无卤阻燃PP外文.docx
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无卤阻燃PP外文.docx
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无卤阻燃PP外文
Areviewofflameretardantpolypropylenefibres
ShengZhang
andA.RichardHorrocks
CentreforMaterialsResearchandInnovation(CMRI),BoltonInstitute,BoltonBL35AB,UK
Received12March2003;
revised26August2003;
accepted5September2003.;
Availableonline24October2003.
Abstract
Flameretardantsforpolypropylene(PP)andtheirpotentialsuitabilityforuseinfibreapplicationsarereviewed.Fiveprincipaltypesofgenericflameretardantsystemsforinclusioninpolypropylenefibreshavebeenidentifiedasphosphorus-containing,halogen-containing,silicon-containing,metalhydrateandoxideandthemorerecentlydevelopednanocompositeflameretardantformulations.
Themosteffectivetodatecomprisehalogen–antimonyandphosphorus–brominecombinations,whichwhilehavinglimitedperformancealsoarefallingenvironmentalpressures.Alternativesarediscussedaswellasmeansofenhancingtheeffectivenessandhenceusefulnessofphosphorus–nitrogenformulationsnormallyusedatconcentrationstoohighforfibreinclusion.Ofspecialinterestisthepotentialforinclusionoffunctionalisednanoclaysandrecentobservationsthatcertainhinderedaminestabilisersareeffectiveatconcentrationsof1%orso.
AuthorKeywords:
Polypropylene;Flameretardant;Fibres;Combustion;Phosphorus;Halogen;Silicon;Metalhydrate;Nanoclay;Nanocomposite
ArticleOutline
1.Introduction
1.1.Thedevelopmentofpolypropylenefires
1.2.Thepropertiesofpolypropylene
2.Thermalandcombustionbehaviour
3.Flameretardantsforpolypropyleneandpolypropylenefibres
3.1.Phosphorus-containingandintumescentflameretardants
3.1.1.Effectofheavymetalions
3.1.2.Effectofsilicon-containingspecies(seealsoSection3.3)
3.2.Halogen-containingflameretardants
3.3.Silicon-containingflameretardants
3.4.Metalhydroxidesandoxides(metalcompounds)
3.5.Nanocomposites
3.6.Othermethods
3.6.1.Graftingandcoating
3.6.2.Hinderedaminelightstabilisers
4.Conclusions
References
1.Introduction
Polypropylenewasthefirstsyntheticstereo-regularpolymertoachieveindustrialimportance[1]anditispresentlythefastestgrowingfibrefortechnicalend-useswherehightensilestrengthcoupledwithlow-costareessentialfeatures;ithasshownconsistentgrowthofabout5%per annumforthelast10years[2].In1999,worldwideconsumptionofpolyolefinfibresexceeded5.5milliontonnesandtheyaccountedfor18%oftheworld'ssyntheticfibreproduction[3].Polypropylenefibreshavebeenwidelyusedinapparel,upholstery,floorcoverings,hygienemedical,geotextiles,carindustry,automotivetextiles,varioushometextiles,wall-coveringsandsoon[4].
1.1.Thedevelopmentofpolypropylenefires
Thesynthesisofhighlycrystallineisotacticpolypropyleneusingstereospecificcatalystswaspatentedin1954byNatta[5].TheyusedheterogeneouscatalystsofthetypediscoveredbyZieglerforthelow-pressurepolymerizationofethylene toyieldlinearhigh-densitypolyethylene.CommercialpolypropyleneproductionwasinitiallyundertakenbyMontecatiniandsubsequentlyexpandedbyICIFibreswhointroducedtheir‘Ulstron’productinlate1950s[6].However,becauseofpatentrestrictionsassociatedwithfibreproduction,fibrouspolypropyleneoftenappearedinthemarketintheformoftapesandfilamentsratherthanfibres;itwasnotuntiltheearly1960sthatstaplefibresstartedtobeseenonthemarket[7].Intheearly1970stheemergenceofextruded,orientatedfilmtechnologyledtoanexpansionofpolypropyleneend-uses,includingtapes/slit-filmandvariousfibrillatedandfibrousproducts[1].
Themonomerpropylene isahydrocarbongasmainlyproducedfrompetroleumrefining.Thepolypropylenechaincomprisesamonomerwithanasymmetriccarbon atomattheC2 position,–CH2CH(CH3)–,andhencethepolymermayexistinthreetypes(isotactic,syndiotacticandatactic)ofmolecularconfigurationsdependingupontherelativeorientationsofthemethylsidegroups[7].Bothisotacticandsyndiotacticformshavemethylgroupssituatedregularlywithrespecttoadjacentgroupsalongthemolecularchainandhavefibre-formingcharacterduetotheirpotentialforcreatingorderinthepolymerstructure.Currently,isotacticpolypropyleneisthemaincommerciallyavailablestereoisomerforuseinorientedfibrefilmsandtapes.AveryrecentEUpatent,however,hasdescribedthepropertiesoffibreswhen0.5–50%byweightofsyndiotacticpolypropylenehavingamulti-modalmolecularweightdistributionisincludedwithatleast50%byweightofanisotacticpolypropylene[8].
