Novel pathway to produce high molecular weight kraft lignin–acrylic acid polymers in acidic

15 Pages·2017·1.49 MB·English

by  Fangong Kong

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Novel pathway to produce high molecular weight
ce. kraft lignin–acrylic acid polymers in acidic
n
M. Lice Citethis:RSCAdv.,2018,8,12322 suspension systems†
Ad
2:20:24 Unporte Fangong Kong,ab Shoujuan Wang,*ab Weijue Gaob and Pedram Fatehi *b
023 1n 3.0 Kraftlignin(KL)producedinkraftpulpingprocesshasalowmolecularweightandsolubility,whichlimitsits
2o
on 2/14/Attributi asupsppliecnastiioonnisnysintedmusttroy.pFroordtuhceefiarswtatitmere,soKlLubwleaslipgonliynm–AeArizpeodlywmitehrawcirtyhlicaahciigdh(AmAo)liencuanlaracwideiicghatqiuneothuiss
oaded mons rweoarckt.ioTnhceopnodliytimonesrizoantitohnerceaarcbtoioxnylawteasgrcoaurpriecdonotuetntusainndgmK2oSle2Ocu8laarswaenigihntitoiaftorer,sualntadntthliegnininflupeonlycmeeorsf
wnlom was systematically investigated. The mechanism of polymerization of KL and AA was discussed
Doe C fundamentally. The resulting lignin–AA polymer was characterized by Fourier Transform Infrared
18. ativ spectrophotometry (FTIR), proton nuclear magnetic resonance (1H-NMR) and elemental analyses. The
9 March 20under a Cre rumensodulealtrrsraasnhtiooaw,c0ied.di1c5tehmnaovtilrtohLne(cid:1)m1poehfneltni.goUnliincndhceyordntrchoeexnyctlroagntridooiuntip,o3n(Pshho-afOn1dH.58)0wcot(cid:3)%nCt,eotnfhteinoictfiaaKrtbLoorp,xry3ol.a5mteootfgerpdoHut,ph1ec0op.0notloeymfntAeaArin/zldaigttinohinne
n 2ed molecularweightofthepolymerwere7.37mmolg(cid:1)1and7.4(cid:4)105gmol(cid:1)1,respectively.Thelignin–AA
Published ocle is licens RADceOccIee:pi1vt0ee.dd10123s2t9nD/dce7Mcraea1mr2cb9he72r1h0210817 CflpoooclmycmpuaelarrteiowdnawspitwehraftpoeorrmlysaAonAlcu,ebtlheoefaltilgiganni1nin0––AgAAALp(cid:1)po1olyclmyomnecererwnitanrsataiaonnmaaolunrmedienaffiiupcmHienhotixgiflhdoeecrcstuuhlsaapnnetn4fs.o5ior.nFauluwrtmahseinrimeuvmoarlueoa,xtteihddee.
Article. This arti rsc.li/rsc-advances suspension,whichshowsitspotentialtobeusedasagreenflocculantinindustry.
s
ces Introduction benecial purposes.7 One of these modications is the poly-
c
A merization of lignin with functional monomers, which can
n
pe Lignin is a natural biomacromolecule, found in wood and increase both the molecular weight and number of functional
O
vascularplants.Over60milliontonsofligninisproducedinthe groupsonligninstructure.Chenetal.8producedapolymerby
pulp and paper industry annually in the world.1 Among tech- reacting lignosulfonate with 1-ethenylbenzene to enhance
nicalligninsproduced,kraligninisthemostdominantone, thermal stability and molecular weight of the polymer. The
but is mainly incinerated as a low cost fuel in the pulping polymerization of lignosulfonate with vinyl monomers, i.e.,
industry leading to the waste of resources and growing envi- acrylic acid, acrylonitrile, and methyl methacrylate, was also
ronmentalproblems.2,3Withthedepletionoffossilfuelandthe studiedinaqueousororganicsolventsinthepastviachemical
improvement of environmental awareness, greater endeavors radical starters9–12 or chemo-enzymatic starters,13 in order to
have been made on developing lignin-based materials. producehighmolecularweightproductswithhighhydrophilic
However,kraligninhasnotyetbeenutilizedeffectively.4,5 or hydrophobic properties. Meister et al.14,15 synthesized acryl-
Lignin is a highly stable and complex compound with amide with kra lignin in dioxane solution and used it as
a three-dimensional aromatic structure formed from three a drilling mud additive. In another report, 1-phenylethylene–
phenylpropanoid monomer units of guaiacyl, syringyl and p- kra lignin polymer was produced in dimethyl sulfoxide solu-
hydroxyphenyl,connectedbyetherandcarbon–carbonbondin tion and used as an oil recovery agent. However, organic
an irregular form.6 Various modication techniques were solvents, such as dioxane and dimethyl sulfoxide, were gener-
carriedoutinthepasttoproducenewlignin-basedproductsfor ally used for facilitating the homogeneous polymerization of
kraligninand other monomers. However,these solvents are
usually toxic, expensive and may need a complex recovery
aKeyLaboratoryofPulpandPaperScienceandTechnologyofMinistryofEducation, processaeruse,whichhamperstheirpracticalapplicationin
China,QiluUniversityofTechnology,Jinan,250353,China industry.
bChemicalEngineeringDepartment,LakeheadUniversity,ThunderBay,ON,P7B5E1,
In the past, the polymerization of lignin in aqueous solu-
Canada.E-mail:[email protected];[email protected];Tel:[phone]
tions was assessed. Ibrahim et al.16 polymerized soda lignin
†Electronic supplementary information (ESI) available. See DOI:
with 2-acrylamido-2-methylpropane in 1 wt% NaOH solution,
10.1039/c7ra12971h
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andtheproduct,sodaligninpolymerwithamolecularweightof D O, trimethylsilyl propanoic acid (TMSP), dimethyl sulphate
2
2.6 (cid:4) 106 g mol(cid:1)1, was used as a drilling mud additive. Fang andpara-hydroxybenzoicacid(analyticalgrades)wereobtained
etal.17alsoproducedacorn-stalklignin–acrylamidepolymerin from Sigma-Aldrich Company, and used as received. Dialysis
NaOH solution and used it as an adsorbent for dye removal membrane (cut off of 1000 g mol(cid:1)1) was obtained from Spec-
from wastewater. However, there is no report about the poly- trumLabs.
merization of kra lignin and acrylic acid in aqueous acidic PolymerizationofKLwithAA.Thereactionswerecarriedout
suspensions,whichisstudiedforthersttimeinthiswork. in a nitrogen atmosphere in 250 mL three-necked asks
Asprovenintheliterature,thecomplexandheterogeneous equippedwithmagneticstirrers.Atrst,2gofligninwassus-
e. structure of lignin played important roles in its polymeriza- pendedin30mLofdeionizedwateratroomtemperatureand
nc tion.10,12,17–19 However, there are contradictory reports on the 300rpmfor20mininthreeneckasks.Aerthat,therequired
M. Lice role of phenolic group in the polymerization of lignin: (1) the amount of AA was addedto the asks and the nal pH of the
0:24 Aported psthruenctoulircepgrrooduupceadctisnathseapnoliynmheibriiztaotrioonw,iwnhgicthowtahseoqbuseinrvoeidd ssoulsupteionnsi.onSsubwseaqsuaednjtulys,tetdhetote3m.5p,eurasitnugre1o.0f mthoel L(cid:1)as1kNsawOaHs
2n
023 12:n 3.0 U hinydthroechploolryimcseorizawtoioondloigfnsitnyr;1e9n(e2)wthitehplhigennoosliuclfgornoautpe1a8cotsrawsiatnh awdejruestpeudrbgeydkewepitihngntihtreogeansksfoirna20wamteirnb.aAthearnwdartdhse,sothluetipornes-
2o
nloaded on 2/14/mmons Attributi acmpgocrreoetnitsuvvhepeeynrlosccieneomnntotehrfrteehalitpafgeoconsrrloyyotlmsfhautaeelecfr,oprizynoawllaitycetimoerme.n4e,o1ro1sinzfioTgaKmnthiLieoernarecns.fa,doInitr.tAeelw.,yA,atAihsasAceos,ctbareioslclleelrerynravloootetenfddciptltrehhiialneaernt,aobttnhhluideect dwatrheteeprti3oeeg0urah0mtgte)hirdnwpoeumaudtsn.aadAtmdhedrecoeouddnrnietffttiaonecoruttfeihoonienuntis.ttiaesaTsumtkhopsperpei(lnrKypa2oootSulrf2ydrOmnees8iret,rrt(woio6zgt0ai%entni(cid:3)ioCbtinwa,asat7eesr0detmaho(cid:3)ceCantiir,onlein8taga0cnitnwii(cid:3)noeaC'ndss,
owCo is crucial for understanding the polymerization of KL and AA 90(cid:3)Cand95(cid:3)C),timeintervals(0.5h,1h,2h,3h,4hand5h),
De
18. ativ fromacademicandindustrialpointsofviews.Inthepolymer- initiatordosages(0.5wt%,1.0wt%,1.5wt%,2.0wt%,2.5wt%
March 20der a Cre iwtzhiaetthiloicnganrrbienao–cxAtyilAoantpe,otghlryeomuaeplirpiozhfaapttioioclnyhayrcedraryocltixicyolangcritdohur(pPosAuAgoh)fKfoeLrsmtmereiigdhcdtaurtreioianncgt, a((10n..30d573,.m20.w7o0lt%,L5(cid:1),.4b1,,a8s0.e.01d,1om0no,l1lig3Ln.(cid:1)5in1a,'ns0dw.11e56ig.m3h)to)a,lnALdA(cid:1)lt1iog,nl0iig.n2n2cinomnmcoeolnlLatrr(cid:1)a1rtaiatoinnodss
n 29 ed un which would also gra PAA onto lignin.20 It is not clear if the 0.38molL(cid:1)1)inordertooptimizethereactionconditions.
