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Flame Retardancy,smoke Suppression And Char Formation Mechanism Of Rigid Polyurethane-polyisocyanurate Foams In Combustion

Posted on:2017-12-26Degree:DoctorType:Dissertation
Country:ChinaCandidate:X LiuFull Text:PDF
GTID:1361330596964338Subject:Materials Science and Engineering
Abstract/Summary:PDF Full Text Request
With increasing demand of insulation materials for energy conservation,rigid polyurethane foam(RPUF)as an excellent insulation material has attracted a lot of attentions from industrial and academe.However,several application problems of RPUF in industry are imperative needed solutions.Firstly,RPUF has a large heat of combustion(HoC),which means high fire hazard load in combustion.Secondly,RPUF is flammable and release large amount of smoke and toxicity.Thirdly,some flame retardant RPUF with liquid phosphonates has a further increase on the pr o-duction of smoke and toxicity,which are not conducive to evacuation and rescue operations.Therefore,the regularity of HoC,flame retardancy and smoke suppres-sion mechanisms should be studied to optimize the fomulas and solve these pro b-lems.This thesis consists of the following four parts:(1)Heat of combustion(HoC)is one of the important parameters evaluated the fire hazard of construction materials and basic date to calculate fire hazard load.In this study,the HoC of various flame retardants and flame retardant RPUF systems were investigated,the relationships of HoC,flame retardant mechanisms and flame retardant properties were analyzed.Test conditions of HoC were optimized by changing the oxygen pressure,the ratio of combustion improver and the mass of samples.Then the HoC of various systems were obtained.Limiting oxygen index(LOI),back temperature test,cone calorimetry(CONE)and X ray photoelectron spectroscopy(XPS)were used to characterized the relationships between HoC,flame retardant mechanisms and flame retardant properties.Results show that the HoC of flame retardant system depend on the elementary composi tion of polymers,the HoC of flame retardants and the flame retardant mechanism.The chemical in-tumescent flame retardant system RPUF/APP has the lowest HoC.The physical in-tumescent flame retardant system RPUF/EG has higher HoC than combined system RPUF/EG/APP.RPUF/TCPP and RPUF/MCA are in the middle.Besides RPUF/EG and RPUF/EG/APP,HoC of other systems decreased with the increase of LOI and barrier action of char layer.Meanwhile,HoC decreased with the reducing of heat released rate and mass loss rate.(2)To reduce the production of smoke and toxicity of flame retardant RPUF,three types of zinc salts,ZnAl2O4,ZnFe2O4,and Zn2SiO4 were prepared.Potential smoke and toxicity suppression by zinc salts in flame retardant polyur e-thane-polyisocyanurate foams(FPUR-PIR)with dimethylmethyl phosphonate(DMMP)and tris(2-chloropropyl)phosphate(TCPP)were investigated.Zinc salts decreased the smoke production in the smoke density rating(SDR)test.CONE test showed that zinc salts delayed the time to second heat release rate peak(pk-HRR)and increased the char residue amount by 3%7%.The evolved gases were an a-lyzed by thermogravimetry coupled with FTIR spectrophotometry(TGA-FTIR).It revealed that zinc salts partially inhibited phosphorus oxide release in to the gas phase,enhanced the condensed phase effect of phosphorus,and delayed the release of isocyanate compounds and hydrogen cyanide from FPUR-PIR.ZnFe2O4 resulted in better char formation at the initial degradation stage of FPUR-PIR and showed an excellent performance in smoke suppression compared with other zinc salts.(3)Based on the research of zinc salts,zinc ferrite,copper ferrite and nickel ferrite were synthesized and incorporated in flame retardant polyurethane-polyisocyanurate(FPUR-PIR)foams with TCPP and DMMP.CONE test showed that ferrites reduced the smoke and toxicity production and improve the flame re-tardancy of PUR-PIR.The addition of ferrites decreased average specific extinction area(av-SEA)of FPUR-PIR by 35%,reduced the total smoke release about 20%and increased residue at 800oC by 8%9%.XPS was employed to analyze the composition of char residue,ZnFe2O4 increased the phosphorus percent in char residue from 0.7%to 3.7%,oxygen content from 14.1%to 25.4%and decreased the C/O ratio from 5.5 to 2.7.Meanwhile,the content of C-C and C=C groups which can improve the thermal oxidation resistance of char layer were increased.The in-vestigations of TG-FTIR and X-ray diffraction(XRD)revealed that ZnFe2O3 re-acted with phosphonates and generated metal phosphate,which enable to keep more fragments from the decomposition of phosphonates in the condensed phase and at-tend to the char formation.At the same time,ferrites reacted with PUR-PIR,the Lewis acid action of ferrites catalyzed the dehydration of PUR-PIR,facilitated the crosslinking of thermal degradation fragments and promote to form the thermal stable char layer,reduced the smoke and toxicity production.(4)The acid catalysis of boron phosphate(BP)in hydroxyl compounds was investigated by adding BP in model compound dipentaerythritol(DPER).BP showed a strong catalysis and char forming action in DPER.Based on this,BP as flame retardant synergist was filled in FPUR-PIR.The smoke suppression and char forming action by acid catalysis of BP were investigated.BP showed a positive a c-tion in increase the flame retardancy.The addition of 3 wt%BP decreased the HRR,TSR and COP by CONE test.But the addition of 5 wt%and 8 wt%BP would de-teriorated the flame retardancy,smoke production was significantly increased.The analysis of evolved gases by TG-FTIR-MS show that BP advanced the release of decomposition gases,reduced the intensity of CO2,-NCO compounds and PO·compounds.Therefore,the smoke and toxicity of FPUR-PIR in combustion were decreased.In additional,the char residue was characterized by XPS,the ad-dition of 3 wt%BP increase the content of graphitic carbon from 52.5%to 58.4%.It means that the thermal oxidation resistance of char layer was improved.
Keywords/Search Tags:rigid polyurethane-polyisocyanurate foams, heat of combustion, flame retardancy, smoke suppression, metal salts, acid catalysis
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