An intumescent flame retardant - expandable graphite: Preparation, characteristics and flame retardance for polyethylene



A combined intumescent flame retardant expandable graphite (EG), with an initial expansiontemperature of 155°C and expansion volume of 515 mL g-1, was successfully prepared based ona chemical intercalation method of material graphite under oxidation of KMnO4, intercalationof H2SO4 and Na4B2O7· 10H2O at the mass ratio C : KMnO4 : H2SO4 (98%) : Na 4B2O7· 10H2Oof 1.0 : 0.4 : 5.5 : 0.6 (H2SO4 diluted to a mass concentration of 80-wt. % before reaction),and characterized by expansion volume (EV), initial expansion temperature, X-ray diffraction(XRD). The flame retarding and thermal properties of LLDPE/EG and LLDPE/EG/APPcomposites (LLDPE-Linear low density polyethylene; APP-ammonium polyphosphate) wereinvestigated and characterized by limiting oxygen index (LOI), Fourier transform infraredspectroscopy (FTIR), thermal gravimetric (TG) and differential thermal analysis (DTA). Theresults showed that addition of EG (30-wt. %) increased the LOI of 70LLDPE/30EG compositeto 28.4 %. Even more, the synergistic effect of 20% EG together with 10% APP improvedthe LOI of 70LLDPE/20EG/10APP composite to 30.5%. At the same time, temperaturescorresponding to a 1% weight loss and a maximum weight loss rate increased at about 50°C and2°C, respectively. The 70LLDPE/10APP/20EG composite exhibited higher flame retardancyeven at a lower residual chars than 70LLDPE/30EG specimen. Cohesive and dense charlayer caused by swollen expanded graphite and decomposing products of APP played a moreimportant role in improving thermal stability and flame retardancy than weight of residualcarbon. The intercalated borate was more effectual in improving the flame retardancy than thedirect additive of Na4B2O7· 10H2O.


Borate; expandable graphite; intumescent flame retardant; polyethylene; synergistic efficiency

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