d oens esterication reaction would happen in an acidic heteroge- Extraction of lignin–AA polymer from reaction media. The
Publishecle is lic neoIunstchoendwiotiroknp,rwehseicnhteidsthheeresienc,onthdeopbojelycmtiveeriozfattihoinssotfudkyr.a pthueriprcoactieodnuroefldigenveinlo–pAeAdpionlyomuerrewaarlsiecrarpraiepdero.2u1tTahcceorredainctgiotno
s Article. This arti ldwiugancstientodwugiesthinneagrcaKrtye2lSiw2cOaa8tceairdssaionnluainbnlietaicalitidgoinrc.inTa–qhAueAemopuaoisnlysmaoilmeurtioowfnitthhwiasasshtcuoigdnhy- slrieogmlnuiotnivo–enAAtwhpaeoslfyomrrsmetrleyfdraocmPiAdiAtheehdsoomtoluotppioHonly,omafne1rd.5tahnteodnpcurenencrtiepraiifctutaegtdeedtAhtAoe
s
ce molecularweight,whichwillfacilitateitsapplicationasaoc- monomerfromlignin–AApolymer.Thedetailedprocedurewas
c
n A culant in wastewater systems. In addition, the inuence of statedintheESI.
pe phenolicgrouponthepolymerizationefficiencywasidentied. PAA preparation. PAA was prepared in the presence of KL
O
This study also intended to report how the functional groups under the conditions of pH 3.5, 0.15 mol L(cid:1)1 lignin concen-
andmolecularweightofsowoodkraligninwillbeaffectedby tration,8AA/ligninmolarratio,80(cid:3)C,3hand1.5wt%initiator.
this polymerization. The properties of the lignin–AA polymer In the absence of KL, PAA was also produced under the same
were determined using a light laser scattering technique, and conditions. Aer the reactions, the solution was treated
theocculationperformanceoftheresultinglignin–AApolymer accordingtotheprocedureusedinourearlierpaper21(available
for an aluminium oxide suspension, as a model suspension inESI†).
system for representing wastes of the mining industry, was ReactionofKLwithPAA.Inonesetofexperiments,thePAA,
evaluatedbyaphotometricdispersionanalyzer. produced in AA system, was reacted with KL under the condi-
tionsof0.15molL(cid:1)1oflignin,8.0molmol(cid:1)1ofPAA/KL,1.5%
Experimental initiator,80(cid:3)C,3handpH3.5.Aerthereaction,thesolution
waspuriedasstatedaboveandthenalproductwasusedfor
Materials
H-NMRanalysis.
Sowood kra lignin sample with a molecular weight (M ) of AA conversion analysis. The AAconversion inthe reactions
w
17890 g mol(cid:1)1 was received from FPInnovations' pilot plant was determined using H-NMR. In this set of experiments,
facilitiesinThunderBay,ON.Thekraligninwasproducedvia 0.2mLofreactionsolutionwascollectedandthenmixedwith
LignoForce™ technology.20 Polydiallyldimethyl-ammonium 0.8mLD Ocontaining5mgmL(cid:1)1trimethylsilylpropanoicacid
2
chloride (PDADMAC, 100000–200000 g mol(cid:1)1), acrylic acid (TMSP) as an internal reference. The NMR spectra of these
(AA),potassiumpersulfate(K S O )(analyticalgrades),sodium samples were recorded using an INOVA-500 MHz instrument
2 2 8
hydroxide (97%, reagent grade), hydrochloric acid (37%, (Varian,USA)witha45(cid:3)pulseandrelaxationdelaytimeof1.0s.
reagent grade), potassium hydroxide (8 mol L(cid:1)1 solution), The area of the peak at 5.95–6.05 ppm was considered for
potassium permanganate (analytical grades), ferrous ammo- determiningtheunreactedAAconcentration,C ,inthereaction
1
niumsulfate(analyticalgrades),0.1molL(cid:1)1hydrochloricacid, solution.TheAAconversionwascalculatedusingeqn(1)
Thisjournalis©TheRoyalSocietyofChemistry2018 RSCAdv.,2018,8,12322–12336 | 12323
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C (cid:1)C wasaddedpereachmmoloftotalphenolichydroxylgroupsof
AAconversion; %¼ 0 1(cid:4)100 (1)
C KL, and the solution was stirred at room temperature for
0
30min.Thesolutionwasthenheatedto80(cid:3)Cfor2h.During
where C was the initial AA concentration in reaction
rseoalucttiioonn,s0moloultLio(cid:1)n1,amndolCL1(cid:1)w1.astheunreactedAAconcentrationin tchoentrineaucotuiosna,dtdhietiopnHooff0.t7hemsoolluLt(cid:1)i1onNawOaHs ksoepluttiaotn1.1U–p1o1n.5thbey
completion of reaction, the solution was acidied to pH 2.5
Analysis of initiator consumption. A set of reaction was using2molL(cid:1)1HClsolutionandprecipitateswerewashedwith
carriedundertheconditionsofat80(cid:3)Cfor3hoursinanitrogen
excessamountofdeionizedwateruntilneutralpHwasobtained
atmospherein250mLthree-neckedasks,butwithoutAA.At
ce. rst, 25 mg of lignin was suspended in 50 mL of deionized and then the precipitates were freeze-dried. The nal product
n wasconsideredasmethylatedKL.Themethylationconditions
