnionof oPf UPUAAF iFlmilmE Elelcetcrtorolylytete
ThTehPeU PAUsAo lisdolpido lypmoleyrmeeler cetrloeclytrtoelyfitlem fwilmas wpraesp aprreedpabryedU Vb-yc uUriVn-gcuarnindgs oalnudti osno-lcuatsiotinn-gcamsteinthgo d.
Inimtiaeltlhyo,dth. eInPiUtiaAllyw, asthme ixPeUdAt ogweatsh ermwixietdh HtoDgDetAher( mwonitohm HerD)DanAd D(maoroncoumreer()p haontdo inDitairaotcour)ref or
3h(.phInotsoeinpiatiraattoer)fl faosrk 3, 2h5. Iwn ts.ep%aroaftel iftlhaisukm, 25p ewrtc.h %lo oraf tleithsaiultma npdercEhClowraates sdailst saonlvde EdCi nwaasc edtiosnsoelvfoerd 12
in acetone for 12 h. The amount of EC used was varied from 0–15 wt. % to find the optimum
h. The amount of EC used was varied from 0–15 wt. % to find the optimum conductivity of the
conductivity of the polymer electrolyte [21]. The two mixtures were then mixed together and stirred
polymerelectrolyte[21]. Thetwomixtureswerethenmixedtogetherandstirredcontinuouslyfor
continuously for another 12 h to obtain a homogenous mixture. After that, the mixture was casted on
another12htoobtainahomogenousmixture. Afterthat,themixturewascastedonaTeflonmold
a Teflon mold (diameter 100 mm) and irradiated 3 times by a medium-pressure mercury vapor lamp
(diameter100mm)andirradiated3timesbyamedium-pressuremercuryvaporlampfromIST-UV
from IST-UV Dryer (Switzerland) at 7.5 mA with the conveyor speed at 3 m/s. The solid film shows
Dryer(Switzerland)at7.5mAwiththeconveyorspeedat3m/s. Thesolidfilmshowsauniformand
a uniform and transparent appearance as depicted in Scheme 1. The solid film was stored in a
transparentappearanceasdepictedinScheme1.Thesolidfilmwasstoredinadesiccatorforonedayto
desiccator for one day to remove the residual solvent and undergo further characterization study.
removetheresidualsolventandundergofurthercharacterizationstudy. Thesamplesweredesignated
The samples were designated as PUA/25Li with 0 wt. %, 3 wt. %, 9 wt. %, 12 wt. % and 15 wt. % EC
asPUA/25Liwith0wt. %,3wt. %,9wt. %,12wt. %and15wt. %ECinallcharacterizations.
in all characterizations.

ScShcehmeem1e. 1T. hTehep rporcoecsessso offp prereppaarrininggs soolliidd ppoollyymmeerr eelleeccttrroollyyttee ffrroomm PPUUAA aanndd LLiCiClOlO4 anadn EdCE. C.
4
2.42..C4.h Cahraacrtaecrtiezraiztaiotinono foSf oSloidlidP PoloylymmeerrE Eleleccttrroollyyttee
InfIrnafrreardedsp sepcetcrtaraw wereerer erceocordrdeeddw wiitthh aann AATTRR--FFTTIIRR,, PPeerrkkiinn EElmlmeer rmmooddele 1l615605 0(W(Walathltahma,m U,SU) Sin) in
thethwe awvaevneunmumbebrerra rnagnegeb ebtewtweeenen4 0400000t oto2 82080c mcm−−11 wwiitthh ssccaannnniinngg rreessoolluuttioionn oof f44 ccmm−1−. 1T.GTAG Awaws as
perpfeorrfmoremdeuds uinsginMg MetteltetrleTr ATA303000(P (PoloalrairsisP Pkkwwyy,,C Coolulummbbuuss OOhh,, UUSS)) ffrroomm 5500 °◦CC toto 60600 0°C◦ Cwwithit ah haehateiantgin g
ratreaotef o1f0 1◦0C °/Cm/minini nina ad dyynnaammiiccn niittrrooggeenn aattmmoosspphheerree aatt 2200 mmLL//mminin flflowow rartaet.e M. Meaenawnhwilhei,l eD,SDCS MCeMtteletrtl er
TA300 was used to study the phase transition of the polymer electrolyte during the heating process.
TA300wasusedtostudythephasetransitionofthepolymerelectrolyteduringtheheatingprocess.
