HAL Id: hal-03190896
https://hal.archives-ouvertes.fr/hal-03190896
Submitted on 6 Apr 2021
HAL is a multi-disciplinary open access
archive for the deposit and dissemination of
sci-entific research documents, whether they are
pub-lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d’enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.
amaranth (Amaranthus cruentus) stems, a new
perspective for building applications
Philippe Evon, Guyonne de Langalerie, Laurent Labonne, Othmane Merah,
Thierry Talou, Stéphane Ballas, Thierry Véronèse
To cite this version:
Philippe Evon, Guyonne de Langalerie, Laurent Labonne, Othmane Merah, Thierry Talou, et al..
Low-density insulation blocks and hardboards from amaranth (Amaranthus cruentus) stems, a new
perspec-tive for building applications. Coatings, MDPI, 2021, 11 (349), pp.349. �10.3390/coatings11030349�.
�hal-03190896�
OATAO is an open access repository that collects the work of Toulouse
researchers and makes it freely available over the web where possible
This is an author’s version published in: http://oatao.univ-toulouse.fr/27647
To cite this version:
Evon, Philippe and de Langalerie, Guyonne and Labonne,
Laurent and Merah, Othmane and Talou, Thierry and Ballas,
Stéphane and Véronèse, Thierry Low‐density insulation blocks and
hardboards from amaranth (Amaranthus cruentus) stems, a new
perspective for building applications. (2021) Coatings, 11 (349).
1-19. ISSN 2079-6412
Official URL:
Articleȱ
LowȬDensityȱInsulationȱBlocksȱandȱHardboardsȱfromȱ ȱ
Amaranthȱ(Amaranthusȱcruentus)ȱStems,ȱaȱNewȱPerspectiveȱforȱ
BuildingȱApplicationsȱ
PhilippeȱEvonȱ1,*,ȱGuyonneȱdeȱLangalerieȱ1,2,ȱLaurentȱLabonneȱ1,ȱOthmaneȱMerahȱ1,3,ȱThierryȱTalouȱ1,ȱ ȱ
StéphaneȱBallasȱ2ȱandȱThierryȱVéronèseȱ2ȱ 1ȱ LaboratoireȱdeȱChimieȱAgroȬindustrielleȱ(LCA),ȱUniversitéȱdeȱToulouse,ȱENSIACET,ȱINRAE,ȱToulouseȱINP,ȱ 4ȱAlléeȱEmileȱMonso,ȱ31030ȱToulouse,ȱFrance;ȱguyonne.delangalerie@gmail.comȱ(G.d.L.);ȱ ȱ Laurent.Labonne@ensiacet.frȱ(L.L.);ȱothmane.merah@ensiacet.frȱ(O.M.);ȱThierry.Talou@ensiacet.frȱ(T.T.)ȱ 2ȱ OvalieȱInnovation,ȱ2ȱRueȱMargueriteȱDuras,ȱ32000ȱAuch,ȱFrance;ȱ ȱ stephane.ballas@ovalieȬinnovation.comȱ(S.B.);ȱthierry.veronese@ovalieȬinnovation.comȱ(T.V.)ȱ 3ȱ DépartementȱGénieȱBiologique,ȱIUTȱA,ȱUniversitéȱPaulȱSabatier,ȱ24ȱRueȱd’Embaques,ȱ32000ȱAuch,ȱFranceȱ *ȱ Correspondence:ȱPhilippe.Evon@ensiacet.fr;ȱTel.:ȱ+33Ȭ(0)562Ȭ446080ȱ Abstract:ȱNowadays,ȱamaranthȱappearsȱasȱaȱpromisingȱsourceȱofȱsqualeneȱofȱvegetableȱorigin.ȱAmȬ aranthȱoilȱisȱindeedȱoneȱofȱtheȱmostȱconcentratedȱvegetableȱoilsȱinȱsqualene,ȱi.e.,ȱupȱtoȱ6%ȱ(w/w).ȱ Thisȱtriterpeneȱisȱhighlyȱappreciatedȱinȱcosmetology,ȱespeciallyȱforȱtheȱformulationȱofȱmoisturizingȱ creams.ȱItȱisȱalmostȱexclusivelyȱextractedȱfromȱtheȱliverȱofȱsharks,ȱcausingȱtheirȱoverfishing.ȱThus,ȱ providingȱaȱsqualeneȱofȱrenewableȱoriginȱisȱaȱmajorȱchallengeȱforȱtheȱcosmeticȱindustry.ȱTheȱamaȬ ranthȱplantȱhasȱthusȱexperiencedȱrenewedȱinterestȱinȱrecentȱyears.ȱInȱadditionȱtoȱtheȱseeds,ȱaȱstemȱ isȱalsoȱproducedȱduringȱcultivation.ȱRepresentingȱupȱtoȱ80%ȱ(w/w)ȱofȱtheȱplantȱaerialȱpart,ȱitȱisȱ composedȱofȱaȱligneousȱfraction,ȱtheȱbark,ȱonȱitsȱperiphery,ȱandȱaȱpithȱinȱitsȱmiddle.ȱInȱthisȱstudy,ȱaȱ fractionationȱprocessȱwasȱdevelopedȱtoȱseparateȱbarkȱandȱpith.ȱTheseȱtwoȱfractionsȱwereȱthenȱusedȱ toȱproduceȱrenewableȱmaterialsȱforȱbuildingȱapplications.ȱOnȱtheȱoneȱhand,ȱtheȱbarkȱwasȱusedȱtoȱ produceȱhardboards,ȱwithȱtheȱdeoiledȱseedsȱactingȱasȱnaturalȱbinder.ȱSuchȱboardsȱareȱaȱviableȱalȬ ternativeȱtoȱcommercialȱwoodȬbasedȱpanels.ȱOnȱtheȱotherȱhand,ȱtheȱpithȱwasȱtransformedȱintoȱcoȬ hesiveȱandȱmachinableȱlowȬdensityȱinsulationȱblocksȱrevealingȱaȱlowȱthermalȱconductivityȱvalue.ȱ Keywords:ȱamaranthȱstem;ȱbark;ȱpith;ȱinsulationȱblocks;ȱhardboardsȱ ȱ 1.ȱIntroductionȱ Amaranthusȱcruentusȱisȱanȱannualȱherbȱnativeȱtoȱtemperateȱandȱtropicalȱregions.ȱItȱisȱ cultivatedȱforȱtheȱnutritionalȱpropertiesȱofȱitsȱseedsȱ[1–3].ȱItȱisȱaȱpromisingȱrawȱmaterialȱ asȱallȱpartsȱareȱpotentiallyȱusableȱforȱbothȱfoodȱandȱnonȬfoodȱapplications.ȱ Theȱamaranthȱseedȱcontainsȱaȱlipidȱfractionȱ(7–8%),ȱrichȱinȱsqualeneȱofȱvegetalȱoriginȱ (5–6%)ȱ[4].ȱActingȱasȱanȱessentialȱintermediateȱinȱtheȱbiosynthesisȱofȱcholesterol,ȱsteroidȱ hormones,ȱandȱvitaminȱDȱforȱhumans,ȱsqualeneȱisȱaȱtriterpeneȱlargelyȱusedȱasȱfoodȱsupȬ plementȱorȱforȱcosmeticsȱ[5].ȱInȱparticular,ȱsqualeneȱisȱusedȱinȱpharmaceuticalȱandȱespeȬ ciallyȱinȱcosmeticȱformulationsȱforȱtheȱtreatmentȱofȱskinȱdisordersȱbecauseȱofȱitsȱmoisturȬ izingȱandȱprotectiveȱactivityȱagainstȱexternalȱagents,ȱe.g.,ȱair,ȱlight,ȱUVȱrays,ȱenvironmenȬ talȱpollution,ȱetc.ȱ[6].ȱItȱisȱaȱgoodȱemollient,ȱandȱtheȱcosmeticȱindustryȱusesȱitȱespeciallyȱ forȱtheȱmanufactureȱofȱmoisturizers,ȱmakeȬup,ȱlipstick,ȱandȱhairȱcareȱproducts.ȱBesidesȱ squalene,ȱitsȱhydrogenatedȱproduct,ȱsqualane,ȱisȱevenȱoftenȱpreferredȱtoȱsqualeneȱasȱitȱhasȱ aȱgreaterȱoxidationȱstability,ȱdueȱtoȱtheȱabsenceȱofȱdoubleȱbondsȱ[7].ȱ Theȱamaranthȱseedȱalsoȱcontainsȱaȱsubstantialȱamountȱofȱproteinsȱ(15%).ȱTheȱlatterȱ couldȱbeȱusedȱforȱbreadȱfloursȱasȱaȱproteinȱreinforcementȱ[8],ȱandȱforȱtheirȱbiocidalȱandȱ Citation:ȱEvon,ȱP.;ȱdeȱLangalerie,ȱG.;ȱ Labonne,ȱL.;ȱMerah,ȱO.;ȱTalou,ȱT.;ȱ Ballas,ȱS.;ȱVéronèse,ȱT.ȱLowȬDensityȱ InsulationȱBlocksȱandȱHardboardsȱ fromȱAmaranthȱ(Amaranthusȱ ȱ cruentus)ȱStems,ȱaȱNewȱPerspectiveȱ forȱBuildingȱApplications.ȱCoatingsȱ 2021,ȱ11,ȱ349.ȱhttps://doi.org/ȱ 10.3390/coatings11030349ȱ AcademicȱEditor:ȱYongȱX.ȱGanȱ Received:ȱ23ȱFebruaryȱ2021ȱ Accepted:ȱ15ȱMarchȱ2021ȱ ȱ Published:ȱ18ȱMarchȱ2021ȱ Publisher’sȱNote:ȱMDPIȱstaysȱneuȬ tralȱwithȱregardȱtoȱjurisdictionalȱ claimsȱinȱpublishedȱmapsȱandȱinstiȬ tutionalȱaffiliations.ȱ ȱ
Copyright:ȱ ©ȱ 2021ȱ byȱ theȱ authors.ȱ
Licenseeȱ MDPI,ȱ Basel,ȱ Switzerland.ȱ Thisȱarticleȱ isȱanȱopenȱaccessȱarticleȱ distributedȱ underȱ theȱ termsȱ andȱ conditionsȱofȱtheȱCreativeȱCommonsȱ Attributionȱ (CCȱ BY)ȱ licenseȱ (http://creativecommons.org/licenses /by/4.0/).ȱ
antioxidantȱactivitiesȱ[9].ȱInȱaddition,ȱtheyȱwouldȱbeȱpotentiallyȱusableȱforȱtheirȱemulsifyȬ ingȱcapacityȱ(surfactantsȱforȱfoodȱorȱinȱcosmeticȱcreams)ȱ[10]ȱorȱforȱtheirȱadhesiveȱproperȬ tiesȱinȱtheȱpanelȱindustryȱ[11–13].ȱ
Lastly,ȱtheȱamaranthȱseedȱisȱparticularlyȱrichȱinȱstarchȱ(upȱtoȱ55%).ȱAfterȱitsȱplasticiȬ zation/gelatinizationȱ (plusȱ theȱ denaturationȱ ofȱ proteins)ȱ throughȱ aȱ thermoȬmechanoȬ chemicalȱ preȬtreatmentȱ usingȱ theȱ twinȬscrewȱ extrusionȱ technology,ȱ amaranthȱ seedȱ (orȱ cake)ȱcouldȱthusȱbeȱpossiblyȱtransformedȱintoȱthermoplasticȱgranulesȱforȱinjectionȬmoldȬ ingȱapplicationsȱ[14,15].ȱ Duringȱamaranthȱcultivation,ȱaȱstemȱisȱalsoȱproduced.ȱRepresentingȱupȱtoȱ80%ȱ(w/w)ȱ ofȱtheȱplantȱaerialȱpart,ȱitȱisȱcomposedȱofȱaȱpithȱfractionȱinȱitsȱmiddle,ȱandȱaȱbarkȱ(i.e.,ȱaȱ woodyȱpart,ȱorȱligneousȱfraction)ȱonȱitsȱperiphery.ȱToȱourȱknowledge,ȱtheȱscientificȱliterȬ atureȱdoesȱnotȱreferȱtoȱworksȱthatȱhaveȱalreadyȱusedȱtheȱamaranthȱstemȱinȱtheȱmanufacȬ tureȱofȱbioȬbasedȱmaterials,ȱparticularlyȱforȱconstructionȱapplications.ȱNevertheless,ȱtheȱ useȱofȱnaturalȱfibersȱ(orȱaggregates)ȱinȱcompositesȱasȱaȱreplacementȱforȱmineralȱfillersȱorȱ glassȱorȱcarbonȱfibersȱhasȱmanyȱadvantages.ȱEspecially,ȱcompositesȱmadeȱfromȱnaturalȱ byȬproductsȱareȱhighlyȱrecyclable,ȱenvironmentallyȱfriendly,ȱcostȬeffective,ȱandȱalsoȱsafeȱ forȱsociety.ȱByȱwayȱofȱanȱexample,ȱflaxȱandȱjuteȱfibersȱhaveȱalreadyȱshownȱtheirȱfullȱpoȬ tentialȱforȱtheȱreinforcementȱofȱanȱacrylicȱresin,ȱtheȱobtainedȱcompositesȱbeingȱusableȱinȱ theȱautomotiveȱsectorȱ[16].ȱInȱaddition,ȱwithȱaȱpithȱinȱitsȱmiddleȱandȱaȱbarkȱonȱitsȱperiphȬ ery,ȱtheȱstructureȱofȱtheȱamaranthȱstemȱisȱcloseȱtoȱthatȱofȱsunflower,ȱwhichȱisȱalreadyȱusedȱ inȱtheȱbuildingȱsector.