1.2.Thepropertiesofpolypropylene
Thereasonfortherapidexpansioninproductioncapacityforpolypropyleneisitsadvantageoverpolyethylene incostandproperties.Aneconomicedgeinrawmaterialcostandthehighefficiencycatalystshavemadepolypropyleneaverylow-costfibre-formingplasticmaterial.Anumberofpropertiesareresponsibleforthewidespreadusageofpolypropylene.ThegeneralpropertiesofisotacticpolypropyleneareshowninTable1 [9].
Table1.Propertiesofisotacticpolypropylene
Fibre-formingatacticpolypropyleneispartiallycrystalline,i.e.itpossessesatwo-phasesystemcomprisingcrystallineandnon-crystallineregions.Themolecularchainsofcrystallineisotacticpolypropyleneexistinhelicalcoilshavingthreemonomerunitsper repeatinghelixwithalengthof0.65nmforeachrepeatunit.Themethylgroupsarearrangedsystematicallyaroundthehelixformingthreelateralrowsabout120°apartandthusclosepackingispossible.
2.Thermalandcombustionbehaviour
Thecrystallinemeltingpointofisotacticpolypropylenewithacrystallinityofaround45%andcontaining90–95%isotacticmaterialisquotedas165°C[10].TheTg valueofisotacticpolypropylenerangesfrom?
6?
130to25°Cdependingonmethodofmeasurementandheat-annealingtreatments[10].Atacticpolypropylenehasaglasstransitiontemperature(Tg)of?
6?
112to?
6?
115°Candnodefinedmeltingpoint.Table2 showsthethermodynamicalpropertiesofpolypropylene.
Table2.Thethermodynamicalpropertiesofpolypropyleneat230°C
H,enthalpy;S,entropy;P=pressure.
Becauseofitswhollyaliphatichydrocarbonstructure,polypropylenebyitselfburnsveryrapidlywitharelativelysmoke-freeflameandwithoutleavingacharresidue.Ithasahighself-ignitiontemperature(570°C)andarapiddecompositionratecomparedwithwoodandothercellulosicmaterialsandhencehasahighflammability.TheheatofcombustionforpolypropylenewasreportedbyEinseleetal.[11]tobe40kJ/gandthisishigherthanmanyotherfibre-formingpolymers.GurniakandKohlhaas[12]investigatedthecombustibilitytestscarriedoutonfourdifferentbackingfabrics:
spunbondedpolypropylene,wovenpolypropylenetapewithnylon/polypropylenebondedstaplefibrefabrics,spunbondedBikofilament(polyestercore,nylonsheath),andFreudenberg'sLutradurT5012spunbondedpolyester.Theyfoundthatthelowestflammabilitywasachievedbythespunbondedpolyesterproduct.Thisisasignificantobservationinthatpolypropylenecompeteswithpolyesterintermsoftensilepropertiesandprice,butitdoeshaveinferiorfireperformance.
Polypropylenepyrolysisisdominatedbyinitialchainscissions;consequentlyconsiderableresearchhasbeenundertakenintheconversionofwastepolypropyleneintocleanhydrocarbonfuels[13 and14]orothervaluableproductssuchaslubricants[15 and16].ThethermaldegradationofbothisotacticPPandatacticPPhasbeeninvestigatedundernon-isothermalconditions.Themaximumvolatileproductevolutiontemperaturewas420°CforatacticPPand425°CfortheisotacticPP.Therecoveryofcarbon asorganicvolatileproductscompriseddienes,alkanes,andalkenes.MajorcompoundsareforinstanceC9compounds,like2-methyl-4-octene,2-methyl-2-octene,2,6-dimethyl-2,4-heptadiene,2,4-dimethyl-1-heptene,2-methyl-1-octene.Thehydrogencontentofpyrolysisproductsobtainedbyflashpyrolysisat520°C,indicatesthemagnitudeoftheflammabilityproblemintermofitsfuel-formingpotential[17].Anabundanceofunsaturatedvolatilefuelfragmentsrenderstheflameretardationproblemevenmoresevereasthelonger,less-volatilemoleculesbehaveassecondaryfuelsources,whichdecomposefurther[18 and19].
Coolflamecombustionofpolypropyleneat350°Cleadstotheformationoftoxiccompoundswhichcancausedeathinmice,probablybecauseofincompletecombustionandCOformation[20].WhilethefirehazardcausedbytextilesingeneralhasbeenreviewedbyHorrocks[21]andChristian[22],theparticularhazardofpolypropylenewasnotedintheManchesterWoolworthFireof1979wherepolypropyleneupholsterycoversoverpolyurethane foamfillinginastackedfurniturepile wereidentifiedasthefirstmaterialignitedandwereresponsiblefortherapidgrowthofthatfire.The12deathsassociatedwiththisfiregaverisetotheneedtouseflameretardanttextilesinUKdomesticfurnishingsforthefirsttimein1980[23].
Hirschler[24]studiedthefirehazardandtoxicpotencyofthesmokefromburningpolypropylenein1987.Grand[25]investigatedtheeffectofexperimentalconditionsontheevolutionofcombustionproductsofpolypropylenebyusingamodifiedtoxicitytestapparatus.In2000,ShemwellandLevendis[26]studiedtheparticulate(soot)emissionsfromburningpolypropyleneandfourotherplastics.Resultsshowedthatboththeyieldsandthesizedistributionsoftheemittedsootwereremarkablydifferentforthefiveplasticsburned.Sootyieldsincreasedwithanincreaseofthenominalbulk(global)equivalenceratio(φ).Combustionofpolystyreneyieldedthehighestamountsofsoot
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