ContentslistsavailableatScienceDirect
Carbohydrate
Polymers
jo u r n al h om ep age :w w w . e l s e v i e r . c o m / l o c a t e / c a r b p o l
Synthesis
and
characterization
of
hydrogels
from
cellulose
acetate
by
esterification
crosslinking
with
EDTA
dianhydride
André
M.
Senna
a,∗,
Kátia
Monteiro
Novack
a,
Vagner
R.
Botaro
a,baUniversidadeFederaldeOuroPreto,35400-000,OuroPreto,MinasGerais,Brazil
b,UniversidadeFederaldeSãoCarlos,18052-780,Sorocaba,SãoPaulo,Brazil
a
r
t
i
c
l
e
i
n
f
o
Articlehistory:
Received5March2013
Receivedinrevisedform13May2014
Accepted12August2014
Availableonline19August2014
Keywords: Hydrogel Celluloseacetate EDTAdianhydride Esterificationcrosslinking
a
b
s
t
r
a
c
t
Hydrogels were preparedfrom cellulose acetate with a degreesubstitution (DS) 2.5dissolved in dimethylformamidebyesterificationcrosslinkingwithEthylenediaminetetraaceticdianhydride(EDTAD) catalyzedbytriethylamine.Subsequentconversionoftheunreactedcarboxylgroupstosodium carbox-ylatesbytheadditionofaqueousNaHCO3wasperformedtoenhancethewateraffinityofthegels.The absorbencyoftheproductswasstronglydependentontheamountofEDTADthatwasesterifiedto cellu-loseacetate,andthehighestabsorbencywasobservedforthehydrogelcomposedofapproximately0.36 moleculesofEDTADperrepeatunitofcelluloseacetate.Thehydrogelsweresynthesizedwithdifferent degreesofcrosslinkingandwereanalyzedbyIRspectral(FTIR),nearinfrared(NIR),thermogravimetry analysis(TGandDTG),andcrosslinkdensityevaluationbyFlory-Rehnertheory.Thehydrogelshave syn-thesizedwithmolarratiosEDTAD/OHgroups:[1/1],[1/2],and[0.1/1].Thecapacityforwaterabsorbency wasstudiedandcomparedwiththewaterabsorbencyoftheCA
©2014ElsevierLtd.Allrightsreserved.
1. Introduction
Theapplicationofhydrogelsdatesbackto1960,whenWichterle
andLimintroducedtheuseofhydrophilicnetworksofcross-linked
poly(2-hydroxyethylmethacrylate)assoftcontactlensmaterial.
Hydrogelsareextremelysuitablefora varietyofapplicationsin
thepharmaceuticalandmedicalindustry.Becausetheyare
capa-bleofretaininglargeamountsofwaterandbecauseoftheirsoftand
rubberyconsistence, theyclosely resembleliving tissues.
More-over,theirhighwatercontentalsocontributestotheirexcellent
biocompatibility(Vlierberghe,Dubruel,&Schacht,2011).
Becauseof theincreasing focus onenvironmental problems
associatedwithsyntheticpolymers,thereisanemergingtendency
towardtheuseof naturallyoccurringpolymersinsteadof
syn-thetic ones.Among these natural polymers,cellulose, which is
composedof(1→4)--glucopyranoserepeatingunitsandforms
fibrous structures with high crystallinity, is a prime candidate
asastartingmaterialforbiodegradablesuperabsorbentpolymers
becauseitisthemostabundantbiopolymeronearth(Kono&Fujita,
2012).
∗ Correspondingauthor.Tel.:+5515997346363.
E-mailaddresses:decaosenna@hotmail.com(A.M.Senna),knovak@iceb.ufop.br
(K.M.Novack),vagner@ufscar.br(V.R.Botaro).