ȱForȱtheseȱdifferentȱreasons,ȱitȱisȱreasonableȱtoȱassumeȱthatȱtheȱpithȱ andȱbarkȱparticlesȱfromȱtheȱamaranthȱstemȱcouldȱalsoȱbeȱusedȱforȱtheȱmanufactureȱofȱbioȬ basedȱbuildingȱcompositeȱmaterials,ȱthusȱprovidingȱrealȱbenefitsȱforȱtheȱnearȱfuture.ȱ Firstly,ȱpithȱparticlesȱrevealȱanȱalveolarȱstructureȱcloseȱtoȱthatȱofȱexpandedȱpolystyȬ rene.ȱTheȱsameȱwasȱtrueȱforȱtheȱpithȱfractionȱcomingȱfromȱsunflowerȱstemȱ[17],ȱandȱthisȱ hasȱrecentlyȱallowedȱtheȱdevelopmentȱofȱsunflowerȬbasedȱlowȬdensityȱinsulationȱmateriȬ alsȱforȱbuildingsȱ[18–20].ȱTheȱconstructionȱsectorȱgeneratesȱmajorȱenvironmentalȱimpacts,ȱ e.g.,ȱ consumptionȱ ofȱ nonȬrenewableȱ rawȱ materials,ȱ greenhouseȱ gasȱ (GHG)ȱ emissions,ȱ wasteȱproduction,ȱetc.ȱ[21].ȱNumerousȱresearchȱprojectsȱareȱthereforeȱcurrentlyȱaimedȱatȱ developingȱalternativeȱmaterialsȱwithȱlowȱenvironmentalȱcosts.ȱInȱparticular,ȱtheȱuseȱofȱ plantȱcoȬproductsȱinȱbuildingȱmaterialsȱisȱparticularlyȱinteresting.ȱIndeed,ȱvegetableȱagȬ gregatesȱareȱrenewable.ȱTheyȱareȱmainlyȱproducedȱlocally,ȱandȱtheyȱalsoȱconstituteȱaȱcarȬ bonȱsink.ȱ Inȱthisȱtopic,ȱaȱlowȬdensityȱinsulationȱblockȱconsistingȱsolelyȱofȱsunflowerȱpithȱpartiȬ clesȱandȱaȱstarchȬbasedȱglueȱwasȱrecentlyȱdevelopedȱ[20].ȱItsȱgoodȱmechanicalȱresistanceȱ allowedȱmachining.ȱInȱaddition,ȱitsȱthermalȱinsulatingȱabilityȱinȱdryȱstateȱ(32ȱmW/(m.K)ȱ atȱ25ȱ°C)ȱwasȱequivalentȱtoȱthoseȱofȱstoneȱwoolȱandȱexpandedȱpolystyrene,ȱthereforeȱcorȬ respondingȱtoȱcurrentȱstandardsȱforȱheatȱtransfer.ȱHowever,ȱwhileȱtheȱthermalȱconductivȬ ityȱofȱexpandedȱpolystyreneȱwasȱnotȱaffectedȱbyȱambientȱhumidity,ȱthatȱofȱtheȱsunflowerȬ basedȱsamplesȱincreasedȱbyȱaboutȱ15%ȱ(i.e.,ȱreducedȱinsulatingȱproperties),ȱwhichȱwasȱ explainedȱbyȱtheȱhighlyȱhygroscopicȱnatureȱofȱtheseȱbioȬbasedȱmaterials.ȱConversely,ȱtheȱ latterȱ revealedȱ aȱ highȱ waterȱ vaporȱ permeabilityȱ (i.e.,ȱ fiveȱ toȱ tenȱ timesȱ higherȱ thanȱ exȬ pandedȱpolystyrene).ȱTheirȱpowerȱasȱwaterȱregulatorsȱcouldȱbeȱusefulȱinȱhousesȱtoȱreguȬ lateȱindoorȱhumidityȱvariation.ȱForȱexample,ȱtheȱriskȱofȱcondensationȱatȱtheȱinterfaceȱbeȬ tweenȱdifferentȱlayersȱofȱmaterialsȱcouldȱbeȱlimited,ȱandȱthisȱcouldȱbeȱusefulȱinȱtheȱcaseȱofȱ theȱrenovationȱofȱoldȱbuildingsȱ[20].ȱ Aȱmoreȱrecentȱimprovementȱhasȱbeenȱtheȱapplicationȱofȱaȱsurfaceȱtreatmentȱmadeȱofȱ glycerolȱestersȱtoȱmakeȱtheseȱsunflowerȬbasedȱinsulationȱblocksȱmoreȱresistantȱtoȱmicroȬ bialȱgrowthȱ[22].ȱEvenȱinȱtheȱpresenceȱofȱtheȱglycerolȱesters,ȱtheȱpotentialȱofȱtheȱlightȱinȬ sulationȱ madeȱ ofȱ sunflowerȱ pithȱ wasȱ highlighted,ȱ withȱ aȱ 50ȱ kg/m3ȱ densityȱ andȱ aȱ 35ȱ mW/(m.K)ȱthermalȱconductivityȱatȱ25ȱ°C.ȱItsȱhighȱwaterȱvaporȱpermeabilityȱwasȱalsoȱpreȬ served.ȱTheȱantimicrobialȱefficiencyȱofȱglycerolȱestersȱwasȱevidenced,ȱcontributingȱtoȱbetȬ terȱprotectionȱofȱtheseȱbioȬbasedȱmaterialsȱfromȱmicrobialȱproliferation.ȱAtȱtheȱsameȱtime,ȱ
aȱnonȬflammabilityȱclassificationȱhasȱbeenȱsurprisinglyȱassignedȱtoȱtheȱuntreatedȱinsulaȬ tionȱmaterials.ȱ
Onȱitsȱside,ȱtheȱamaranthȱbarkȱrevealsȱaȱhighȱamountȱofȱlignocellulosicȱfibers.ȱSuchȱaȱ characteristicȱcouldȱallowȱitsȱuseȱasȱaȱmechanicalȱreinforcementȱinsideȱbiocomposites,ȱinȱ particularȱinjectionȬmoldableȱmaterialsȱ[23,24]ȱorȱfiberboardsȱ(e.g.,ȱhardboards).ȱForȱthisȱ secondȱ purpose,ȱ theȱ barkȱ preȬtreatmentȱ throughȱ twinȬscrewȱ extrusionȬrefiningȱ couldȱ makeȱthisȱreinforcementȱcapabilityȱevenȱmoreȱimportant,ȱthanksȱtoȱanȱimprovementȱinȱ theȱmorphologicalȱcharacteristicsȱofȱtheȱfibersȱ(i.e.,ȱincreaseȱinȱtheirȱmeanȱaspectȱratio,ȱdeȬ finedȱasȱtheȱratioȱofȱtheȱlengthȱtoȱtheȱdiameter,ȱafterȱrefining).ȱ TheȱtwinȬscrewȱextrusionȱtechnologyȱhasȱalreadyȱprovenȱitselfȱinȱtheȱprocessingȱofȱ biomass,ȱincludingȱmechanicalȱpressingȱofȱvegetableȱoilȱfromȱvariousȱoilseeds,ȱcontinuousȱ liquid/solidȱextractionȱofȱactiveȱbiomolecules,ȱstarchȱplasticization,ȱproteinȱdestructurizaȬ tionȱandȱdenaturation,ȱcompoundingȱofȱmatrix/fiberȱtypeȱthermoplasticȱgranules,ȱproducȬ tionȱofȱsecondȬgenerationȱbioethanol,ȱetc.ȱ[25,26].ȱEspecially,ȱitȱhasȱalsoȱrecentlyȱbeenȱusedȱ asȱanȱalternativeȱtoolȱforȱtheȱthermoȬmechanicalȱdefibrationȱofȱvariousȱagriculturalȱbyȬ productsȱorȱthoseȱresultingȱfromȱaȱfirstȱagroȬindustrialȱtransformationȱsuchȱasȱriceȱstrawȱ [27,28],ȱcorianderȱstrawȱ[13,29],ȱoleaginousȱflaxȱshivesȱ[30,31],ȱandȱsunflowerȱbarkȱ[22],ȱ priorȱtoȱhotȱpressing.ȱ Theȱfunctionȱofȱdefibrationȱisȱtoȱbreakȱdownȱtheȱligninsȱthatȱprotectȱcelluloseȱandȱ hemicelluloses.ȱThisȱpreȬtreatmentȱcontributesȱtoȱincreaseȱtheȱfiberȬspecificȱsurfaceȱandȱtoȱ promoteȱtheirȱselfȬadhesionȱ[30].ȱTheȱappliedȱpreȬtreatmentsȱareȱmostȱoftenȱmechanical,ȱ thermal,ȱand/orȱchemicalȱonesȱ[32].ȱAsȱaȱfirstȱnonȬexpensiveȱsolution,ȱaȱsimpleȱgrindingȱ enablesȱtheȱimprovementȱofȱtheȱparticleȱsizeȱprofileȱofȱmicrometricȱfibersȱ[30,33,34].ȱDeȬ fibrationȱisȱhoweverȱmuchȱmoreȱefficientȱwhenȱthermoȬmechanicalȱpulpsȱareȱproduced.ȱ Widelyȱusedȱinȱtheȱpaperȱindustry,ȱtheȱthermoȬmechanicalȱdefibrationȱcanȱbeȱcarriedȱoutȱ fromȱdifferentȱpulpingȱprocessesȱ[35],ȱincludingȱdigestionȱplusȱdefibrationȱ[36]ȱandȱsteamȱ explosionȱ [37–41].ȱ Moreȱ originalȱ preȬtreatmentȱ methodsȱ involvingȱ enzymesȱ haveȱ alsoȱ beenȱconsideredȱ[42–44].ȱHowever,ȱtheyȱhaveȱtheȱdisadvantageȱofȱbeingȱratherȱdifficultȱtoȱ implementȱonȱaȱlargeȱscale.ȱ
TwinȬscrewȱextrusion,ȱonȱtheȱotherȱhand,ȱcanȱbeȱmoreȱeasilyȱdeployedȱinȱtheȱindusȬ try.ȱAboveȱall,ȱitȱhasȱrecentlyȱshownȱitsȱfullȱpotentialȱforȱanȱefficientȱthermoȬmechanicalȱ defibrationȱofȱlignocellulosicȱbyȬproductsȱatȱaȱmoderateȱcost.ȱItȱwasȱcomparedȱwithȱaȱdiȬ gestionȱ plusȱ defibrationȱ processȱ fromȱ theȱ paperȱ industryȱ forȱ theȱ preȬtreatmentȱ ofȱ riceȱ strawȱ[27].ȱAȱsignificantlyȱreducedȱcostȱ(i.e.,ȱnineȱtimesȱless)ȱwasȱobservedȱforȱtheȱextruȬ sionȬrefiningȱprocess.ȱInȱparallel,ȱthisȱtechnologyȱwasȱmuchȱmoreȱefficient,ȱevenȱwithȱreȬ ducedȱamountȱofȱwaterȱaddedȱ(i.e.,ȱ0.4–1.0ȱinsteadȱofȱatȱleastȱ4.0ȱinȱtheȱcaseȱofȱtheȱpulpingȱ method),ȱasȱtheȱlengthȱofȱtheȱrefinedȱfibersȱwasȱbetterȱpreservedȱusingȱtheȱextrusionȬreȬ finingȱprocess:ȱ21.2–22.6ȱforȱtheirȱaverageȱaspectȱratioȱinsteadȱofȱ16.3–17.9ȱinȱtheȱcaseȱofȱ theȱdigestionȱplusȱdefibrationȱprocess.ȱWithȱsuchȱsignificantlyȱimprovedȱmechanicalȱreinȬ forcementȱcapability,ȱtheȱextrusionȬrefinedȱriceȱstrawȱthusȱenabledȱtheȱmanufactureȱofȱfiȬ berboardsȱwithȱparticularlyȱpromisingȱusageȱpropertiesȱ[28].ȱTheȱoptimalȱoneȱwasȱmoldedȱ afterȱtheȱadditionȱofȱ8.9%ȱ(w/w)ȱcommercialȱBiolignin™ȱ(i.e.,ȱaȱpureȱandȱnonȬdeterioratedȱ Organosolvȱligninȱextractedȱfromȱwheatȱstrawȱusingȱaȱmixtureȱofȱaceticȱacidȱandȱformicȱ acid)ȱasȱaȱbinder.ȱWithȱaȱdensityȱofȱ1414ȱkg/m3,ȱtheȱlatterȱrevealedȱveryȱhighȱbendingȱ propertiesȱ(i.e.,ȱstrengthȱatȱbreakȱandȱ elasticȱmodulusȱofȱ50ȱMPaȱandȱ8.6ȱGPa,ȱ respecȬ tively),ȱsimultaneouslyȱwithȱgoodȱwaterȱresistanceȱ(i.e.,ȱthicknessȱswellingȱandȱwaterȱabȬ sorptionȱofȱ24%ȱandȱ18%,ȱrespectively,ȱafterȱ24ȱhȱsoakingȱinȱwater).ȱSuchȱaȱriceȱstrawȬ basedȱmaterialȱcouldȱbeȱusedȱasȱaȱloadȬbearingȱboardȱunderȱhighȱstress.ȱ AnotherȱrecentȱstudyȱfocusedȱonȱtheȱextrusionȬrefiningȱofȱcorianderȱstrawȱ[13].ȱTheȱ resultsȱobtainedȱduringȱthisȱstudyȱconfirmedȱtheȱinterestȱofȱtheȱtwinȬscrewȱextrusionȱpreȬ treatmentȱwithȱregardȱtoȱtheȱaverageȱaspectȱratioȱofȱtheȱobtainedȱfibres,ȱwhichȱwasȱevaluȬ atedȱatȱvaluesȱofȱbetweenȱ22.9ȱandȱ26.5ȱdependingȱonȱtheȱamountȱofȱwaterȱaddedȱduringȱ extrusion,ȱasȱopposedȱtoȱonlyȱ4.5ȱinȱtheȱcaseȱofȱaȱstrawȱthatȱwasȱsimplyȱcrushedȱusingȱaȱ hammerȱmill.ȱDuringȱthisȱstudy,ȱfiberboardsȱcombiningȱtheȱstrawȱasȱaȱreinforcementȱandȱ
