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NaturalFiber-ReinforcedBiodegradable andBioresorbablePolymerComposites

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NaturalFiber-Reinforced

AdaPui-YanHung

AlanKin-takLau

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ListofContributorsix Prefacexi

1Naturalfiber-reinforcedpolymer-basedcomposites1 AlanKin-takLauandKarenHoiYanCheung

1.1Introduction1 1.2Silkwormsilkfiber5

1.3Chickenfeatherfiber12 1.4Conclusion16 References16

2Particleboardsfromagriculturallignocellulosicsandbiodegradable polymerspreparedwithrawmaterialsfromnaturalresources19

ElectraPapadopoulouandKonstantinosChrissafis

2.1Introduction19

2.2Composites:Types,production,andadvantagesoverrawwood19

2.3BiodegradableandBioresourceablepolymericmaterials21

2.4Agriculturalmaterialsusedincomposites23

2.5Reviewofparticleboardsmanufacturedwithagriculturalmaterials andbiodegradeable/bioresourceablepolymersinthe lastdecade23

2.6Applications—Market27

2.7Conclusions29 References29

3Greencompositesmadefromcellulosenanofibersandbio-based epoxy:processing,performance,andapplications31

3.1Introduction31

3.2Howtopreparethecellulose-basedaerogelpreform33

3.3Makingcellulosenanocomposite35

3.4Mechanical,microstructural,andtribologicalcharacterization37

3.5Sampleresultsobtainedfrommechanical,microstructural, andtribologicaltests38 References47

4Biodegradablefiber-reinforcedpolymercompositesfor constructionapplications51

C.Rivera-Go´mezandC.Gala´n-Marı´n

4.1Introduction51

4.2Polymercompositesforconstructionapplications52

4.3Polymerstabilizedearthblocks54

4.4Analysisoftheinfluenceofthefibertype60

4.5Lifecycleassessmentofpolymercompositeblocks65

4.6Futuretrends68

Acknowledgments69 References69

5Bleachedkraftsoftwoodfibersreinforcedpolylacticacid composites,tensileandflexuralstrengths73 FrancescX.Espinach,Jose´ A.Me´ndez,LuisA.Granda, MariaA.Pelach,MarcDelgado-AguilarandPereMutje´

5.1Introduction73

5.2Materialsandmethods75

5.3Resultsanddiscussion77

5.4Conclusions86 References87

6Silkforsustainablecomposites91

DarshilU.ShahandFritzVollrath

6.1Introduction91

6.2Silkasaparticulatereinforcementinbiofoams92

6.3Nonwovenandwovensilklaminatecomposites101

6.4Evaluatingthesustainabilityofsilkanditcomposites106 Acknowledgments107 References108

7Effectsofcellulosenanowhiskerspreparationmethodsonthe propertiesofhybridmontmorillonite/cellulosenanowhiskers reinforcedpolylacticacidnanocomposites111 RezaArjmandi,AzmanHassan,M.K.MohamadHaafiz andZainohaZakaria

7.1Introduction111

7.2Materialsandmethods113

7.3Testingandcharacterization116

7.4Resultsanddiscussion117

7.5Conclusion132 Acknowledgments133 References133

8Bio-basedresinsforfiber-reinforcedpolymercomposites137 YongshengZhang,ZhongshunYuanandChunbao(Charles)Xu

8.1Introduction137

8.2Biophenolicresins139

8.3Bio-basedepoxyresins144

8.4Bio-basedpolyurethane(BPU)146

8.5Celluloseacetate149

8.6Biopolyesters150

8.7Biopolyolefins153

8.8Summaryandfutureperspectivesofbioresins154 Acknowledgments155 References155

9Processingoflignocellulosicfiber-reinforcedbiodegradable composites163 SaurabhChaitanya,AmrinderP.SinghandInderdeepSingh

9.1Introduction163

9.2ChallengesinprimaryprocessingofLFBC165

9.3Processingofbiocomposites168

9.4Conclusions178 References178 Index183

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ListofContributors

RezaArjmandi UniversitiTeknologiMalaysia,JohorBahru,Malaysia

BamdadBarari UniversityofWisconsin-Milwaukee,Milwaukee,WI,United States

SaurabhChaitanya IndianInstituteofTechnologyRoorkee,Roorkee, Uttarakhand,India

KarenHoiYanCheung HongKongGreenBuildingCouncil,Kowloon,Hong Kong,SARChina

KonstantinosChrissafis AristotleUniversityofThessaloniki,Thessaloniki, Greece

MarcDelgado-Aguilar UniversityofGirona,Girona,Spain

FrancescX.Espinach UniversityofGirona,Girona,Spain

C.Gala ´ n-Marı´n UniversidaddeSeville,Seville,Spain

LuisA.Granda UniversityofGirona,Girona,Spain

M.K.MohamadHaafiz UniversitiSainsMalaysia,Penang,Malaysia

AzmanHassan UniversitiTeknologiMalaysia,JohorBahru,Malaysia

AlanKin-takLau SwinburneUniversityofTechnology,Hawthorn,Melbourne, VIC,Australia

Jose ´ A.Me ´ ndez UniversityofGirona,Girona,Spain

PereMutje ´ UniversityofGirona,Girona,Spain

ElectraPapadopoulou CHIMARHELLASSA,Kalamaria,Thessaloniki,Greece

MariaA.Pelach UniversityofGirona,Girona,Spain

KrishnaM.Pillai UniversityofWisconsin-Milwaukee,Milwaukee,WI,United States

C.Rivera-Go ´ mez UniversidaddeSeville,Seville,Spain

DarshilU.Shah UniversityofCambridge,Cambridge,UnitedKingdom

AmrinderP.Singh UniversityInstituteofEngineeringandTechnology,Punjab University,Chandigarh,India

InderdeepSingh IndianInstituteofTechnologyRoorkee,Roorkee,Uttarakhand, India

FritzVollrath UniversityofOxford,Oxford,UnitedKingdom

Chunbao(Charles)Xu InstituteforChemicalsandFuelsfromAlternative Resources,WesternUniversity,London,ON,Canada

ZhongshunYuan InstituteforChemicalsandFuelsfromAlternativeResources, WesternUniversity,London,ON,Canada

ZainohaZakaria UniversitiTeknologiMalaysia,JohorBahru,Malaysia

YongshengZhang InstituteforChemicalsandFuelsfromAlternativeResources, WesternUniversity,London,ON,Canada x

Preface

Inthematerialscienceandengineeringworld,mostresearchersoftenrefertopivotalerasinhumanhistorybythematerialsthatdominatedthem—mostnotably, startingfromtheStoneAge,thenBronzeAge,andtheIronAge.Alltheseperiods lastedforalongperiodoftime.Sincetwocenturiesago,thedevelopmentof cement(1824),carbonfiber(1879),fiberglass(1938),Polyester(1941),andthe discoveryofnanostructuralmaterials,likethefullerencemolecule(1985)andcarbonnanotubes(1991),hasrevolutionizednewresearchfocusesondesigningnew structuralmaterialswithbetterpropertiesandqualities,fordifferentkindsofengineeringapplications.However,duetotheshortageofnaturalresources,suchasfossilfuels,manycountrieshavebeenstrivingforbetteralternativestouserenewable resourcesfornewmaterialdevelopmentandenergyharvesting.