Inprinciplecellulosehydrogelscanbepreparedfromacellulose
solutionthroughphysicalcrosslinking.Becausecellulosehasmany
hydroxylgroupswhichcanformahydrogenbondinglinked
net-work.However,celluloseisverydifficulttodissolveincommon
solvents. Recently, newsolvents, suchas
N-methylmorpholine-N-oxide(NMMO),ionicliquids(ILs),andalkali/urea(orthiourea)
aqueoussystemshavebeendevelopedtodissolvecellulose,
provid-inggreatopportunitiesforthepreparationofcellulosehydrogels.
Bacterialcellulose(BC)isalsoastrongcandidateforthe
fabrica-tionofcellulose-based hydrogels,sincecertainbacterialspecies
possessestheabilitytocreatepurecellulosehydrogels(Chang&
Zhang,2011).
Celluloseacetate(CA)isawell-knownderivativeofcellulose
andhasbeenusedinabroadfieldofapplicationssuchasan
adhe-sive, film base in photographyor in separation processes (e.g.,
filtering, reverse osmosis).Cellulose acetate is produced either
by heterogeneous or homogeneous acetylation of cellulose. In
contrasttocellulose,celluloseacetatepossessesamuchless
crys-talline structure and thus exhibits bettersolubility in common
organicsolventssuchasacetone(Botaro&Dantas,2012;Tsioptsias,
Sakellariou,Tsivintzelis,Papadopoulou,&Panayiotou,2010).
Inthisstudy,theattentionisfocusedonEDTADasacroosslinker
inthepreparation ofabsorbentpolymersfromcelluloseacetate
withDS2.5.EDTADhastwoanhydridesinitsstructure,eachof
whichreactsquicklywithcertainfunctionalgroupssuchas
hydro-xylstoundergocrosslinking.Inthereactionofcelluloseacetate
http://dx.doi.org/10.1016/j.carbpol.2014.08.017
A.M.Sennaetal./CarbohydratePolymers114(2014)260–268 261
withEDTAD,twofree carboxylicacidgroupswereformedwith
simultaneouscrosslinkingofcelluloseacetatechains:hence,the
absorbencyoftheproductisexpectedtobeenhancedin
compar-isonwiththatofcelluloseacetate.Thispaperdescribesadetailed
study of the synthesis of hydrogels fromcellulose acetate and
EDTAD.Inaddition,thewaterabsorptionbehavioroftheproduct
wereinvestigatedtorevealtheformationofanexcellentabsorbent,
whichisdescribedherein.
Thispaperaimsathighlightingthedevelopmentincellulose
acetate-based hydrogels with emphasis onthe synthesis,
char-acterization,and properties.Recent literaturehasbeencitedto
summarizeworkoncellulose-basedhydrogel,but,noreportsin
theliteratureonsynthesisofhydrogelwithcelluloseacetateand
EDTAD.
The hydrogels were analyzed byIR spectral (FTIR),
thermo-gravimetry analysis(TG and DTG),and of thecrosslink density
wasdeterminedfromthedegreeofswellingusingFlory-Rehner
theory.Thehydrogelshave synthesizedwithvaryingdegreesof
crosslinking.
2. Experimental
2.1. Materials
Thecelluloseacetate(CA)withadegreeofsubstitution(DS)2.5
thathasbeenusedinthisstudywasacquiredcommerciallyfrom
theRHODIA®group(CAusedintheproductionofcigarettefilters).
Dimethylformamide(DMF)whichhasbeenusedassolventand
triethylamineasacatalystwereobtainedcommercially,bothwith
apurityof99%.Asampleofcelluloseacetate,withDS 2.44and
averagemolecularweightequalto50.000g/molhasbeenusedasa
standardfortheanalysisindeterminingthedegreeofsubstitution
(DS).ThisCAwassuppliedbySigma–Aldrich®.
CAhasbeenimmersedinethyletheratroomtemperaturefor
1hand30mininethanolandafteritwasdriedinanovenat80◦C
for24h.Thisprocedurehasbeenusedtoremoveimpuritiesfrom
thesurfaceofcelluloseacetate.TheDMFandtriethylaminehave
beenusedasreceived.
