Synergistic Effect Of Expandable Graphite And Different Additives On Flame-retardant Properties Of Rigid Polyurethane Foam

Rigid polyurethane foam (RPUF) with small thermal conductivity, high compressiveproperty, good bondability, etc, are widely used for thermal insulationin exterior wall ofbuilding, keeping pipes heat or cold, and other fields. However, RPUF could burn easily andproduce toxic smog, those smog would harm to human body. Thereby to RUPF usedextensively, flame retardant should be added in RPUF. Expandable graphite (EG) with goodperformance of anti flaming and low pollution， has been payed more attention in numerousflame retardants, but it also has some problems, such as size effect, compatibility, etc. Anothereffective method to improve the flame-retardant properties of RPUF is use two or more flameretardants, especially EG with other flame retardants on RPUF have good applied prospect.In this study, limiting oxygen index (LOI), smoke density rating (SDR),thermogravimetric analysis (TGA) were detected, EG, phosphorus, nitrogen, halogen,inorganic flame retardants and other materials were investigated. EG with different flameretardants added in RPUF were also detected. Orthogonal test and control variable methodwere used to detect DMMP, MCA and ammonium polyphosphate (APP)/pentaerythritol(PER)/melamine(MA) as the compositions of intumescent flame retardant (IFR)combining with EG in the RPUF.The data showed that,(1) When only one flame retardant (20%) was added in RPUF, theLOI values of EG(29.0%) and DMMP (28.1%) were the highest, and for nitrogen and halogensystem, MPP and TCEP had highest LOI (24.8%，25.8%). Inorganic and other materialsincreased LOI limited，but can decreased smoke density.(2) EG with DMMP increased LOI of RPUF most (35.4%). While nitrogen,halogen-containing flame retardants with EG also showed good flame retardant effects. Butthe inorganic flame retardants did not show significant synergistic effects. Compared withRPUF with only one flame retardant, the SDR were improved when EG with other flameretardants added in RPUF, and the maximum smoke desity (MSD) appeared lately with EGincreased. With20%of EG/TCEP (1:1) in RPUF, loss rate of weight loss was declined,amount of residual carbon(700℃) was increased. The data showed EG/TCEP had goodsynergistic flame retardant effect on RPUF.(3) The effect of EG on the LOI was the highest, while DMMP/EG/MCA was7%/15%/7%, LOI of RPUF up to38.1%, SDR was lowest (45.33%) while DMMP/EG/MCAwas5%/10%/7%. When APP/PER/MA was9%/3%/9%, the LOI was highest (26.5%), andthe SDR was53.31%, the LOI was lower compared with only added EG (29.0%) and SDRlower compare with20%EG. MSD appeared (1min) later than20%IFR (0.75min). The datashowed, various flame retardants added in RPUF showed synergetic effect, the effect of EGon LOI was significant.In conclusion, all kinds of flame retardant with EG added in RPUF could improved LOI, delayed MSD appear time, declined loss rate of weight loss, so synergistic flame retardanteffect was remarkable, therefore EG with flame retardants (system) has extensive appliedprospect.