木材保护与改性4_wood_fire_retardance_02

Chapter4Chemistryoffireretardancy4.1Preface4.2Thechemistryofpyrolysisandcombustion4.3Mechanismsoffireretardancy4.4Fire-retardantformulations4.5Futureresearches4.1PrefaceWoodanditsproductsarecloselyrelatedtopeople’slives.Moreandmorepeopleliketodecoratetheirroomwithwood,andwoodybuildingsdrawmoreandmoreattentions.Butasweknownwoodarecombustiblematerials,whichnotonlythreattopeople’slivesandpossessions,butalsolimitedtheirapplicationareas.Withtheincreaseofhighbuildingsandlargemansions,firebecomesthemaintroubleneedingtobesolved.indoordecoration,building,gardening,andsoonThecharmingwoodinThemodernwoodenbuildingisverypopularinmostofthecountries.In2000,90percentoftheAmericannewvilla(别墅)wasbuiltupofwood.AndAmongthe330,000highriseresidences,275,000wasbuiltupofwood.InCanada,woodindustryisthemainstayindustry,thetechniquesofmanufactureandinstallationarequitemature.Atpresent,morethanhalfofthenewhousesinJapanarebuiltupofwoodorwoodproducts.Exceptforwoodenhouses,mostofthepublicbuildingssuchasfactory,school,hotel,gymnasiumandsoonarebuiltupofwoodorwoodproducts.willyoubelievethatwoodenbuildingcangrowupinChinainthefuture?ThechiefcriminaloffireWoodWoodisthecriminaloffire.Woodenbuildingshouldbelimitedordiscarded.It’safalseandunadvisableidea.why?WoodSteelcementplastictheextensivelyappliedmaterialstheonlyrenewablematerialInfact,woodespeciallylargescaleofwoodenproductsarefireproofmaterial.Why?woodprotectingscienceP108Inourmind,reinforcedconcreteisakindoffireproofmaterial,andstrongenoughtoresistviolentcollision(猛烈撞击).Butreinforcedconcretehasamortaldefect(致命的缺点).Wouldyoutellmewhat’sthefataldefecttoreinforcedconcreteathighertemperature?Reinforcedconcreteturnssoftwhenundergoinghightemperature.Normally,thestrengthofsteelreducesbyhalfwhenthetemperatureexceeded300°C,andfallsdownwhenthetemperatureexceeded500°C.Therefore,fireretardingisoftheutmostimportance.Coffer(orsafe)保险柜:制作材料？金属金属和木（竹）材其它1.Isitnecessarytopreventingwoodfromfire,why?2.Accordingtoyouropinion,whichkindofwood(assortedbytheirapplicationareas)shouldbeprotectedfromfire?3.Fromthepicturesabove,pleasetellmethemostseriousthreatsinafire.4.2ThechemistryofpyrolysisandcombustionIncludingfourstages:(1)Thetemperatureofwoodisimprovedundertheheat.(2)Woodgraduallydegradesandpyrolyzes,thefollowingmaterialproduces:CO2,CO,CH4,CH2=CH2,R-CHO,R-CO,andsoonTar(includingphenol(酚类),aldehyde(醛类),carbonylchemicals(羰基化合物)FlammablegasesheatLowmolecularchemicalsAndflammablegases(3)FlammablegasesheatCatchfireandcombustionTherearefournecessaryconditionsfortheflammablecombustionofwood:combustiblegases,heat,oxygenandradicalgroups。(4)CombustioncontinuesHeatconductstotheadjacentwoodCombustionprovidelargeamountofheatWoodtemperatureimprovedPyrolysisbegins,thenignition,combustion,firespread,andsoonLargeamountofsmokealsoproducedduringthecombustionofwood,thecompositionofthesmokeislistedinthefollows:Combustiblegases:CO,CH4,H2,CH2=CH2,R-CHO,R-CO,andsoonNoncombustiblegases:CO2,H2OTar:phenol,aldehyde(醛类),carbonylchemicalsCharcoal:combustibleresidue.Pyroligneousacid(木醋液):mainlyformicacid(蚁酸)oraceticacid(乙酸)SometermsofcombustionFlamecombustion(有焰燃烧)：luminousburningatthegasstate.木材进行发光的气相燃烧。Smoulding(有焰燃烧)：nonluminousburningwithsmog.木材燃烧时处于一种无可见光而有烟雾的燃烧。Flamelesscombustion(红热燃烧)：aphlogistic(无焰)combustionatasolidstate.木材处于固相状态而没有火焰的燃烧，也叫无焰燃烧。4.3Mechanismsoffireretardancy•Preventtheescapeofvolatileproductsbyformingaglassybarrier.•Preventsoxygenfromreachingthesubstrate•Insulatesthewoodsurfacefromhightemperatures(1)Barriertheories(障碍理论)(2)Thermaltheories(热理论)•Fire-retardantsmayincreasethethermalconductivityofwoodtodissipatetheheatfromthesurfacefasterthanitissuppliedbytheignitingsource;•Affectchemicalandphysicalchangessothattheheatisabsorbedbythechemical.Forexample:chemicalscontentcrystalwater.(3)Dilutionbynoncombustiblegasestheories(不燃气体稀释理论)Noncombustiblegasesreleasedbythedecompositionofthefire-retardantChemicals,whichdilutethecombustiongases,andformanonflammableGaseousmixture.(4)Freeradicaltraptheories(自由基捕集理论)Fire-retardantchemicalsreleasefreeradicalinhibitorsatpyrolytictemperaturesthatinterruptthechainpropagationmechanismofflammability.CO，CO2，H2O，HO·和其它成分(1)HO·十CO→CO2+H·(2)H·十O2→HO·十O·(3)O·+H2→HO·+H·(5)Increasedcharcoal/reducedvolatilestheories(炭量增加/挥发性气体减少理论)书上P118反应式Fire-retardantchemicalslowerthetemperatureatwhichpyrolysisoccurs,directingthedegradationpathwaytowardmorecharcoalproductionandfewervolatiles.(6)Reduceheatcontentofvolatilestheories(挥发物热含量下降理论)Thisstepiscloselyrelatedwiththeories(5),thatistheories(5)and(6)functiontogether,resultinginmorechar,fewervolatilesandlowerheatcontentofvolatiles.4.4Protectionofwoodwithfire-retardant4.4.1Treatingmethods4.4.2woodfireretardant4.4.1TreatingmethodsPhysicalmethodsReducetheratioofcombustiblematerialbymixingwoodwithNoncombustiblematerials.Forexample:boardmadeupofwoodandcement,orfiberglass（玻璃纤维）,plaster（石膏）orasbestus（石棉）.Coverthesurfaceofwoodwithmetalboardorfireproofboard.Chemicalmethods:Theapplicationoffireretardant.ImpregnateintothewoodAppliedaspaintorsurfacecoatingsTwoclas