2.2. SynthesisofEDTAdianhydride(EDTAD)
TheEDTA(disodiumsalt)(50.0g)wassolubilizedindeionized
water(500mL),andthentheconcentratedHClwasadded
drop-by-dropuntiltotalprecipitationoftheEDTA(tetraacid).Thesolid
obtainedwasfiltered,washedwithethanol95%,diethylether,and
thendriedinanovenfor2hat105◦Candlefttocoolinadesiccator.
TheEDTA(tetraacid)(180g)wassuspendedinanhydrouspyridine
(310mL)andthenaceticanhydride(240mL)wasadded.The
mix-turewasstirredat65◦Cfor24h.ThentheEDTADwasobtainedasa
solidandwasfiltered,washedwithaceticanhydride,diethylether,
driedundervacuum,and storedindesiccators (Karnitz,Gurgel,
Freitas,&Gil,2009).
2.3. HydrogelsSynthesis
TheCAwithDS2.5(20g)wassolubilizedin100mLof
dimethyl-formamide(DMF)atroomtemperatureundervigorousstirringin
mechanicalstirrerat300rpm.TheEDTADwasdissolvedinDMFat
90◦Cunderstrongstirring.AftercompletedissolutionoftheCAand
EDTAD,bothweremixedwithvigorousstirringandwereadded
to4mLoftriethylamine.Thesuddenincreaseinviscosityofthe
systemshowedtheendofthereaction.Thesynthesized
hydro-gelsweretransferredtoaPetridishandremainedfor48htocure
indesiccators.Thegelwasmilledinamixerinaqueousmedium,
filteredanddriedinanovenat75◦Cuptoconstantweight.The
preparationofhydrogelsfromCAwasperformedinhomogeneous
mediumandtriethylamineasanesterificationcatalyst.The
reac-tionmixturebecameincreasinglyviscoussoonafteraddingEDTAD
asacrosslinker,andthemorphologyofmixturegraduallychanged
fromsolutiontogelabout10–20minafterstartingthereaction.
Thehydrogels werepreparedfromCAaccordingtothescheme
presentedinFig.1.
2.4. Determinationofdegreeofsubstitution(DS)accordingto
ASTMD871-96
Atotalof0.5gofcelluloseacetatesampleswasweighed
accu-ratelyandtransferredtoa250mLflask;toeachsample20mLof
75%aqueousethanolwasaddedandthenheatedfor30minat60◦C.
Then20mLof0.5MNaOHsolutionwasaddedtoeachsampleand
againheatedat60◦Cfor15min.Thesameprocedurewasalsodone
foracontrolsystem(notcontainingCA).Theflaskswerestoppered
andallowedtostandatroomtemperaturefor72h.Theexcessalkali
inthesampleandcontrolwastitratedwithHCl(0.5M)using
phe-nolphthaleinasindicator.Anexcessofacidwasadded(1mL)and
thealkaliwereallowedtodiffusefromtheregeneratedcellulose
overnight.Thedisappearanceofthepinkcolorindicatedcomplete
neutralizationofthealkali.Thesmallexcessofacidwasthenback
titratedwithsodiumhydroxide toaphenolphthaleinend point
(untilthesolutionhadacquiredfaintpinkcolor)(Shaikh,Pandare,
Nair,&Varma,2009).
2.5. Fouriertransforminfraredspectroscopy(FTIR)and
thermogravimetricanalysis(TGA)
TheFTIRspectrumwasobtainedaftergrindingthesampleinto
apowderandmixingwithKBrpowder.Thepowdermixturewas
compressed intoa transparentdisk and scanned from4000 to
500cm−1 usingtheaverageof32scans.TheThermogravimetric
analysis (TGand DTG) was performedin a synthetic air
atmo-sphere(78%ofnitrogenand22%ofoxygen)withaheatingrampof
20◦C/minandmaximumtemperatureof900◦C.