ThTehsetu sdtuydwy awsacso cnodnudcutcetdedb ebtewtweeeenn− −5500 ◦°CC ((ffoorr 00%% EECC)), ,00 °◦CC (w(witihth EECC) )tot o15105 0°C◦,C a,ta 1t01 0°C◦ Cscascnanninngin g
rate under nitrogen atmosphere at 10 mL/min flow rate. The structural information was studied by
rateundernitrogenatmosphereat10mL/minflowrate. Thestructuralinformationwasstudiedby
using XRD model D-5000 Siemen (Tempe, AZ, USA). The diffraction angle, 2θ, is in the range of 3 to
usingXRDmodelD-5000Siemen(Tempe,AZ,USA).Thediffractionangle,2θ,isintherangeof3to
60 at 0.004 °/S. Scanning electron microscopy, SEM model JEOL JSM-7600F (Singapore) was used to
60at0.004◦/S.Scanningelectronmicroscopy,SEMmodelJEOLJSM-7600F(Singapore)wasusedto
investigate the surface morphology of the PUA electrolyte. Prior to analysis, the sample was coated
investigatethesurfacemorphologyofthePUAelectrolyte. Priortoanalysis,thesamplewascoated
with gold to avoid electrostatic charging.
withgoldtoavoidelectrostaticcharging.
Polymers2018,10,1142 4of18
ElectrochemicalStudy
Theroom-temperatureionicconductivityofthePUASPEwasstudiedbyusingElectrochemical
ImpedanceSpectroscopy(EIS)usingHioki3532-50LCRHi-tester(Nagano,Japan)thatwasinterfaced
toacomputerinthefrequencyrangeof50Hzto500kHz. Thefilmwascutintodiscshapeswith
16mmdiameterand5.13 cm2 contactsurfacearea. The filmthicknesswas0.05cm. Thefilmwas
sandwichedbetweentwostainlesssteel(SS)electrodes. Theionicconductivity,σ,wascalculatedbased
onthefollowingequation:
(cid:16) (cid:17) l
σ Scm−1 = (1)
A×R
b
where l is the thickness of the film, A is the area and R is the bulk resistance obtained from the
b
EISmeasurement. Theratiowhichgavethehighestconductivitywillbesubjectedtotemperature
dependencestudyfromroomtemperature,303to383K.
The same ratio was used to study the electrochemical properties of the polymer electrolyte
by using Linear Sweep Voltammetry (LSV) and Transference Number (TN) employing Princeton,
Versa-STAT-4. ForLSV,thesamplewasassembledinasymmetricSS/PE/Liconfigurationusing10mV
scanrateintherangeof0–7V.Samplepreparationswerecarriedoutinthegloveboxwithlessthan
0.1ppmH OandO .
2 2
ForTNmeasurement,thePUAelectrolytewasassembledinaSS/PE/SSandpolarizedunder
afixeddirectcurrentvoltagewith0.1V.Thevalueoft wascalculatedfromthecurrentversustime
ion
plotbyapplyingWagner’spolarizationtechniquefollowingtheequation:
I −I
t = o ss (2)
ion
I
o
I
t = ss (3)
ele I
o
wheret isionicTN,t —electronicTN,I —initialcurrent,I —thesteady-statecurrent.
ion ele 0 ss
Theequationsfordielectricconstant(ε ),dielectricloss(ε),realelectricalmodulus(M ),imaginary
r i r
electricalmodulus(M)andtanσwerewrittenasbelow:
i
Z
εr = ωC (cid:0)Z2i+Z2(cid:1) (4)
o r i
Z
εi = ωC (cid:0)Z2r+Z2(cid:1) (5)
o r i
ε
Mr = (cid:0)ε2+rε2(cid:1) (6)
r i
ε
Mi = (cid:0)ε2+i ε2(cid:1) (7)
r i
ε
tanδ = r (8)
ε
i
whereC =ε A/t,ε =permittivityoffreespaceandω=2πf.