oaded on 2/14/2023 12:20:24 AM. mons Attribution 3.0 Unported Lice atoswawicbzauonnueaieitnsfdtntdihopecnoerHreefndies.entnCtlirAysattaarlhrinnlowoasrKudedtniooirtsa2soulhwaSurnagwd2atKmhOsiiraeo2zdoo8srSmenu,fc2adtstOotoihd.hnnntpe8jAeihuicotauresiecittaemtnanoteartsihntoedctsrsaierttaiatuiicuutnsoottlimaonfniuo3oamrdnso.tn5weuepewo.roesaspfSerarsos0Hrimc1mlue.aiu7s0adpdita5.(npilid5inacog.gleeruaynaad.Lls,.nrnoy(cid:1)2iects2dnaf1ooaet1.gncanedTt0til1thitkhrwb.orme0oaeoynilltLgmishsbneanaoaownesmaafclkeclkwLpsropspe(cid:1)aetnlttHaers1iodctsnsNramiuo)mdat.raflitraaTfoaOitiariohhenkndtHndeeees-- litcwwawinrinnaieeetdresanhHuetcuctme2yhdlosOnienieseicff2ntdndeecetttidort,rthooeeniteofianhtntnterpPtemensTrhPa,eHtea-thrsOnboOeeK-tlfHOaneOLcopcH–t1fceths,o.okeoawwnrnpfnaithorctdeehilanciprcclhttbaiahghroorienebysxfidqyotnKphlruxa.roLeyitoInxlentadyoortgluneonergacroeedttrg-uheodmredpoeurebsupktp,tyophrhooaHiflyfcduydo2mmerOrlntioiheegt2ngetrenthieunrezinynntratlsmedatp.sisteoeaeteIrrinnmddfoayixpaetKltihktlffihdLeeaieessss--
wnlom containingsolutionwaspipettedtoa100mLErlenmeyerask. thatareformedbyionizationofthephenolicligninmoietiesor
oC by alkali-induced cleavage of the cyclic a-aryl ether bonds in
18. Dative Tfehreronu,s10ammmLoonfiu0m.5 MsulHfa2tSeOs4osluoltuiotnionwearneda1d0demdLtoofth0.e025asMk phenolicligninmoieties.24Thequinone-methideintermediates
March 20der a Cre wwhasiletisttriartreindgacgoanisntsatnt0l.y0.0A2eMroKnMemnOin4otfostairrpinergm,tahneesnotluptiinonk (brseyedeuthFcetiigo.cnlSe2aovfiangPEehS-oOI†fH)tahgreerobuenpnazlcleyonnoetxeirndintizgeindiniKnLKto.L25,d,26irceaTsruhbleotixntyrgleiacitnmacetihdnest
9 un endpoint.Ablanktitrationwasconductedon10mLofferrous
Article. Published on 2This article is licensed coaomnnmecqeonnntP(ir2uear)mtsiuoslnfuaoltffeaptceeornssotuellnufatt(cid:1)itoeLgni(cid:3)nint¼h1em0som(cid:4)luLMtioofn(cid:4)thw(cid:4)eaEs02(cid:1)V.c5aElMc0u(cid:5)Hla(cid:4)2tSe3dO4b.aTs(he2de) cT1tmtiho.ao0einbnsmdmleesidbtto2uirlo.adnnALmys(cid:1)e.e1eawmrnHabtds2hrSdaetOhnrti4eereedapanrtdamodnipaeddlenyircsattoi,ilseynt.zshseeioddTfsehoftroerleuredat4itsao8easndmhpwspeuaarlsmeosixnnpigdecleuoets-lthtlrreaeaecrlaeiatzetfeeldoiddrsetuKemfsdrLoieniimnnng-
s Polymerization of treated lignins with AA. The polymeriza-
s
cce where E is the volumes (L) of KMnO4 solution used for the tionconditionsofacetylatedKL,methylatedKLsandperoxide-
n A endpoint for blank sample. E0 is the volumes (L) of KMnO4 treatedKLswithAAwerexedatpH3.5,ligninconcentration
pe solution used for the endpoint for actual sample, M is the 0.15molL(cid:1)1,AA/ligninmolarratio8.0,80(cid:3)C,3hand1.5wt%
O
molarity(molL(cid:1)1)ofKMnO ,Visthevolume(L)ofthesample initiator. Aer polymerization, the polymer was puried
4
andmisthemolarmassofK S O . accordingtotheprocedurestatedearlier.Thecarboxylategroup
2 2 8
Acetylationoflignin.InordertounderstandifAAcanreact contentwasmeasuredaccordingtothemethoddetailedinthe
withotherreactionsitesonKL(inadditiontophenolichydroxyl following section, and the increased carboxyl group of lignin
groups) under acidic conditions, the acetylation of lignin was was determined (via subtracting the carboxylate group of
carriedoutaccordingtothemethoddescribedbyAndesetal.22 lignin–AApolymerfromthetotalcarboxylategroupofKL).
Inthissetofexperiments,0.5gofKLwasdissolvedin6mLof Presenceofunreactedkralignininthepolymerization.As
pyridine–acetic anhydride (1/1, v/v) by stirring for 30 min at statedpreviously,theunreactedKLmayexistinthenallignin–
300rpm,25(cid:3)Candthenkeptinthedarkatroomtemperature AApolymeraerthereaction.Inordertoevaluatethis,acetone
for72h.Thesolutionwasaddeddrop-wiselyto120mLofcold wasusedtoextracttheunreactedligninfromlignin–AApolymer
water and then centrifuged and washed 3 times. The solvent
wasremovedfromthesampleusingafreezedryerandthenal
productwasconsideredasacetylatedligninsample. Table 1 Methylation conditions and Ph-OH content of methylated
Methylation of KL. In order tounderstand the relationship lignin
between Ph-OH group content of KL and polymerization, KL
Sample KL 1 2 3
was methylated according tothe method reported inthe liter-
Dimethylsulphate/ 0 0.25 0.50 1.0
ature.23ThereactionschemeisavailableinESI(Fig.S1†).Inthis phenolicgroupofKL,
method,onlyPh-OHgroupofKLcanbemethylated,whilethe molmol(cid:1)1
aliphatic hydroxyl group of KL is methylated marginally.23 A Ph-OHgroup, 1.73 1.41 1.02 0.70
1.0gofKLwasdissolvedin15mLof0.7molL(cid:1)1NaOHsolution mmolg(cid:1)1lignin
Carboxylategroup, 0.37 0.38 0.36 0.36
at room temperature by stirring at 300 rpm for 20 min. Aer mmolg(cid:1)1lignin
that,0.25mmol,0.50mmolor1.0mmolofdimethylsulphate
12324 | RSCAdv.,2018,8,12322–12336 Thisjournalis©TheRoyalSocietyofChemistry2018
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Table2 HydrogenperoxidetreatmentconditionsandPh-OHcontentofperoxide-treatedlignin
Ligninconcentration, H O ,wt%, Time, Temperature, Carboxylategroup, Ph-OH,
2 2
Sample wt% basedonlignin h (cid:3)C mmolg(cid:1)1 mmolg(cid:1)1
1 5 18 1 90 1.65 0.74
2 5 8 1 80 1.06 0.95
3 5 4 1 80 0.65 1.23
4 5 4 0.5 80 0.43 1.39
KL — — — — 0.37 1.73
e.