2.6. NIRspectroscopy
NIRspectrawereobtainedfromtheCA,GEDTA12,pure
cellu-lose,and EDTAacidin powderin cuvetteswithafront surface
window with32mmdiameter anda depthof 10mm,ona UV
3600UV–vis–NIRspectrophotometer(SHIMADZU®),witha
spec-tral bandwidthof 10nm, 2nm data interval, and 50 scans per
spectrum. TheNIR spectrawereobtainedin diffusereflectance
mode,andafterwardsconvertedtoapparentabsorbance(A),using
theformulaA=−logR.
2.7. Determinationofcrosslinkingdensity
Determination of percentage swelling: The hydrogel was
immersedin selectedsolvents:chloroform[ı=9,3 (cal/cm3)1/2],
acetone[ı=9,9(cal/cm3)1/2],ethylacetate[ı=9,05(cal/cm3)1/2],
ethanol[ı=26,2(cal/cm3)1/2],diethylether[ı=7,4(cal/cm3)1/2],
water[ı=23,4(cal/cm3)1/2],andbenzene[ı=9,2(cal/cm3)1/2],ıis
solubilityparameter.
Determinationofpercentageswellingwasdetermined
accord-ingtoASTM,1979andASTM1239-55.Afterequilibriumtheswollen
samplesweredriedinthermobalance.Thepercentageofswelling
wascalculatedusingEq.(1).
S%=
(W−W0)W0
×100, (1)
where:S%isthepercentageofswelling,Wisthefinalweight,
Fig.1. ReactionofEDTAdianhydride(EDTAD)andcelluloseacetate(DS2.5)inDMF/Triethylamine.Esterificationcrosslinkingandgraftingoccursimultaneously.
2.8. Determinationoftotalamountofcrosslinkerinthehydrogels
Inthisprocedure,thetetrasodiumEDTAwhichwasproduced
bythealkalinehydrolysiswastitratedwitha standardsolution
ofCaCl2.0.5gofhydrogelssampleswasweighedaccuratelyand
transferredtoa250mLflask;toeachsample,20mLof75%aqueous
ethanolwasaddedandthenheatedfor30minat60◦C.Then20mL
of0.5MNaOHsolutionwasaddedtoeachsampleandagainheated
at60◦Cfor15mL/min.Thesameprocedurewasalsodonefora
con-trolsystem(notcontaininghydrogels).Theflaskswerestoppered
andallowedtostandatroomtemperaturefor72h.Thesolutions
werefiltered,transferredinto100mLvolumetricflaskand
com-pleteduptothemarkwithdistilledwater;10mLwastransferredto
Erlenmeyersflasksandadded10mLofammoniacalbufferpH∼10
andindicatorEriochromeblack.Thensamplesweretitratedwith
standardsolutionof0.01MCaCl2 totheendpoint(colorchange
bluetoburgundy).
ThistitrationallowedtheweightofEDTAinthepolymeric
net-worktobemeasured. The percentage ofEDTA crosslinked and
graftedin thehydrogelsample couldbedeterminedusingEqs.
(2–4):(2)EEDTA=ET−Acetyl,
%Cr=
EEDTA mmEDTA −1 ×100, (3) %Gr=(100−%Cr), (4)where EEDTA is the amount of ester formed by EDTAD and
AC(inmmol), ET is thetotal amount of ester (acetate,
EDTAD-crosslinkedandEDTAD-grafted)inmmol,Acetylistheamountof
acetylinmmol(resultsobtainedfromthedegreeofsubstitution
ofCA), %Cris thepercentage ofEDTAD-crosslinked, mmEDTAis
theconcentrationofEDTAinhydrogelsinmmoland%Gristhe
percentageofEDTAD-grafted.