Overthepastdecade,manystudieshavebeendonetolookatthepossibilitiesof usingnaturalmaterials,suchasplant-basedoranimal-basedfiberstomixwithdifferenttypesofsoftmaterialstoformanewclassofbiocomposites.Thetermof “biocomposite”referstoamaterialwhichisformedbyamatrixandareinforcementofnaturalfiber.Thematrixcanbeapolymericorcementitiousmaterial dependingonapplications.Thefibernormallyplaysaroleintakingloadwhilethe matrixprotectsthefiberbyholdingthemtogether,avoidingenvironmentaldegradation,andmaintainingtheshapeofresultantstructures.Themajorpurposeofbiocompositesistoensurethatthenewmaterialsareeitherrecyclableor biodegradableafterdisposal.Theresinisalsomadeofrenewableresources,to allowanewcompositetobedegradednaturally,withouttheneedforextrachemicalsorenergytodecomposeit.

Commontypesofplant-basedfibersarecropfiberswhichareextractedfrom cotton,flax,hemp,sisal,orregeneratedcellulosematerials.Biocompositesmadeby plant-basedfiberarecommonlyseeninautomobile,construction,andsomeinterior componentsinsideaircraftorrailwaycoaches.Infact,plant-basedfiberhasbeen commonlyusedsinceancienttimes;e.g.,strawwasaddedintomudtomakeawall forahouse.Animal-basedfibers,commonlyextractedfromspiders,silkworm cocoons,chickenfeathers,andevenhumanhair,havealsodemonstratedtheireffectivenessofreinforcingbiocompatibleandbioresorbablepolymersforimplantapplications.Asthemajorcontentofthesefibersisprotein,itissuitabletobemixed withbioresorbablepolymersfortemporaryreinforcingelementsusedinsidethe humanbody.

Inviewoftheimportanceofthisfield,thisbookcollectscomprehensiveinformationaboutthedevelopmentofnaturalfiber-reinforcedbiodegradablepolymer composites.Itcontainsatotalof9chapters,whichcoverawiderangeofstudies

andapplicationsofnaturalfiber-reinforcedbiodegradableorbioresorbablepolymer composites.

Chapter1,Naturalfiber-reinforcedpolymer-basedcomposites,givesanoverviewofrecentdevelopmentofnaturalfiber-reinforcedpolymermaterials.Different typesoffiberandtheirpotentialapplicationsareintroduced.Theeffectivenessof usingsilk-basedbioresorblepolymercompositeforstemcellgrowthisalso discussed.

Chapter2,Particleboardsfromagriculturallignocellulosicsandbiodegradable polymerspreparedwithrawmaterialsfromnaturalresources,introducestheuseof agriculturewastes,mainlyextractedparticlesfromwoodtomixwithpolymerto formanewclassofcomposites.Therecentdevelopmentofwood/polymercompositesisdiscussedinthechapter.Productionprocesseswiththeconsiderationofcost factorsandconsumptionratearealsoanalyzed.

Chapter3,Greencompositesmadefromcellulosenanofibersandbio-based epoxy:processing,performance,andapplications,providesanoverviewofcellulose nanofibers(CNFs)-reinforcedpolymercomposites.CNFsarebio-basednanostructureswithremarkablyhighmechanicalpropertiesascomparedwithothernatural fibers.Theirmanufacturingprocessandthepropertiesofcompositesarealso introduced.

Chapter4,Biodegradablefiber-reinforcedpolymercompositesforconstruction applications,discussestheimportanceoffibersurfacetreatment,whichcanenhance thebondingstrengthand,thus,theoverallmechanicalpropertiesofnatural fiber-reinforcedpolymercomposites.ThePinebleachedfiber(PBF)contentforits optimalmechanicalpropertiesinPolylacticacid(PLA)matrixenvironmentis discussed.

Chapter5,Bleachedkraftsoftwoodfibersreinforcedpolylacticacidcomposites, tensileandflexuralstrengths,presentstheuseofnaturalpolymerintheconstructionindustrytomakebricks,blocks,andpanels.Biodegradablepolymerswereused tostabilizeanaturalfiber-reinforcedsoilmaterial.Severalexperimentaltests showedthatthemechanicalpropertiesofsoilmaterialwereimprovedsubstantially. Microscopicimagesalsoshowedthatagoodbondingbetweenthenaturalfiberand matrixwasachieved,whichgovernedthesuccessofstresstransferinthematerial.

Chapter6,Silkforsustainablecomposites,describesthepotentialityofusing silkfiberforbio-basedcompositematerials.Thisfibercanbeusedformakingbiodegradablepolymercompositesfordifferentengineeringapplications.Thestructure ofcocoonsilkfibersandtheirpropertiesarediscussed.Themechanicalproperties ofanewtypeofsilk-reinforcedbiofoamisalsointroduced.

Chapter7,Effectsofcellulosenanowhiskerspreparationmethodsonthepropertiesofhybridmontmorillonite/cellulosenanowhiskersreinforcedpolylacticacid nanocomposites,investigatesthemanufacturingprocessandmechanicalproperties ofmontmorillonite/cellulosenanowhisker-reinforcedbiodegradablepolymercomposites.Bothnanowhiskerandmontmorillonitearenanostructuralfillersthatcanbe usedtoenhancethepropertiesofpolymers.Thischapterprovidesacomprehensive viewonhowtoproducethecompositesandtheirpotentialapplications.

Chapter8,Bio-basedresinsforfiber-reinforcedpolymercomposites,givesa comprehensiveviewondifferenttypesofbioresinsthatcanbeusedtomakebiocomposites.Theseresinsareextractedfromrenewablenaturalresources.Thestructuresofdifferentbiomassaredescribedandanalyzedontheirusefulnessand applications.

Chapter9,Processingoflignocellulosicfiber-reinforcedbiodegradablecomposites,discussesthepropertiesandproductionprocessesoflignocellulosefiberreinforcedbiopolymers.Thecomparisonofdifferenttypesoflignocellulosicfiber withsyntheticfibers,suchascarbonandglassfibers,isgiven.Thesefibersare verysensitivetoprocessingtemperatureandtheirapplicationsarehighlyrestricted bytheproductionprocess.

Theeditorwouldliketoexpresshissincereappreciationandthankstoallthe authorsandcoauthorsfortheirscientificcontributiontothisbook.Ialsoapplaud Elsevierfortheirsupportandencouragementforarrangingandeditingthisbook, andtheirstafffortheirspecialattentionandtimelyresponse.