O O O
3. ResultsandDiscussion
TheFTIRspectraofPUAwith25wt. %LiClO indifferentconcentrationsofECarepresented
4
in Figure 1. The foremost interest in the PUA polymer electrolytes are region-free and hydrogen
bonded–NHstretchingmode(3800–3100cm−1),oxygenatomsofthecarbonyl(C=O)(1750–1710cm−1,
1650cm−1),aminefunctionalgroups(C–NandN–H)(1550–1500cm−1)andetherandestergroup
(C-O-C) (1300–1000 cm−1) stretch of acrylate group [22]. The carbonyl group of first band was
electrostaticallyinteractingwithinthepolymerchainandwithLi+ions,andthelatterisinteracting
Polymers2018,10,1142 5of18
throughH-bonds. TheabsorptionpeakoffreeandH-bonded–NHstretchingofPUAhaveshifted
(3500cPmoly−m1ertso 203178,0 100, cxm FO−R1 P)EaEnRd REsVhIoEwW e danincreaseinthewavenumberwhendopingwithlith5i uofm 18 salt
duetocoordinationofLi+ionstonitrogenatomsofthe–NHgroups.Thepeakbetween1072–1173cm−1
(3500 cm−1 to 3700 cm−1) and showed an increase in the wavenumber when doping with lithium salt
wasassignedfortheC-O-Cstretchingbandforacrylategroup.Theurethanegroupsexperiencedashift
due to coordination of Li+ ions to nitrogen atoms of the –NH groups. The peak between 1072–1173
toalowerfrequency(1750cm−1to1740cm−1). Whenaddingsalt,H-bondedC-O-Cgroupsbecome
cm−1 was assigned for the C-O-C stretching band for acrylate group. The urethane groups experienced
freeduae sthoifta nto ian tleorwaecrt iforneqoufenLciy+ (i1o7n5s0 wcmit−h1 ttoh e17e4t0h ecmro−1x).y Wgehnena nadddiitnsga sbaillti,t yH-tboofnodremd CH--Ob-oCn gdrsou[2p3s, 24].
ThePUbAecormegei ofrneei ndtueer atoc taionn inotefrlaitchtiiounm ofs Lail+t iwonitsh waitnh atdhed iettihoenr ooxfyEgCeni nantdh eitsr eagbiiolinty otfo ofoxrymg eHn-baotondmss of
thecar[b2o3,n24y]l. (TCh=e OP)U(A1 7r5e0g–io1n7 1in0tecrmac−ti1o)na onfd litehtihuemr asanldt wesitthe rang raodudpiti(oCn- Oof- CEC) (i1n3 t0h0e– r1e0g0io0nc mof −o1x)ysgterne tch
ofacryaltaotmesg roof uthpe. cTahrbeopneyal k(Co=fOp)o (l1y7m50e–r17e1l0e cctmro−l1)y taendsh eothwesr annods eigstneirfi gcraonutpc (hCa-nOg-Ces) o(1f3w00a–v10e0n0u cmmb−1e) rin
stretch of acrylate group. The peak of polymer electrolyte shows no significant changes of
theregionofbothcarbonylgroupandesterofstretchacrylategroupuponadditionofEC.However,
wavenumber in the region of both carbonyl group and ester of stretch acrylate group upon addition
anincorporationofECintopolymerelectrolyteshowedhighintensitypeakofC=Ocarbonylgroupof
of EC. However, an incorporation of EC into polymer electrolyte showed high intensity peak of C=O
PUA.Thus,theplasticizerisessentiallyafillerdispersedinpolymericcomposite[16]. Withadditionof
carbonyl group of PUA. Thus, the plasticizer is essentially a filler dispersed in polymeric composite
lithiumsaltthepeaksshiftedtowardhigherfrequencyandthepeakofC=OofPUAgaveahigh-intense,
[16]. With addition of lithium salt the peaks shifted toward higher frequency and the peak of C=O of
strong,andsharppeakat1719–1712cm−1. Theadditionof25wt. %lithiumshiftedtheintensityabout
PUA gave a high-intense, strong, and sharp peak at 1719–1712 cm−1. The addition of 25 wt. % lithium
7cm−1s.hTifhteids tshheo iwnteednsaitny ianbtoeurta 7c tcimon−1.o Tchciusr srheodwbeedt wane ienntecraarcbtioonn yolccgurroruedp bwetiwtheelint hcaiurbmonsyall tg.rTouhpe woxityhg en
atomslaitchtiuams eslaelct.t rTohne dooxnygoerna atotommss aanctd afso erlmectcrooon rddoinnaotre abtoomnsd sanwd itfohrmth ecoloitrhdiiunmatei nbotnhdes swtriuthc ttuhree of
polymelirthhiuomst .inT hthues s,tvruibctruarteio onf pfroelqyumeenr chyossth. iTftheuds,t voibaralotiwone rfrweqauveenncuy mshbifeter.d to a lower wavenumber.