2.9. Determinationofthewaterabsorbency
The hydrogels were immersed in distilled water at 25 and
A.M.Sennaetal./CarbohydratePolymers114(2014)260–268 263
undervacuum.Thedeterminationofpercentageofabsorptionwas
performedwithathermobalanceprogramedwithheatingupto
105◦C.Tocalculatethepercentageofabsorptionofwaterwasused
Eq.(1).Absorbencymeasurementsweretakenforthreesamples
ofeachproduct,andtheaverageofthethreevalueswasplotted
againsttheabsorbencytime.
3. Resultsanddiscussion
3.1. Determinationofdegreeofsubstitution(DS)accordingto
ASTMD871-96
Thedegreeofsubstitution(DS)oftheCAwasconfirmed.The
supplierhasindicatedDS2.5andtheresultfoundwas2.56±0.03.
3.2. Hydrogelssynthesis
Esterificationwasallowedtoproceedatroomtemperaturefor
48h(cure), and then thereaction productwas triturated.
Sub-sequentconversionoftheunreactedcarboxylgroupstosodium
carboxylatesintheproductbytheadditionofaqueousNaHCO3
wasperformedtoenhancethewateraffinity.Finally,theproduct
waspurified,washedwithdistilledwaterandethanol,dried,and
thenscreenedthrougha60meshsievetoobtainawhitegranular
product.Samplesofhydrogelsthatwereusedinthedetermination
crosslinkingdensity,byFTIRandTG/DTGwerenotneutralizedwith
NaHCO3.
3.3. FTIRanalysis
Followingthecrosslinkingesterificationreactionof cellulose
acetate(DS2.5)withEDTAD,theobtainedproductshowed
sev-eralnewabsorptionbandsintheFTIRspectrum,inadditiontothe
originalpeaksfrompurecelluloseacetate,asshowninFig.2.The
increaseintheabsorptionbandat1755cm−1wasassignedtothe
C Ostretchingvibrationofthecarboxylicacid(EDTAacid),and
theabsorptionappearingat1643cm−1 wasassignedtotheC O
asymmetricstretchingvibrationofthecarboxylicacid.Formation
ofthecarboxylicacidintheproductswasalsoconfirmedbythe
typicalabsorptionat1385cm−1,arisingfromthecarbonyl
symmet-ricstretchingvibration(Silverstein,Bassler,&Morril,2005).The
IRanalysisindicatesthatthehydroxylgroupofcelluloseacetate
(DS2.5)mayhaveesterifiedwithEDTAD,resultinginthe
forma-tionofcarboxylicacidaswellascrosslinkingbetweenthecellulose
acetatechains.TheresultsofFTIRcorroboratewithresultsobtained
byKono&Fujita,(2012).
Fig.3.
3.4. NIRspectroscopy
Themain differences betweenthe spectraof purecellulose,
GEDTA11, EDTAacid, and CAare in theabsorbancies at
wave-lengthsto1932,1723,and1427nm(Langkilde&Svantesson,1995).
At1932nm(characteristicfor(RCOOR1)andROHvibrations),the
explanationforthehigher absorbanceoftheCA,isthe
proxim-ityofthepolymericchainsdue thehydrogenbonding between
thefreeOHgroupsoftheCA,intheGEDTA11thechainsof
cel-luloseacetatearefartherapartduetothepresenceofcrosslinkand
theformationofathree-dimensionalnetwork.Thus,thenumber
ofrepeatingunitsofCA(acetylatedcellobiose)issmallerinthe
GEDTA11.Table2showsthatthegreaterthedegreeof
crosslink-ing,thesmallerthepercentageofrepeatingunitsofCApercm3,this
explainsthehigherabsorbanceoftheCA.Becauseeachrepeating
unitoftheCA(DS2.5)hasfiveacetategroups(esters)andasshown
inFig.1,onediesterisformedduringcrosslinkingofEDTADand
CA.Thustheamountofestersislessperunitvolume,which
con-tributedtolowerabsorbance.Anothercontributiontothedecrease
inabsorbanceat1932nm,istheconsumptionoftheOHgroupsof
theACinthecrosslinkingesterification.