c
n
AM. d Lice samples extracted from the reaction medium in soxhlet angle laser detectors). For KL measurement, the columns of
20:24 nporte eexxttrraaccttoedr ffroorm12thhe.liIgnnitnh–isAAcapsoel,ymtheeruansrkeraacteldiglniginniinsscoalnubblee oPfAtSe1t0ra6hMy,dProAfSu1r0a3na(TnHdFP)AaSt110.02.m5wLemreinu(cid:1)s1e.dFowritlhiganinx–eAdApoowlymraeter
2023 12:on 3.0 U aincearcteationnea,mbouutntlig(anbionu–AtA2.0p–o2l.y5mge)roifssianmsopllueb,lMe.027,,2w8aIsnimtiaalilny-, mwiethasuaremxeednt,otwhercaoteluomfn0s.1ofmPoAlAL2(cid:1)016NaanNdOP3AsAo2l0u3tiowneraetu0s.e7d0
oaded on 2/14/mons Attributi tewaxnaitnsaraleacmditreia-nddsrsawieopidftrhteah-aneecxdsetarttoahmcnetpeneldefdo,rrMile1t1de2,rwihpna.asAapwnereeo,irvgatehnhnededatethax1netr0nda5ctthht(cid:3)iCeeonpsfa,oemtrrhc1pee2nlesthasam.gwTeephorleeef msswyyhssLttileememm,iasnan.(cid:1)nPa1do.tltpyTesmohtlyeyprtec(enwotelhaupsymlomenlnyamedteoeemxrtsiopdwecerel)earfateouvurreesttehhwdeeaaaPssqAsusAteeatocnhuadastairsn3dy5fssrt(cid:3)ofeCommri.olniMrggbneaoianntnih–c-
wnlom unreactedligninwascalculatedusingeqn(3): AA via treating lignin–AA polymer in different acidic environ-
Doe C M (cid:1)M ments so that the molecular weight of PAA chain attached to
18. ativ Unreacted lignin %¼100(cid:4) 0M 1 (3) lignin can be identied. However, this experiment was unsuc-
n 29 March 20ed under a Cre conFtuenntcstioofnlaiglngirnouapndanliaglnysinis–.ATAhpeoclayrmboexrsylwateereg0rmouepasaunrdedPuhs-OinHg picneossAs4ef.bdu0oluumantsdL1te0hro0efamlciaiggdcneiocitfniccaopirnaanrddthirtioyieofddnrliiKsgdLnpeir/snpoa–yhmAriibApdilitpeninoewglya1mtsh/1ieinsr(iawtvin/aavals)llyyasssloisuslou.sptdieoencnodmebdy-
d oens an automatic potentiometric titrator (785 DMP Titrino, Met- stirringfor30minat300rpmand25(cid:3)C;andthenthesolution
Article. PublisheThis article is lic rpA1oomhleymLrm,soetfirSr,w0rmi.i8nt,zgwmeraaoltsal2naL0dd(cid:1)0d)1.erpdpAombttooaufs1ost0ri0u05mm.0m6Lhionygdf,rd4ooefxmiioddLnreiiozeifednd0a.Kw52L%a5te0oprrmacrolLaing-hbntayeiindank–rioAenxrAg-. aetcioxcmcenetetysaslsi.antaAeimngKeorLuKw.nLatTrdwh(5sea0,strmhekseeLup)slttooilifnvngiecnaestodwwlauaarttkseiorrpnealmanwcdoeavsceaedttnht2ferr5inofmu(cid:3)pCgoethdufo/erwresda2as4mhinehpdlaetno3s
s ybenzoicacidsolutionwasaddedasaninternalstandard,and usingafreezedryer.TheacetylatedKLwasdissolvedin10mLof
cces the solution was titrated with 0.1 mol L(cid:1)1 hydrochloric acid tetrahydrofuran(THF)bystirringat300rpmfor30minatroom
A
n solution.Duringthetitration,withthedecreaseinthepHofthe temperature, and then ltered with a PTFE lter having
e
Op sample solutions, three endpoints appeared in sequence a diameter of 13 mm and pore size of 0.2 mm. The ltered
(V01;V02 andV03; respectively). The corresponding three sampleswereusedforamolecularweightanalysis.Forlignin–
endpointsinthetitrationcurveofblanksamplewerespecied AApolymeranalysis,about50mgofairdriedpolymersamples
asV1,V2andV3,respectively.ThecarboxylategroupandPh-OH was dissolved in 10 mL of 0.1 mol L(cid:1)1 NaNO3 solution and
contents of samples were calculated according to eqn (4) and lteredwitha0.2mmnylonlter(13mmdiameter).Theltered
(5).29 The reported data in this paper is the average of three solutionswereusedformolecularweightanalysis.
repetitions. Hydrodynamic diameter of lignin–AA polymer. The hydro-
(cid:1) (cid:3)
mmol dynamicdiametersoflignin–AApolymersweremeasuredusing
Phenolic hydroxylgroup
g a dynamic light scattering instrument (type BI-200SM Broo-
(cid:6)(cid:7) (cid:8) (cid:9)
C V0 (cid:1)V0 (cid:1)ðV (cid:1)V Þ khaven Instruments Corp., USA). The light source was a solid
¼ HCl 2 1 2 1 (4) statelaserwithamaximumpowerof35mWandawavelength
m
of 637 nm. The experimental procedure was adopted as
(cid:1) (cid:3) (cid:6)(cid:7) (cid:8) (cid:9)
mmol C V0 (cid:1)V0 (cid:1)ðV (cid:1)V Þ describedbyYanetal.30Thelignin–AApolymerwasdissolvedin
Carboxylate group g ¼ HCl 3 m2 3 2 1mgmL(cid:1)1NaClsolutionatpH10.5tomake0.2wt%polymer
concentration.Theobtainedsolutionwasstirredfor30minat
(5)
300rpmand25(cid:3)C.Then,thesolutionwaskeptfor24hwithout
whereCHClistheconcentrationofHClsolution(0.1mmolL(cid:1)1) stirring to have a well-dissolved polymer in the solution. Aer
astitrant,misthemass(g)ofthesample. that,thesamplesolutionof20mLwaslteredwitha0.45mm
Molecularweightanalysis.Themolecularweightofsamples disposable syringe lter prior to the size measurement. Five
was determined using a Gel Permeation Chromatography measurementswereperformedforeachsampleandthemean
system, Malvern GPCmax VE2001 Module + Viscotek TDA305 valuewasreported.Theanalysiswasconductedat25(cid:5)0.02(cid:3)C.
with multi-detectors (UV, RI, viscometer, low angle and right- Thescatteringanglewassetat90(cid:3).
Thisjournalis©TheRoyalSocietyofChemistry2018 RSCAdv.,2018,8,12322–12336 | 12325
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RSCAdvances Paper
Elemental analysis. The elemental analysis was performed addedintoDDJtoinducetheocculationprocess.Thedegree
forKLand lignin–AApolymer usingElementar VarioEL Cube ofocculationwaspresentedasarelativeturbidity,whichwas
Elemental Analyzer by a method described in the literature.31 calculated from the variations in the DC voltages of the PDA
Thesampleswererstlydriedintheovenat105(cid:3)Covernightin analyzer beforeand aer adding lignin–AA polymer according
ordertoremoveanymoisture.Approximately,2mgofsamples totheeqn(6).33,34Thereporteddatainthispaperistheaverage
were used for determining carbon, hydrogen and oxygen ofthreerepetitions.
(cid:1) (cid:3)
contentsofthesamples. V
Fourier transform infrared (FTIR). Fourier transform s ln V0
e. infraredspectroscopy(FTIR)analysiswasconductedonKLand sr¼ sf ¼ (cid:1)Vf(cid:3) (6)
M. Licenc laitgn1i0n5–A(cid:3)CApoovleyrmniegrhs.tTahneds0a.m05plgesowfetrheesrastmlypdlersiedwains tuhseedovfeonr i ln V0i
20:24 Anported asonrayl)y.sTisheusspinegctFraTwIRer(eBrreuckoerrdeTdeninsoartr3a7n,sGmeirtmtaanncye,mAoTdReaincctehse- wsuhsepreenssiionis(btehfeoreinaidtidailngtulribgindiinty–AAofptohlyemaelru);msifniisumtheoxnidael
023 12:n 3.0 U sracnangsep60er0scamm(cid:1)p1leanwder4e00c0oncdmu(cid:1)c1tewdi.th4cm(cid:1)1resolution,and32 AtuArbpiodliytymoefr)a;luV0miisniiunmitiaolxibdaesesuDsCpevnoslitoange(a(weartearddsoinlugtiloignn);inV–i
oaded on 2/14/2mons Attributio 5alin0gna1gliHynLz-–(cid:1)eNAd1MAcwRpoinothlcayenm1naHtelry-raNswtiMiseo.rRneT.dahTniehsaseloyKslsLvoieslud.atTniinohdtneolswDiaga2mnsOipnswtl–eiiArtsrhAeo1df0pdf.oo2rlriypem3Hd0eKarmtLaiwna4en0trdoe– as(wtlauintmhdoisnuitfuomlrignothxineid–eADAsCupsvpooellyntmasgieoern);oaafnaedrluaVmdfdiinsiniutghmeligDonxCiind–veAolAstaupgsoepleyonmfseitorh.ne
nlm fullydissolvethematerials.TheNMRspectraofthesesamples Results and discussions
wo
18. Doative C wUeSrAe)wreicthorade4d5(cid:3)upsuinlsgeaanndINrOelVaxAa-5ti0o0nMdeHlazyitnimstreuomfe1n.0ts(V.arian, ReactionmechanismofpolymerizationofKLandAA
