Synthesis and characterization of polyethylene

Abstract

A combined intumescent flame retardant expandable graphite (EG), with an initial expansion temperature of 155°C and expansion volume of 515 mL g-1, was successfully prepared based on a chemical intercalation method of material graphite under oxidation of KMnO4, intercalation of H2SO4 and Na4B2O7· 10H2O at the mass ratio C : KMnO4 : H2SO4 (98%) : Na4B2O7· 10H2O of 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/APP composites (LLDPE-Linear low-density polyethylene; APP-ammonium polyphosphate) were investigated and characterized by limiting oxygen index (LOI), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric (TG) and differential thermal analysis (DTA). The results showed that addition of EG (30-wt. %) increased the LOI of 70LLDPE/30EG composite to 28.4 %. Even more, the synergistic effect of 20% EG together with 10% APP improved the LOI of 70LLDPE/20EG/10APP composite to 30.5%. At the same time, temperatures corresponding to a 1% weight loss and a maximum weight loss rate increased at about 50°C and 2°C, respectively. The 70LLDPE/10APP/20EG composite exhibited higher flame retardancy even at a lower residual char than 70LLDPE/30EG specimen. The intercalated borate was more effectual in improving the flame retardancy than the direct additive of Na4B2O7· 10H2O.