theȱcakeȱresultingȱfromȱtheȱextractionȱofȱvegetableȱoilȱfromȱtheȱcorianderȱseedsȱasȱaȱproteinȱ binderȱwereȱmanufacturedȱthroughȱhotȱpressing.ȱAllȱbiocompositesȱmadeȱofȱtheȱextruȬ sionȬrefinedȱcorianderȱfibersȱhaveȱshownȱbetterȱusageȱproperties,ȱandȱtheȱoptimalȱ100%ȱ corianderȬbasedȱboardȱwasȱtheȱoneȱcontainingȱ40%ȱ(w/w)ȱcake.ȱTheȱlatterȱhadȱtheȱnextȱ characteristics:ȱ1195ȱkg/m3ȱdensity,ȱ29.1ȱMPaȱflexuralȱstrengthȱatȱbreak,ȱ3.9ȱGPaȱelasticȱ modulus,ȱ24%ȱthicknessȱswelling,ȱandȱ24%ȱwaterȱabsorption.ȱLessȱdenseȱandȱwithȱlowerȱ bendingȱpropertiesȱthanȱtheȱoptimalȱhardboardȱdevelopedȱbyȱThengȱetȱal.ȱfromȱriceȱstrawȱ [28],ȱitȱstillȱhadȱaȱwaterȱresistanceȱafterȱ24ȱhȱimmersionȱofȱtheȱsameȱorderȱofȱmagnitude,ȱ thanksȱtoȱaȱheatȱpostȬtreatmentȱappliedȱafterȱhotȱpressing.ȱItsȱbendingȱpropertiesȱwereȱ nonethelessȱsufficientȱtoȱuseȱitȱinȱdryȱconditions,ȱforȱgeneralȱpurposesȱ(e.g.,ȱcarcasses,ȱdoȬ mesticȱflooring,ȱetc.)ȱasȱwellȱasȱfurnitureȱgradeȱandȱloadȬbearingȱboardȱ(e.g.,ȱshelving).ȱ Additionally,ȱtheȱVOCȱandȱcarbonylȱcompoundȱemissionsȱfromȱthisȱhardboardȱwereȱstudȬ ied,ȱandȱnoȱformaldehydeȱemissionȱwasȱdetectedȱ[29].ȱInȱcomparisonȱwithȱmostȱofȱtheȱ woodȬbasedȱmaterialsȱavailableȱonȱtheȱmarketȱ(e.g.,ȱmediumȬdensityȱfiberboardȱ(MDF)ȱorȱ chipboard,ȱwhichȱhaveȱalsoȱbeenȱtestedȱinȱthatȱstudy),ȱitȱwasȱthusȱmoreȱenvironmentallyȱ andȱhumanȬhealthȱfriendly.ȱ AȱsingleȱtwinȬscrewȱextruderȱcanȱevenȱbeȱusedȱbothȱasȱaȱcontinuousȱfiberȬrefiningȱ toolȱandȱasȱaȱtoolȱforȱaddingȱcontinuouslyȱanȱexogenousȱbinderȱtoȱtheȱpreviouslyȱrefinedȱ fibers,ȱresultingȱatȱtheȱextruderȱoutletȱinȱanȱhomogeneousȱpremixȱmadeȱofȱreinforcingȱ fibersȱandȱaȱbinder,ȱreadyȱtoȱbeȱtransformedȱintoȱcohesiveȱfiberboardsȱthroughȱhotȱpressȬ ingȱ[13,31].ȱ Inȱrespectȱwithȱtheȱbiorefineryȱconceptȱofȱwholeȱplants,ȱthisȱstudyȱaimedȱtoȱdevelopȱ aȱcontinuousȱmechanicalȱprocessȱallowingȱtheȱfractionationȱofȱtheȱamaranthȱstemȱintoȱ barkȱandȱpith,ȱandȱtoȱinvestigateȱtheȱuseȱofȱthoseȱtwoȱfractionsȱforȱbuildingȱmaterialȱapȬ plications.ȱ Twoȱ familiesȱ ofȱ innovativeȱ bioȬbasedȱ materialsȱ wereȱ investigated,ȱ i.e.,ȱ bulkȱ (looseȱfill)ȱinsulationȱandȱlowȬdensityȱblocksȱfromȱtheȱpithȱfractionȱonȱtheȱoneȱhand,ȱandȱ hardboardsȱfromȱtheȱbarkȱfractionȱonȱtheȱotherȱhand.ȱTheȱuseȱasȱaȱnaturalȱbinderȱofȱtheȱ solidȱresidueȱ(i.e.,ȱtheȱcake)ȱobtainedȱafterȱextractionȱofȱvegetableȱoilȱfromȱtheȱamaranthȱ seedsȱusingȱanȱapolarȱsolventȱwasȱalsoȱinvestigatedȱinȱthisȱstudy,ȱdueȱtoȱitsȱnaturalȱrichȬ nessȱinȱproteinsȱandȱespeciallyȱstarch.ȱ 2.ȱMaterialsȱandȱMethodsȱ 2.1.ȱRawȱMaterialsȱandȱNaturalȱBindersȱ Theȱamaranthȱ(Amaranthusȱcruentus)ȱstemsȱandȱseedsȱusedȱinȱthisȱstudyȱwereȱfromȱ theȱSouthȬWestȱpartȱofȱFrance.ȱTheyȱwereȱcultivatedȱnearȱtheȱcityȱofȱAuchȱduringȱtheȱsumȬ merȱofȱ2018.ȱTheyȱwereȱsuppliedȱbyȱOvalieȱInnovationȱ(Auch,ȱFrance).ȱ TheȱstarchȬbasedȱbinderȱusedȱforȱproducingȱtheȱlowȬdensityȱinsulationȱblocksȱhadȱanȱ 85%ȱ(w/w)ȱstarchȱcontent.ȱSuppliedȱbyȱBostikȱ(Colombes,ȱFrance)ȱwithȱreferenceȱnumberȱ 28474,ȱitȱisȱusuallyȱusedȱasȱaȱglueȱforȱwallpapers.ȱ TheȱamaranthȬbasedȱbinderȱ(AB)ȱusedȱforȱobtainingȱtheȱhardboardsȱwasȱpreparedȱ fromȱtheȱseedsȱsuppliedȱbyȱOvalieȱInnovation.ȱFirstly,ȱtheȱlatterȱwereȱgrindedȱusingȱaȱFossȱ (Hilleroed,ȱDenmark)ȱCyclotecȱ1093ȱsampleȱmillȱfittedȱwithȱaȱ1ȱmmȱscreen.ȱDeoilingȱwasȱ thenȱconductedȱusingȱaȱSoxhletȱ extractionȱapparatusȱ(LenzȱLaborglas,ȱWertheim,ȱGerȬ many),ȱandȱcyclohexaneȱasȱextractingȱsolvent.ȱ 2.2.ȱAnalyticalȱMethodsȱ MineralȱcontentȱinsideȱamaranthȱpithȱandȱbarkȱwereȱdeterminedȱaccordingȱtoȱtheȱISOȱ 749:1977ȱstandardȱ[45].ȱAnȱestimationȱofȱtheȱthreeȱparietalȱconstituents,ȱi.e.,ȱcellulose,ȱhemȬ icelluloses,ȱandȱlignins,ȱwasȱmadeȱfromȱtheȱADFȬNDFȱ(ADF,ȱAcidȱDetergentȱFiber;ȱNDF,ȱ NeutralȱDetergentȱFiber)ȱmethodȱofȱVanȱSoestȱandȱWineȱ[46,47].ȱTheȱwaterȬsolubleȱcomȬ ponentsȱwereȱdeterminedȱbyȱmeasuringȱtheȱmassȱlossȱofȱtheȱtestȱsampleȱafterȱ1ȱhȱinȱboilingȱ water.ȱAllȱdeterminationsȱwereȱmadeȱinȱtriplicate.ȱ ȱ ȱ
2.3.ȱGrindingȱofȱAmaranthȱStemsȱandȱSeparationȱbetweenȱBarkȱandȱPithȱParticlesȱ TheȱgrindingȱofȱamaranthȱstemsȱwasȱdoneȱusingȱanȱElectraȱ(Poudenas,ȱFrance)ȱGouluȱ Nȱhammerȱmillȱwithȱnoȱgrid.ȱTheȱseparationȱbetweenȱbarkȱandȱpithȱparticlesȱwasȱthenȱ conductedȱusingȱaȱvacuumȱcleaner.ȱTheȱsuctionȱstepȱwasȱrepeatedȱthreeȱtimes,ȱfirstȱonȱaȱ Ritecȱ600ȱ(Signes,ȱFrance)ȱvibratingȱsieveȱshakerȱandȱthenȱtwiceȱonȱaȱroughȱandȱinclinedȱ conveyorȱbelt.ȱ Duringȱtheȱinitialȱsievingȱstage,ȱtheȱsieveȱshakerȱwasȱfittedȱwithȱtwoȱsievesȱwithȱaȱ meshȱofȱ2ȱmmȱandȱ1ȱmm,ȱrespectively,ȱfromȱtopȱtoȱbottom.ȱThreeȱdifferentȱfractionsȱmadeȱ ofȱdenseȱbarkȱparticlesȱwereȱthusȱgenerated,ȱi.e.,ȱfinesȱ(<1ȱmm),ȱandȱmediumȱ(fromȱ1ȱtoȱ2ȱ mm)ȱandȱlargeȱparticlesȱ(>2ȱmm).ȱAdditionally,ȱthanksȱtoȱtheȱvacuumȱcleanerȱpositionedȱ aboveȱtheȱupperȱsieve,ȱtheȱlightȱpithȱparticlesȱwereȱsuckedȱcontinuously.ȱ Theȱthreeȱbarkȱfractionsȱcollectedȱatȱtheȱlevelȱofȱtheȱsieveȱshakerȱwereȱalmostȱpure.ȱ Onȱtheȱopposite,ȱtheȱpithȱoneȱstillȱcontainedȱsomeȱbarkȱimpurities,ȱwhichȱwereȱsuckedȱ simultaneouslyȱwithȱtheȱpithȱparticles.ȱTwoȱadditionalȱpurificationȱextraȬstepsȱwereȱthusȱ required.ȱTheȱlatterȱwereȱconductedȱusingȱanȱinclinedȱconveyorȱbeltȱmadeȱofȱaȱroughȱrubȬ berȱband.ȱAȱventilatorȱwithȱanȱairȱspeedȱfromȱ1.0ȱtoȱ2.5ȱm/sȱwasȱpositionedȱatȱ1.3ȱmȱfromȱ theȱbottomȱofȱtheȱconveyorȱbelt,ȱandȱtheȱvacuumȱcleanerȱatȱitsȱbottom.ȱTheȱmovementȱofȱ theȱconveyorȱbeltȱwasȱatȱconstantȱspeed,ȱfromȱbottomȱtoȱtop.ȱ Theȱpithȱfractionȱtoȱbeȱpurifiedȱwasȱfedȱatȱaȱconstantȱmassȱflowȱrateȱontoȱtheȱconveyorȱ beltȱjustȱinȱfrontȱofȱtheȱventilator.ȱInȱdoingȱso,ȱtheȱventilationȱopposedȱtheȱmovementȱofȱ theȱconveyorȱbelt,ȱandȱthisȱallowedȱtheȱpithȱparticles,ȱwhichȱwereȱlightȱandȱratherȱcylinȬ dricalȱinȱshape,ȱtoȱrollȱdownȱtoȱtheȱbottomȱofȱtheȱdeviceȱwhereȱtheyȱwereȱsucked.ȱTheȱbarkȱ particlesȱ toȱ beȱ removed,ȱ onȱ theȱ otherȱ hand,ȱ wereȱ muchȱ denserȱ andȱ hadȱ anȱ elongatedȱ shape,ȱsoȱthatȱtheyȱremainedȱattachedȱtoȱtheȱroughȱsurfaceȱofȱtheȱrubberȱband.ȱTheyȱcouldȱ thenȱbeȱpickedȱupȱfromȱtheȱtopȱofȱtheȱdevice.ȱInȱorderȱtoȱobtainȱaȱpithȱfractionȱwithȱaȱ purityȱofȱmoreȱthanȱ90%ȱ(w/w),ȱtwoȱsuccessiveȱpassesȱofȱtheȱpithȱonȱtheȱconveyorȱbeltȱwereȱ necessary,ȱusingȱanȱangleȱofȱinclinationȱequalȱtoȱ32°ȱandȱ23°,ȱrespectively.ȱ
InȱFigureȱ1,ȱaȱschematicȱdiagramȱofȱtheȱfractionationȱprocessȱofȱtheȱamaranthȱstems,ȱ includingȱ theirȱ grindingȱ andȱ thenȱ theirȱ separationȱ betweenȱ barkȱ andȱ pithȱ particlesȱ throughȱ threeȱ successiveȱ suctionȱ stages,ȱ isȱ presented.ȱ Thisȱ diagramȱ alsoȱ includesȱ theȱ buildingȱmaterialsȱobtainedȱfromȱeachȱofȱtheseȱtwoȱfractionsȱandȱtheȱequipmentȱusedȱtoȱ obtainȱthem.ȱ ȱ Figureȱ1.ȱSchematicȱdiagramȱofȱtheȱfractionationȱprocessȱofȱtheȱamaranthȱstemsȱintoȱbarkȱandȱpithȱ fractions,ȱandȱbuildingȱmaterialsȱobtainedȱfromȱtheseȱfractions.ȱ ȱ ȱ
2.4.ȱSievingȱofȱPithȱParticlesȱ