9 March 20under a Cre mbileiStthyooloudfbKdilLeitsaycnraidbnleaidglynbsiiynsL–oAafpApKpaLonlayenmtdaelrl.i3wg2anAsibndo–euAtteA0rm.p5oignlyeomdfeKbrLa.soTerhdleiognsnotilhnu–e- hatomPlorowolpytopicsHesdciisrsesauiocsntuioaolnflyKsc2sShu2epOmp8reie.nsTsaehcdei,dfirbceececoarnauddsieitciaotlhnpesoieslyfficmoceniersinizdcaeytrioeondf
n 2ed AApolymerwasaddedto50mLofdeionizedwateratdifferent lower than that inalkaline and neutral conditions.35 Toinves-
s Article. Published o This article is licens aaNsnpuHaJw1s,t2saapU5nteueSntmsrsAisbnLi)owagEanteh1nrrlw.ede0sanhmcssmahokcolaeeellykenrLecet(r(cid:1)tnrIeni1fdn(uaN1sog0aakevO0n.addHT3rahp1tdome01rr0si0)1e,u0d.Bas00tprumare3pntn0omssl1wi(cid:3)o0LCfin5o(cid:1)ckr1fw(cid:3)o5HSCarcs2m,iS2eiwOimnnhth4.mi.isTcTeochhr,lhuseEeehtndsideoui,lsnippnoteheitnrndoe-, wdctciooingistnnaachddtloeiivcttaeiiotnoohrnennecdisseninwniatttnaihrasduaaltetiinanKolvtcnk2heeSsase2ltoioOinfgfc8eaolttihnccgeoeosdnnuniiwncmndehiipntoteiitntaonirtonaotintsnrrieoiwuatnoitnaafestddooeKsfrari2mt0dSa8.2eci7O0lci5ado8(cid:3)rimCcgiunpaanLonad(cid:1)sedbie1rts.ria3eolInknahtca,coeliwtuidnhaorieecssf
cces determinethesolubilityofKLandlignin–AApolymerinwater lignin(i.e.,concentrationofunreactedK2S2O8was0.40gL(cid:1)1in
n A atdifferentpHs.TodeterminethesolubilityofKLorlignin–AA acidic vs. 0.37 g L(cid:1)1 in alkaline solutions). However, the
Ope polymer, the mass of NaOH or H2SO4 added for adjusting the unreacted K2S2O8 was 0.22 g L(cid:1)1 in acidic and 0.72 g L(cid:1)1 in
pHwastakenintoaccount. alkalinesolutioninthepresenceoflignin,indicatingthatlignin
Zeta potential and occulation of aluminium oxide probably inhibited the consumption of K S O under alkaline
2 2 8
suspension.Thezetapotentialofaluminiumoxidesuspensions conditions.Thus,moreradicalswereproducedatlowpHbythe
was analyzed (2.5 wt% at pH 6 and 8) via a zeta potential redox systems in the presence of lignin, promoting polymeri-
analyzer,ZetaPALS(BrookhavenInstrumentsCo.,USA).Inthis zation under acidic conditions. The results in this study indi-
study,1mLofthesuspensionwasmixedwith20mLofa1mM catedthatthemechanismofgenerationoffreeradicalswasnot
KCl solution. The zeta potential of the mixture was analyzed solelyattributedtotheproductionoftwosulfateradicalsfrom
aer30secondsofmixing.Allthemeasurementswerecarried theinitiator.Theredoxsystemofpersulfate-phenolicmoieties
out three times at room temperature. The occulation perfor- oflignincouldbealsoinvolvedandaffectedbypH.36Theself-
manceoflignin–AApolymerinanaluminiumoxidesuspension decomposition of potassium persulfate in the initiator system
wasevaluatedbyaphotometricdispersionanalyzer(PDA,PDA generate sulfate radicals.37 Sulfate radicals can remove
3000, Rank Brothers, UK), which was connected to a dynamic hydrogen from the hydroxyl groups on lignin and generate
drainagejar(DDJ).Inthissetofexperiment,450mLdeionized lignin macro radicals. Once the macromolecular radicals are
waterwithdifferentpHswasrstlypouredintotheDDJwithout generated, they react with the monomers and initiate the
any mesh. The system circulated water through PDA and DDJ polymerization.38,39
for 10 min to reach a steady ow rate of 50 mL min(cid:1)1. Then, The nal KL–AA polymer from acidic and alkaline systems
50 mL of a 2.5 wt% aluminium oxide suspension at different hasverydifferentchargedensity(1.86meqg(cid:1)1underalkaline
pHs was added to the DDJ while stirring at 100 rpm. The vs.7.22meqg(cid:1)1underacidiccondition)andmolecularweight
suspensionwascirculatedinthesystemcontinuouslyataow (0.46(cid:4)105gmol(cid:1)1underalkalinevs.7.4(cid:4)105gmol(cid:1)1under
rateof50mLmin(cid:1)1.Aerreachingasteadystatecondition,the acidiccondition).TheAAconversionofAAhomopolymerization
lignin–AA polymer solution with 0.1 g L(cid:1)1 concentration was systematpH3.5and10.5wasmeasuredandpresentedinFig.1.
TheAAconversionofreactionatpH3.5reached90.1%in2h,
12326 | RSCAdv.,2018,8,12322–12336 Thisjournalis©TheRoyalSocietyofChemistry2018
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however, it was only 38.8% at pH 10.5. Also, the molecular
weightsofPAAsfromthereactionconductedatpH3.5andpH
10.5weredeterminedtobe4.26(cid:4)105gmol(cid:1)1and0.83(cid:4)105g
mol(cid:1)1, respectively. This phenomenon was also observed in
another work.35 One can conclude that the higher charge
density and molecular weight of KL–AA polymer, prepared
under acidic condition (pH 3.5), could be due to the fact that
lignin accelerated the radical formation and thus more AA
e. conversion.
c
n In this study, the polymerization of KL and AA was carried
M. Lice out in an acidic aqueous suspension through heterogeneous
0:24 Aported PreAaActiporne.pTaroedclairnifythifisKsLtuadnydwPAasAuresaecdt vfoiar eisntveersiticgaattiionng, tthhee
2n
oaded on 2/14/2023 12:mons Attribution 3.0 U r1ocdiseHaniadrat-bcNovntoaiMKoxoilytLnRal;oabbacitlleneecltuuawgilsrnryetoisrenEuainstSptioKIhnsfLe(goFthafatihgnceP.iadAdptSAirP3(coAi†a)dsA)nytu,hsdwcstetheiastmeolhoiswp,ftaeehaKnrdandLitdtiwachctnaiahhttdthiayooPntdnuAro(iotAriPx)eayrAatnelhcAaigtencirwottioitenaouirasnpmbt,sgoeiwrtrnowa.hafTetiKheceehnddLe ppFiregea.s2kesncoTehfeaPnAddiAsatrdbibisduentniocoentooeffxKmisLot.loencutlharewperiogdhtuocftPoAfAacfreotmylaKtLe–dAKALinatnhde
nlm PAA formed during the polymerization reaction of KL and AA
wo AA; demonstrating that (i) the polymerization of AA onto KL
oC cannotbereinitiatedtoformKL–AApolymers.
March 2018. Dder a Creative thlihgyednIrtiponocwlhmyalmsoorleeirrcceiuzpaalocetriistod.e1nd9l,4id0gtinhIdnianntooduttihrdoepcnrcpeouovtriloyoomucnsceutrwhrizooaorstnkeio,ganwlrieopouhdfpaesstsitcciynrrigebarneloedkuaptalhinnoadetf t(mnihoie)rtotihnupogtaxhhryetlibcageibprnsoazeutyneplicceianrnoafddtphiahcelaeiplnrsheoawalictacitcsihoynpndoo,rrtoatdixnoyednltegoc(ritofiaiul)bipglie,nntiihnntehmaaecrooidalmebiccsauetslinyecscsrteiednmiogdf,,
9 un phenolichydroxylgroupinKL,thepolymerizationofAAandKL
Article. Published on 2This article is licensed Cdhatinhio6sbieHmtsoio5apnoCctrgdoiHeaerdtni2nio–oormHaunKdsiL(in9ceraa0ednnlauesktcrrctgiilaSnioilOeggnsmn4a2ioon(cid:1)coflicf(cid:1)dKr1iatLCc)hd6arapiHomcnoau5dlolOygsnmhA,–gHAewt.cr2hhih1z(eie8acDm9thhui.oi8eocanmartkleorocegltaairyhnlocteidtucimuoplocnsroweu,lid(cid:1)enpas1trt)bKue,yrbLep,oa4thnn1ho,e4ddef2- wcfttorhhaareasnmIinasnnfbaoeltsirdrtgeadninnnnioicstnietftoiehcnarrieasnrdtdedosaiiycntcpshattrilaeeesocms.lniiedgs,TnintoocchifencetKoeormLnsfatddaoiKfniilytLcediacoiwultnfshlasafeKs.orLgrmwrmoefeuweiagdnishncubttgryieooPtdfnAhPsAeaAniraAndasidftsoiaihcaratmorolawsred,nmditchaiianneyl
s noxyl radicals from phenolic lignin units, and with smaller
ces probability,benzylicradicalsfromnon-phenolicligninunits.It Fig.2.