In1723nm(characteristicforCH2 vibrations)theabsorbance
washigherintheGEDTA11.BecauseforeachcrosslinkedEDTAD
therearesixCH2groups,whileineachrepeatingunitofCAthere
aretwoCH2groups,sohigherabsorbanceinGEDTA11.In1427nm
(characteristicforcombinationsofCHandCH2vibrations)thelarge
amountofCHgroupsintheCAcontributedtothehigherabsorbance
(Workman,2000).Thepurecellulosewasusedtoinvestigate
over-lapsinthespectrum.Itwasfoundpossibletodistinguishstructural
differencesbetweenCAandGEDTA11byspectraNIR.Throughthe
NIRspectrawaspossibletoobtainadditionalinformationsabout
thestructureofhydrogels.
3.5. TGandDTG
Celluloseacetateisdegradedinthreesteps.Thefirststepfrom
theroomtemperature(25◦C)to330◦Crepresentsthevolatilization
ofthevolatilematter,and/ortheevaporationofresidualabsorbed
water. Thesecondstepstartsat330◦C andends at500◦C, and
representsthemainthermaldegradationofthecelluloseacetate
chains.Thethirdstepstartsat500◦C,andrepresentsthe
carboniza-tionoftheproductstoash.Theresultsofthermaldegradationof
celluloseacetatecorroborateresultsobtainedbyHanna(Hanna,
Basta,El-Saied,&Abadir,1999).
Aftersynthesis reactionshaveformedcarboxylicacidgroups
derivedfromEDTA-tetraacetic(EDTAacid)inthecrosslink.The
TGandDTGcurvesshowthatthehydrogelislessthermallystable
thantheCA.ThiseventmayberelatedtotheC Nbondpresentin
thecrosslinkinginthehydrogels.TheFig.4(E)showsthattheC N
bondhaslowerbindingenergy,andthusisdegradedintolower
temperatures.
ThethermalstabilityofEDTAismuchlowerthanAC,thus,the
inclusionofEDTAD-graftedandEDTAD-crosslinkedinthepolymer
networkmakesaproportionatedecreaseinthethermalstabilityof
thehydrogel.BecausetheCApresentslinearchainswhichprovide
agreatextentofformationofhydrogenbondsconferringthermal
stabilityofthepolymer.Theinclusionofcrosslinkcausesthe
phys-icalseparationoftheCAchainsandconsequentlythedecreasein
theintermolecularinteractionswithalargedecreaseinthethermal
stabilityofthehydrogel.
3.6. Determinationofcrosslinkingdensity
TheFlory-Rehnertheorystemsfromthecombinationthe
Flory-Hugginstheoryforpolymersolventwiththetheoryofstatistical
mechanicsofthefreeenergyvariationcausedbyswelling.The
fol-lowingequationisrelatedtocrosslinkdensityinsystemswhere
theymovesimultaneouslyandatthesamespeed(“affine
defor-mation”)duringtheswellingofthesample.
v
=− ln(1−Vr)+Vr+V2r] V1(V1r/3−V2r) , (5)where:=Crosslinkdensitywhich corresponds tothe
effec-tive number of chainsper unit volume (=/Mc)Eq. (6), is
thedensityofthepolymerandMcis averagemolecularweight
betweencrosslink).Vr=reducedvolume (samplevolumebefore
swelling/samplevolumeafterswelling).=parameterof
polymer-solventinteraction.V1=molarvolumeofthepuresolvent.
Inthemethodofswelling intheequilibrium,thepolymeris
immersedinsolventsselectedwitharangeofvaluesofsolubility
parameter.Thevalueofthesolubilityparameterofthepolymeris
Fig.2.FTIRspectraofGEDTA11andcelluloseacetate(A)andGEDTA0.11andcelluloseacetate(B).
ismaximized.Thedegreeofswelling intheequilibriumis
rep-resented by the parameter Q. The parameter Q is determined
experimentallybytherelation:
Q=(m−m0)
m0× ,
(7)
where“mo”istheweightofdrypolymer,“m”istheweightof
swollenpolymerandthesolventdensity.