Toȱ determineȱ theȱ particleȱ sizeȱ distributionȱ ofȱ theȱ pithȱ particles,ȱ aȱ Retschȱ ASȱ 300ȱ (Haan,ȱGermany)ȱvibratoryȱsieveȱshakerȱwasȱused.ȱTheȱthreeȱimplementedȱsievesȱhadȱaȱ meshȱofȱ4ȱmm,ȱ2ȱmmȱandȱ1ȱmm,ȱrespectively,ȱfromȱtopȱtoȱbottom.ȱAȱsieveȱaccelerationȱofȱ 1.5×ȱgȱandȱaȱsievingȱtimeȱofȱ10ȱminȱwereȱchosenȱforȱsieving.ȱ 2.5.ȱTwinȬScrewȱExtrusionȬRefiningȱofȱFibersȱfromȱAmaranthȱBarkȱ Amaranthȱbarkȱparticlesȱwithȱaȱdiameterȱofȱmoreȱthanȱ2ȱmmȱandȱaȱmoistureȱcontentȱ ofȱ6.0ȱ±ȱ0.0%ȱwereȱextrusionȬrefinedȱinȱtheȱpresenceȱofȱwaterȱusingȱaȱClextralȱ(Firminy,ȱ France)ȱEvolumȱHTȱ53ȱcoȬrotatingȱandȱcoȬpenetratingȱtwinȬscrewȱextruder.ȱTheȱscrewsȱ wereȱ53ȱmmȱinȱdiameterȱ(D),ȱandȱtheȱbarrelȱwasȱ36ȱDȱinȱlengthȱwithȱnineȱsuccessiveȱmodȬ ules,ȱeachȱ4ȱDȱinȱlength.ȱ TheȱthermoȬmechanicalȱfiberȱpreȬtreatmentȱwasȱinspiredȱbyȱaȱpreviousȱworkȱdevelȬ opedȱfromȱtheȱcorianderȱstrawȱ[13].ȱAmaranthȱbarkȱwasȱfedȱusingȱaȱweightȱdosingȱdeviceȱ inȱmoduleȱ1,ȱandȱwaterȱwasȱinjectedȱusingȱaȱpistonȱpumpȱatȱtheȱendȱofȱmoduleȱ2.ȱInȱparȬ ticular,ȱ toȱ preventȱ waterȱ fromȱ cloggingȱ theȱ twinȬscrewȱ extruder,ȱ aȱ filtrationȱ moduleȱ equippedȱwithȱtwoȱfilterȱgridsȱmadeȱofȱ1ȱmmȱdiameterȱholesȱwasȱpositionedȱatȱtheȱendȱofȱ theȱbarrel,ȱi.e.,ȱinȱpenultimateȱposition.ȱTheȱexcessȱofȱwaterȱwasȱthusȱremovedȱ(inȱtheȱformȱ ofȱanȱaqueousȱfiltrate).ȱ TheȱscrewȱprofileȱusedȱwasȱthatȱofȱUitterhaegenȱetȱal.ȱ[13].ȱInȱparticular,ȱtwoȱsuccesȬ siveȱpairsȱ(i.e.,ȱ2ȱDȱinȱlength)ȱofȱBBȱbilobeȱpaddlesȱmountedȱinȱaȱstaggeredȱpatternȱ(i.e.,ȱ withȱaȱ90°ȱangle)ȱwereȱpositionedȱinȱmoduleȱ5ȱtoȱensureȱintimateȱmixingȱandȱhomogeniȬ zationȱofȱsolidȱandȱliquidȱphases.ȱInȱaddition,ȱfourȱsuccessiveȱpairsȱ(i.e.,ȱ1.5ȱDȱinȱlength)ȱ ofȱCF1Cȱscrewsȱ(i.e.,ȱconjugatedȱcutȬflight,ȱ singleȬflightȱscrewsȱwithȱleftȬhandedȱpitch)ȱ wereȱpositionedȱatȱtheȱbeginningȱofȱmoduleȱ9.ȱThanksȱtoȱtheȱintenseȱmechanicalȱshearȱ appliedȱtoȱtheȱrawȱmaterialȱinȱthisȱlocation,ȱthisȱenabledȱanȱefficientȱextrusionȬrefiningȱofȱ fibersȱinȱamaranthȱbark.ȱ Theȱtemperatureȱprofileȱusedȱwasȱasȱfollows:ȱ25ȱ°Cȱforȱmoduleȱ1ȱ(feedingȱmodule),ȱ 50ȱ°Cȱforȱmoduleȱ2,ȱ80ȱ°Cȱforȱmoduleȱ3,ȱ100ȱ°Cȱforȱmodulesȱ4ȱtoȱ7,ȱandȱ110ȱ°Cȱforȱmoduleȱ 9ȱ(thermoȬmechanicalȱrefiningȱmodule).ȱ Theȱscrewȱrotationȱspeedȱwasȱ250ȱrpm.ȱTheȱinletȱflowȱrateȱofȱamaranthȱbarkȱparticlesȱ wasȱ10ȱkg/h.ȱThreeȱdifferentȱinletȱflowȱratesȱofȱwaterȱwereȱtestedȱ(i.e.,ȱ10ȱkg/h,ȱ20ȱkg/hȱandȱ 40ȱkg/h,ȱrespectively),ȱcorrespondingȱtoȱliquid/solidȱratiosȱofȱ1,ȱ2,ȱandȱ4,ȱrespectively.ȱ 2.6.ȱMoldingȱofȱInsulationȱBlocksȱandȱHardboardsȱ TheȱcompressionȱmoldingȱofȱtheȱinsulationȱblocksȱwasȱconductedȱatȱroomȱtemperaȬ tureȱinsideȱanȱaluminiumȱmoldȱwithȱ15ȱcmȱsidesȱusingȱaȱconventionalȱhydraulicȱpress.ȱAȱ pressureȱofȱ9ȱkPaȱwasȱappliedȱatȱroomȱtemperatureȱforȱ5ȱminȱtoȱtheȱmixtureȱcomposedȱofȱ pithȱparticlesȱ(bulkȱtestȱsampleȱvolumeȱequalȱtoȱ2700ȱcm3),ȱstarchȬbasedȱbinderȱ(10%ȱ(w/w)ȱ inȱproportionȱtoȱtheȱsumȱofȱtheȱpithȱandȱbinderȱmasses),ȱandȱwaterȱ(3.7%ȱ(w/w)ȱforȱtheȱ binderȱtoȱwaterȱratio).ȱForȱtheȱmediumȱsizeȱ(2–4ȱmm)ȱofȱpithȱparticlesȱonly,ȱstarchȬbasedȱ binderȱcontentsȱofȱ15%,ȱ20%ȱandȱ25%ȱ(w/w)ȱwereȱalsoȱtested.ȱ Onceȱmolded,ȱtheȱinsulationȱblocksȱwereȱdriedȱatȱ60ȱ°CȱinȱaȱFranceȱEtuvesȱ(Chelles,ȱ France)ȱXL2520ȱventilatedȱovenȱuntilȱconstantȱweightȱ(i.e.,ȱmassȱvariationȱlessȱthanȱ0.1%ȱ afterȱ24ȱh).ȱTheȱdryingȱstepȱwasȱconductedȱwithȱtheȱobjectiveȱtoȱeliminateȱtheȱwaterȱaddedȱ toȱdissolveȱtheȱbinder.ȱAsȱtheȱexternalȱstarchyȱbinderȱusedȱwasȱwithȱphysicalȱcuring,ȱtheȱ adhesionȱwasȱachievedȱasȱwaterȱevaporated.ȱ
Theȱ hotȱ pressingȱ ofȱ hardboardsȱ wasȱ conductedȱ usingȱ 400ȱ tonsȱ capacityȱ Pinetteȱ EmidecauȱIndustrieȱ(ChalonȬsurȬSaône,ȱFrance)ȱheatedȱhydraulicȱpress.ȱTheȱconditionsȱ wereȱstandardȱonesȱ[13,30],ȱi.e.,ȱ200ȱ°Cȱforȱtheȱmoldȱtemperature,ȱ20ȱMPaȱforȱtheȱappliedȱ pressure,ȱandȱ5ȱminȱforȱtheȱmoldingȱtime.ȱ
Aȱ150ȱmmȱ×ȱ150ȱmmȱaluminiumȱmoldȱwasȱusedȱtoȱperformȱbothȱcompressionȱmoldȬ ingȱandȱhotȱpressing.ȱTheȱmaterialȱthicknessȱwasȱ4ȱcmȱandȱaroundȱ4.5ȱmm,ȱrespectively,ȱ
forȱtheȱinsulationȱblocksȱandȱhardboards.ȱAllȱmaterialsȱwereȱthenȱequilibratedȱinȱaȱclimaticȱ chamberȱatȱ60%ȱrelativeȱhumidityȱ(RH)ȱandȱ25ȱ°Cȱuntilȱconstantȱweightȱ(i.e.,ȱmassȱvariaȬ tionȱlessȱthanȱ0.1%ȱafterȱ24ȱh).ȱTheȱequilibrationȱlastedȱaroundȱthreeȱweeks,ȱafterȱwhichȱ theȱmaterialsȱwereȱanalyzed.ȱ 2.7.ȱDensityȱMeasurementsȱ Theȱbulkȱdensityȱofȱtheȱpithȱandȱbarkȱparticlesȱwasȱmeasuredȱusingȱaȱ2ȱLȱtestȱtube.ȱ Onceȱfilledȱwithȱtheȱparticles,ȱtheȱlatterȱwereȱweighedȱinȱorderȱtoȱdetermineȱtheȱbulkȱdenȬ sity.ȱTheȱtappedȱdensityȱofȱbarkȱparticles,ȱbeforeȱandȱafterȱtheȱextrusionȬrefiningȱstep,ȱwasȱ determinedȱusingȱaȱGranuloshopȱ(Chatou,ȱFrance)ȱDensitapȱETDȬ20ȱvolumenometer.ȱAllȱ determinationsȱwereȱcarriedȱoutȱinȱtriplicate.ȱ Theȱdensityȱofȱtheȱinsulationȱblocksȱandȱhardboardsȱwasȱconductedȱfromȱtheȱbendingȱ testȱspecimens.ȱAnȱelectronicȱdigitalȱslidingȱcaliperȱhavingȱaȱresolutionȱofȱ0.01ȱmmȱwasȱ usedȱtoȱmeasureȱtheirȱthickness,ȱwidth,ȱandȱlength,ȱallowingȱtheȱspecimenȱvolumeȱtoȱbeȱ calculated.ȱInȱparallel,ȱallȱtheȱtestȱspecimensȱwereȱalsoȱweighed,ȱenablingȱtheirȱdensityȱtoȱ beȱdetermined.ȱAllȱdeterminationsȱwereȱcarriedȱoutȱfourȱtimes.ȱ 2.8.ȱPhysicalȱCharacterizationȱofȱtheȱBuildingȱMaterialsȱ Theȱflexuralȱpropertiesȱofȱtheȱinsulationȱblocksȱandȱhardboardsȱwereȱmeasuredȱusingȱ theȱthreeȱpointsȱbendingȱtechniqueȱaccordingȱtoȱtheȱISOȱ16978:2003ȱstandardȱ[48].ȱTheȱ universalȱtestingȱmachineȱusedȱforȱthoseȱtestsȱwasȱanȱInstronȱ(Norwood,ȱMA,ȱUSA)ȱ5500Rȱ machineȱfittedȱwithȱaȱ500ȱNȱloadȱcell.ȱAllȱtestȱspecimensȱwereȱ3ȱcmȱwide,ȱandȱ12ȱcmȱlong.ȱ Theȱgripȱseparationȱwasȱ8ȱcm,ȱandȱtheȱtestȱspeedȱwasȱ2ȱmm/min.ȱAllȱdeterminationsȱwereȱ conductedȱfourȱtimes.ȱ Theȱthermalȱconductivityȱofȱlooseȱpithȱparticlesȱandȱinsulationȱblocksȱwasȱmeasuredȱ atȱ25ȱ°CȱusingȱaȱNeotimȱ(Albi,ȱFrance)ȱFP2Cȱthermalȱconductivimeterȱwithȱaȱhotȱwire.ȱAȱ 5%ȱaccuracyȱwasȱobtainedȱforȱtheseȱmeasurements.ȱDuringȱtheȱhotȱwireȱtest,ȱanȱelectricȱ currentȱthroughȱtheȱlinearȱwireȱgeneratedȱheat,ȱwhichȱresultedȱinȱtheȱincreaseȱofȱtheȱtemȬ peratureȱofȱtheȱmaterialȱtested.ȱTheȱwireȱlengthȱwasȱconsideredȱasȱinfinite,ȱandȱitsȱdiameȬ terȱasȱnegligible.ȱTheȱwireȱandȱthermocoupleȱwereȱincludedȱinȱaȱKaptonȱprobe.ȱDuringȱ theȱtest,ȱtheȱprobeȱwasȱplacedȱinȱtheȱmiddleȱofȱtheȱpithȱparticlesȱarrangedȱinȱbulk,ȱorȱbeȬ tweenȱtwoȱsamplesȱofȱtheȱinsulationȱblock.ȱAsȱtheȱmaterialȱtestedȱwasȱconsideredȱasȱsemiȬ infinite,ȱtheȱheatȱconductionȱequationȱwasȱsolvedȱinȱcylindricalȱcoordinates.ȱThisȱallowedȱ theȱdeterminationȱofȱtheȱthermalȱconductivity.ȱThen,ȱtheȱthermalȱresistanceȱwasȱdeducedȱ fromȱtheȱthermalȱconductivityȱvalueȱbyȱconsideringȱaȱ4ȱcmȱthicknessȱforȱtheȱlooseȱpithȱ particlesȱasȱforȱtheȱinsulationȱblocks.ȱBeforeȱtheȱtest,ȱtheȱpithȱparticlesȱwereȱequilibratedȱ inȱaȱclimaticȱchamberȱunderȱtheȱsameȱconditionsȱasȱthoseȱusedȱforȱtheȱinsulationȱblocks,ȱ i.e.,ȱ60%ȱRHȱandȱ25ȱ°Cȱforȱthreeȱweeks.ȱAllȱdeterminationsȱwereȱconductedȱinȱtriplicate.ȱ Theȱthicknessȱswellingȱofȱhardboardsȱwasȱmeasuredȱafterȱ24ȱhȱimmersionȱinȱwaterȱ accordingȱtoȱtheȱISOȱ16983:2003ȱstandardȱ[49].ȱExpressedȱinȱmassȱpercentage,ȱtheirȱwaterȱ absorptionȱlevelȱwasȱdeterminedȱatȱtheȱsameȱtime.ȱAllȱdeterminationsȱwereȱconductedȱ fourȱtimes.ȱ 2.9.ȱStatisticalȱAnalysesȱ Resultsȱareȱexpressedȱasȱmeanȱvalueȱ±ȱstandardȱdeviation.ȱOneȬwayȱanalysisȱofȱvarȬ ianceȱ(ANOVA)ȱwasȱusedȱinȱorderȱtoȱexamineȱtheȱsignificanceȱofȱtheȱeffectȱofȱfactorsȱonȱ studiedȱtraits.ȱDuncan’sȱmultipleȱrangeȱtestȱwasȱusedȱtoȱcompareȱindividualȱmeansȱatȱaȱ 5%ȱprobabilityȱlevel.ȱ ȱ ȱ
3.ȱResultsȱ 3.1.ȱSeparationȱbetweenȱPithȱandȱBarkȱ Immediatelyȱafterȱtheirȱharvesting,ȱamaranthȱstemsȱhadȱtoȱbeȱdriedȱ(50ȱ°C,ȱ48ȱh)ȱtoȱ facilitateȱtheirȱstorageȱoverȱtime.ȱTheirȱstructureȱwasȱthenȱmanuallyȱstudiedȱfromȱtenȱspecȬ imens.ȱTheyȱwereȱcomposedȱofȱaȱlightȱpithȱfractionȱinȱtheirȱmiddleȱ(24%ȱ(w/w)),ȱandȱaȱbarkȱ one,ȱfibrousȱandȱrigid,ȱinȱtheirȱperipheryȱ(76%ȱ(w/w))ȱ(Figureȱ2a).ȱ Theȱstructureȱofȱtheȱamaranthȱstemȱisȱreminiscentȱofȱsunflowerȱorȱevenȱcorn.ȱNeverȬ theless,ȱtheȱelementsȱofȱtheȱamaranthȱstemȱareȱnotȱyetȱvalorizedȱinȱtheȱfieldȱofȱrenewableȱ materials.ȱConversely,ȱpithȱandȱbarkȱfractionsȱfromȱsunflowerȱstemsȱhaveȱbeenȱtheȱsubjectȱ ofȱrecentȱworkȱtoȱtransformȱthemȱintoȱlowȬdensityȱinsulatingȱblocksȱ[22],ȱorȱrigidȱ[11]ȱandȱ semiȬrigidȱ[22]ȱpanels,ȱrespectively.ȱ ȱ Figureȱ2.ȱ(a)ȱPhotographȱofȱtheȱamaranthȱstemȱ(crossȱsection);ȱ(b)ȱPhotographȱofȱtheȱoptimalȱinsuȬ lationȱblockȱfromȱtheȱBPȱpithȱfraction;ȱ(c)ȱPhotographȱofȱtheȱoptimalȱhardboardȱ(HB6)ȱfromȱextruȬ sionȬrefinedȱbark.ȱ