SwinburneUniversityofTechnology,Melbourne,VIC,Australia

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Naturalfiber-reinforced polymer-basedcomposites

andKarenHoiYanCheung2

1SwinburneUniversityofTechnology,Hawthorn,Melbourne,VIC,Australia, 2HongKongGreenBuildingCouncil,Kowloon,HongKong,SARChina

1.1Introduction

1

Overthepastfewdecades,researchandengineeringinteresthasbeenshiftingfrom traditionalmonolithicmaterialstofiber-reinforcedpolymer-basedcompositesdue totheiruniqueadvantagesofhighstrengthtoweightratio,noncorrosiveproperty, andhighfracturetoughness.Thesecompositematerialsconsistingofhighstrength fibers,suchascarbon,glass,andaramid,andlowstrengthpolymericmatrix,have nowdominatedtheaerospace,leisure,automotive,constructionandsporting industries.Unfortunately,thesefibershaveseriousdrawbackssuchas(1)nonrenewable;(2)nonrecyclable;(3)highenergyconsumptioninthemanufacturingprocess;(4)healthriskwheninhaled;and(5)nonbiodegradable.Biodegradationisthe chemicalbreakdownofmaterialsbytheactionoflivingorganismswhichleadstoa changeinphysical,mechanical,andchemicalproperties.Itisaconceptofvast scope,rangingfromthedecompositionofenvironmentalwastesinvolvingmicroorganismstohost-inducedbiomaterials.

Althoughglassfiber-reinforcedpolymercompositeshavebeenwidelyuseddue totheiradvantagesoflowcostandmoderatestrengthformanyyearstoprovidesolutionstomanystructuralproblems,theuseofthesematerials,inturnwouldinducea seriousenvironmentalproblemthatisnowofconcerninmostWesterncountries. Recently,duetoastrongemphasisonenvironmentalawarenessworldwide,ithas broughtmuchattentioninthedevelopmentofrecyclableandenvironmentallysustainablecompositematerials.Environmentallegislationaswellasconsumerdemand inmanycountriesareincreasingthepressureonmanufacturersofmaterialsandendproductstoconsidertheenvironmentalimpactatallstagesoftheirlifecycle,includingrecyclingandultimatedisposal.IntheUnitedState,itencouragesmanufacturers toproducematerialsandproductsbypracticingthe4Rs,whichare(1) Reduce the amountandtoxicityoftrashtobediscard(sourcedreduction);(2) Reusecontainers andproducts;(3) Repair whatisbroken;and(4) Recycle asmuchaspossible,which includesbuyingproductswithrecycledcontent.Aftertheseprocessesaregone,the materialsfinallyareentitledtobedisposedintolandfill.

http://dx.doi.org/10.1016/B978-0-08-100656-6.00001-7

Themostcommontypesofconventionalcompositesareusuallycomposedof epoxy,unsaturatedpolyesterresin,polyurethanes,orphenolicreinforcedbyglass, carbon,oraramidfibers.Thesecompositestructuresleadtotheproblemofconventionalremovalaftertheendoftheirlifetime,asthecomponentsarecloselyinterconnected,relativelystable,andthusdifficulttobeseparatedandrecycled.The recentdevelopmentofaircraft,suchasBoeing787andAIRBUS350,useover 50%ofcompositesastheirstructuralcomponents.Aseriousproblemthatbringsa strongdebateisontherecyclabilityofthecompositesaftertheendoftheirservice life.Duringtheproductionprocess,theuseofenergytomakefibersandresinsis anotherarguableitem.However,theadvantageofusingthesematerialsisdueto theirlight-in-weight,noncorrosiveproperties,andtheeaseofmanufacturingin differentformsandshapeswithoutinvolvingtheuseofheavyequipment. Therefore,ifthenaturalfiberandbiodegradablematrixareusedforanewtypeof biocompositeandcanachievesimilarfunctionsandstrengthasglassfiberreinforcedpolymer(GFRP)composites,itwouldhelpsolvemanyenvironmental problemsaddressedaboveandhelpimprovethelivingenvironmentinourplanet.

Withinthepastfewyears,therehasbeenadramaticincreaseintheuseofnaturalfibers,suchasleavesfromflax,jute,hemp,pineapple,andsisal,formakinga newtypeofenvironmentally-friendlycomposite.Recentadvancesinnaturalfiber development,geneticengineering,andcompositescienceoffersignificantopportunitiesforimprovedmaterialsfromrenewableresourceswithenhancedsupportfor globalsustainability.Ingeneral,twotypesofnaturalfibersareidentifiedfor makingfiber-reinforcedpolymer;theyare(1)plant-basedfibersand(2)animalbasedFibers.Fortheformer,duetotheirabundantsupplyinthenaturalenvironment,therawmaterialcostisrelativelylowandcancompetewithsyntheticfibers, suchasglasstomakethecomposites.Animalfibers,however,aredifficultto collectfromwildlifeand,normally,havetobeobtainedfromhome-fedanimals, suchasspidersandcocoons.

Byusingtheplant-basednaturalfiberasreinforcementofpolymer-basedmaterialsthereductionoftheuseofsyntheticfibersandundegradablepolymerforcompositestructurescanbetargeted.Excessiveuseofpetroleum-basedplasticsinduces hugeamountsofnondecomposablesolidwastewhichcausesaseriousdepletionof landfillcapacities.Theawarenessofthesoaringwasteproblemsontheenvironmenthasawakenedanewinterestintheareaofmaterialsscienceandengineering. Becauseoftheincreasingenvironmentalconsciousnessinthesociety,itisacritical topicforresearcherstostudydifferentalternativestoreplacenonrenewablematerials,especiallyforpetroleum-basedplastics.Therefore,differenttypesoffullybiodegradablematerialshavebeendevelopedrecently,assubstitutionsfor nonbiodegradablepetroleum-basedplastics,andevenmetalliccomponents [1 4]

Amongallthenaturalfibers,sisal [5],hemp [5],basalt [6],kenaf [7],flax [8], andbamboofibers [9] arethemostcommontypestobeusedduetotheirabundant supplyinthenaturalenvironment.However,theskillofhowtoextractthe fiberswithconsistentphysical,material,andmechanicalpropertiesiskey.Besides thesurfacetreatmentandprocessingtemperatureofthefibers,alsotheirhighmoistureabsorbabilityisafactorthatmakesthemdifficulttobeusedinhigh-end 2NaturalFiber-ReinforcedBiodegradableandBioresorbablePolymerComposites

engineeringproductsandstructures.Insomescenarios,theprocessingtemperature ofthermosetorthermoplasticsduringtheinjectionmodelingprocessmaycausethe thermaldegradationoffibers,whichsubstantiallyreducesthemechanicalstrength ofthecomposites.

Vaisanenetal. [10] haveaddressedtheadvantagesofusingorganicwasteand residuesfromagriculturalandindustrialprocessestodevelopanewclassofcomposites,inwhichsomeofthemaregoodatarelativelyhighservicingtemperature condition(B300 C). Fig.1.1 showsthethermaldecompositionrangesfornatural fiberpolymer-basedcompositesatdifferenttemperatures.Ingeneral,naturalfibers aredegradedattemperaturesstartingfrom200 Cupto500 C(fromhemicelluloses tolignin).Inthecivilengineeringindustry,theuseofnaturalfiberstoreinforce cementitiousmaterialshavebecomemorepopularduetotheadvantagesoflow cost,lowdensity,moderatestrength,andlocalavailabilityindifferentcountries. However,themoistureabsorptionproblemofplant-basedfibersisstillacritical issuethataffectstheresultantstrengthofthecomposites [11].