Ac As presented in Fig. 2, the molecular weight of PAA in the
pen wmaosdeallssohardepsiogrnteidcainntltyhleowlietrerfaretuerrea42dicthalast(baecentzyyllaitcedradliigcanlisn) presenceofKL(111700gmol(cid:1)1)wasmuchlowerthanthatin
O the absence of KL (426300 g mol(cid:1)1), illustrating that (i) KL
than the untreated lignin samples. To clarify whether the
functioned as a chain transfer agent in this polymerization
polymerization of KL and AA occurred through the benzylic
system,and(ii)thechaintransferreactionbetweenKLandPAA
radicalsintheacidicconditions,theacetylatedKLwasusedto
chain radicals formed some lignin radicals for this polymeri-
polymerize with AA. The nal product was analyzed using 1H-
zation.Asitiswellknown,thechaintransferinpolymerization
NMR (Fig. S4 in ESI†) and showed that the characteristic
system not only results in a reduced molecular weight of the
polymer, but may also affect the polymerization rate, which
dependsonthereinitiationreactionratebetweenchaintransfer
radicalsandmonomers.InordertounderstandtheeffectofKL
on the polymerization rate, the AA conversion in KL–AA poly-
merization system and AA homopolymerization system was
determinedandshowninFig.3.ItisapparentthatKLslightly
increased the AA conversion, illustrating that the reinitiation
reactionratebetweenligninradicalsandmonomersissimilar
orslightlyhigherthanthatofpropagationreactionofAAchain
radicals, which is also consistent with the ndings in the
polymerizationoflignosulfonatewithAAintheliterature.43The
reason for this behaviour can be ascribed to a greater decom-
position of the initiator in the presence of KL (as discussed
earlier).
Basedontheanalysisabove,theproposedreactionscheme
Fig.1 AAconversionintoproducePAAatpH3.5and10.5asfunction ofKLandAApolymerizationisshowninScheme1.Assowood
ofreactiontime.
Thisjournalis©TheRoyalSocietyofChemistry2018 RSCAdv.,2018,8,12322–12336 | 12327
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monomerstoformPAAchainradicals(reaction(3)).9,11TheKL
radicals(ligninc)reactwithmonomer(AA)toformpropagated
lignin–AA chain radicals (reaction (4)). In addition, the PAA
chain radicals and lignin–AA radicals in the system can react
with KL to form KL radicals through a chain radical transfer
reaction(reaction(5)),andtheKLradicalsthenreinitiateAAto
form lignin–AA chain radicals (reaction (6)). Finally, the prop-
agated AA chain radicals and propagated lignin–AA chain
e. radicals react with each other to produce PAA homopolymer
nc andlignin–AApolymerthroughterminationreactionasshown
M. Lice in reactions (7). As a result, the carboxylate groups are intro-
Ad
20:24 nporte Fig.3 AAconversioninKL–AAsystemandAAsystemasfunctionof ducIemdpoancttooKfLPhan-OdHthgeromuopleocnulatrheweKigLh–AtAofpKoLlyimseinriczraetaiosend..As
023 12:n 3.0 U reactiontime. sKhLowwnasincoSncvheermteed1t,otheethOeHr ogrrocuaprboonnytlhestpruhcetnuorleiscisntruthcteurenoafl
2o
nloaded on 2/14/mmons Attributi pfKuoonLrlimytismse,4dek4rnbiiztoyawwthinaeosanttocdrhbeeoaecscoetcminoompnto,opsotiphtsireeoednsseup(nrlrtefianaKtcceLtiiporaiannldly(it1cho)a)ifl,sswcsochcanhinciefhemirntyehil.teianIanllclryoethhabociestl ppamg(cid:1)ooe1lleayy,rmmsbuteeurrrreet.adpTti.ritoonTddghcueelacwcPrtri,iehtfwhay-sOhteihHindciihstct,iowoatnthoo1tueer.l5nPdo9thrro-emOfdpHmKoulcLyocemlowtnheagtres(cid:1)ei1znPoahrtatsi-igOooiennHfraKrcltleLoryaenbc1att.etei7ifnon3ontgrmoewfwmateinhtrohdeel
wo
oC withphenolichydroxylgroupofKLtogeneratephenoxyradicals K S O .AerpolymerizationwithAA,thePh-OHcontentofKL
De 2 2 8
18. ativ and its resonance radicals (reaction (2)). The formation of the wasfurtherdecreasedto0.55mmolg(cid:1)1.Onecanconcludethat
March 20der a Cre KmfoLromrreadAsuiAclafralastdewicriaallldsliec(aAadlAsc.t)oA.Tlmshooe,rtAehAdeersacuodlfmiactapelosrsatihdtieiocnnalrisenaccraetnawicnittiihotinaott(eh1eA)raAAntAdo twthhheeicpPhohl-wyOmaHsermciozaanittnieolnynt.aitntriKbLutdeedcltionethdedpuarrintigcipthaetiopnolyomf Perhi-zOaHtioinn,
9 un
n 2ed
d oens
ec
Publishcle is li
Article. This arti
s
s
e
c
c
A
n
e
p
O
Scheme1 ProposedreactionschemeofpolymerizationofKLandAAinitiatedbyK S O underacidicconditions.
2 2 8
12328 | RSCAdv.,2018,8,12322–12336 Thisjournalis©TheRoyalSocietyofChemistry2018
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Inanothersetofexperiments,theimpactofPh-OHcontent ESI†).TheresultsshowedthatAAwasnotpolymerizedwiththe
of KL on the polymerization efficiency was determined via acetylatedperoxide-treatedlignin,illustratingthefactthatthere
treatingKLwithhydrogenperoxide,whichcanreducethePh- were no other reaction sites on the peroxide-treated lignin.
OH content of lignin.45,46 The H O treatment conditions and Therefore, it can be concluded that the more signicant
2 2
thePh-OHcontentofthetreatedligninarelistedinTable2.As increaseinthecarboxylategroupofperoxide-treatedlignin–AA
seeninTable2,byincreasingthedosageofH O ,thetemper- polymer was attributed to the easier accessibility of AA to the
2 2
ature and time of the treatment, the Ph-OH content of the phenolic hydroxyl group of KL, as the reaction site for the
resultingKLsdecreased;whereas,thecarboxylatecontentofthe polymerizationwasstillphenolicgroupofperoxidetreatedKL.
e. treatedKLsincreased,whichwasduetotheoxidationofKLby This phenomenon was also observed by Phillips et al.19 in the
c
n H O .46,47ThetreatedanduntreatedKLswerepolymerizedwith polymerizationofstyreneandcalciumlignosulfonate.