Figure1.FT-IRspectraofPUAelectrolyteatdifferentloadingofECplasticizer.
Figure 1. FT-IR spectra of PUA electrolyte at different loading of EC plasticizer.
The effect that plasticizing has on PUA/LiClO polymer electrolyte is shown in Figure 2.
The effect that plasticizing has on PUA/LiClO4 4polymer electrolyte is shown in Figure 2. The
Thespsepcetrcatrash sohwowsst hthee bbuullkk rreessiissttaannccee fofor r252 5wwt. %t. %ECE aCt ~a1t0~−4 1o0h−m4, odhecmre,adseincgre taos ~i1n0g−5t aot ~251 0w−t5. %at o2f5 EwC.t . %
ofEC.AA ggrraapphh ooff lloogg ccoonndduucctitviivtyit yvevresrussu scocnocnencetrnattrioanti oonf oEfCE aCddaeddd eind iFnigFuirgeu 3r es3hoswhso wthse thheighheigr her
conduccotinvdituyctaivcihtyie avcehdievwedit hw9ithw 9t .w%t. %o fofE ECC aanndd tthhee vvaalulue eisi islliulslutrsattreadt eind TianblTea 1b. lTeh1e. aTdhdietioand dofi tEioCn of
EC shoshwoewdedfl uflcutcutuaatitningg vvaalluuee ooff ccoonndduuctcitviivtyit yanadn dnon aoppaaprpenatr etnretntdr ecnadn bcea nobbseerovbedse. rHvoewd.evHero, wthee ver,
theoptoipmtiummumco cnodnduuctcitvivitityy 77..8866 ×× 101−04 −S4/cSm/ hcamd hacahdieavcehdi ewvitehd 9w witt.h %9 owf Et.C%, wohficEhC w,wash oinceh owrdaesr ohnigehoerr der
than 0 wt. % EC. The conductivity decreased with addition of 3 to 6 wt. % of EC then the conductivity
higher than 0 wt. % EC. The conductivity decreased with addition of 3 to 6 wt. % of EC then the
increased and decreased again at 12 wt. % of EC. EC acts as an organic plasticizer in the polymer
conductivity increased and decreased again at 12 wt. % of EC. EC acts as an organic plasticizer
electrolyte, enhancing the conductivity of the polymer electrolyte [20]. With the addition of 9 wt. %
in the polymer electrolyte, enhancing the conductivity of the polymer electrolyte [20]. With the
EC, the conductivity improvement might be due to the high dielectric constant of the plasticizer,
additionof9wt. %EC,theconductivityimprovementmightbeduetothehighdielectricconstantof
increasing the number of ions by weakening the columbic force between anion and cation salts.
theplaTshtiecriezfeorr,e,i ndcisrseoacsiiantigonth oef snaultms ibne trhoe fsyiostnesmb iyncwreeaasekde nainndg mthoreec forelue mLib+ iiocnfso crcaen bbee tpwroedeuncaedn i[o1n6].a nd
cationMsaolrtes .LTi+h ieornesf oarned, dEiCss omcoialetciounleso fcasna lttrsaninsfuthsee sinytsot etmhe ipnoclryemaseer dmaantrdixm aondre ifnrcereeaLsei+ tihoen cshcaainn be
producseedgm[1e6n]t.alM moorbeilLitiy+, iloeandsinagn dtoE eCnhmanocleemcuelnets ocfa ncotnrdauncstfiuvistey.i nHtoowtheveepr,o tlhyem ceorndmuacttrivixitya nsdtaritnsc troe ase
thechainsegmentalmobility, leadingtoenhancementofconductivity. However, theconductivity
Polymers2018,10,1142 6of18
Polymers 2018, 10, x FOR PEER REVIEW 6 of 18
decrease, since its saturated level for EC results in less space for Li ions to move within the polymer
startstodecrease,sinceitssaturatedlevelforECresultsinlessspaceforLiionstomovewithinthe
matrix [20]. The ionic conductivity could be explained by interaction between polymer LiClO4 and
polymermatrix[20].TheionicconductivitycouldbeexplainedbyinteractionbetweenpolymerLiClO
4
EanCd. TEhCe. mThaeinm tharineet hinreteeraincttieornacs taiomnosnagm tohnegmt hareem ioanr-eioionn i-niotenraicnttieorna cbteiotwnebeent wLei+e cnaLtioi+ncs aatniodn sClaOn4d-
anions; ion-dipole interaction between Li+ cations and chlorine in polymer; and ion-molecule
ClO -anions;ion-dipoleinteractionbetweenLi+cationsandchlorineinpolymer;andion-molecule
4
iinntteerraaccttiioonn bbeettwweeeenn LLii++ aanndd EECC.. PPoollyymmeerr LLiiCCllOO4--EECC wwiitthh ddiiffffeerreenntt ccoommppoouunnddss ooff ppoollyymmeerr ––LLii++,,
