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PolymerJournal(2010)42,583–586

&TheSocietyofPolymerScience,Japan(SPSJ)Allrightsreserved0032-3896/10$32.00doc.xuehai.net

ORIGINALARTICLE

CaCO3/chitin-whiskerhybrids:formationofCaCO3crystalsinchitin-basedliquid-crystallinesuspension

YuyaYamamoto,TatsuyaNishimura,TsuguyukiSaitoandTakashiKato

CaCO3/chitin-whiskerhybridswerepreparedusingtheliquid-crystallinesuspensionofthechitinwhisker.Suspensionsofchitinnanowhiskerswereobtainedbyacidhydrolysisofchitinpowder.Thesuspensioncontainingabout5wt%ofwhiskersexhibitedlyotropicliquid-crystallinebehavior.Thesuspensionwasconvertedtoagelformwhenitwasexposedtoammoniumcarbonatevapor.CaCO3crystalswereformedfor30daysinchitingelsastemplates.ThenucleationofCaCO3occurredintheliquid-crystallinechitinmatrixandtheCaCO3crystalsdepositedinthechitingelstoformhybridswithaninterpenetratedthree-dimensionalstructure.Scanningelectronmicroscopyimageofthefracturedsampleofthehybridshowedthatthegelmatrixwas lledwithCaCO3crystals.ThermogravimetricanalysisrevealedthatthecompositionofCaCO3/polymer/H2Oisabout2:6:2inweight.Thisapproachinspiredbybiomineralizationmaybeusefulforthedevelopmentofinorganic/organichybridmaterials.PolymerJournal(2010)42,583–586;doi:10.1038/pj.2010.32;publishedonline5May2010Keywords:biomineralization;CaCO3;chitin;hybrid;liquidcrystal

INTRODUCTION

Theprocessusedbylivingorganismstoproduceinorganic/organichybridsiscalledbiomineralization.1–3Naturalbiomineralssuchasbone,teethandthenacreoftheshellhavehighmechanicalstrengthandopticalproperties.Inthesebiominerals,thepropertiesarecloselyrelatedtotheirhierarchicallyorderedstructures.Forinstance,thenacreoftheshellhasalayeredstructurecomposedofabout95wt%CaCO3andabout5wt%organicmatrices.4–6Thelayeredstructureinduceshighmechanicalstrengthandpearlluster.Anothertypeofbiomineralthatissofterthanthenacreoftheshellistheexoskeletonofthecray sh.7Itiscomposedofabout50wt%CaCO3andabout50wt%organicmacromoleculessuchaschitinandproteins.Intheexoskeleton,chitin bershaveahelicalstructure8,9thatisanalogoustothecholestericliquid-crystallineorder.Thesechitin bersarecomplexedwithproteinsandCaCO3.Thesenaturalbiomineralsofferideasfornewinorganic/organichybridmaterials.10–16Avarietyofcalcium-basedhybridmaterialshavebeenreported.17–26WepreviouslyreportedthatCaCO3thin- lmcrystalswereformedonchitinmatricesinthepresenceofacidicpolymers.17–21Moreover,orientedCaCO3crystalswereobtainedinanorientedchitinmatrix.27Thisresultshowsthattheorderedmatrixisimportantforfurtherstructurecontrolofinorganic/organichybridmaterials.Ourintentionhereistouseorderedchitinwhiskersfortheformationofhybrids.Herein,wereportontheformationofCaCO3crystals/chitin-whiskerhybridsusingtheliquid-crystallinesuspensionofthechitinwhisker.

EXPERIMENTALPROCEDUREChitinpuri cation

Chitin(a-chitinfromcrab)wasstirredatroomtemperaturein5%KOHsolutionforseveralhourstoremovetheresidualprotein.Thereafter,thechitinsamplewasbleachedwithNaClO2aqueouscontainingsodiumacetatebufferfor6hat801C.Thebleachedsamplewascollectedbycentrifugationandwashedseveraltimeswithdeionizedwater.

Disintegrationofchitin

Puri edchitinwassuspendedinwaterat0.1–0.3%concentrations.ThechitinslurrywasadjustedtothepHvalueof3bytheadditionofseveraldropsofdilutehydrochloricacid.Ultrasonicationwasappliedtotheslurryfor2minusinganultrasonichomogenizerat19.5kHzand300Woutputpower(7mmintheprobetipdiameter,US-300T,Nihonseiki,Tokyo,Japan).Thedisin-tegratedchitinwascollectedby ltration.

Acidhydrolysisofchitin

Suspensionsofchitinnanowhiskerswerepreparedbyacidhydrolysisoftheresultantchitin.Thedisintegratedchitin(5g)wastreatedwith100mlof4MHClsolutionat1041Cfor90min.ThesamplewasthenwashedwithdistilledwateruntilthepHvalueofthesupernatantsolutionincreasedtoaround2.TheobtainedsuspensionwasthendialyzedagainstdistilledwatertoadjustthepHvalueof3.Thesuspensionwasthenconcentratedbydialysisagainstsaturatedpolyethyleneglycol(Mw¼20000)solution.

CrystallizationofCaCO3

Puri edwaterobtainedfromanAutopureWT100puri cationsystem(Yamato,Tokyo,Japan,relativeresistivity:maximum1.8Â107Ocm)wasused

DepartmentofChemistryandBiotechnology,SchoolofEngineering,TheUniversityofTokyo,Hongo,Bunkyo-ku,Tokyo,Japan

Correspondence:ProfessorTKato,DepartmentofChemistryandBiotechnology,SchoolofEngineering,TheUniversityofTokyo,Bunkyo-ku,Tokyo113-8656,Japan.E-mail:kato@chiral.t.u-tokyo.ac.jp

Received16February2010;revised26March2010;accepted4April2010;publishedonline5May2010

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