* Aleksandra Przewoźnik, student, Faculty of Civil Engineering, Cracow University of Technology. TECHNICAL TRANSACTIONS CIVIL ENGINEERING 5-B/2014 CZASOPISMO TECHNICZNE BUDOWNICTWO ALEKSANDRA PRZEWOŹNIK * POLYURETHANE – ALTERNATIVE TO MINERAL WOOL AND POLYSTYRENE POLIURETAN – ALTERNATYWA DLA WEŁNY MINERALNEJ I STYROPIANU Abstract Polyurethane was discovered in 1937. It is a common name for material which can be hidden under many forms, such as, rigid foam, flexible foam, coatings, sealants, adhesives and elastomers. The main constituents are isocyanate and polyol. Depending on the components and proportions it can have different properties. Polyurethane is widely used in industry and has a variety of uses in everyday life. Rigid foam is used in building construction as a thermal insulation. It is produced by the so-called polyurethane system. This material is light and durable. Besides, it has closed-cell structure and a low thermal conductivity. Keywords: polyurethane, isocyanate, polyol, thermal insulation, thermal conductivity, foam Streszczenie Poliuretan został wynaleziony w 1937 roku. Jest to popularna nazwa dla materiału, który może być ukryty pod wieloma formami, między innymi sztywnej pianki, elastycznej pianki, powłok, substancji łączących, past uszczelniających i elastomerów. Jego głównymi składnikami są izo- cyjanian i poliol. Zależnie od ich proporcji i użytych dodatków może on mieć różne właści- wości. Poliuretan ma wiele zastosowań w przemyśle i życiu codziennym. W budownictwie do izolacji cieplnej używana jest sztywna pianka. Jest ona produkowana w procesie zwanym sys- temem poliuretanowym. Jest to materiał przede wszystkim lekki i wytrzymały na wiele czyn- ników zewnętrznych. Ponadto cechuje się zamkniętą strukturą i niską przewodnością cieplną. Słowa kluczowe: poliuretan, izocyjanian, poliol, izolacja cieplna, przewodność cieplna, piana
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Polyurethane was discovered in 1937. It is a common name for material which can behidden undermany forms, such as, rigid foam, flexible foam, coatings, sealants, adhesivesandelastomers.Themainconstituentsareisocyanateandpolyol.Dependingonthecomponentsandproportionsitcanhavedifferentproperties.Polyurethaneiswidelyusedinindustryandhasavarietyofuses ineveryday life.Rigid foam isused inbuildingconstructionasa thermalinsulation. It is produced by the so-called polyurethane system. This material is light anddurable.Besides,ithasclosed-cellstructureandalowthermalconductivity.
Słowa kluczowe: poliuretan, izocyjanian, poliol, izolacja cieplna, przewodność cieplna, piana
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1. History of polyurethane
Productionofpolyurethane(PU)fromothersubstanceswasdiscoveredandpatentedbytheGermanchemistOttoBayerin1937.AtthebeginningofWorldWarIItherewasadeficitofrubberanditreachedhighprices.ThisledtoasituationthattherubberbegantobereplacedwithPU.Oneexampleofsuchanapplicationistheuseofrigidpolyurethanefoamtosealtheaircraftandprotectivecoatingofmetal,woodandstone.Duringthewar,PUhasbecomemoreandmorepopularbecauseofitspropertiesandbegantobeproducedonaglobalscale.Inthefiftiesitwasavailableonthecommercialmarketintheformofelastomers,adhesivesand rigid foam. At the end of the decade, the widespread use also introduces flexiblepolyurethanefoamsimilartotheonethatiscurrentlyverypopularinmanyareas.Overthenextyears,theresearchwasongoingonthedevelopmentofPUapplicationsmainlyintheautomotiveindustry,construction,clothingandmedicalequipment.Inthe70sPUbegantobeusedasathermalinsulationofbuildingsintheformofspray.Inthe80sitwasusedintheproductionofcarsasamaterialwhichabsorbsimpactenergyandtherebyimprovesthesafetyofthepassengers.Inthe90sthefirstmedicaltubingwasmadewithpolyurethaneelastomer.In2001thecartiresstartedtocontainPUinordertoincreasetheirefficiency.Nowadays,mostpeoplearenotfamiliarwiththeuseofPUbecauseitisoftenhiddeninvariousformsineverydayproducts[1–3].
2. Types of polyurethanes
PUishiddenundermanyforms.Itscompositionischaracterizedbytwomaincomponents.Namely:an isocyanateandapolyolderivedfrompetroleum.Bymixing themalongwithpresenceofvariouscatalysts,stabilizersandotheradditives,PUofdifferentpropertiesmaybecreated.Differentproportionsandcomponentscaninfluencethecomposition,flexibility,rigidity, insulation and other properties needed for a particular use. PU can be found inseveralforms.Oneofthemistheflexiblefoamthatcanbeeasilyshaped.Thismaterialischaracterizedbylightness,durabilityandresistancetodeformation.Rigidfoamhasaverygood insulation.There are two kinds of rigid foam: polyurethane rigid foam (PUR) andpolyisocyanurate rigid foam (PIR).Their compositions are similar, but in the secondonethereismoreisocyanateattheextenseofpolyol.ThisdifferencecausesthePIRtohavebetterfireresistantproperties,butbecauseofthehighercostanddifficultyofproductionitislessoftenproduced.PUcanalsobepresentincoatings,adhesives,sealants,andelastomers.Thecoatingsenhancetheappearanceanddurabilityoftheproducts.Adhesivesaredurableandstrong.Sealantslayerdoesnothavetobethickinordertofulfilitsfunctionandelastomersare resistant toenvironmental influencesandadaptwell to thevariablestress.Oneof thetypes of PU is thermoplastic polyurethane which can be processed in many ways, forexample,byextrusion,injection,blowandcompressionmoldingequipment.Itisalsohighlyflexible,resistanttoabrasion,impactandinfluenceofweather.PUisalsousedasabinder,forexampleinthemanufactureoforientedstrandboard.Notonlytojoinfibresandparticlestoeachother,butalsotoimpartflexibilityandimproveendurance[1,3–5].