Basedȱ onȱ theȱ sameȱ principleȱ asȱ forȱ sunflower,ȱ theȱ amaranthȱ stemȱ fractionsȱ couldȱ thereforeȱbeȱusedȱasȱbasicȱelementsȱforȱvalorizationȱinȱtheȱmaterialsȱsector.ȱIndeed,ȱtheȱ pithȱcouldȱbeȱusedȱasȱthermalȱinsulationȱwhileȱtheȱbarkȱfractionȱcouldȱbeȱusedȱforȱtheȱ productionȱofȱdenseȱboardsȱthroughȱhotȱpressing.ȱ TheȱlargeȱdifferenceȱinȱdensityȱbetweenȱbarkȱandȱpithȱparticlesȱenabledȱtheirȱcontinȬ uousȱmechanicalȱseparationȱthroughȱaȱtwoȬstageȱprocessȱinvolvingȱaȱgrindingȱstepȱofȱtheȱ stems,ȱandȱthenȱaȱsuctionȱone.ȱOnȱtheȱoneȱhand,ȱtheȱgrindingȱstepȱallowedȱtheȱpithȱtoȱbeȱ separatedȱfromȱtheȱbarkȱparticles.ȱOnȱtheȱotherȱhand,ȱduringȱtheȱsuctionȱstep,ȱtheȱuseȱofȱaȱ vacuumȱcleanerȱresultedȱinȱtheȱisolationȱofȱtheȱlighterȱpithȱparticlesȱfromȱthoseȱofȱbark.ȱ Theȱsuctionȱoperationȱwasȱrepeatedȱthreeȱtimes,ȱfirstȱonȱaȱvibratingȱsieveȱshakerȱandȱthenȱ twiceȱonȱanȱinclinedȱconveyorȱbelt.ȱ Tableȱ1ȱshowsȱtheȱmassȱbalanceȱforȱeachȱofȱtheȱthreeȱsuctionȱstagesȱbasedȱonȱ100ȱkgȱ ofȱcrushedȱamaranthȱstem.ȱForȱitsȱpart,ȱTableȱ2ȱshowsȱtheȱevolutionȱofȱtheȱpithȱpurityȱofȱ theȱlightȱfractions,ȱsuckedȱafterȱtheȱsievingȱstepȱ(P1)ȱandȱafterȱeachȱpassageȱonȱtheȱconȬ veyorȱbeltȱ(P2ȱandȱP3),ȱrespectively.ȱTheȱpithȱpurityȱwasȱmeasuredȱtwiceȱbyȱmanuallyȱ separatingȱtheȱresidualȱbarkȱparticlesȱfromȱtheȱpithȱones.ȱTheȱpithȱpurityȱwasȱmultipliedȱ byȱmoreȱthanȱfourȱthanksȱtoȱtheȱtwoȱconveyorȱbeltȱpurificationȱsteps.ȱItȱwasȱgreaterȱthanȱ 90%ȱ(w/w)ȱafterȱtheȱthreeȱconsecutiveȱsuctionȱsteps,ȱwhichȱwasȱconsideredȱsufficientȱtoȱ produceȱlowȬdensityȱinsulationȱblocks.ȱ ȱ ȱ
Tableȱ1.ȱMassȱbalanceȱofȱtheȱfractionationȱofȱ100ȱkgȱamaranthȱstemȱintoȱbarkȱparticlesȱandȱaȱ
suckedȱfractionȱcontainingȱtheȱpithȱonesȱforȱtheȱthreeȱsuccessiveȱsuctionȱstages,ȱandȱmassȱofȱtheȱ twoȱfractionsȱcollectedȱatȱtheȱendȱofȱtheȱseparationȱprocess.ȱ
Fractionȱ Numberȱ1ȱSuctionȱ Numberȱ2ȱSuctionȱ Numberȱ3ȱSuctionȱ MassȱBalanceȱafterȱSuctionȱNumberȱ3ȱ
Barkȱparticlesȱ(kg)ȱ 80.9ȱ 11.7ȱ 2.6ȱ 95.2ȱ1ȱ Pithȱfractionȱ suckedȱoutȱ(kg)ȱ2ȱ 19.1ȱ 7.4ȱ 4.8ȱ 4.8ȱ3ȱ 1ȱAtȱtheȱendȱofȱtheȱfractionationȱprocess,ȱtheȱbarkȱparticlesȱcollectedȱafterȱeachȱsuctionȱstageȱwereȱ mixedȱtogetherȱtoȱformȱaȱsingleȱfractionȱofȱbarkȱparticles.ȱ2ȱTheȱpithȱfractionsȱsuckedȱoutȱafterȱ stagesȱnumberȱ1ȱandȱ2ȱconstitutedȱtheȱinputȱmaterialsȱforȱtheȱfollowingȱstages,ȱi.e.,ȱstagesȱnumberȱ 2ȱandȱ3,ȱrespectively.ȱ3ȱTheȱpithȱfractionȱfromȱstageȱnumberȱ3ȱwasȱtheȱfractionȱusedȱinȱthisȱstudyȱ forȱtheȱmanufactureȱofȱtheȱinsulatingȱmaterials.ȱ Tableȱ2.ȱPurityȱinȱpithȱparticlesȱofȱtheȱsuckedȱfractionȱafterȱeachȱsuctionȱstage.ȱ
SuctionȱStageȱ SuctionȱNumberȱ1ȱ SuctionȱNumberȱ2ȱ SuctionȱNumberȱ3ȱ PurityȱinȱpithȱparȬ ticlesȱ(%ȱ(w/w))ȱ 22.9ȱ±ȱ0.1ȱ 59.0ȱ±ȱ0.3ȱ 91.0ȱ±ȱ0.2ȱ 3.2.ȱChemicalȱCompositionȱofȱPithȱandȱBark,ȱandȱPhysicalȱCharacterizationȱofȱPithȱParticlesȱ Tableȱ3ȱshowsȱtheȱchemicalȱcompositionȱofȱtheȱpithȱandȱbark,ȱbothȱfromȱtheȱamaranthȱ stem.ȱWhileȱtheȱpithȱcontainsȱaȱmedianȱamountȱofȱlignocellulosicȱfibersȱ(47%),ȱbutȱaȱlotȱofȱ mineralsȱandȱwaterȬsolubleȱcomponentsȱ(19%ȱandȱ31%,ȱrespectively),ȱtheȱbarkȱisȱmuchȱ richerȱinȱlignocellulosicȱfibersȱ(64%),ȱandȱitȱhasȱmuchȱlowerȱmineralȱandȱespeciallyȱwaterȬ solubleȱcontents.ȱThus,ȱtheȱbarkȱisȱindeedȱtheȱwoodyȱpartȱ(orȱligneousȱfraction)ȱofȱtheȱ stem.ȱ Inȱadditionȱtoȱtheseȱpreviousȱcomments,ȱitȱshouldȱbeȱpointedȱoutȱhereȱthatȱtheȱsumȱ ofȱtheȱchemicalȱcompoundsȱquantifiedȱinȱbothȱpithȱandȱbarkȱwasȱgreaterȱthanȱ100%.ȱThisȱ isȱexplainedȱbyȱtheȱfactȱthatȱmineralsȱinȱionicȱformȱasȱwellȱasȱsomeȱhemicelluloses,ȱespeȬ ciallyȱthoseȱwithȱtheȱlowestȱmolecularȱweights,ȱmayȱbeȱsolubleȱinȱwater.ȱTheseȱchemicalȱ constituentsȱcouldȱthenȱbeȱquantifiedȱtwice.ȱ Tableȱ3.ȱChemicalȱcompositionȱofȱpithȱandȱbarkȱfromȱamaranthȱstemȱ(%ȱofȱtheȱdryȱmatter).ȱ
Componentsȱ Pithȱ Barkȱ
Mineralsȱ 18.9ȱ±ȱ0.2ȱ 9.3ȱ±ȱ0.3ȱ Celluloseȱ 37.5ȱ±ȱ0.5ȱ 43.6ȱ±ȱ0.6ȱ Hemicellulosesȱ 12.1ȱ±ȱ0.1ȱ 17.6ȱ±ȱ0.4ȱ Ligninsȱ 9.4ȱ±ȱ0.2ȱ 20.3ȱ±ȱ0.6ȱ WaterȬsolubleȱcomponentsȱ 31.2ȱ±ȱ0.2ȱ 14.8ȱ±ȱ0.9ȱ Dueȱtoȱtheirȱalveolarȱstructure,ȱtheȱpithȱparticlesȱwereȱlight,ȱwithȱanȱestimatedȱbulkȱ densityȱofȱonlyȱ32.2ȱkg/m3ȱ(Tableȱ4).ȱTheirȱparticleȱsizeȱdistributionȱisȱalsoȱpresentedȱinȱ Tableȱ4.ȱConsideredȱasȱdustȱ(i.e.,ȱfines),ȱtheȱparticlesȱsmallerȱthanȱ1ȱmmȱhaveȱnotȱbeenȱkeptȱ forȱtheȱmanufactureȱofȱtheȱlowȬdensityȱinsulationȱblocks.ȱTheȱotherȱthreeȱpithȱfractionsȱ generatedȱafterȱsievingȱ(i.e.,ȱSP,ȱMPȱandȱBP)ȱwereȱalsoȱcharacterizedȱinȱbulkȱdensityȱ(Tableȱ 4),ȱandȱtheȱresultsȱobtainedȱrevealedȱsignificantȱdifferences.ȱ Forȱitsȱpart,ȱTableȱ5ȱproposesȱaȱdistributionȱinȱweightȱandȱanotherȱoneȱinȱvolumeȱforȱ theȱSP,ȱMP,ȱandȱBPȱfractionsȱofȱpithȱparticles,ȱinȱproportionȱtoȱtheȱtotalȱweightȱorȱtoȱtheȱ totalȱ volume,ȱ respectively,ȱ ofȱ theȱ mixtureȱ madeȱ ofȱ theseȱ threeȱ pithȱ fractions.ȱ Asȱ aȱ reȬ minder,ȱtheseȱpithȱfractionsȱwereȱtheȱthreeȱonesȱusedȱtoȱproduceȱtheȱlowȬdensityȱinsulaȬ tionȱblocks,ȱonȱtheirȱownȱorȱmixedȱinȱtheȱrightȱweightȱproportions.ȱTheȱresultsȱinȱTableȱ5ȱ showȱrelativelyȱcloseȱweightȱandȱvolumeȱdistributions,ȱwithȱtheȱintermediateȱpithȱfractionȱ
(MPȱparticles)ȱrepresentingȱforȱbothȱdistributionsȱaȱvalueȱcloseȱtoȱ50%,ȱfollowedȱbyȱtheȱ coarserȱfractionȱ(BPȱparticles)ȱandȱthenȱtheȱfractionȱmadeȱupȱofȱtheȱsmallestȱparticlesȱ(SPȱ particles).ȱ Thermalȱconductivityȱmeasurementsȱwereȱalsoȱperformedȱonȱeachȱbulkȱpithȱsampleȱ usingȱtheȱhotȱwireȱmethod.ȱTheȱthermalȱconductivityȱvaluesȱobtainedȱareȱshownȱinȱTableȱ 4.ȱTheȱresultsȱrevealedȱthatȱtheyȱwereȱofȱtheȱsameȱorderȱofȱmagnitudeȱasȱthoseȱofȱaȱcomȬ mercialȱcelluloseȱwaddingȱusedȱasȱbulkȱinsulationȱforȱwhichȱtheȱthermalȱconductivityȱatȱ 25ȱ°Cȱwasȱbetweenȱ38ȱandȱ44ȱmW/(m.K).ȱ Tableȱ4.ȱParticleȱsizeȱdistributionȱofȱtheȱamaranthȱpithȱparticles,ȱandȱbulkȱdensity,ȱthermalȱconȬ ductivityȱandȱthermalȱresistanceȱinȱbulkȱatȱ25ȱ°Cȱofȱallȱpithȱparticlesȱ(mix)ȱandȱtheȱSP,ȱMP,ȱandȱBPȱ fractionsȱgeneratedȱafterȱsievingȱ1.ȱ
PithȱFractionȱ Distributionȱ(%ȱ(w/w))ȱ BulkȱDensityȱ (kg/m3)ȱ Thermalȱ Conductivityȱ (mW/(m.K))ȱ ThermalȱReȬ sistanceȱ6ȱ (m2ȉK/W)ȱ Mixȱ2ȱ 100.0ȱ 32.2ȱ±ȱ1.0ȱbȱ 37.0ȱ±ȱ0.0ȱbȱ 1.081ȱ±ȱ0.000ȱaȱ Finesȱ(<1ȱmm)ȱ 15.0ȱ n.d.ȱ n.d.ȱ n.d.ȱ SPȱ3ȱ 17.8ȱ 29.6ȱ±ȱ0.5ȱcȱ 37.0ȱ±ȱ0.0ȱbȱ 1.081ȱ±ȱ0.000ȱaȱ MPȱ4ȱ 41.7ȱ 32.0ȱ±ȱ0.2ȱbȱ 39.5ȱ±ȱ0.7ȱaȱ 1.013ȱ±ȱ0.018ȱbȱ BPȱ5ȱ 25.5ȱ 39.4ȱ±ȱ0.7ȱaȱ 41.0ȱ±ȱ1.4ȱaȱ 0.976ȱ±ȱ0.034ȱbȱ 1ȱMeansȱinȱtheȱsameȱcolumnȱwithȱtheȱsameȱsuperscriptȱletterȱ(a–c)ȱareȱnotȱsignificantlyȱdifferentȱatȱ
pȱ<ȱ0.05.ȱ2ȱAllȱpithȱfractions.ȱ3ȱSmallȱparticlesȱ(1–2ȱmm).ȱ4ȱMediumȱparticlesȱ(2–4ȱmm).ȱ5ȱBigȱparticlesȱ
(>4ȱmm).ȱ6ȱThermalȱresistanceȱforȱaȱ4ȱcmȱthickȱbedȱofȱpithȱparticles.ȱn.d.,ȱnonȬdetermined.ȱ Tableȱ5.ȱDistributionȱinȱweightȱ(%ȱ(w/w))ȱandȱdistributionȱinȱvolumeȱ(%ȱ(v/v))ȱforȱtheȱSP,ȱMP,ȱandȱ
BPȱfractionsȱofȱpithȱparticles,ȱcalculatedȱinȱproportionȱtoȱtheȱtotalȱweightȱorȱtoȱtheȱtotalȱvolume,ȱ respectively,ȱofȱtheȱmixtureȱmadeȱofȱtheseȱthreeȱpithȱfractions.ȱ
PithȱFractionȱ DistributionȱinȱWeightȱ(%ȱ(w/w))ȱ DistributionȱinȱVolumeȱ(%ȱ(v/v))ȱ
SPȱ 20.9ȱ 23.6ȱ MPȱ 49.1ȱ 51.1ȱ BPȱ 30.0ȱ 25.3ȱ 3.3.ȱLowȬDensityȱInsulationȱBlocksȱfromȱPithȱ LowȬdensityȱinsulationȱblocksȱwereȱproducedȱfromȱpithȱparticlesȱthroughȱcompresȬ sionȱmoldingȱusingȱstandardȱconditionsȱalreadyȱimplementedȱinȱaȱpreviousȱstudyȱ[20],ȱ i.e.,ȱ9ȱkPaȱforȱtheȱappliedȱpressure,ȱ5ȱminȱforȱtheȱmoldingȱtime,ȱandȱ25ȱ°Cȱforȱtheȱmoldȱ temperature.ȱOnceȱmolded,ȱallȱblocksȱwereȱplacedȱinȱaȱventilatedȱovenȱtoȱevaporateȱtheȱ waterȱinitiallyȱaddedȱtoȱdissolveȱtheȱstarchyȱbinder.ȱTheȱadhesionȱwasȱachievedȱafterȱcomȬ pleteȱevaporation,ȱandȱallȱtheȱresultingȱblocksȱwereȱcohesiveȱenoughȱtoȱbeȱmachined.ȱ Blocksȱhavingȱaȱ10%ȱ(w/w)ȱbinderȱcontentȱwereȱproducedȱfromȱtheȱthreeȱsievedȱfracȬ tionsȱandȱfromȱtheȱmixȱmadeȱofȱallȱpithȱparticles.ȱInȱadditionȱtoȱtheseȱfourȱinsulatingȱmaȬ terials,ȱthreeȱotherȱlowȬdensityȱblocksȱmadeȱfromȱtheȱmediumȱpithȱparticlesȱ(MP)ȱwereȱ alsoȱmoldedȱusingȱhigherȱbinderȱcontents,ȱi.e.,ȱ15%,ȱ20%,ȱandȱ25%ȱ(w/w),ȱrespectively.ȱAllȱ theȱcharacteristicsȱofȱtheseȱsevenȱlowȬdensityȱinsulationȱblocksȱareȱpresentedȱinȱTableȱ6.ȱ Theseȱincludeȱdensity,ȱflexuralȱproperties,ȱthermalȱconductivity,ȱandȱthermalȱresistance.ȱ ȱ ȱ
