Study On Novel Halogen-Free Expandable Graphite And Its Flame-Retarded Material

It is widely reported that Expandable Graphite (EG) not only possesses the unique characteristic properties of graphite, but also takes on the unusual chemical and physical properties because of the interactions betweeen intercalated agents and graphite layers. As a typical physical intumescent flame retardant, the study and application of EG have recently become a hot topic in flame retardant fields.In this paper, two methods, direct intercalation and two-step method were used to prepare EG and the process and reaction conditions were discussed in detail. EG intercalated wtih nitrate or phosphorous compounds were successfully prepared by two-step method. The properties of EG as prepared were investigated by expansion volume, weight increment, weight loss and the structure was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS). Moreover, the synergistic flame retardant properties of EG with aluminum trihydrate (ATH) or chemical intumescent flam retardants (IFR) were also studied. Thus, novel flame retardant compounds with high flame retardant efficiency were obtained and used to develop halogen-free flame retardant material with excellent mechanical and flame retardant properties.Following results can be obtained in the paper: (1) Products prepared by two-step method show bigger expansion volume, higher thermal stabilities and more mass increment than those by direct intercalation method, revealing that the two-step method is a better method to prepare EG. Meantime, the moderate reaction temperature of two-step method can be helpful to decrease the danger during experiments. (2) The expansion volume of EG has a linear relationship with the mass increment after intercalation reaction and the weight loss after expansion. Reaction conditions, such as reation time, reaction temperature, dosage of oxidizer, play important roles on the properties of EG. (3) Nitrate as cointercalated agents, was successfully intercalated into the graphite interlayers. EG, as prepared, shows promising expansion volume. For example, the expansion volume of Fe(NO₃)₃-H₂SO₄-EG is 450mL/g and that of NaNO₃-H₂SO₄-EG is 420mL/g. (4) EGs intercalated with phosphorous compounds are successfully prepared. As a result, the expansion volumes of H₃PO₄-H₂SO₄-EG, (NH4)3 PO₄- H₂SO₄-EG and APP-H₂SO₄-EG are 230 mL/g, 280 mL/g and 240mL/g, respectively. The oxidation resistance of EG, as prepared, was obviously improved. (5) EG with different intercalated compounds shows different flame retardant properties. At 25% loading level, the LOI values of EVA flame retarded by Fe(NO₃)₃-H₂SO₄-EG, H₃PO₄-H₂SO₄-EG, (NH₄)₃PO₄-H₂SO₄-EG or APP-H2SO4-EG can reach 21.2%, 26.5%, 27.8% and 29.2%, respectively. Among all EGs prepared, APP-H₂SO₄-EG possesses the best flame retardant property. (6) EG as prepared in the paper possesses better flame retardant properties than traditional flame retardants, such as ATH and IFR. Obvious synergistic effects of EG/ATH or EG/IFR can be found. Base on this, flame retardant materials with good properties have been developed.