Topopularizetheusageofplant-basednaturalfiberincivilinfrastructureapplications,durability,ultraviolet(UV)degradation,andcorrosionresistantandinflammablepropertiesareimportant [12].Fire-retardantfillercompoundsarenormally usedforplant-basednaturalfiber-reinforcedpolymercomposites.Thecriteriaof selectingthefillersarelowcost,relativelyeasyadditionintothepolymer,andhigh fireresistance.Aluminumtrihydroxide(ATH),whichisalsoknownasalumina triydrate,isanactivefire-retardantfillercompoundmostoftenusedinpolymers andpolymercomposites.Thiscompoundisdecomposedduringthedehydration process,toformcarbon-inorganicresiduesandfinallybecomesafoam-likestructuretoisolateheatrelease.Itwasprovedthatusingasmallamountoffire-retardant compound(ammoniumpolyphosphate[APP])withkenafandhydrophobicplastic (PP)canimprovethefire-retardantabilityby200%,withwoolitis250%.

Figure1.1 Thermaldecompositionrangesfornaturalfiberpolymercompositesand subsequenteffectsonthecharacteristicsofthecompositeconstituent [10] (VOCs 5 volatile organiccompounds).

Color darking, evolution of VOCs
Loss of mechanical strength

4NaturalFiber-ReinforcedBiodegradableandBioresorbablePolymerComposites

Animalfibers,duetotheirhighprotein-basedcontent,aresuitableforbiomedical engineeringapplications,particularforthedesignofimplantstructures,likebond fixators.Amaterialthatcanbeusedformedicalapplicationsmustpossessalotof specificcharacteristics.Themostfundamentalrequirementsarerelatedtobiocompatibility,i.e.,nottohaveanyadverseeffectonthehosttissues;therefore,thosetraditionalcompositestructureswithnonbiocompatiblematrixorreinforcementare substitutedbybioengineeredcomposites. Table1.1 summarizesseveralimportant factorsthatneedtobeconsideredinselectingamaterialforthebiomedical

Table1.1 Keyfactorsfortheselectionofmaterialsforbiomedical applications [2]

FactorsDescription

Chemical/ biological characteristics

1stLevelmaterial properties

2ndLevel material properties

Specific functional requirements (basedon applications)

● Chemical composition (bulkand surface)

● Adhesion

● Biofunctionality

● Bioinert

● Bioactive

● Biostability

● Biodegradation behavior

Physical characteristics Mechanical/ structural characteristics

● Density

Processingand fabrication

● Surfacetopology

● Texture

● Roughness

● Form& geometry

● Coefficientof thermal expansion

● Electrical conductivity

● Color,aesthetics

● Refractiveindex

● Opacityor translucency

● Elasticmodulus

● Shearmodulus

● Poisson’sratio

● Yieldstrength

● Compressive strength

● Hardness

● Flexuralmodulus

● Flexuralstrength

● Stiffnessor rigidity

● Fracture toughness

● Fatiguestrength

● Creepresistance

● Frictionand wearresistance

● Adhesion strength

● Impactstrength

● Proofstress

● Abrasion resistance

● Reproducibility,quality,sterilizability,packaging,secondary processability

Characteristicsofhost:tissue,organ,species,age,sex,race,healthcondition,activity, systemicresponse

Medical/surgicalprocedure,periodofapplication/usage

Cost

Figure1.2 Stress straincurvesfordifferentfibers.

Source:GuineaGV,ElicesM,Perez-RiguerioJ,PlazaGR.Structureandpropertiesofspider andsilkwormsilkfortissuescaffolds.In:Basu,editor.AdvancedinSilkScienceand Technology.Chapter10.NewYork:Elsevier;2015.

applications [13].Spiderandsilkwormsilksareidentifiedasgoodreinforcementsfor makingcompositesfortissuescaffolds.Themechanicalpropertiesofthesefibersas comparedwithNylonisshownin Fig.1.2.Itisobviouslyseenthatthespidersilks (Nephilainaurata and Argiopetrifasciata)possesshightensilemodulusandstrength ascomparedwithNylon6.6andcocoonsilks [14,15].However,themainconcern fortheuseofthesesilksistheconsistencyofwherethesilkshaveoriginated.

Bioengineeringreferstotheapplicationofconceptsandmethodsofthephysical sciencesandmathematicsinanengineeringapproachtowardssolvingproblemsinthe repairandreconstructionsoflost,damaged,ordeceasedtissues.Anymaterialthatisused forthispurposecanberegardedasabiomaterial.AccordingtoWilliams [16],abiomaterialisamaterialusedinimplantsormedicaldevices,intendedtointeractwithbiologicalsystems.Thosecommontypesofmedical devicesincludesubstituteheartvalves andartificialhearts,artificialhipandkneejoints,dentalimplants,internalandexternal fracturefixators,andskinrepairtemplates etc.Oneofthemajorfeaturesofcomposite materialsisthattheycanbetailor-madetomeetdifferentapplications’requirements.

1.2Silkwormsilkfiber

Naturalfibersaresubdividedbasedontheirorigins,comingfromplants,animals, orminerals.Generally,plant-basednaturalfibersarelignocellulosesinnatureand

arecomposedofcellulose,hemicellulose,andlignin,suchasflax,jute,sisal,and kenaf;whereasanimal-basednaturalfibersareofproteins,likewool,spiderand silkwormsilks,andchickenfeathers.Theenhancedenvironmentalstabilityofsilk fibersincomparisontoglobularproteinsisduetotheextensivehydrogenbonding, thehydrophobicnatureofmuchoftheprotein,andthesignificantcrystallinity. Manyresearchershavestudiedtheuseof Bombyxmori cocoonsilkfabricsasa reinforcementtomakeacomposite.Sericinproteinonthesurfaceofsilkfibercan serveasabindertobondthefabrictogetherbytheactionofpressureandheat. However,formakinganadvancedcomposite,thislayerofsericinhastobe removedbyboilingwatertoensureagoodbondingbetweenthefibersandapolymermatrixresults.

Silkproteins—knownassilkfibroins—arestoredintheglandsofinsectsand spidersasanaqueoussolution.Duringthespinningprocess,asilkwormaccelerates anddeceleratesitsheadinarcsforeachchangeofdirection,andtheconcentration ofsilkinthesolutionisgraduallyincreasedandfinallyanelongationstressis appliedtoproduceapartlycrystalline,insolublefibrousthreadinwhichthebulkof thepolymerchainsinthecrystallineregionsareorientedparalleltothefiberaxis. Fasterspinningspeedleadstostrongerbutmorebrittlefibers,whereasaslower speedleadstoweakerandmoreextensiblefibers.Atevengreaterspeed,silktoughnessdecreases,mainlyduetothelossofextensibility [17].

Cocoonsarenaturalpolymericcompositeshellsmadeofasinglecontinuoussilk strandwithlengthintherangeof1000 1500mandconglutinatedbysericin [18]. Thisproteinlayerresistsoxidation,isantibacterialandUVresistant,anditalso absorbsandreleasesmoistureeasily.Thisproteinlayercanbecross-linked,copolymerized,andblendedwithothermacromolecularmaterials,especiallyartificial polymers,toproducematerialswithimprovedproperties.Inaverage,thecocoon productionisabout1milliontonnesworldwide,andthisisequivalentto 400,000tonnesofdrycocoon(see Fig.1.3).Inthetissueengineeringarea,silks havebeenidentifiedasakindofbiomaterial,usedinthehealingprocessforbone, tendons,orligamentrepairs.Slowlydegradingbiomaterialswhichcanmaintaintissue integrityfollowingimplantation,whilecontinuallytransferringtheload-bearing burdentothedevelopingbiologicalfunctionaltissuearedesired.Insuchphenomena,

Figure1.3 Rawcocoonsilks(A)andsideviewofthesilkfiber(B).

