* AleksandraPrzewoźnik,student,FacultyofCivilEngineering,CracowUniversityofTechnology.

TECHNICAL TRANSACTIONSCIVIL ENGINEERING

5-B/2014

CZASOPISMO TECHNICZNEBUDOWNICTWO

ALEKSANDRAPRZEWOŹNIK*

POLYURETHANE–ALTERNATIVETOMINERALWOOLANDPOLYSTYRENE

POLIURETAN–ALTERNATYWADLAWEŁNYMINERALNEJISTYROPIANU

A b s t r a c t

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.

Keywords: polyurethane, isocyanate, polyol, thermal insulation, thermal conductivity, foam

S t r e s z c z e n i e

Poliuretanzostałwynalezionyw1937roku.Jesttopopularnanazwadlamateriału,którymożebyćukrytypodwielomaformami,międzyinnymisztywnejpianki,elastycznejpianki,powłok,substancjiłączących,pastuszczelniającychielastomerów.Jegogłównymiskładnikamisąizo-cyjanianipoliol.Zależnieodichproporcjiiużytychdodatkówmożeonmiećróżnewłaści-wości.Poliuretanmawielezastosowańwprzemyśleiżyciucodziennym.Wbudownictwiedoizolacjicieplnejużywanajestsztywnapianka.Jestonaprodukowanawprocesiezwanymsys-temempoliuretanowym.Jesttomateriałprzedewszystkimlekkiiwytrzymałynawieleczyn-nikówzewnętrznych.Ponadtocechujesięzamkniętąstrukturąiniskąprzewodnościącieplną.

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.

Whilechoosingtheinsulation,attentionismainlypaidtothermalconductivity,butotherpropertiesarealsoimportant.TheEPSisthelightest.HowevertheweightofmaterialwiththethicknessneededtoachievethesameheattransfercoefficientiscomparabletotheweightoftherequiredPUR.TheMWisincomparablyheavierthanEPSandPURandischaracterizedbynon-flammabilityandfireresistance.ThePURhasworsefirepropertiesbutPIRallowstoovercometheproblem[8–11].

233Ta b l e 1

Comparing thickness of the thermal insulation obtained using expanded polystyrene, mineral wool and polyurethane rigid foam

U=0.25[W/(m2∙K)]

Heatinsulatingmaterial Thermalconductivity Thicknessofinsulation

Expandedpolystyrene 0.038[W/(m∙K)] 14[cm]

Mineralwool 0.037[W/(m∙K)] 13[cm]

Polyurethanerigidfoam 0.024[W/(m∙K)] 9[cm]

6. Conclusions

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-

cje4/2011,DomWydawniczyMedium,Warszawa2011.