Tableȱ6.ȱCharacteristicsȱofȱtheȱlowȬdensityȱinsulationȱblocksȱproducedȱfromȱpithȱparticlesȱthroughȱ
compressionȱmoldingȱ(9ȱkPa,ȱ5ȱmin,ȱ25ȱ°C)ȱ1.ȱ
PithȱParȬ
ticlesȱ ContentȱBinderȱ (%)ȱ Densityȱ (kg/m3)ȱ Flexuralȱ Strengthȱ (kPa)ȱ Elasticȱ Modulusȱ (kPa)ȱ ThermalȱConȬ ductivityȱ (mW/(m.K))ȱ ThermalȱReȬ sistanceȱ2ȱ (m2ȉK/W)ȱ Mixȱ 10ȱ 131.4ȱ±ȱ2.4ȱaȱ 59.3ȱ±ȱ4.5ȱbȱ 510ȱ±ȱ29ȱcȱ 60.3ȱ±ȱ1.5ȱaȱ 0.664ȱ±ȱ0.017ȱdȱ SPȱ 10ȱ 115.8ȱ±ȱ2.2ȱcȱ 15.8ȱ±ȱ1.9ȱfȱ 169ȱ±ȱ21ȱgȱ 57.5ȱ±ȱ0.6ȱbȱ 0.696ȱ±ȱ0.007ȱcȱ MPȱ 10ȱ 102.4ȱ±ȱ5.9ȱeȱ 23.0ȱ±ȱ3.4ȱeȱ 299ȱ±ȱ44ȱfȱ 54.8ȱ±ȱ1.5ȱdȱ 0.731ȱ±ȱ0.020ȱaȱ MPȱ 15ȱ 108.1ȱ±ȱ1.9ȱdȱ 29.5ȱ±ȱ4.5ȱdȱ 343ȱ±ȱ40ȱeȱ 54.8ȱ±ȱ0.5ȱdȱ 0.731ȱ±ȱ0.007ȱaȱ MPȱ 20ȱ 128.9ȱ±ȱ3.9ȱaȱ 45.3ȱ±ȱ3.1ȱcȱ 647ȱ±ȱ28ȱaȱ 56.5ȱ±ȱ1.3ȱbcȱ 0.708ȱ±ȱ0.016ȱbcȱ MPȱ 25ȱ 130.9ȱ±ȱ1.5ȱaȱ 44.7ȱ±ȱ5.9ȱcȱ 582ȱ±ȱ15ȱbȱ 60.3ȱ±ȱ0.5ȱaȱ 0.664ȱ±ȱ0.006ȱdȱ BPȱ 10ȱ 120.7ȱ±ȱ1.7ȱbȱ 84.5ȱ±ȱ8.2ȱaȱ 468ȱ±ȱ17ȱdȱ 56.0ȱ±ȱ1.4ȱcȱ 0.715ȱ±ȱ0.018ȱbcȱ 1ȱMeansȱinȱtheȱsameȱcolumnȱwithȱtheȱsameȱsuperscriptȱletterȱ(a–g)ȱareȱnotȱsignificantlyȱdifferentȱatȱ pȱ<ȱ0.05.ȱ2ȱThermalȱresistanceȱforȱaȱ4ȬcmȱthickȱlowȬdensityȱinsulationȱblock.ȱ 3.4.ȱTwinȬScrewȱExtrusionȬRefiningȱofȱBarkȱ DuringȱtheȱtwinȬscrewȱextrusionȬrefiningȱpreȬtreatment,ȱtheȱamaranthȱbarkȱunderȬ goesȱdefibringȱ(i.e.,ȱdestructuring)ȱdueȱtoȱtheȱmechanicalȱstressesȱandȱtemperatureȱinȱtheȱ extruder.ȱThreeȱdifferentȱinletȱflowȱratesȱofȱwaterȱwereȱtestedȱinȱthisȱstudy,ȱi.e.,ȱ10ȱkg/h,ȱ 20ȱkg/h,ȱandȱ40ȱkg/h,ȱrespectively,ȱthusȱcorrespondingȱtoȱliquid/solidȱratiosȱvaryingȱfromȱ 1.0ȱtoȱ4.0.ȱTheȱresultsȱofȱtheȱamaranthȱbarkȱrefiningȱtreatmentȱinȱtwinȬscrewȱextruderȱareȱ shownȱinȱTableȱ7.ȱAsȱaȱfirstȱresultȱofȱthisȱtreatment,ȱtheȱthreeȱextrudatesȱobtainedȱhadȱtheȱ formȱofȱfluffyȱmaterials,ȱwithȱsignificantlyȱreducedȱapparentȱandȱtappedȱdensitiesȱcomȬ paredȱtoȱthoseȱofȱtheȱsimplyȱgroundȱbarkȱparticlesȱ(i.e.,ȱ147.7ȱ±ȱ1.3ȱkg/m3ȱandȱ148.5ȱ±ȱ4.2ȱ kg/m3,ȱrespectively).ȱ Whenȱtheȱquantityȱofȱwaterȱincreased,ȱthisȱfacilitatedȱtheȱtransportȱofȱtheȱsolidȱmateȬ rialȱwhoseȱresidenceȱtimeȱinȱtheȱtwinȬscrewȱextruderȱdecreased.ȱThus,ȱtheȱextrudateȱobȬ tainedȱhasȱundergoneȱlessȱshearing,ȱandȱitsȱfiberȱlengthȱwasȱthereforeȱbetterȱpreserved.ȱ Thisȱwasȱpreviouslyȱevidencedȱinȱtheȱcaseȱofȱriceȱstrawȱ[27],ȱandȱtheȱsameȱwasȱtrueȱinȱthisȱ study.ȱNonetheless,ȱtheȱvaluesȱobtainedȱforȱbothȱapparentȱandȱtappedȱdensitiesȱofȱtheȱ extrusionȬrefinedȱfibersȱremainedȱinȱtheȱsameȱorderȱofȱmagnitudeȱforȱtheȱthreeȱtestedȱliqȬ uid/solidȱratios.ȱ LookingȱatȱtheȱcontentȱinȱwaterȬsolublesȱremainingȱinȱtheȱextrudate,ȱtheȱvaluesȱobȬ tainedȱwereȱallȱthreeȱsignificantlyȱdifferent.ȱWithȱaȱhigherȱliquid/solidȱratio,ȱtheȱflowȱrateȱ ofȱtheȱfiltrateȱcollectedȱatȱtheȱpenultimateȱmoduleȱincreased,ȱalsoȱbringingȱwithȱitȱmoreȱ waterȬsolubleȱcomponentsȱinitiallyȱpresentȱinȱtheȱbark.ȱTheȱextrudateȱobtainedȱfromȱtheȱ higherȱliquid/solidȱratioȱ(i.e.,ȱ4.0)ȱwasȱthereforeȱmoreȱdepletedȱinȱwaterȬsolubleȱcompoȬ nents.ȱFromȱtheȱextrusionȬrefiningȱdataȱinȱTableȱ7,ȱtheȱflowȱrateȱofȱwaterȬsolubleȱcomȬ poundsȱextractedȱfromȱtheȱbarkȱandȱcontainedȱinȱtheȱfiltrateȱcouldȱbeȱcalculated.ȱTheseȱ extractedȱwaterȬsolubleȱcompoundsȱwereȱthenȱexpressedȱasȱaȱpercentageȱofȱtheȱincomingȱ waterȬsolublesȱinȱbark,ȱforȱtheȱthreeȱliquid/solidȱratiosȱtestedȱ(i.e.,ȱ1.0,ȱ2.0ȱandȱ4.0).ȱTheȱ resultsȱwereȱ11.7%,ȱ32.9%,ȱandȱ54.2%,ȱrespectively.ȱItȱwasȱthereforeȱwellȱobservedȱthatȱtheȱ extractionȱyieldȱinȱwaterȬsolubleȱcomponentsȱincreasedȱwithȱtheȱamountȱofȱwaterȱadded.ȱ Toȱconclude,ȱalthoughȱthreeȱliquid/solidȱratiosȱhaveȱbeenȱtestedȱinȱtheȱtwinȬscrewȱ extruder,ȱonlyȱtheȱextrudateȱproducedȱusingȱtheȱliquid/solidȱratioȱofȱ4.0ȱhasȱbeenȱusedȱinȱ theȱproductionȱofȱhardboardsȱthroughȱhotȱpressing.ȱIndeed,ȱdueȱtoȱtheȱhigherȱamountȱofȱ waterȱaddedȱduringȱtheȱthermoȬmechanicalȱdefibrationȱofȱtheȱamaranthȱbarkȱparticlesȱinȱ theȱtwinȬscrewȱextruder,ȱtheȱlengthȱofȱtheȱfiberȱbundlesȱwasȱbetterȱpreserved.ȱ ȱ ȱ
Tableȱ7.ȱInletȱflowȱrateȱofȱwater,ȱliquid/solidȱratio,ȱoutletȱflowȱrateȱofȱtheȱfiltrate,ȱcontentȱofȱwaterȬ solubleȱcomponentsȱinȱtheȱfiltrate,ȱextractionȱyieldȱinȱwaterȬsolubleȱcomponents,ȱandȱapparentȱandȱ tappedȱdensitiesȱofȱtheȱextrudateȱafterȱdryingȱforȱtheȱthreeȱtwinȬscrewȱextrusionȬrefiningȱexperiȬ mentsȱappliedȱtoȱtheȱamaranthȱbarkȱparticlesȱ(10ȱkg/hȱforȱtheirȱinletȱflowȱrate)ȱ1.ȱ ExperimentȱNumberȱ 1ȱ 2ȱ 3ȱ Inletȱflowȱrateȱofȱwaterȱ(kg/h)ȱ 10ȱ 20ȱ 40ȱ Liquid/solidȱratioȱ 1ȱ 2ȱ 4ȱ Outletȱflowȱrateȱofȱtheȱextrudateȱ(kg/h)ȱ 13.2ȱ 13.9ȱ 13.7ȱ Moistureȱinȱtheȱextrudateȱ(%)ȱ 28.6ȱ±ȱ0.6ȱcȱ 37.6ȱ±ȱ0.3ȱbȱ 38.2ȱ±ȱ0.1ȱaȱ WaterȬsolublesȱinȱtheȱextrudateȱ (%ȱofȱtheȱdryȱmatter)ȱ 13.1ȱ±ȱ0.1ȱaȱ 10.8ȱ±ȱ0.6ȱbȱ 7.5ȱ±ȱ0.1cȱ Outletȱflowȱrateȱofȱtheȱfiltrateȱ(kg/h)ȱ 0.1ȱ 12.7ȱ 29.7ȱ Dryȱmatterȱinȱtheȱfiltrateȱ(%)ȱ 1.1ȱ±ȱ0.0ȱcȱ 5.9ȱ±ȱ0.1ȱaȱ 3.2ȱ±ȱ0.3ȱbȱ Waterȱevaporatedȱ(%)ȱ2ȱ 67.0ȱ 17.0ȱ 16.7ȱ ExtractionȱyieldȱinȱwaterȬsolublesȱ(%)ȱ 11.7ȱ 32.9ȱ 54.2ȱ Apparentȱdensityȱofȱextrudateȱ(kg/m3)ȱ 63.3ȱ±ȱ1.6ȱbȱ 69.9ȱ±ȱ2.0ȱaȱ 63.5ȱ±ȱ0.6ȱbȱ Tappedȱdensityȱofȱextrudateȱ(kg/m3)ȱ 70.6ȱ±ȱ1.3ȱbȱ 74.5ȱ±ȱ1.9ȱaȱ 71.7ȱ±ȱ1.3ȱbȱ 1ȱMeansȱinȱtheȱsameȱlineȱwithȱtheȱsameȱsuperscriptȱletterȱ(a–c)ȱareȱnotȱsignificantlyȱdifferentȱatȱpȱ<ȱ 0.05.ȱ2ȱTheȱdifferenceȱbetweenȱtheȱcumulativeȱinletȱflowȱrateȱ(barkȱparticlesȱplusȱwater)ȱandȱtheȱ cumulativeȱoutletȱoneȱ(extrudateȱplusȱfiltrate)ȱcanȱbeȱexplainedȱbyȱtheȱlossȱofȱpartȱofȱtheȱaddedȱ waterȱbyȱevaporation,ȱatȱtheȱlevelȱofȱtheȱfiltrationȱmoduleȱandȱatȱtheȱoutletȱofȱtheȱbarrel.ȱ 3.5.ȱHardboardsȱfromȱBarkȱ Hardboardsȱwereȱproducedȱthroughȱhotȱpressingȱfromȱgroundȱ(GB)ȱorȱextrusionȬ refinedȱ(ERB)ȱamaranthȱbarkȱparticles.ȱTheȱmoldingȱconditionsȱusedȱwereȱasȱfollows:ȱ200ȱ °Cȱforȱtheȱmoldȱtemperature,ȱ20ȱMPaȱforȱtheȱappliedȱpressure,ȱandȱ5ȱminȱforȱtheȱmoldingȱ time.ȱInȱparticular,ȱtheȱ200ȱ°CȱmoldȱtemperatureȱwasȱusedȱasȱoptimalȱtemperatureȱtoȱenȬ sureȱanȱefficientȱmobilizationȱofȱtheȱinternalȱbindersȱinsideȱbark,ȱi.e.,ȱfreeȱsugars,ȱhemicelȬ lulosesȱandȱligninsȱ[13,30].ȱThanksȱtoȱtheȱadhesiveȱabilityȱofȱtheseȱchemicals,ȱcohesiveȱ hardboardsȱwereȱobtainedȱwithoutȱexogenousȱbinder.ȱ Anȱimprovementȱinȱtheȱmoldingȱprocessȱconsistedȱinȱaddingȱtoȱtheȱbarkȱparticlesȱanȱ amaranthȬbasedȱbinderȱ(AB).ȱThisȱexogenousȱbinderȱhadȱtheȱformȱofȱgrindedȱandȱdeoiledȱ amaranthȱseeds,ȱandȱitȱwasȱtheȱstarchȱandȱtoȱaȱlesserȱextent,ȱproteinsȱcontainedȱinȱABȱthatȱ haveȱgivenȱitȱitsȱaptitudeȱforȱadhesion.ȱ Allȱtheȱcharacteristicsȱofȱtheȱsixȱhardboardsȱproducedȱ(HB1ȱtoȱHB6)ȱareȱpresentedȱinȱ Tableȱ8.ȱTheseȱincludeȱdensity,ȱflexuralȱpropertiesȱandȱwaterȱresistance.ȱInȱaddition,ȱtheseȱ characteristicsȱwereȱalsoȱcomparedȱinȱTableȱ8ȱwithȱthoseȱofȱtwoȱcommercialȱwoodȬbasedȱ materials,ȱi.e.,ȱMDFȱandȱchipboardȱ(CH).ȱ Tableȱ8.ȱDensity,ȱflexuralȱproperties,ȱandȱwaterȱresistanceȱofȱhardboardsȱ(HB)ȱproducedȱfromȱ groundȱandȱextrusionȬrefinedȱbarksȱ(GBȱandȱERB,ȱrespectively)ȱthroughȱhotȱpressingȱ(200ȱ°Cȱmoldȱ temperature,ȱ20ȱMPaȱappliedȱpressure,ȱandȱ5ȱminȱmoldingȱtime)ȱ1,ȱandȱcomparisonȱwithȱtheȱpropȬ ertiesȱofȱtwoȱcommercialȱwoodȬbasedȱmaterialsȱ(i.e.,ȱMDFȱandȱchipboardȱ(CH)).ȱ Hardboardȱ
Numberȱ FormȱBarkȱ ABȱ(%)ȱ Densityȱ(kg/m3)ȱ
Flexuralȱ Strengthȱ (MPa)ȱ Elasticȱ Modulusȱ (GPa)ȱ Thicknessȱ Swellingȱ (%)ȱ WaterȱAbȬ sorptionȱ(%)ȱ
HB1ȱ GBȱ 0ȱ 1234ȱ±ȱ28ȱaȱ 13.2ȱ±ȱ2.4ȱdȱ 2.1ȱ±ȱ0.4ȱdȱ 143ȱ±ȱ11ȱaȱ 124ȱ±ȱ8ȱaȱ
HB2ȱ GBȱ 20ȱ 1248ȱ±ȱ34ȱaȱ 18.8ȱ±ȱ1.7ȱcȱ 2.7ȱ±ȱ0.4ȱbcȱ 136ȱ±ȱ10ȱaȱ 124ȱ±ȱ7ȱaȱ
HB3ȱ GBȱ 40ȱ 1242ȱ±ȱ31ȱaȱ 18.5ȱ±ȱ2.3ȱcȱ 2.1ȱ±ȱ0.4ȱdȱ 132ȱ±ȱ20ȱaȱ 132ȱ±ȱ11ȱaȱ
HB4ȱ ERBȱ 0ȱ 1244ȱ±ȱ35ȱaȱ 19.8ȱ±ȱ1.6ȱcȱ 2.4ȱ±ȱ0.2ȱcdȱ 71ȱ±ȱ4ȱbȱ 56ȱ±ȱ2ȱbȱ