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3. The use of polyurethane
TheuseofPUdependsontheforminwhichitisproducedandspecificpropertiesrelatedto this. Flexible foams are usedmainly in the furniture and upholstery as supplementaryfillingmaterial. PUR and PIR are primarily used in construction as insulation. It is alsoavailableinanumberofdevicesasaninsulator.PUisexploitedintheautomotiveindustrybecauseof its lightweight,durabilityandinsulation.It isusedintheproductionofmanyparts,suchas,carbody,bumpersandseats.InmedicinePUcanbefoundinhospitalbedsheets,curtainsandalsoinshort-termimplants.PUisexploitedinthemanufactureofpaints,lacquers,glues,compositewood,clothing,footwearandmanyaccessoriesusedineverydaylife[3,4].
Fig.1.Thevarietyofpolyurethaneapplications[2]
4. Characteristics of rigid polyurethane foams
Asthermalinsulationinconstruction,PURismainlyused.Itisproducedbytheso-calledpolyurethane system. It consists of polyol chemically reactingwith toluene diisocyanate(TDI)ordiphenylmethanediisocyanate (MDI)with thepresenceofsuitablecatalystsandadditives.Asafoamingagent,pentanesorlow-boiling,inertsolventsmaybeused,usuallyderivedfromhalogens.Duringthereactionthereisanincreaseoftemperature,evaporationoftheblowingagentstartsandthevolumeofthefoamexpands.TheobtainedPUfoamsmustbeinaclosedcellstructureinordertobeusedasthermalinsulationmaterial.Thisprocess,simplified to the laboratory conditions, is shown in Fig. 2. For the industrial productionofPURequipmentisneeded,whichincludesstorage,metering,heating,dosingandmixingingredients.Dependingontheapplicationofthefinalproduct,mixingunitcanbeloworhighpressureorintheformofsprayusingspecialsprayguns.Somemanufacturersalsopractisehand-mixingthat,alongwiththerightexperience,ensuresgoodqualityofthematerial.
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Fig.2.Theformationofpolyurethanefoam[2]
PURhasaclosedcellstructure,whichis90%filledwithgas.Thedensityisintherangeof 24–60 kg/m3. Noticeable is the fact that with increasing density, the water absorptiondecreasesandthecompressivestrengthincreases.Thelevelofwaterabsorptionisintherange of 0.3–0.4%by volumeof thematerial.The thermal conductivity is about 0.024W/(m∙K)and isnotdependentonhumidity.ThewatervapourpermeabilityofPUR isvery lowdueto theclosedstructureand is70g/m2/24h.PURis resistant to thebiologicaleffectsof theenvironment and does not reactwith grease, organic solvents and diluted acids and alkali.However,itissusceptibletothenegativeeffectsofUVradiation.Becauseofthis,itiscoveredwithaspecialpaintorplastertoprotectthefoamfromtheradiation.PURisaslowburningandself-extinguishingmaterialwhichcanwithstandtemperaturesupto150°C[1,3,5–7].
5. Comparison of insulation: polyurethane rigid foam, mineral wool and expanded polystyrene
Themostcommoninsulatingmaterialsaremineralwool(MW)andexpandedpolystyrene(EPS). Comparing the thermal insulation obtained using thesematerials and PUR, cleardifferencescanbeseen.Oneofthemisthethicknessofinsulationneededtoachievethesameheattransfercoefficientwhenotherlayersarethesame.InordertoachievetheheattransfercoefficientofU=0.25W/(m2∙K)14cmofEPSshouldbeused,13cmofMWand9cmofPUR.ThecombinationofthesedataandthethermalconductivityofmaterialscanbefoundinTable1.
The most common thermal insulating materials on the market in Poland are MWand EPS. However, the PUR and PIR insulation is gaining attention due to its superiorthermalperformanceanddecreasingcostsofproduction.These are important advantagesin the increasingly stringent thermal requirements of buildings because the traditionalinsulation materials must increase its already considerable thickness to about 20 cm.Inaddition,researchtoimprovethepropertiesofthePUisongoinganditmakesthismaterialmoreattractiveontheconstructionmarket.
R e f e r e n c e s
[1]www.polyurethanes.org,access:19.08.2013.[2]www.puhse.com,access:19.08.2013.[3]www.polyurethane.americanchemistry.com,access:19.08.2013.[4]www.polyurethanes.basf.de,access:20.08.2013.[5]PołygaM.,Poliuretan-materiał dla budownictwa,Izolacje7-8/2010,DomWydawni-
czyMedium,Warszawa2010.[6]WronaM.,Uszczelnienie, wypełnienie, wygłuszenie – pianki poliuretanowe w budow-
nictwie, Izolacje5/2009,DomWydawniczyMedium,Warszawa2009.[7]SzycherM.,Szycher’s handbook of polyurethanes,CRCPress,2013.[8]www.termoorganika.com.pl,access:12.02.2012.[9]www.rockwool.pl,access:12.02.2012.[10] Pałasz J., Pianki poliuretanowe PUR/PIR a inne materiały termoizolacyjne, Izola-
cje11–12/2010,DomWydawniczyMedium,Warszawa2010.[11] Dreger M., Izolacje z pianki poliuretanowej a wyroby z wełny mineralnej, Izola-