Figure1.4 AlamarBlueassayonfHobsseededonneatPLAandsilk/PLAcomposite (A)andconfocalimageoncellsseededonasilk/PLAcomposite(B).

thegradualtransferoftheload-bearingburdentothedevelopingand/orremodeling tissueshouldsupporttherestorationandmaintenanceoftissuefunctionoverthelifeof thepatient.Aseriesoftestswereconductedtoinvestigatethecellgrowthproperties byconsideringfetalhumanosteoblasts(fHobs),whicharecellsthatareresponsiblefor boneformation.Itwasfoundthatsilkfiber/PLAcompositescouldenhancecellgrowth ontheirsurface. Fig.1.4 showsanAlamarBlueassayonfHobsseededonneat PLAandsilk/PLAcomposite,anditisobviousseenthatthemanycellsaregrown withtime.

Silkfibersspunoutfromsilkwormcocoonsconsistoffibroininaninnerlayer andsericininanouterlayer;allareprotein-based.Fromtheoutsidetotheinside layersofthecocoon,thevolumefractionsofsericindecreaseswhiletherelative contentoffibroinincreases.Also,itisknownthatsilkfibroinconsistsofboth hydrophilicandhydrophobicregions,whichisablock-likepolymericsystem. Thesefibershaveahighlynonuniformcross-sectionalgeometrywithrespectto bothshapeandabsolutedimensions.Bychangingthereelingconditions,silkworm silkscanbestronger,stiffer,andmoreextensible,approachingtothepropertiesof spiderdraglinesilks [19].Eachrawsilkthreadhasalengthwisestriation,consisting oftwoseparatebutirregularlyentwinedfibroinfilaments(brin)embeddedinsericin.Silksericinisaminorproteinthatenvelopssilkfibroinfibersandgluesthem togethertoformcocoonshape.Fibroinandsericininsilkaccountforabout75and 25wt%respectively.Silkfibersarebiodegradableandhighlycrystallinewitha well-alignedstructure.

1.2.1Mechanicalproperties

Composition,structure,andmaterialpropertiesofsilkfibersproducedbyspiders, silkworms,scorpions,mites,andfliesmaydifferwidelydependingonthespecific

sourceandtheuncontrollablereelingconditionsofthoseinsects.Spinningunder controlledconditionswillhavemoreuniformcross-sectionalareaofsilkfibers, reproduciblemolecularalignment,andfewermicrostructuralflaws.Thesizeand weightofcocoonsdecreasewithanincreaseintemperatureandcocoonscanbear efficientlybothexternalstaticforcesanddynamicimpactloadings [20].Anormal compactcocoonexhibitsahighabilityofelasticdeformationwithanelasticstrain limithigherthan20%inbothlongitudinalandtransversedirections.Theanisotropicpropertiesaremainlyduetothenonuniformdistributionandorientationsofsilk segmentsandtheinnerlayerofcocoonhaslowporosity(highersilkdensity)anda smalleraveragediameterofsilk,therefore,thereisanincreaseinelasticmodulus andstrengthfromtheoutsidetotheinsidelayers.Thatis,thethinnerthesilk,the highertheelasticmodulusandtensilestrengthandthemaximumvaluesatthe innermostlayer.Ontheotherhand,attemperaturesabovetheglasstransitiontemperature,thecocoonanditslayersbecomesofterandsofterandbehavesimilartoa rubber-likematerial.Silkfibershavehighertensilestrengththanglassfiberor syntheticorganicfibers,goodelasticity,andexcellentresilience [21].Theyresist failureincompression,arestableatphysiologicaltemperatures,andthesericin coatingisawater-solubleproteinaceousglue. Table1.2 showsthecomparisonof themechanicalpropertiesofcommonsilktypes(silkwormandspiderdragline)to severaltypesofbiomaterialfibersandtissuescommonlyusedtoday.

Fibroinisasemicrystallinepolymerofnaturalfibrousproteinmainlyconsisting oftwophases [22]:namely β sheetcrystalsandnoncrystalline,includingmicrovoidsandanamorphousstructure,bywhichthestructureofthesericincoatingis amorphousandactsasanadhesivebindertomaintainthefibroincoreandtheoverallstructuralintegrityofthecocoon.Degummingisakeyprocessduringwhich sericinisremovedbythermochemicaltreatmentofthecocoon.Althoughthissurfacemodificationcanaffectthetensilebehaviorandthemechanicalpropertiesof silksignificantly,itisnormallydonetoenhanceinterfacialadhesionbetweenthe fiberandthematrix.

Inaddition,accordingtoAltman [23],silksareinsolubleinmostsolvents, includingwater,diluteacid,andalkali.Thereactivityofsilkfiberswithchemical agentsispositivelycorrelatedtothesizeoftheinternalandexternalsurfaceareas [24].Whenfabricatingsilk-basedcomposites,theamountofresingainedbyfibers isstronglyrelatedtothedegreeofswellingofthenoncrystallineregions,i.e.,the amorphousregionsandthemicrovoidsinsidethefibers.

1.2.2Applications

1.2.2.1Woundsutures

Silkfibershavebeenusedinbiomedicalapplicationsparticularlyassuturesby whichthesilkfibroinfibersareusuallycoatedwithwaxesorsiliconetoenhance materialpropertiesandreducefraying.Butinfact,therearelotsofconfusing questionsabouttheusageofthesefibersasthereistheabsenceofadetailedcharacterizationofthefibersused,includingtheextentofextractionofthesericin 8NaturalFiber-ReinforcedBiodegradableandBioresorbablePolymerComposites

Table1.2 Mechanicalpropertiesofdifferenttypesofpotential naturalfibersforcompositeapplications

coating,thechemicalnatureofwax-likecoatingssometimesused,andmanyrelated processingfactors.Forexample,thesericinglue-likeproteinsarethemajorcause ofadverseproblemswithbiocompatibilityandhypersensitivitytosilk.Thevariabilityofsourcematerialshasraisedpotentialconcernswiththisclassoffibrousprotein.Yet,silk’sknotstrength,handlingcharacteristics,andabilitytolaylowtothe tissuesurfacemakeitapopularsutureincardiovascularapplicationswherebland tissuereactionsaredesirableforthecoherenceofthesuturedstructures [25].

1.2.2.2Scaffoldstissueengineering

Athree-dimensionalscaffoldpermitstheinvitrocultivationofcell polymer constructsthatcanbereadilymanipulated,shaped,andfixedtothedefectsite [26]

Thematrixactsasthetranslatorbetweenthelocalenvironment(eitherinvitroor invivo)andthedevelopingtissue,aidinginthedevelopmentofbiologicallyviable functionaltissue.However,duringthe1960stotheearly1980s,theuseofvirgin silknegativelyimpactedthegeneralacceptanceofthisbiomaterialfromthesurgicalpractitionerperspective,e.g.,thereactionofsilktothehosttissueandthe inflammatorypotentialofsilk.Recently,silkmatricesarebeingrediscoveredand reconsideredaspotentiallyusefulbiomaterialsforarangeofapplicationsinclinical repairsandinvitroasscaffoldsfortissueengineering.