HB5ȱ ERBȱ 10ȱ 1279ȱ±ȱ47ȱaȱ 32.4ȱ±ȱ2.6ȱbȱ 2.9ȱ±ȱ0.3ȱbȱ 77ȱ±ȱ4ȱbȱ 60ȱ±ȱ1ȱbȱ
MDFȱ[29]ȱ –ȱ –ȱ 589ȱ±ȱ4ȱ 20.7ȱ±ȱ2.1ȱ 1.5ȱ±ȱ0.1ȱ 20ȱ±ȱ1ȱ 51ȱ±ȱ5ȱ CHȱ[29]ȱ –ȱ –ȱ 710ȱ±ȱ7ȱ 10.2ȱ±ȱ1.5ȱ 1.4ȱ±ȱ0.1ȱ 25ȱ±ȱ1ȱ 58ȱ±ȱ3ȱ 1ȱMeansȱinȱtheȱsameȱcolumnȱwithȱtheȱsameȱsuperscriptȱletterȱ(a–d)ȱareȱnotȱsignificantlyȱdifferentȱatȱ pȱ<ȱ0.05.ȱ 4.ȱDiscussionȱ 4.1.ȱPhysicalȱCharacterizationȱofȱPithȱParticlesȱ Onceȱisolated,ȱpithȱparticlesȱwereȱsieved,ȱresultingȱinȱtheȱnextȱparticleȱsizeȱdistribuȬ tion:ȱ18%ȱforȱsmallȱparticlesȱ(SP)ȱ(fromȱ1ȱtoȱ2ȱmm),ȱ42%ȱforȱmediumȱparticlesȱ(MP)ȱ(fromȱ 2ȱtoȱ4ȱmm),ȱandȱ25%ȱforȱbigȱparticlesȱ(BP)ȱ(>4ȱmm)ȱ(Tableȱ4).ȱFinesȱ(<1ȱmm)ȱrepresentedȱ 15%ȱ(w/w)ȱbutȱtheyȱwereȱnotȱusedȱinȱtheȱpresentȱstudy.ȱAllȱpithȱparticlesȱrevealedȱanȱalȬ veolarȱstructure,ȱandȱthisȱresultedȱinȱlowȱbulkȱdensities,ȱe.g.,ȱonlyȱ30ȱkg/m3ȱforȱtheȱsmallerȱ particleȱsizeȱ(SP).ȱ DespiteȱtheȱfactȱthatȱsmallȱpithȱparticlesȱhadȱfewerȱinterȬparticleȱvoids,ȱdueȱtoȱaȱbetterȱ arrangementȱ(i.e.,ȱstacking)ȱofȱtheȱparticlesȱinȱrelationȱtoȱeachȱother,ȱitȱwasȱtheseȱsmallerȱ particlesȱ (SP)ȱ thatȱ revealedȱ theȱ lowestȱ bulkȱ densityȱ valueȱ (Tableȱ 4).ȱ Thisȱ couldȱ beȱ exȬ plainedȱbyȱtheȱfactȱthatȱtheȱlargerȱonesȱ(BP)ȱand,ȱtoȱaȱlesserȱextent,ȱtheȱmediumȱonesȱ(MP)ȱ stillȱcontainedȱsomeȱlongȱfibersȱfromȱtheȱbarkȱfractionȱafterȱtheȱsievingȱstepȱofȱtheȱpithȱ particles.ȱForȱtheȱBPȱfraction,ȱtheȱdecreaseȱinȱbulkȱdensityȱthatȱshouldȱhaveȱbeenȱobservedȱ dueȱtoȱmoreȱinterȬparticleȱvoidsȱwasȱthereforeȱlargelyȱcompensatedȱbyȱtheȱpresenceȱofȱ theseȱdenserȱbarkȱfibers,ȱwhichȱcontributedȱtoȱincreaseȱtheȱdensityȱofȱtheȱBPȱpithȱfraction.ȱ Conversely,ȱtheȱsmallerȱparticlesȱwereȱtooȱsmallȱtoȱcontainȱresidualȱbarkȱfibersȱafterȱsievȬ ing.ȱ Asȱseenȱpreviouslyȱwithȱbulkȱdensity,ȱtheȱthermalȱconductivityȱatȱ25ȱ°Cȱofȱtheȱbulkȱ pithȱthereforeȱalsoȱincreasedȱwithȱtheȱparticleȱsize,ȱwithȱtheȱresidualȱbarkȱparticlesȱpresentȱ inȱtheȱBPȱfractionȱbeingȱdenserȱandȱaboveȱallȱmoreȱconductiveȱthanȱtheȱpithȱparticlesȱ(TaȬ bleȱ4).ȱ Theȱamaranthȱpithȱthusȱappearsȱasȱaȱpromisingȱbulkȱrawȱmaterialȱforȱtheȱthermalȱ insulationȱofȱbuildings,ȱasȱpreviouslyȱobservedȱforȱsunflowerȱpithȱ[20,22].ȱThisȱmakesȱitȱ possibleȱtoȱpositionȱtheȱpithȱorȱoneȱofȱitsȱsievedȱfractions,ȱespeciallyȱtheȱsmallerȱoneȱ(i.e.,ȱ theȱSPȱfraction)ȱforȱwhichȱtheȱthermalȱconductivityȱandȱthermalȱresistanceȱareȱsignificantlyȱ differentȱfromȱtheȱtwoȱothers,ȱinȱtheȱbuildingȱinsulationȱmarket.ȱForȱexample,ȱitȱcouldȱbeȱ blownȱintoȱtheȱatticȱofȱhousesȱorȱusedȱasȱaȱfillingȱforȱtheȱinteriorȱpartitions.ȱHowever,ȱitȱ remainsȱtoȱbeȱseenȱhowȱtheȱpithȱparticlesȱwillȱbehaveȱoverȱtime.ȱIfȱtheȱpithȱisȱcompacted,ȱ itȱcouldȱbecomeȱdenserȱoverȱtheȱyearsȱandȱitsȱthermalȱconductivityȱwillȱincrease.ȱInȱtheȱ sameȱway,ȱforȱlongȬtermȱuse,ȱitȱwillȱalsoȱbeȱnecessaryȱtoȱjudgeȱtheȱpith’sȱbehaviourȱtoȱfireȱ andȱitsȱabilityȱtoȱresistȱfungi.ȱ Forȱfutureȱwork,ȱtheȱcoatingȱofȱtheȱpithȱparticlesȱbyȱaȱhydrophobingȱagentȱ(e.g.,ȱhyȬ drogenatedȱoils,ȱvegetableȱoilȱderivatives,ȱetc.)ȱandȱaȱfireproofingȱproductȱwouldȱimproveȱ theirȱwaterȱandȱfireȱresistances,ȱrespectively.ȱInȱtheȱsameȱway,ȱglycerolȱestersȱcouldȱbeȱaȱ bioȬbasedȱ solutionȱ favourableȱ toȱ renderȱ theȱ pithȱ particlesȱ moreȱ resistantȱ toȱ microbialȱ growthȱwhenȱcoatedȱatȱtheirȱsurfaceȱ[22].ȱ 4.2.ȱLowȬDensityȱInsulationȱBlocksȱfromȱPithȱ CohesiveȱlowȬdensityȱinsulationȱblocksȱwereȱproducedȱthroughȱcompressionȱmoldȬ ingȱthanksȱtoȱtheȱadditionȱofȱtheȱstarchyȱbinder.ȱAȱprogressiveȱincreaseȱinȱtheȱdensityȱofȱ theȱblocksȱmadeȱofȱMPȱparticlesȱwasȱobservedȱwithȱtheȱbinderȱcontentȱ(Tableȱ6).ȱInȱparalȬ lel,ȱtheȱbendingȱperformanceȱofȱtheȱblocksȱimprovedȱsinceȱaȱlargerȱbinderȱquantityȱalȬ lowedȱtheȱpithȱparticlesȱtoȱbeȱbetterȱimpregnatedȱwithȱtheȱstarchyȱglue.ȱLogically,ȱtheȱ overallȱcohesionȱofȱtheȱblockȱwasȱthusȱprogressivelyȱimproved.ȱHowever,ȱthisȱdensificaȬ tionȱresultedȱinȱaȱlowerȱinternalȱporosityȱinsideȱtheȱblocks,ȱwhichȱthenȱhadȱaȱhigherȱandȱ higherȱthermalȱconductivityȱandȱthereforeȱaȱlowerȱandȱlowerȱthermalȱresistance.ȱ
AsȱtheȱMPȬbasedȱblocksȱremainedȱmachinableȱevenȱwithȱonlyȱ10%ȱ(w/w)ȱbinder,ȱthisȱ contentȱwasȱretainedȱforȱtheȱotherȱpithȱfractionsȱ(Figureȱ3)ȱsinceȱitȱwasȱexpectedȱtoȱgiveȱtoȱ theȱinsulatingȱblocksȱaȱbetterȱthermalȱinsulationȱperformance.ȱForȱsuchȱbinderȱcontentȱ added,ȱtheȱdensestȱandȱmostȱconductiveȱinsulatingȱblockȱwasȱtheȱoneȱmadeȱfromȱtheȱmixȱ ofȱpithȱparticles,ȱwhichȱcouldȱbeȱexplainedȱbyȱtheȱfactȱthatȱthisȱfractionȱstillȱcontainedȱ aboutȱ9%ȱ(w/w)ȱofȱbarkȱimpuritiesȱ(Tableȱ2).ȱForȱtheȱblocksȱmadeȱfromȱtheȱsievedȱfractions,ȱ theȱvaluesȱobtainedȱforȱtheȱdensityȱandȱthermalȱconductivityȱwereȱsignificantlyȱdifferent.ȱ AȱsignificantȱreductionȱinȱtheȱdensityȱandȱthermalȱconductivityȱwasȱobservedȱwithȱinȬ creasingȱparticleȱsizeȱwhenȱcomparingȱtheȱmaterialsȱmadeȱfromȱtheȱSPȱandȱMPȱfractions,ȱ respectively.ȱTheȱmostȱlikelyȱreasonȱforȱsuchȱaȱresultȱwasȱtheȱpresenceȱofȱmoreȱinterȬparȬ ticleȱvoidsȱinȱtheȱcaseȱofȱtheȱblockȱmadeȱfromȱtheȱmediumȱsizeȱparticles.ȱConversely,ȱandȱ asȱitȱwasȱalreadyȱobservedȱforȱtheȱbulkȱpithȱparticles,ȱaȱsignificantȱincreaseȱinȱtheȱdensityȱ and,ȱtoȱaȱlesserȱextent,ȱinȱthermalȱconductivityȱwasȱobtainedȱforȱtheȱblockȱmadeȱfromȱtheȱ biggerȱparticles.ȱThisȱwasȱevidentlyȱdueȱtoȱtheȱsubstantialȱamountȱofȱdenseȱbarkȱimpuriȬ tiesȱremainingȱinsideȱtheȱBPȱfractionȱafterȱsieving.ȱ ȱ Figureȱ3.ȱ(a)ȱPhotographȱofȱtheȱlowȬdensityȱinsulationȱblockȱmadeȱfromȱtheȱMPȱsievedȱfractionȱofȱ pithȱparticles;ȱ(b)ȱPhotographȱofȱtheȱlowȬdensityȱinsulationȱblockȱmadeȱfromȱtheȱBPȱsievedȱfracȬ tionȱofȱpithȱparticles;ȱ(c)ȱPhotographȱofȱtheȱlowȬdensityȱinsulationȱblockȱmadeȱfromȱtheȱSPȱsievedȱ fractionȱofȱpithȱparticles;ȱ(d)ȱPhotographȱofȱtheȱlowȬdensityȱinsulationȱblockȱmadeȱfromȱtheȱmixȱofȱ theȱSP,ȱMP,ȱandȱBPȱpithȱparticles.ȱAllȱtheȱinsulationȱblocksȱhaveȱaȱ10%ȱ(w/w)ȱstarchyȱbinderȱconȬ tent.ȱ Forȱthisȱ10%ȱ(w/w)ȱbinderȱcontent,ȱtheȱflexuralȱperformanceȱofȱtheȱinsulatingȱblocksȱ madeȱfromȱtheȱsievedȱfractionsȱrevealedȱsignificantȱdifferences,ȱandȱitȱincreasedȱwithȱtheȱ sizeȱofȱtheȱpithȱparticlesȱused.ȱIndeed,ȱtheȱlargerȱtheȱparticlesȱwere,ȱtheȱsmallerȱwasȱtheirȱ cumulativeȱsurfaceȱarea.ȱThus,ȱwithȱtheȱpithȱparticlesȱfromȱtheȱBPȱfraction,ȱmoreȱstarchȬ basedȱadhesiveȱwasȱpresentȱonȱtheirȱsurface,ȱwhichȱresultedȱinȱaȱbetterȱbondingȱofȱtheȱ particlesȱtoȱeachȱotherȱandȱthereforeȱbetterȱmechanicalȱperformanceȱinȱbendingȱofȱtheȱcorȬ respondingȱblock.ȱTheȱflexuralȱstrengthȱofȱtheȱblockȱoriginatingȱfromȱtheȱmixȱofȱallȱtheȱ pithȱparticlesȱwasȱalsoȱsignificantlyȱdifferentȱandȱlogicallyȱmedian,ȱi.e.,ȱsituatedȱbetweenȱ thoseȱofȱtheȱMPȱandȱBPȬbasedȱblocks.ȱ
Forȱtheȱoptimalȱ10%ȱ(w/w)ȱbinderȱcontent,ȱtheȱbestȱcompromiseȱbetweenȱflexuralȱandȱ heatȱinsulationȱpropertiesȱwasȱobtainedȱusingȱbigȱparticlesȱ(>4ȱmm)ȱ(Tableȱ6).ȱLightȱandȱ insulating,ȱ thisȱ optimalȱ BPȬbasedȱ blockȱ (Figuresȱ 2bȱ andȱ 3b)ȱ especiallyȱ preservedȱ veryȱ goodȱmachinability,ȱandȱitȱcouldȱthusȱbeȱpositionedȱatȱallȱlevelsȱofȱtheȱbuildings,ȱe.g.,ȱ walls,ȱfloors,ȱroofs,ȱetc.ȱHowever,ȱitsȱthermalȱconductivityȱatȱ25ȱ°Cȱ(56ȱmW/(m.K))ȱwasȱ higherȱtoȱthoseȱofȱsunflowerȬbasedȱinsulationȱpanelsȱ[20,22]ȱandȱespeciallyȱcommercialȱ expandedȱpolystyreneȱ[20]:ȱ38–41ȱmW/(m.K)ȱandȱonlyȱ32ȱmW/(m.K),ȱrespectively.ȱTheseȱ resultsȱmadeȱitȱaȱslightlyȱlessȱefficientȱinsulatorȱthanȱtheȱtwoȱotherȱmaterialsȱmentionedȱ above.ȱIndeed,ȱbasedȱonȱtheȱthermalȱresistanceȱofȱtheseȱthreeȱtypesȱofȱinsulatingȱmaterials,ȱ definedȱasȱtheȱratioȱofȱtheȱmaterialȱthicknessȱtoȱitsȱthermalȱconductivity,ȱtheȱthicknessȱofȱ theȱamaranthȬbasedȱoptimalȱblockȱshouldȱbeȱincreasedȱbyȱ37–47%ȱorȱbyȱupȱtoȱ75%,ȱreȬ spectively,ȱtoȱreachȱtheȱsameȱthermalȱinsulatingȱcapacityȱasȱsunflowerȬbasedȱlowȬdensityȱ blocksȱorȱpolystyrene.ȱ However,ȱtheseȱresultsȱareȱonlyȱpreliminary,ȱandȱsomeȱimprovementsȱareȱstillȱpossiȬ ble.ȱOnȱtheȱoneȱhand,ȱaȱbetterȱpurificationȱofȱtheȱBPȱpithȱparticles,ȱwhichȱwouldȱthenȱconȬ tainȱaȱlowerȱproportionȱofȱbarkȱimpurities,ȱshouldȱleadȱtoȱaȱreductionȱinȱtheȱthermalȱconȬ ductivityȱofȱtheȱobtainedȱinsulatingȱblock.ȱOnȱtheȱotherȱhand,ȱanȱadaptationȱofȱtheȱcomȬ pressionȱmoldingȱconditionsȱshouldȱalsoȱimproveȱtheȱinsulatingȱcapacityȱofȱtheȱamaranthȬ basedȱblock.ȱForȱfutureȱwork,ȱ itsȱ waterȱvaporȱpermeabilityȱwillȱalsoȱhaveȱ toȱbeȱdeterȬ mined.ȱAsȱforȱtheȱlowȬdensityȱblocksȱmadeȱfromȱsunflowerȱpithȱ[20,22],ȱitȱshouldȱbeȱquiteȱ high,ȱwhichȱcouldȱalsoȱmakeȱthisȱinsulatingȱmaterialȱaȱpromisingȱwaterȱregulator.ȱ