Theparameterofinteractionpolymer-solvent,canbe
decom-posedintocomponentsof entropy(s)and enthalpy(h),as a
measureofenergyfree.Thus:
=s+h, (8)
h= (ı1−ı2)
2
RT , (9)
whereRisthegasconstant,Tisabsolutetemperature,ı1andı2is
thesolubilityparameterofthesolventandpolymerrespectively.
Inconditionsofmaximumswelling,thecontributionofhis
min-imalandthevalueoftheinteractionparameterisalmostequal
totheentropycontribution.Theliteraturehasusedthevalueof
0.34fors(Blanks&Prausnitz,1964;Dudek&Bueche,1964).The
crosslinkingdensity()andthecorrespondingaveragemolecular
weightbetweencrosslinkingpoints(Mc)werecalculatedbyEq.(5)
and(6).
To investigate the correlation between the percentage of
swelling(%S)andMcwassynthesizedahydrogelwithcrosslink
density
=1.19×10−6, Mc=1.1×106, and density 1.308g/cm3.Thishydrogelwassynthesizedonlytocollecttheresultsofswelling
intheequilibriumandplotagraphwiththeresultsofthe
hydro-gelspresentedinthiswork,becausethiswaytheinvestigationof
A.M.Sennaetal./CarbohydratePolymers114(2014)260–268 265
Fig.3. NIRspectraofpurecellulose,CA,EDTAacid,andGEDTA11intheregion1900–1300nm.
Table1
ResultsobtainedbyFlory-Rehnertheory.
Resultsofthedeterminationofcrosslinking
Gel GEDTA11 GEDTA12 GEDTA0.11
Percentageofabsorptionintheequilibrium 1142 2450 6800
Maximumswellingintheequilibrium,Q(cm3/g) 12.1 26.0 72.0
Reducedvolume,Vr 0,0581 0,0205 0,0106
Densityofgel,(g/cm3) 1.368 1.332 1.297
Solubilityparameterofthegel,ı2 12.1 12.1 12.1
Interactionparameterpolymer-solvent, 0.34 0.34 0.34
Densitycrosslink,(g/cm3). 1.6×10−5 4.4×10−6 8.2×10−7
Averagemolecularweightbetweencrosslink,Mc 8.2×104 3.1×105 1.6×106
Fig.4.TGofcelluloseacetateandEDTAacid(A),DTGofcelluloseacetateandEDTAacid(B),TGofcelluloseacetateandGEDTA11(C),TGofcelluloseacetate,EDTAacidand GEDTA11(D),averagebondenthalpies(E).
Thehydrogelspresentedhigherswellingindimethylformamide
(Fig.5A).TheFig.5BshowsthatthecorrelationbetweenS%andMc
isverygood.Thus, themethodusedtodeterminethecrosslink
densityinthehydrogelsisaccurate.
Fig.6.
3.7. Determinationoftotalamountofcrosslinkeragentinthe
hydrogels
Fortheelucidationofthestructuralfeaturesofeach gel,the
A.M.Sennaetal./CarbohydratePolymers114(2014)260–268 267
Fig.5.Valuationofthepercentageofswelling(S%)tothehydrogelsindifferentsolvents(4A).Correlationbetweenthepercentageofswelling(S%)andMc(5B).
Table2
ReactionconditionsandresultsoftheesterificationcrosslinkingofcelluloseacetatewithEDTAD.