Silk,asaprotein,issusceptibletoproteolyticdegradationinvivoandovera longerperiodoftimeinvivowillslowlybeabsorbed.Degradationratesmainly dependonthehealthandphysiologicalstatusofthepatient,themechanicalenvironmentoftheimplantationsite,andthetypesanddimensionsofthesilkfibers. Theslowrateofdegradationofsilkinvitroandinvivomakesitusefulinbiodegradablescaffoldsforslowtissueingrowthssincethebiodegradablescaffoldsmust beabletoberetainedattheimplantationsite,includingmaintainingtheirmechanicalpropertiesandsupportingthegrowthofcells,untiltheregeneratedtissueis capableoffulfillingitsdesiredfunctions.Thedegradationrateshouldbematched withtherateofneotissueformationsoasnottocompromisetheload-bearingcapabilitiesofthetissue.

Additionally,scaffoldstructures,inc ludingthesizeandconnectiveofpores, determinethetransportofnutrients,m etabolites,andregulatorymoleculesto andfromcells.Thematrixmustsupportc ellattachment,spreading,growth, anddifferentiation.Meineletal. [26] concentratedoncartilagetissueengineeringwiththeuseofsilkproteinscaffoldsandtheauthorsidentifiedandreported thatsilkscaffoldsareparticularlysuitablefortissueengineeringofcartilage startingfromhumanmesenchymalstemcells(hMSC),whicharederivedfrom bonemarrow,mainlyduetotheirhighporosity,slowdegradation,andstructural integrity.

Recentresearchwithsilkhasfocusedonthedevelopmentofawireropematrix forthedevelopmentofautologoustissue-engineeredanteriorcruciateligaments (ACL)usingapatient’sownadultstemcells [27].Silkfibroinoffersversatilityin matrixscaffolddesignforanumberoftissueengineeringneedsinwhichmechanicalperformanceandbiologicalinteractionsaremajorfactorsforsuccess,including bone,ligaments,tendons,bloodvessels,andcartilage.Silkfibroincanalsobeprocessedintofoams,films,fibers,andmeshes.

1.2.3Silk-basedbiocomposites

Annamariaetal. [28] discoveredthatenvironment-friendlybiodegradablepolymers canbeproducedbyblendingsilksericinwithotherresins.Nomuraetal. [29] identifiedthatpolyurethanefoamsincorporatingsericinaresaidtohaveexcellent moisture-absorbingand-desorbingproperties.Hatakeyama [30] hasalsoreported producingsericin-containingpolyurethanewithexcellentmechanicalandthermal properties.Sericinblendswellwithwater-solublepolymers,especiallywithpolyvinyl 10NaturalFiber-ReinforcedBiodegradableandBioresorbablePolymerComposites

alcohol(PVA).Ishikawaetal. [31] investigatedthefinestructureandthephysical propertiesofblendedfilmsmadeofsericinandPVA.Moreover,arecentpatent reportedonaPVA/sericincross-linkedhydrogelmembraneproducedbyusing dimethylureaasthecross-linkingagenthadahighstrength,highmoisturecontent, anddurabilityforusageasafunctionalfilm [32]

Silkfibroinfilmhasgooddissolvedoxygenpermeabilityinawetstatebutitis toobrittletobeusedonitsownwheninadrystate;whereasforchitosan,itisa biocompatibleandbiodegradablematerialwhichcanbeeasilyshapedintofilms andfibers.Parketal.andKweonetal. [33,34] haveintroducedanideaofsilk fibroin/chitosanblendsaspotentialbiomedicalcompositesasthecrystallinityand mechanicalpropertiesofsilkfibroinaregreatlyenhancedwithincreasingchitosan content.

Anothertypeofbiocompositeisthesilkfibroin/alginateblendsponges.Forbiotechnologicalandbiomedicalfields,silkfibroin’sreproducibility,environmental andbiologicalcompatibility,andnontoxicityareofbenefitinmanydifferentclinicalapplications.Asthecollectiveproperties,especiallymechanicalproperties,of silkfibroinspongesinadrystatearetooweaktohandleaswounddressing,they canbeenhancedbyblendingsilkfibroinfilmswithothersyntheticornaturalpolymers,e.g.,thepolysaccharidesodiumalginate.

Furthermore,KatoriandKimura [35] andLeeetal. [36] examinedtheeffectof silk/poly(butylenessuccinate)(PBS)biocomposites.Theyfoundthatthemechanicalproperties,includingtensilestrength,fracturetoughness,andimpactresistance, andthermalstabilityofbiocompositeswouldbegreatlyaffectedbytheir manufacturingprocesses.Moreover,agoodadhesionbetweenthesilkfibersand PBSmatrixwasfoundthroughtheobservationandanalysisbyscanningelectron microscope(SEM)imaging.

Themechanicalpropertiesof Bombyxmori,twisted Bombyxmori,andTussah silkfiberswerealsoinvestigatedthroughtensilepropertytests.Itwasfoundthat Tussahsilkfiberexhibitedbettertensilestrengthandextensibilitycomparedwith theothers.However,thestiffnessofallsampleswasalmostthesame.Thismaybe duetothedistinctionofthesilkwormraisingprocessandthecocoonproducingand spinningconditions.BasedontheWeibullanalysis,itwasshownthatthe Bombyx mori silkfiberhasabetterreproducibilityintermsofexperimentalmeasurement, thanthatoftheTussahsilkfiber.Thismaybeduetothedegummingtreatment whichhasaneffectonthemicrostructureofthefiber.

Byusingsilkfiberasreinforcementforbiodegradablepolymer,themechanical propertieschangesubsta ntially.Cheungetal. [37] havedemonstratedthattheuse ofsilkfibertoreinforcePoly(lacticacid)(PLA)canincreaseitselasticmodulus andductilityby40and53%,respectively,ascomparedwithapristinesample.It wasalsofoundthatthebiodegradab ilityofsilk/PLAbiocompositeswas alteredwiththecontentofthesilkfibe rinthecomposites.Itreflectsthatthe resorbabilityofthebiocompositesusedinsidethehumanbodycanbecontrolled, inwhichthisisthekeyparameterofusingthisnewtypeofmaterialforbone platedevelopment.

1.3Chickenfeatherfiber

Animal-basednaturalfibers,likechickenfeatherfiber(CFF),haveattractedmuch attentiontodifferentproductdesignandengineeringindustriesrecently,andthe useofCFFasreinforcementsforpolymer-basedbiodegradablematerialshas emergedgradually.Theadvantagesofusingthesenaturalfibersovertraditional reinforcingfibersinbiocompositematerialsaretheirlowcost,lowdensity, acceptablespecificstrength,recycability,biodegradabilityetc.Naturalfibersgenerallyhavehighspecificmechanicalproperties.

