Thermal analysis and other techniques were employed to characterize two expandable graphite samples. The expansion onset temperatures of the expandable graphite's were ca.220°C and 300°C respectively. The key finding is that the commercial products are not just pure graphite intercalation compounds with sulfuric acid species intercalated as guest ions and molecules in between intact graphene layers. A more realistic model is proposed where graphite oxide-like layers are also randomly interstratified in the graphite flakes. These graphite oxide-like layers comprise highly oxidized graphene sheets which contain many different oxygen-containing functional groups. This model explains the high oxygen to sulfur atomic ratios found in both elemental analysis of the neat materials and in the gas generated during the main exfoliation event.

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Graphite foams were prepared from a coal tar pitch that was partially converted into mesophase. Expandable graphite was used instead of an inert gas to "foam" the pitch.

A novel intumescent additive was synthesized by neutralizing 3,5-diaminobenzoic acid hydrochloride salt with ammonium dihydrogen phosphate. This compound, which melts at 257°C, decomposes concurrently to release carbon dioxide gas. The flame retardant performance of this compound as a primary fire retardant and in combination with expandable graphite was evaluated by cone calorimetry. Cone calorimeter results revealed that addition of 10 wt.% expandable graphite alone lowers peak heat release rate of carbon black-pigmented polyethylene from 710 ± 109 kW m -2 to 342 ± 15 kW m -2 , while addition of 27 wt.% of the novel intumescent lowered it to 400 ± 16 kW m -2 . Combinations of these two additives were able to decrease the peak heat release rate even further. Furthermore, the novel intumescent additive reduced the flame out time from 773 ± 307 s to 537 ± 69 s although all other expandable graphite containing samples increased it.

Polyethylene was flame retarded with an intumescent flame retardant at 27 wt.% and expandable graphite at 10 wt.% either on its own or in combination with 10 wt.% or 20 wt.% of the intumescent. Two grades of each flame retardant type were used. They differed primarily with respect to the onset temperature for exfoliation (commercially sourced expandable graphite types) or decomposition (intumescents). The latter were the highdecomposition-onset-temperature intumescent 3,5-diaminobenzoic acid phosphate and the commercially available low-decomposition-onset-temperature ethylenediamine phosphate. The fire performance of pressed sheets with a nominal thickness of 3.2 mm was tested in a cone calorimeter at a radiant flux of 35 kW m 2 . The best char yields were obtained with compositions containing 3,5-diaminobenzoic acid phosphate. Despite this, the best fire overall performance was realized using ethylenediamine phosphate, together with the lowexfoliation-onset-temperature expandable graphite. Formulations based on this intumescent compound ignited later, reached the peak heat release rate earlier, and also burned longer irrespective of the expandable graphite grade used. This can be attributed to the formation, at the burning surface, of a more cohesive char with better thermal and mass transfer barrier properties. This explains why compositions based on ethylenediamine phosphate as intumescent outperformed those containing 3,5-diaminobenzoic acid phosphate in terms of the peak heat release rate and other important fire indices.

Summary Low‐density polyethylene was flame retarded by combinations of expandable graphite with either ethylenediamine phosphate or 3,5‐diaminobenzoic acid phosphate. Cone calorimeter, laser pyrolysis, and open flame exposure tests (supported by video and infrared camera data capture and analysis) were conducted to assess ignition and burn behavior. Cone calorimeter results indicated substantial reductions in the peak heat release rates for all flame‐retarded samples but with reduced ignition times and increased flame out times. Smoke generation was suppressed in the presence of expandable graphite. Infrared and video data from open flame fire tests indicated cohesive bonding of expanded strings and thermal shielding properties in all binary systems. All binary systems delivered fire retardation exceeding any of the single fire retardant compounds. They were also able to withstand higher temperatures before ignition, burn through, or sag occurred. All ethylenediamine phosphate‐containing binary systems prevented sample burn through, maintaining structural integrity of samples until eventual melting of the polymer media occurred. Thermogravimetric analysis laser pyrolysis results confirmed the good thermal shielding imparted by the intumescent additives. Copyright © 2016 John Wiley & Sons, Ltd.