Gel WCAa nCAb %CAc AT1(mmol/cm3)d AT2(g/cm3)e A.EDTAf %Crg %Grh nEDTAI
GEDTA11 1.144 0.0021 83.6 0,7663 0.224 4.61×1020 98.26 1.74 0.36
GEDTA12 1.256 0.0024 94.3 0.2593 0.076 1.56×1020 98.39 1.61 0.11
GEDTA0.11 1.281 0.0024 98.8 0.0553 0,016 3.3×1019 98.54 1.46 0.02
aGramsofCApercm3ofgel.
b Molofrepeatunit.
c PercentageofCA.
d mmolofEDTApercm3ofgel.
eGramsofEDTApercm3ofgel.
f NumberofEDTAmoleculespercm3ofhydrogel.
gPercentagesofthecrosslinkedEDTAmoleculesintotalesterifiedEDTAineachgel.
h PercentagesofthegraftedEDTAmoleculesintotalesterifiedEDTAineachgel.
I NumberofEDTAmoleculesperrepeatunitofCA.
ofcrosslinked-EDTADand grafted-EDTAD(%Crand%Gr,
respec-tively)weredeterminedbythetitrationmethodfortheestimation
ofthetotalamountofestercontents.In1cm3ofthehydrogel,it
wassupposedthattherewasXmmolofcrosslinkedEDTADand
YmmolofgraftedEDTAD.AsshowninFig.1,onediesterandtwo
carboxylicacidgroupsareformedduringcrosslinking,whereasthe
graftreactionresultedintheformationofoneesterandthree
car-boxylicacidgroups.InComparingtheresultsinTable2withresults
obtainedbyKonoandFujita(2012)ispossibletoconcludethatthe
resultsofpercentageofEDTAD-crosslinkedandthepercentageof
EDTAD-graftedaresimilar.
Toobtaintheresultsshown inTable2 titration results, and
thedensityofthehydrogels(Table1)wereused.Thefollowing
equationswereusedtoobtaintheresultsofTable2.
[WCA=(−AT2)], (10)
nCA= WCA M1RU , (11) %CA=WCA ×100 , (12) AT1=mmolEDTASV , (13)AT2=
weightSVEDTA(g), (14)M1RU=molarweightofrepeatunit(534.5g/mol),=densityof
hydrogel(g/cm3),SV=samplevolume(cm3).
3.8. Determinationofthewaterabsorbency
Potentiometrictitrationwasperformedin1cm3 ofGEDTA11
with100mLofdistilledwatertofindthepHvaluethatallofthe
carboxylicacidgroupsareneutralizedcompletely.Thevaluefound
was8.5,thisvaluewasusedasareferenceintheneutralizationin
thehydrogelsusedintestingwaterabsorbency.
Thewaterabsorbencyisdependentonthetemperatureandalso
theamountofcarboxylategroupsinthehydrogels.Incomparison
betweenhydrogelsandCA;wasconcludedthatthehydrogelsare
morehydrophilicthantheCAandthusabsorbmorewater.Withthe
increaseofcarboxylategroupsinthehydrogels,theioniccharacter
alongthepolymerchainincreases.Withincreasingtemperature,
increasesthediffusionofwater intothehydrogeland thusthe
absorptionofwaterincreases.
4. Conclusion
The hydrogels were prepared from cellulose acetate (DS
2.5)viasimple esterification crosslinking of EDTADunder mild
conditions. Simultaneous crosslinking and grafting of EDTAD
occurredbytheformationofdiesterandmonoesterlinkages.The
characterizationsperformedbythetechniquesofTGandDTG,FTIR
anddeterminationofcrosslinkdensityprovedtobeeffectivein
characterizationofhydrogels.Thehydrogelswereproducedwith
rawmaterialsoflowcost,throughasimpleprocedureatroom
tem-peratureandthehydrogelsarederivedfromcellulose,whichisa
renewableresource.
Acknowledgements
The authors thank thefinancial supportfrom the following
BrazilianGovernmentAgency:ConselhoNacionalde
Desenvolvi-mentoCientíficoeTecnológico-CNPq,Rhodia®Group(France)by
supplyingthecellulose acetate.Theauthorsarealsogratefulat
UniversidadeFederaldeSãoCarlos-Sorocaba-SP.
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