4
polymer –Li+/EC and Li+/EC exist by these interactions. The oxygen of C=O in EC is an electron donor
polymer–Li+/ECandLi+/ECexistbytheseinteractions. TheoxygenofC=OinECisanelectron
wdohnicohr wpahritcihcippaartetisc iipna cteosminpectoitmiopne twitiitohn CwliOth4– CalnOd –paonlydmpeorl.y Tmheer .LTih+/eECLi +in/tEeCraicntitoenra ectxiiosnts enxoistt sonnolyt
4
between Li+ and another two oxygen atoms of C=O group, but also between Li+ and another two
onlybetweenLi+andanothertwooxygenatomsofC=Ogroup,butalsobetweenLi+andanothertwo
oxygen atoms in the ring structure of EC. Moreover, Li+/EC interaction plays an important role in the
oxygenatomsintheringstructureofEC.Moreover,Li+/ECinteractionplaysanimportantroleinthe
ccoonndduuccttiivviittyy ooff tthhee ppoollyymmeerr LLiiCCllOO4--EECC ssyysstteemm.. TThhee aaddddiittiioonno offE ECCl leeaaddsst toot thheef oforrmmaatitoionno offa aL Li+i+//EECC
4
complex and enhances the flexibility of polymer chains by decreasing the crystalline fraction of the
complexandenhancestheflexibilityofpolymerchainsbydecreasingthecrystallinefractionofthe
polymer Li+ complex [25].
polymerLi+complex[25].
Table 1. Ionic conductivity of PUA electrolyte with EC plasticizer.
Table1.IonicconductivityofPUAelectrolytewithECplasticizer.
EC, wt. % Conductivity, σ (S cm−1)
EC,wt.% Conductivity,σ(Scm−1)
0% 6.40 × 10−5
0% 6.40×10−5
3% 3.51 × 10−6
3% 3.51×10−6
66%% 77..0055× × 1100−−66
99%% 77..8866× × 1100−−44
1122%% 77..5599× × 1100−−66
1155%% 55..9955× × 1100−−66

Figure2.NyquistplotofPUAelectrolytewithECplasticizer.
Figure 2. Nyquist plot of PUA electrolyte with EC plasticizer.
Polymers2018,10,1142 7of18
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Polymers 2018, 10, x FOR PEER REVIEW 7 of 18

Figure3.LogconductivityofPUAelectrolyteatvariedconcentrationsofECplasticizer.
Figure 3. Log conductivity of PUA electrolyte at varied concentrations of EC plasticizer.
Figure 3. Log conductivity of PUA electrolyte at varied concentrations of EC plasticizer.
The conductivity of polymer electrolyte at ambient temperature to 100 ◦C was fitted using
The conductivity of polymer electrolyte at ambient temperature to 100 °C was fitted using
The conductivity of polymer electrolyte at ambient temperature to 100 °C was fitted using
Arrheniustheory. Thetemperaturedependenceionicconductivitywasstudytoanalyzemechanismof
Arrhenius theory. The temperature dependence ionic conductivity was study to analyze mechanism
Arrhenius theory. The temperature dependence ionic conductivity was study to analyze mechanism
iontransportationinpolymerelectrolytes. Thelogσversus1000/TgraftedinFigure4showedlinear
of ion transportation in polymer electrolytes. The log σ versus 1000/T grafted in Figure 4 showed
of ion transportation in polymer electrolytes. The log σ versus 1000/T grafted in Figure 4 showed
plotwell-fittedwithArrheniustheoryasfollows:
linear plot well-fitted with Arrhenius theory as follows:
linear plot well-fitted with Arrhenius theory as follows:
σσσ= ==A AAexeepxxpp[ [E[EEaaa///kkkTTT]]] ((9(99)) )
wwwhhheeerrreee AAA iiisss aaa cccooonnnssstttaaannnttt wwwhhhiiiccchhh iiisss ppprrrooopppooorrrtttiiiooonnnaaalll tttooo ttthhheee aaammmooouuunnnttt ooofff ccchhhaaarrrgggeee cccaaarrrrrriiieeerrrsss,,, EEEaaa iiisss aaaccctttiiivvvaaatttiiiooonnn eeennneeerrrgggyyy,,,
k is Boltzmann constant and T represents the absolute temperature in K.
kk iiss BBoollttzzmmaannnn ccoonnssttaanntt aanndd TT rreepprreesseennttss tthhee aabbssoolluutteet teemmppeerraattuurreei ninK K..