Duetoanincreasingpublicawarenessofenvironmentalprotection,theapplicationofnaturalfibersinbiocompositematerialshasbeenincreasedrapidlyinthe pastfewyears.CFF,becauseoftheirrenewableandrecyclablecharacteristics,have beenappreciatedasanewclassofreinforcementsforpolymer-basedbiocomposites.However,thefullunderstandingoftheirmechanicalproperties,surface morphologies,environmentalinfluencesduetomoistureandchemicalattacks, bondingcharacteristicsbetweensilkfibroinandthesurroundingmatrix,andthe manufacturingprocessisessential.

1.3.1Chickenfeather

Accordingtothesurveyconductedrecently,achickenprocessingplantproduces about4000poundsofchickenfeatherseveryhour.Inmostwesterncountries,these feathersareusedas(1)featherfiberfeed;(2)airfilterelementsthatreplacetraditionalwoodpulps(retardingthetreecut-downrate);and(3)lightweightfeather composites.Chickenfeathersareapproximately91%protein(keratin),1%lipids, and8%water.Theaminoacidsequenceofachickenfeatherisverysimilartothat ofotherfeathersandalsohasagreatdealincommonwithreptiliankeratinfrom claws [38].Thesequenceislargelycomposedofcystine,glycine,proline,andserine,andcontainsalmostnohistidine,lysine,ormethionine.Infact,aCFFismade upoftwoparts,thefibersandthequills(see Fig.1.5).Thefibersarethinfilamentousmaterialsthatmergefromthemiddlecorematerialcalledquills.Insimple terms,thequillisahard,centralaxisoffwhichsoft,interlockingfibersbranch. Smallerfeathershaveagreaterproportionoffiber,whichhasahigheraspectratio thanthequill.Thepresenceofquillamongfibersresultsinamoregranular,lightweight,andbulkymaterial.Atypicalquillhasdimensionsontheorderofcentimeters(length)bymillimeters(diameter).Fiberdiameterswerefoundtobeinthe rangeof5 50 μm.ThedensityofCFFislighterthantheothersyntheticandnaturalreinforcements,thus,CFFinclusioninacompositecouldpotentiallylowercompositedensity,whereasthedensityofatypicalcompositewithsyntheticreinforcing increasesasfibercontentincreases.Hence,lightweightcompositematerialscanbe producedbytheinclusionofCFFtoplasticswhichevenreducesthetransportation cost.Thebarbsattheupperportionofthefeatherarefirm,compact,andclosely knit,whilethoseatthelowerportionaredowny,i.e.,soft,loose,andfluffy.The downfeatherprovidesinsulation,andtheflightfeatherprovidesanairfoil,protects 12NaturalFiber-ReinforcedBiodegradableandBioresorbablePolymerComposites

Figure1.5 (A)SEMimageofthetertiarystructureofachickenfeather.(B)Atypicalchicken featherfiber.

Source:ParkSJ,LeeKY,HaWS,ParkSY.Structuralchangesandtheireffecton mechanicalpropertiesofsilkfibroin/chitosanblends.JApplPolymSci1999;74:2571 5.

SEMimagesofachickendownfeatherfiber.

thebodyfrommoisture,theskinfrominjury,andprovidescolorsandshapesfor displays. Fig.1.6 showsthecross-sectionalviewsoftheflightanddownfeather fibers.Itisobviousthatflightfeatherfiberexistsinahollowformwhiledownfiber issolid.Intermsoffiberreinforcement,theuseofdownfiberappearsmuchbetter thantheuseofflightfiber.

ThemoisturecontentofCFFisanimportantfactorthatcanhighlyinfluence theirweightandmechanicalproperties.ThemoisturecontentofprocessedCFFs canvarydependinguponprocessingandenvironmentalconditions.Theglass

Figure1.6

transitiontemperature(Tg)ofthefeatherfibersandinnerquillsisapproximately 235 Cwhilefortheouterquillsitis225 C.HighTgrepresentsthatatighterkeratinstructureisformedtowhichwaterismorestronglybonded.Fibersandinner quillsdonotbegintolosewaterbelow100 C.Themoistureevolutiontemperature oftheCFFandquilloccursintherangeof100 110 C.Thissuggeststhatitmay bepossibletohavefully-dryfibersandinnerquillsat110 C.

Thelengthanddiameter(sometimesintheformofbundles)ofCFFwould highlyaffecttheirpropertiesandtheimpregnatabilityofresinintoaresultantcomposite.Therefore,thecontrolofresintemperature(thus,itsviscosity),whileatthe sametimemanagingthesonication(ultrasonicvibration)timetofacilitatetheresin penetrationrateintothefibersareessential.Shortorlongerfiberswouldhighly affectthestresstransferabilityaswellastheshearstrengthofthecomposites.The fibers,themselves,alsowouldbeabarriertothemovementofpolymerchains insidethecompositesandmayresultinincreasingthestrengthandthermalproperties,butreducethefracturetoughness.Thesepropertieswillbestudiedindetailin thissection.

1.3.2CFF/PLAbiocomposites

MixingCFFwithbiopolymers,e.g.,PLA,canformabiodegradablecomposite usedforplasticproductsandimplantapplications.Inpreparationofthecomposite, chickenfeatherwasimmersedinalcoholfor24h,thenwashedinawater-soluble organicsolvent,anddriedunder60 Cfor24h [38].CFFwithadiameterofabout 5 μmandlengthof10 30mmwereseparatedfromthequillandthenused. Fig.1.4 showsanSEMphotographofaCFF. Fig.1.7 showstherelationsbetween CFFcontentandpeakstressandmodulusofelasticity,respectively.Themodulus ofelasticityofCFF/PLAcompositeincreaseswiththeCFFcontentandreachesthe

Figure1.7 RelationshipbetweentensilepropertiesandCFFcontent.

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dans cette écume gelée, cherchant les places où elle était demeurée intacte, plus profonde et plus blanche. Et il s’agitait, ruait, faisait des mouvements de frotteur qui cire un plancher.

Je demeurai stupéfait.

Je murmurai:

—Ah çà! tu perds la tête?

Il répondit sans s’arrêter: «Pas du tout, je me lave les pieds. Figure-toi que j’ai levé la belle Sylvie. En voilà une chance! Et je crois que ma bonne fortune va s’accomplir ce soir même. Il faut battre le fer pendant qu’il est chaud. Moi, je n’avais pas prévu ça, sans quoi j’aurais pris un bain.»

Pol conclut: «Vous voyez donc que la neige est utile à quelque chose.»

Mon matelot, fatigué, avait cessé de ramer. Nous demeurions immobiles sur l’eau plate.

Je dis à l’homme: «Revenons.» Et il reprit ses avirons.

A mesure que nous approchions de la terre, la haute montagne blanche s’abaissait, s’enfonçait derrière l’autre, la montagne verte.

La ville reparut, pareille à une écume, une écume blanche, au bord de la mer bleue. Les villas se montrèrent entre les arbres. On n’apercevait plus qu’une ligne de neige, au-dessus, la ligne bosselée des sommets qui se perdait à droite, vers Nice.

Puis, une seule crête resta visible, une grande crête qui disparaissait elle-même peu à peu, mangée par la côte plus proche.

Et bientôt on ne vit plus rien, que le rivage et la ville, la ville blanche et la mer bleue où glissait ma petite barque, ma chère petite barque, au bruit léger des avirons.