Asȱforȱtheȱpithȱparticlesȱusedȱinȱbulk,ȱadditionalȱdevelopmentsȱwillȱalsoȱbeȱrequiredȱ toȱimproveȱtheȱdurabilityȱofȱtheȱoptimalȱlowȬdensityȱinsulationȱblockȱbeforeȱproposingȱitȱ toȱ theȱ market.ȱ Aȱ reductionȱ inȱ itsȱ waterȱ sensitivityȱ couldȱ beȱ achievedȱ thanksȱ toȱ theȱ replacementȱofȱtheȱstarchyȱbinderȱbyȱanotherȱpolysaccharideȱbinderȱwithȱphysicalȱcuring,ȱ e.g.,ȱalginatesȱandȱespeciallyȱCitrusȱpectinsȱandȱchitosanȱ[50].ȱItȱcouldȱbeȱalsoȱachievedȱ thanksȱtoȱitsȱcoatingȱbyȱhydrophobingȱagentsȱevenȱifȱitsȱabilityȱasȱaȱwaterȱregulatorȱmayȱ beȱpartiallyȱimpairedȱafterȱsuchȱpostȬtreatment.ȱTheȱadditionȱofȱaȱfireproofingȱproductȱtoȱ theȱformulationȱwouldȱalsoȱrenderȱtheȱamaranthȬbasedȱblockȱmoreȱresistantȱtoȱfire.ȱLastly,ȱ glycerolȱestersȱappearȱasȱaȱpromisingȱrenewableȱsolutionȱtoȱprotectȱitȱagainstȱmicrobialȱ growthȱ[22].ȱ 4.3.ȱHardboardsȱfromȱBarkȱ Theȱhighȱlignocelluloseȱcontentȱforȱbarkȱ(43.6%ȱcellulose,ȱ17.6%ȱhemicelluloses,ȱandȱ 20.3%ȱlignins)ȱcontributedȱtoȱitsȱpotentialȱforȱproducingȱhardboardsȱ(HB),ȱi.e.,ȱdenseȱfiȬ berboards,ȱthroughȱhotȱpressing.ȱCohesiveȱhardboardsȱwereȱobtainedȱwithȱnoȱexternalȱ binderȱaddedȱ(HB1ȱandȱHB4)ȱ(Tableȱ8),ȱdueȱtoȱtheȱadhesiveȱabilityȱofȱsomeȱchemicalsȱinȬ sideȱbarkȱ(i.e.,ȱfreeȱsugars,ȱhemicelluloses,ȱandȱlignins).ȱBothȱHB1ȱandȱHB4ȱboardsȱcouldȱ thusȱbeȱconsideredȱasȱpromisingȱbinderlessȱfiberboards.ȱ Especially,ȱ theȱHB4ȱhardboardȱobtainedȱfromȱaȱpreviouslyȱextrusionȬrefinedȱbarkȱ (ERB),ȱusingȱwaterȱatȱaȱ4ȱliquid/solidȱratio,ȱwasȱmuchȱmoreȱmechanicallyȱresistantȱ(+50%ȱ forȱflexuralȱstrength)ȱthanȱthatȱfromȱgroundȱbarkȱ(GB).ȱThisȱwasȱalreadyȱobservedȱforȱ corianderȱstrawȱ[13],ȱandȱforȱshivesȱfromȱoleaginousȱflaxȱ[30].ȱTheȱextrusionȬrefiningȱpreȬ treatmentȱcontributedȱtoȱaȱmuchȱmoreȱfavorableȱfiberȱmorphologyȱ(largeȱincreaseȱinȱtheirȱ meanȱaspectȱratio),ȱjustȱasȱtoȱanȱefficientȱseparationȱbetweenȱcellulose,ȱhemicelluloses,ȱandȱ ligninsȱinsideȱtheȱextrudedȱmaterial,ȱthusȱfacilitatingȱtheȱmobilizationȱofȱinternalȱbindersȱ duringȱhotȱpressing.ȱ Anȱadditionalȱimprovementȱinȱtheȱbendingȱpropertiesȱwasȱobtainedȱbyȱaddingȱtoȱtheȱ barkȱgrindedȱandȱdeoiledȱamaranthȱseeds.ȱHere,ȱbecauseȱofȱitsȱrichnessȱinȱproteinsȱandȱ especiallyȱstarch,ȱthisȱABȱamaranthȬbasedȱbinderȱwasȱusedȱasȱaȱnaturalȱexternalȱbinder,ȱ andȱitsȱbindingȱabilityȱwasȱevidencedȱforȱtheȱgroundȱbark,ȱjustȱasȱforȱtheȱextrusionȬrefinedȱ one.ȱInȱaddition,ȱespeciallyȱforȱtheȱERBȱfibrousȱreinforcement,ȱtheȱmoreȱtheȱamaranthȬ basedȱbinderȱadded,ȱtheȱmoreȱtheȱflexuralȱstrengthȱandȱtheȱmoreȱtheȱelasticȱmodulus.ȱTheȱ
bestȱ flexuralȱ propertiesȱ wereȱ obtainedȱ whenȱ addingȱ 20%ȱ ABȱ toȱ ERBȱ (Tableȱ 8).ȱ Suchȱ amountȱofȱABȱaddedȱallowedȱtheȱERBȱfibersȱtoȱstickȱwellȱtogether.ȱ Fromȱtheȱpointȱofȱviewȱofȱsensitivityȱtoȱwaterȱofȱtheȱhardboardsȱproduced,ȱusingȱtheȱ extrusionȬrefinedȱbarkȱdividedȱtheȱthicknessȱswellingȱandȱwaterȱabsorptionȱvaluesȱbyȱupȱ toȱ2ȱforȱaȱpanelȱwithoutȱexogenousȱbinder,ȱandȱbyȱupȱtoȱ1.5ȱforȱaȱpanelȱhotȱpressedȱwithȱ 20%ȱamaranthȬbasedȱbinderȱaddedȱ(Tableȱ8).ȱTheȱinterestȱofȱtheȱpreliminaryȱdefibrationȱ ofȱtheȱamaranthȱbarkȱinȱaȱtwinȬscrewȱextruderȱregardingȱtheȱwaterȱresistanceȱofȱtheȱobȬ tainedȱpanelsȱisȱthusȱindisputable.ȱ Theȱoptimalȱhardboardȱ(HB6)ȱ(Figureȱ2)ȱhasȱaȱ36ȱMPaȱflexuralȱstrength,ȱwhichȱisȱsigȬ nificantlyȱdifferentȱfromȱallȱtheȱotherȱstrengthȱvaluesȱinȱtheȱpresentȱstudy.ȱThisȱvalueȱisȱ alsoȱ23%ȱhigherȱthanȱthatȱofȱanotherȱfiberboardȱrecentlyȱdevelopedȱfromȱcorianderȱ(29ȱ MPa)ȱ[13].ȱItȱisȱalsoȱmuchȱhigherȱthanȱtheȱflexuralȱstrengthsȱofȱtwoȱcommercialȱwoodȬ basedȱmaterialsȱtestedȱinȱaȱpreviousȱstudyȱ[29],ȱi.e.,ȱMDFȱandȱchipboard:ȱ73%ȱandȱupȱtoȱ 251%,ȱrespectivelyȱ(Tableȱ8).ȱHB6ȱboardȱisȱthusȱundoubtedlyȱaȱviable,ȱsustainableȱalternaȬ tiveȱforȱreplacingȱcurrentȱbuildingȱwoodȬbasedȱmaterialsȱlikeȱplywood,ȱchipboard,ȱOSB,ȱ MDF,ȱetc.ȱAccordingȱtoȱtheȱNFȱENȱ312ȱstandardȱ[51],ȱitȱisȱalreadyȱusableȱforȱinteriorȱfitȬ tingsȱ(includingȱfurniture)ȱinȱaȱdryȱenvironmentȱ(P2ȱtypeȱboard).ȱInȱadditionȱtoȱfurniture,ȱ itsȱpossibleȱusesȱinȱbuildingsȱincludeȱinteriorȱpartitions,ȱunderlaysȱforȱfloors,ȱpanelsȱforȱ suspendedȱceilings,ȱetc.ȱHowever,ȱitsȱfireȱresistanceȱwillȱhaveȱtoȱbeȱcharacterizedȱbeforeȱ usingȱitȱinsideȱhouses.ȱTheȱadditionȱofȱaȱflameȱretardantȱtoȱtheȱformulationȱpriorȱtoȱhotȱ pressingȱmayȱbeȱconsideredȱinȱtheȱeventȱofȱpoorȱfireȱresistance.ȱ Theȱoptimalȱboardȱneverthelessȱrevealsȱaȱgreaterȱsensitivityȱtoȱwaterȱafterȱ24ȱhȱimȬ mersionȱthanȱcommercialȱMDFȱorȱchipboardȱtypeȱpanelsȱ(Tableȱ8).ȱWithȱmuchȱimprovedȱ waterȱresistanceȱ(10%ȱmaxȱthicknessȱswelling),ȱitȱcouldȱalsoȱbeȱusedȱasȱaȱP7ȱtypeȱboard,ȱ i.e.,ȱaȱboardȱworkingȱunderȱhighȱstress,ȱusedȱinȱhumidȱenvironment.ȱForȱfutureȱwork,ȱ multipleȱsolutionsȱcouldȱbeȱinvestigatedȱtoȱimproveȱtheȱwaterȱresistance.ȱFirstly,ȱaȱreducȬ tionȱinȱthicknessȱswellingȱcouldȱbeȱattainedȱthanksȱtoȱaȱheatȱpostȬtreatment.ȱThisȱwasȱalȬ readyȱevidencedȱforȱtwoȱtypesȱofȱrenewableȱfiberboards,ȱi.e.,ȱoneȱmadeȱofȱcorianderȱstrawȱ asȱreinforcementȱandȱpressȱcakeȱfromȱseedsȱasȱbinderȱ[13],ȱandȱanotherȱmadeȱofȱoleagiȬ nousȱflaxȱshivesȱasȱreinforcementȱandȱplasticizedȱlinseedȱcakeȱasȱbinderȱ[31].ȱAtȱtheȱendȱ ofȱthisȱpostȬtreatment,ȱanȱincreaseȱinȱtheȱflexuralȱstrengthȱwasȱevenȱobservedȱatȱtheȱsameȱ timeȱasȱtheȱreductionȱinȱthicknessȱswellingȱforȱtheseȱtwoȱinnovativeȱmaterials.ȱ Inȱorderȱtoȱmeetȱtheȱsameȱobjectiveȱofȱincreasingȱwaterȱresistance,ȱotherȱtreatmentsȱ mayȱbeȱtestedȱafterȱhotȱpressing,ȱe.g.,ȱcoating,ȱchemical,ȱorȱsteamȱtreatmentȱ[30].ȱInȱparticȬ ular,ȱtheȱapplicationȱofȱaȱcoatingȱbasedȱonȱvegetableȱoilsȱorȱtheirȱderivativesȱcouldȱbeȱaȱ promisingȱrenewableȱsolutionȱtoȱimproveȱtheȱstabilityȱinȱtheȱboardȱdimensionȱafterȱsoakȬ ingȱinȱwater.ȱAmongȱtheseȱbioȬsourcedȱadditives,ȱdryingȱoilsȱsuchȱasȱlinseedȱoilȱorȱhydroȬ genatedȱoilsȱthatȱhaveȱtheȱpropertyȱofȱbeingȱsolidȱatȱroomȱtemperatureȱappearȱtoȱbeȱgoodȱ candidates.ȱ Forȱfutureȱindustrialȱprocessȱintensification,ȱoneȱsingleȱextruderȱpassȱwouldȱallowȱ theȱcontinuousȱproductionȱofȱaȱpremixȱreadyȱtoȱbeȱmoldedȱthroughȱhotȱpressing,ȱandȱasȬ sociatingȱtheȱrefinedȱfibersȱfromȱamaranthȱbarkȱasȱmechanicalȱreinforcement,ȱtheȱamaȬ ranthȬbasedȱbinderȱandȱevenȱwaterȬrepellentȱand/orȱflameȬretardantȱadditivesȱ[31].ȱInȬ deed,ȱinȱadditionȱtoȱitsȱabilityȱevidencedȱinȱthisȱstudyȱtoȱrefineȱplantȱfibers,ȱtheȱtwinȬscrewȱ extrusionȱtechnologyȱisȱalsoȱknownȱforȱitsȱparticularlyȱintenseȱmixingȱabilityȱ[25,26].ȱFromȱ theȱsameȱmachine,ȱtheȱamaranthȱbarkȱcouldȱthusȱbeȱextrusionȬrefinedȱinȱtheȱpresenceȱofȱ waterȱinȱtheȱfirstȱhalfȱofȱtheȱscrewȱprofile.ȱThen,ȱtheȱdeoiledȱamaranthȱseedsȱandȱanyȱadȬ ditivesȱcouldȱbeȱaddedȱinȱitsȱmiddleȱthanksȱtoȱaȱsideȱfeeder.ȱFinally,ȱtheȱsecondȱhalfȱofȱtheȱ screwȱprofileȱcouldȱbeȱusedȱforȱtheȱintimateȱmixingȱofȱallȱtheseȱcomponentsȱwithȱeachȱ other.ȱUsingȱtheȱasȬdescribedȱcombinedȱprocess,ȱtheȱpremixȱwouldȱbeȱproducedȱatȱaȱreȬ ducedȱcostȱbeforeȱbeingȱtransformedȱintoȱhardboards.ȱ ȱ ȱ