FFFigiigguuurerree4 .44..A AArrrrhrrhheenenniuiiuusssp pplolloottto oofffi oiioonnniciiccc occoonnnddduuuctccittviivvitiiyttyyo ofoffP PPUUUAAA///LLLiiiCCClllOOO444///EEECCC (((999 wwwttt... %%%))) eeellleeeccctttrrrooolllyyyttteee...
Polymers 2018, 10, x FOR PEER REVIEW 8 of 18
Polymers2018,10,1142 8of18
The pseudo-activation energy, Ea of the polymer electrolyte was determined from the Arrhenius
grTahpeh.p –sEeau/dk ois- adcetinvoatteidon onen tehreg gyr,aEpaho sfltohpeep aonldy mtheer aeclteicvtartoiloynte enwearsgyd eiste 0r.m29i neeVd. Tfrhoem vathlueeA orfr ahcetniviuastion
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thro[2u4g].h Tahne ivoanl-ubelo ocfk iTnNg efloerc tProUdAe efalellctrraoplyidtely isw 0i.t9h9,t iamned iaf tPhUeAel eecletrcotrlyotlyeties wpritihm aprlialsytiicoizneirc i[s2 40]..95,
TherevsapluecetiovfeTlyN. fTohrisP UclAeaerlleyc trreovlyetaelsi sth0.a9t9 ,Lain sdalat PcUomApelleexcetrso lwytiethw PitUhAp laasntdic iPzeUrAis e0l.e9c5t,rroelsypteec wtivitehly .EC
Thibseccloeamrleys reavne aallsmthoastt Lpiesrafletcct oimonpilce xceosnwdiuthctPoUr. ATahned rPeUpoArteelde ctiroonliyct eTwNit hofE Cbiboepcoolmymesear nealelmctorosltyte
percfoecnttaiionniincgc coonrdnu scttaorrc.h Tbhye Lrieewpo &rte Rdaimonesich T(2N01o3f) [b2i6o]p iosl y0m.98e rweiltehc tiroonliyct ecocnodnutactiniviintyg ocof r3n.21st a×r 1c0h−4 S
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Mo[n2i7s]h. a(2016),whichcouldbeusedforenergystoragedevices[27].

FiguFrieg5u.reN 5o.r Nmoarlimzeadlizpeodla priozlaatriioznatciounrr ceunrtrveenrts vuesrtsiumse tifmoreP fUorA P/ULAiC/LlOiC4/lOE4C/E(C9 w(9t .w%t.) %el)e ecltercotlryotley.te.
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FFigiguurree6 6..L LinineeaarrS SwweeeeppV Vooltlatammmmeetrtyryo offP PUUAA//LLiiCCllOO44//EECC ((99 wwtt.. %%)) eelleeccttrroollyyttee..