M. Lice AA2, a2nd the carboxylate group of the resulting lignin–AA poly- Participation of KL in polymerization. To investigate the
Ad
0:24 porte monecrawrbaosxmyleaatesucroendt.enFitgo.f4KpLr–eAsAenptoslytmheeri.mItpcaacntobfePsehe-OnHthaotftKhLe pwaitrhticAiApa,taicoentoonfelwigansinuseindathsiasshoelvteernotgteoneeoxtursacptoulnymreearcitzeadtiKonL
2n
023 12:n 3.0 U Pinhc-rOeHasecdocnatrebnotxyolfatleiggnrionuphoafsthaelinneaalrporleylmateior,nisnhdiipcawtiinthgththaet (tiifonp,ressinencet)KfrLomhasthaehliiggnhins–oAluAbpiloitlyymineracaeteornethbeuptolliygmnienr–izAaA-
2o
nloaded on 2/14/mmons Attributi trgthheraoeeTcuOtompioHfeonutfrghstrKyhiotlLeeaurtpfaeaondsradsttetlhiasignescnhctpirhenoedeaslyrstmeewoldaeittrthhciioazeanrdbptsiiohhoffxeniepyn.rleobgnleirttcowuaseptmernuoocufptnhuKterLsen–oAoolfAficKpphLohyldeiysnrmootxehliyrecl, epatdiinoeotmalhnyle,myorsneitbsshrytearwtarhaetpiesnleiiirgsnnctiseettonhdialtauitatnobgrtleTehtareioebnaflleitagmuc3nen.eitnnrIone'tnsaotechprtseretoodhalpeubetlsariiegtocininnedcis.inecTwohterrfeeerAeaarAtcemnhsiuoenedltnttstha.9ffoeI8fenr.ce8tttha%hecides-,
wo
oC group were polymerized with AA. The increased carboxylate absenceoftheinitiator,thepercentageoftheunreactedlignin
De
18. ativ group had a linear relationship with the phenolic hydroxyl wasalsohigherthan99%,whichcouldberegardedasevidence
March 20der a Cre ghrygoduurropexotyhflaKgtrL,oa(uFtpigao.fh4K)i,gLhdeoamnmoponouslntyrmtateoirnfigzpahtthieoenniom.liIcptoihsrytaadlnrsocoxeysolefegpnrhoiuennptoholiincs tAuhnAa,rteibancaitsteiidcaatolllirygnnainondrewaKacLstiominninotichmceuarlpre(oodlyn.mlHyeo0rwi.z6ea1vt–eio1r,.n1i,n3ttwhhete%pa)rm.eFsoeuunrntctheeoorff-
9 un
n 2ed either peroxide-treated lignin or methylated lignin, the more, the reaction was very fast as the amount of unreacted
d oens increased carboxylate groups for lignin–AA polymers are lignin was marginal even aer 0.5 h of the reaction. One can
ec
Publishcle is li shiymdriloaxry.lHgroowuepv,etrh,ewiinthcrdeaesceredacsainrbgotxhyelaatemgoruonuptoofftthheerpehseunltoinligc cinonthcleupdoelfyrmomeritzhaetiaonnalwysitihstAhAatianlmacoidsticalcloonfdthiteioKnLs.participated
s Article. This arti pstorluTycmhtueerrreewaosafoslnimgsnofiorneratphrioesrnppohueernnocoxemiddeefnotrorenpaemtmroigexhnidttebc-oetrm(eia)pttaehrdeedKmLwo.ritehotpheant Effectsofreactionconditions
s
cce aer methylation, and (ii) the lower molecular weight and Initiator. The effect of initiator dosage on the carboxylate
A
n higher solubility of peroxide-treated KL compared with meth- groupcontentandmolecularweightoflignin–AApolymerwas
e
Op ylatedlignin.Inotherwords,themoreopenstructureprovides investigated and the results are shown in Fig. 5. With the
higheraccessibilityofAAtothereactionsitesonKL.Toclarify increase in the initiator dosage from 0.5 wt% to 1.5 wt%, the
this,theacetylatedperoxide-treatedligninwasreactedwithAA carboxylate group content increased from 4.0 mmol g(cid:1)1 to
andthenalproductwasanalyzedusing1H-NMR(Fig.S5†in 5.38 mmol g(cid:1)1. Further increase in the dosage marginally
increased the carboxylate group content. However, the molec-
ular weight of lignin–AA polymer decreased from 7.9 (cid:4) 105 g
mol(cid:1)1 to 4.8 (cid:4) 105 g mol(cid:1)1 when the dosage of the initiator
Table3 ReactionconditionsandpercentageofunreactedKLa
AA/lignin Initiator, Percentageof
molarratio, Time, wt%on unreacted
Sample n:1 h ligninmass lignin,%
1 1:1 0.5 1.5 1.07
2 1:1 2 1.5 1.13
3 0.5:1 2 1.5 1.08
4 2:1 2 1.5 0.61
5 1:1 2 0 99.3
6 0:1 2 1.5 98.8
7 0:1 2 0 99.5
aOther reaction condition: temperature 80 (cid:3)C, lignin concentration
Fig. 4 Relationship between Ph-OH group of KL and increased 0.15molL(cid:1)1,pH3.5.
carboxylategroupofKL–AApolymer.
Thisjournalis©TheRoyalSocietyofChemistry2018 RSCAdv.,2018,8,12322–12336 | 12329
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e.
c
n
AM. d Lice Fig.6 Carboxylategroupcontentandmolecularweightoflignin–AA
0:24 porte pcoonlycmeenrtraastiofunn,c0t.i1o5nmooflreLa(cid:1)c1,tiAoAn/tliigmnein(pmHo,l3a.r5r,aintioiti,a5to.5r,,81.05(cid:3)wCt)%.,lignin
2n
2:U
023 1n 3.0 Fig. 5 Carboxylate group content, molecular weight and hydrody-
oaded on 2/14/2mons Attributio 8n(pa0Hm(cid:3)C3ic.,5d3,ialhimg).neintercoonfcligennitnra–tAioAnp0o.l1y5mmeroalsLa(cid:1)1f,uAnAc/tiloignnionfminiotilaatrorradtioosa5g.5e, mamwffeoeeirlgc(cid:1).ht1eTt,dhsrehethsoipewneccecrhdteiavaaresgnleeys.adciFencunerlstteihhtreyaertaiconainnrdbcriomnexaoytsllhaeecteeuinplagorrtlhoywumeepeirgraaihtznitaodtoimofmntahorrlegeaictpneuoalllaolyyrf-
nlm lignin and AA due to an increased AA content in the reaction
owCo increasedfrom0.5to3.0wt%.Itwaswellknownthatthelower medium.52 However, when the ratio of AA/KL was higher than
March 2018. Dder a Creative twaohcoelcuoudnlrdogsuefarnogrdcemehorafoittnwnh.o4el8i,i4pgn9noiTstinishai,tebowirlphi,toitilcheyhsemf(weei)rowiauzealrdsttmihorneaelsrluoanlfdtuilciimnaglnbsaien(rgprooaanlfydmlionneAgrgAcwiPctieAatsnhA) 1pan3ro.d5Tb,eAambAthlpy(ecedararhobtmouomrixneyo.alpatToteehdlyegmtrhoeeauffrtipezdcaaettsncioedonlefMraorwtefeawdcAetAtriheoentcooptnoegslmyetamnpneeetrrr)aa.i5tzt0eua,5tr3iePoAnoAnofwtKhaLes
d on 29 ensed un sneugmmbeenrtoafttsahcohretdPtAoAlisgengimneinntantatalcKhLe–dAtAoplioglnymineirnorn(iai)laKLla–rAgAe acarerbporxeyslaetnetegdroiunpFaingd. 8m.oIlteccualnarbweesigehent otfhlaitgnwinit–hAArispionlgymtheer
Article. PublisheThis article is lic ppsPheooAygdllAyymrmmoseedeengyrrtmn.oIawennmnotltuiihcgwledndofiuionianlr.mdmcInrebeetertaehsrgceearoaslfaedt,luetitedgehrneocitnnoahsylseidtgi,hgrnaeonisdniapy,ncrlieaatasnrmmegtneliayccyn.edunTimooaotmfbccleehlartoraenoinrffgygosefthPhttoAhhirsAeet, raigcen(cid:1)aa1dlcltyaminofrodnolemt5ec.mu41l.pa(cid:4)1re2rw1am0etu5imgrgheotlmfrogoo(cid:1)fml1(cid:1)li1ag6,nn0rdi(cid:3)enCs0–p.At4eoAc(cid:4)8tpi0v1oe(cid:3)0llCy5ym,.gteThmrheieocnlai(cid:1)cnrr1bectoaroexsaey6sld.ae5tsd2erimganrmmotuahotpel-
cess the hydrodynamic diameters of lignin–AA polymers produced cmaorbreoxeyfflaectetivgeroauccpesasnodfAmAomlecounloamr weretioghthtearreeaactttiroinbusitteedsotontthhee
Ac were measured via using different initiator dosages and pre-
n lignin at a higher temperature, which could be due to the
e sented inFig.5. Withthe increaseinthe initiator dosage,the
p extended conformation of lignin molecules and the dissocia-
O
hydrodynamic diameter of the polymer decreased, illustrating
tion of lignin from its self-assembly of aggregates at a high
the polymer produced at high initiator dosage probably had
temperature.54,55Inaddition,theresultsinFig.8suggeststhat
more of shorter PAA segment. It should be noted that, the
thepolymerizationofKLwithAAisendothermicreactionasit
hydrodynamicdiametersofKLwere6.1nm.Thedistributions
waspromotedatahighertemperature.Whenthetemperature
of hydrodynamic diameter of KL and KL–AA polymer are was higher than 90 (cid:3)C, both carboxylate group and molecular
provided in Fig. S6 in ESI† and the results depicted better
uniformityforKL–AApolymerthanforKLinthesolution.