Blanc et Bleu a paru dans le Gil-Blas du 3 février 1885, sous la signature: M.

LIVRE DE BORD.

Le Livre de bord a paru dans le Gaulois du 17 août 1887.

Maupassant en a utilisé un long fragment (p. 65 à 69 du présent volume) que nous ne réimprimons pas, mais qu’il est indispensable de relire pour l’intelligence du dernier épisode de cette nouvelle.

ÉTENDU sur un des divans qui servent aussi de couchette, dans le petit yacht de mon ami Berneret, je parcourais un livre de bord, tandis que lui dormait de tout son cœur, en face de moi.

C’était un garçon bizarre, un sauvage qui, depuis dix ans, n’avait guère quitté son bateau, un cotre de vingt tonneaux nommé Mandarin.

Chaque été il parcourait les côtes du Nord de France, de Belgique, de Hollande ou d’Angleterre, et, chaque hiver, les côtes de la Méditerranée, l’Algérie, l’Espagne, l’Italie, la Grèce.

Il aimait ce bercement solitaire sur le flot toujours agité.

La terre immobile l’ennuyait, et les hommes bavards l’exaspéraient.

Ils sont ainsi quelques-uns, vivant dans cette boîte remuante, étroite et longue, qu’on nomme un yacht. On les voit arriver dans un port, au coucher du soleil. De son pont, l’homme en casquette bleue regarde de loin le mouvement humain sur le quai; puis il marche, jusqu’à la nuit, d’un pas vif et régulier, d’un bout à l’autre de son bateau.

Au point du jour, le lendemain, on ne l’aperçoit plus; il est reparti sur la mer, il fuit, il flotte, il rêve ou il dort. Il est seul.

Six mois plus tard, on le revoit très loin de là, dans un autre port, sous un autre ciel, errant encore, errant toujours.

Bien que Berneret fût un vieux camarade, il demeurait une énigme pour moi. C’était donc avec une curiosité très éveillée et très vive que je lisais son livre de bord.

Pendant qu’il dormait j’en ai copié trois pages.

20 mai, Saint-Tropez.—Rien. J’ai passé une de ces journées délicieuses où l’âme semble morte dans le corps bien vivant. Un léger vent d’ouest nous a poussés des Salins-d’Yères à SaintTropez, d’une façon douce et régulière, sans une vague, sans une oscillation. Nous glissions sur la mer plate, bleue, une mer qu’on voudrait embrasser et où on se baigne avec tendresse, pour sentir sur la peau sa caresse un peu fraîche.

A cinq heures le Mandarin, qui avait laissé arriver vent arrière pour gagner l’entrée du golfe de Grimaud, vira de bord et approcha du port bâbord amures. La brise tombait tout à fait; mais, comme il portait son grand flèche de beau temps, le cotre filait encore assez vite. Il passa deux tartanes et une goélette faisant même route que nous.

Le golfe de Grimaud s’enfonce dans la terre comme un lac magnifique entouré de montagnes couvertes de forêts de pins.

A l’entrée, Saint-Tropez à gauche, Saint-Maxime à droite. Tout au fond, Grimaud, ancienne cité bâtie en partie par les Maures autour d’un mont pointu qui porte sur son faîte l’antique château des Grimaldi.

Nuit excellente à Saint-Tropez.

21 mai.—Levé l’ancre à trois heures du matin, pour profiter du courant d’air de Fréjus; ce fut à peine un souffle qui nous conduisit au large, puis plus rien. A huit heures nous n’avions pas fait deux milles, et je compris que je coucherais en mer si je n’armais pas l’embarcation pour remorquer le yacht.

Je fis donc descendre deux hommes dans le canot, et à trente mètres devant nous ils commencèrent à nous traîner. Un soleil enragé tombait sur l’eau, brûlait le pont du bateau, nous écrasait sous une chaleur si lourde qu’il fallait, pour lever le bras, faire un effort considérable.

Les deux hommes, devant nous, ramaient d’une façon très lente et régulière, comme deux machines usées qui ne vont plus qu’à peine, mais qui continuent sans arrêt leur effort mécanique de machines.

Enveloppé dans un gandoura d’Alger, en soie blanche, fine et légère, qui frôlait ma peau presque sans la toucher, étendu sur des coussins sous la tente, au pied du mât, j’ai rêvassé pendant six heures de suite.

Plus je vieillis, plus l’agitation humaine me semble sotte et puérile. Quand je songe que de grosses émotions bouleversent un pays entier, je veux dire les classes éclairées, c’est-à-dire les plus niaises, parce qu’une chanteuse, un soir, a été soupçonnée d’avoir bu un verre de champagne de trop, avant d’entrer en scène!

Vers trois heures de l’après-midi, nous avions doublé la pointe du Drammond, et nous nous présentions à l’entrée de la rade d’Agay.

Lire p. 65, La rade d’Agay... à p. 69, autour d’eux.)

22 juillet.—Quitté le Havre à six heures du matin, par bon vent nord-nord-est.

A huit heures la brise fraîchissant, j’ai fait amener le flèche, ne gardant que la misaine et le foc, et j’ai louvoyé sans m’éloigner à plus de cinq milles de terre.

A dix heures, le vent tomba comme je me trouvais par le travers de Saint-Jouin, non loin du cap d’Antifer, et je jetai l’ancre pour me faire conduire à la côte, monter la Valeuse et déjeuner à l’auberge bien connue d’Ernestine.

Les rochers de Saint-Jouin sont les plus beaux de toute cette côte nord de la France. On dirait des ruines de châteaux forts écroulés avec la falaise. Et les sources jaillissent au milieu de ces éboulements.

Au milieu de la dure montée, un étroit sentier grimpe sur le flanc de la falaise droite et blanche; un filet d’eau claire et glacée jaillit d’un trou et arrose en dévalant un joli tapis de cresson.

Près de cette fontaine charmante, on a placé un banc de bois où l’on s’arrête, où l’on se repose, où l’on boit dans le creux de la main en dominant la mer, la longue ligne des côtes et, à ses pieds, le chaos des roches tombées. Sur ce banc, de loin, j’avais aperçu deux êtres. En approchant, je vis qu’ils se tenaient les mains, au mouvement qu’ils firent pour les séparer. Quand je fus encore plus près, je la reconnus tout à coup, elle!

Mais lui?... Lui, c’était un autre.

Une heure plus tard, comme nous avions encore déjeuné dans la même salle, et comme je causais avec la patronne, une amie, je lui demandai:

—Quelle est donc cette jeune femme, là-bas?

—Comment! vous ne la connaissez pas? Mais d’où sortez-vous?

C’est la petite Jeanne Riga, du Vaudeville.

—Ah! Et le monsieur?

—Oh! lui... je ne sais point.

Et comme je retournais à mon bord, avec une joie égoïste je songeais à cette comédienne de l’amour qui jouait si bien, si bien, cette comédie-là, qu’elle m’avait rendu tout triste, un soir. Et je plaignais ceux pour qui elle la jouait si bien.

TABLE DES MATIÈRES.

Au lecteur

Cette version numérisée reproduit dans son intégralité la version originale

La ponctuation a pu faire l'objet de quelques corrections mineures.

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