Inthisresearch,ECwasaddedasplasticizertoincreaseionicconductivity,σ,inthePUAsolid
In this research, EC was added as plasticizer to increase ionic conductivity, σ, in the PUA solid
polymerelectrolyte. ThiswasbecauseEC(smallorganicmolecules)hadhighdielectricconstantand
polymer electrolyte. This was because EC (small organic molecules) had high dielectric constant and
lowvaporpressure[1]. Toprovethat, logdielectricconstant(log ε )andlogdielectricloss(log ε)
low vapor pressure [1]. To prove that, log dielectric constant (log εrr) and log dielectric loss (log εii)
versuslogfrequencyfordifferentpercentagesofECplasticizerwithfixedLicontent(25%Li)were
versus log frequency for different percentages of EC plasticizer with fixed Li content (25% Li) were
plottedandshowninFigure7. Fromthefigure,itcanbeseenthatlogε andlogε hadhighervalues
plotted and shown in Figure 7. From the figure, it can be seen that log εrr and log εii had higher values
atlowfrequencyofabout2Hz. Thismaybeduetoelectrodepolarizationeffect[28],whileathigh
at low frequency of about 2 Hz. This may be due to electrode polarization effect [28], while at high
frequency, itwasobservedthatlog ε andlog ε hadlowervaluesbecauseoftheperiodicreversal
frequency, it was observed that log εrr and log εi ihad lower values because of the periodic reversal of
ofelectricfieldoccurringathighspeed,andthiscausedtheionstohaveinsufficienttimetodiffuse
electric field occurring at high speed, and this caused the ions to have insufficient time to diffuse into
into the electric field [28]. Furthermore, with the addition of EC plasticizer, it will cause a large
the electric field [28]. Furthermore, with the addition of EC plasticizer, it will cause a large amount of
amountofchargecarrierstolocalizealongwithmobileions. Thus,itwillhelptoimprovethevalueof
charge carriers to localize along with mobile ions. Thus, it will help to improve the value of ionic
ionicconductivity[1]. Figure8presentedtherealelectricalmodulus(M )andimaginaryelectrical
conductivity [1]. Figure 8 presented the real electrical modulus (Mr) and imraginary electrical modulus
modulus(M)withlogfrequencyfordifferentratiopercentagesofECplasticizeraddedintothefixedLi
(Mi) with loig frequency for different ratio percentages of EC plasticizer added into the fixed Li
content. BothM andM hadavalueofalmostzerowithalongtailwhenapproachinghighfrequency.
content. Both Mrr and Mii had a value of almost zero with a long tail when approaching high frequency.
This happened because of the electrode polarization phenomena, which makes it an insignificant
This happened because of the electrode polarization phenomena, which makes it an insignificant
contribution[28]. Thepresenceofthelongtailatlowfrequency(1.5Hzto4.5Hz)observedthatthere
contribution [28]. The presence of the long tail at low frequency (1.5 Hz to 4.5 Hz) observed that there
wasalargecapacitanceassociatedwiththeelectrodes[29]. Otherthanthat,athighfrequency,bothM
was a large capacitance associated with the electrodes [29]. Other than that, at high frequency, bothr
andM observedincreasedlinearity. FromFigure8,itcanbeseenthatM peakwasmuchhigherthan
Mr andi Mi observed increased linearity. From Figure 8, it can be seen thrat Mr peak was much higher
M peaks. ThiswasduetothesamplesofPUAsolidpolymerelectrolytebeinganionicconductor[29].
thian Mi peaks. This was due to the samples of PUA solid polymer electrolyte being an ionic conductor
Figure6comparedthevariationoftanσwithlogfrequencyfordifferentadditionsofpercentagesof
[29]. Figure 6 compared the variation of tan σ with log frequency for different additions of
ECplasticizerintotheLicontent. FromFigure9,itcanbeseenthatthetanσpeaksweregradually
percentages of EC plasticizer into the Li content. From Figure 9, it can be seen that the tan σ peaks
shiftedto3.5Hzto5.0Hz(higherfrequency). WithincreaseinECplasticizer,itcanhelptoincrease
were gradually shifted to 3.5 Hz to 5.0 Hz (higher frequency). With increase in EC plasticizer, it can
theamorphouscontentinthePUAsolidpolymerelectrolyte[27]. Asthetanσpeaksshiftedtoward
help to increase the amorphous content in the PUA solid polymer electrolyte [27]. As the tan σ peaks
theright-handside,itwillreducetherelaxationtime(τ),whichcanbedemonstratedfromTable2.
shifted toward the right-hand side, it will reduce the relaxation time (τ), which can be demonstrated
FromFigure9,PUA25%Li+9%EChadthelowestτwhichwas0.0955×10−4swithhighestionic
from Table 2. From Figure 9, PUA 25% Li + 9% EC had the lowest τ which was 0.0955 × 10−4 s with
conductivityupto7.86×10−4Scm−1.
highest ionic conductivity up to 7.86 × 10−4 S cm−1.
Polymers2018,10,1142 10of18
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FiguFreig7u.rVe a7r.i aVtaiorinatoifon(a )oflo (ga)ε lroagn εdr (abn)dl o(bg)ε liovge rεsi uvserlsougsf lroegq ufreenqcuyePnUcyA P/ULiAC/lLOiC4/lOEC4/EeCle cetlreocltyrotelys.tes.