Reaction time. The effects of reaction time on the carbox-
ylate group and molecular weight of lignin–AA polymer are
showninFig.6.Itcanbeseenthatbothcarboxylategroupand
molecular weight increased with extending the reaction time.
The carboxylate group and molecular weight of lignin–AA
polymersignicantlyincreasedfrom2meqg(cid:1)1to5.32meqg(cid:1)1
and from 1.0 (cid:4) 105 to 5.0 (cid:4) 105 g mol(cid:1)1, respectively. The
increasesinthecarboxylategroupandmolecularweightcould
be attributed to the addition of monomers to the growing of
graedchainsatanextendedreactiontime.50,51
AA/ligninmolarratio.TheinuenceofAA/ligninmolarratio
onthecarboxylategroupandmolecularweightofthepolymeris
showninFig.7.ItcanbeobservedthatbychangingAA/lignin
molarratiofrom1.4to10.8,thecarboxylategroupandmolec- Fig.7 Carboxylategroupcontentandmolecularweightoflignin–AA
ular weight increased rapidly to 7 meq g(cid:1)1 and 7.1 (cid:4) 105 g p1.o5lywmt%er,liagsninacfuonnccteionntraotifonA,A0/.l1ig5nminolmLo(cid:1)l1a,r3rha,ti8o0((cid:3)pCH)., 3.5, initiator,
12330 | RSCAdv.,2018,8,12322–12336 Thisjournalis©TheRoyalSocietyofChemistry2018
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To investigate the relationship between carboxylate group
andmolecularweightoflignin–AApolymer,thedatapresented
inpreviousguresisplottedinFig.10.Asseen,themolecular
weightofthepolymerincreasedlinearlywiththeincreaseinthe
carboxylate group content, indicating that the increase in the
molecular weight of the polymer was mainly attributed to the
PAA segment in the KL–AA polymer. The linear relationship
betweencarboxylategroupcontentandmolecularweightisY¼
e. 1.0618X(cid:1)0.9738,R2¼0.9462,whereYisthemolecularweight
nc ((cid:4)105gmol(cid:1)1)andXisthecarboxylategroupofKL–AApolymer
M. Lice (mmolg(cid:1)1).Thisformulacanbeusedtocorrelatethemolecular
20:24 Anported Iwneiagdhdtiotifolnigtnoint–hAeAmpoolleycmuelarrwwitehigihtst,cathrbeoHxyylaotfelgigrnoiunp–AcoAnpteonlyt-.
023 12:n 3.0 U pFiogl.y8meCraarsbaofxuynlactteiognrooufptecmopneternattuarned(pmHo,l3e.c5u,lianritwiateoigr,h1t.5ofwlitg%n,inlig–nAiAn msaemrsplwesithwedrieffmereeanstucraerdboaxnydlapteregsreonutpedcoinntFeingt.s1f0o.rTthhee Hsaymoef
nloaded on 2/14/2mmons Attributio cwteoemnigcpheentrtardtaeuticrorene,am0se.a1d5d,emwtohhlieLc(cid:1)hi1n,wAitAaia/sltiogdrnuinelemstosolteahffrereacfttiaoicv,te8.4t.0,h9,a3Atlhst)ho.e, ahihghigehr al(lciicaggodrnnibeliieotnnedx––ry/AAmlliaAAnitneeppeaoogdrllr)yyommmuinepoerrl,esmicsldlouauillydsuathrtrniaaowotvntieensisgdghhiiotfffthwecartaatehnneleivtynbemeenawogtrleheerronceeuuelargltapahirtroeolcndidogs,unnhtcfiihonpeerd–wmAfioAautrhtnmwiodtihentehdesr
wo
oC temperature favored the chain termination and chaintransfer different conditions. The higher H of samples with lower
De y
18. ativ reactions as well as the competing homopolymerization (PAA) carboxylate group may imply that, when the amount of
March 20der a Cre rceaarLbctioigxonynil.na1t0ec,2o8g,n4r3c,o5e2unptraantidonm.oTlheecuelffaercwtseoigfhltigonfinligcnoninc–eAnAtraptoiolynmoenr cthhaigerbhpocoxalyyrlmabtoeexryglwraoatuespglir(naoenuadprm(oarnoldmecohurilegahrligMwneWiing)hwtth)aesofpinopvloyolmylvmeerder,gebwnuaetsrwalotiewthd,
9 un
n 2ed areshowninFig.9.Asisobserved,byconcentratingligninin acoilshapeconformation.
d oens the solution, the carboxylate group and molecular weight of Basedontheresultsshowninpreviousgures,theoptimal
s Article. Publishe This article is lic mluwmitgeooenldlnli(cid:1)nao1tsm–oaAienttAhrc0erpr.ea1oiadn5lsyicemcmrdaeeolapsrlsreiaLondn(cid:1)bcd1araebmtlaiihglsoieentuydiinnnottifotcoicoa7font.pl3oclh7iresenimmnotrnoomalltaieoicmcoluhngoly,(cid:1)ends1wgratholonixigcydfnhlo7irrna.am4rdrea(cid:4)ilcdiaagi1tlnct0srai5inlabsg–s-, cg7Kmor.L3oan,7sudAspmi)At,im/o8Kan0noLsld(cid:3)mgCfo(cid:1)omra1lnpaoadrrnloedr3cdauu7thil.coa4.irnU(cid:4)1g0nw1.dl0ie0eg,i5rngignhitnhitmt–eiAasooetAlfo(cid:1)crp1oK,o1nrLl.ey5d–smiApwtAieeotrc%ntwpisv(,eoebrltlyeahyms.e0eT.edc1hra5oirsbnmreloioalgxiclygnhlLniane(cid:1)itnde–1
s
ce AA polymer.56–58 When lignin concentration was higher than AApolymerwasselectedforfurtheranalysis.
c
n A 0.15molL(cid:1)1,thephenolichydroxylradicalshadmorechances
Ope tointeractwithotherligninradicals,suchasbenzylorphenolic Characterizationoflignin–AApolymer
hydroxyl radicals, by disproportionation or radical coupling
reactions.4,50Thus,theactiveradicals,capableofinitiatingthe FTIR. The FTIR spectra of KL–AA polymer prepared under
polymerization of monomers, were ineffectively consumed, theoptimalconditionsandKLsarepresentedinFig.11.Both
KL and KL–AA polymer showed a broad band around
leadingtothedeclinedmolecularweightandcarboxylategroup.
3400cm(cid:1)1,whichisassignedtotheOHstretchingofphenolic
Fig.9 Carboxylategroupcontentandmolecularweightoflignin–AA
polymerasafunctionofligninconcentration(pH,3.5,initiator,1.5wt%, Fig.10 Relationshipbetweencarboxylategroupcontentoflignin–AA
AA/ligninmolarratio,10.0,3h,80(cid:3)C). polymerwithitsmolecularweight(basedon1.5wt%initiator).
Thisjournalis©TheRoyalSocietyofChemistry2018 RSCAdv.,2018,8,12322–12336 | 12331