Anisotropy of expandable graphite to explain its behavior as a flame-retardant (original) (raw)
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Journal of Fire Sciences, 2014
Polyethylene was flame retarded with two intumescent-type additives, 3,5-diaminobenzoic acid phosphate and ethylenediamine phosphate, which differ with respect to their decomposition onset temperatures, along with varying ratios of two grades of expandable graphite, also differing with respect to their onset temperatures for exfoliation. Hot-pressed sheet specimens were subjected to evaluation in a cone calorimeter. Although the best char yields were obtained with formulations containing the higher decomposition temperature intumescent, 3,5-diaminobenzoic acid phosphate, the overall best performance was realized using the lower decomposition temperature intumescent, ethylenediamine phosphate, when compounded together with the low exfoliation temperature expandable graphite. These results are attributed to the formation, at the burning surface, of a more cohesive char with better thermal and mass transfer barrier properties.
Intumescent polypropylene: Reaction to fire and mechanistic aspects
Fire Safety Journal, 2019
The concept of intumescence was applied to make flame retarded polypropylene (PP). This paper examines two types of intumescence in PP based on expandable graphite (EG, physical expansion) and on modified ammonium polyphosphate (AP760, chemical expansion). Reaction to fire of PP containing EG and AP760 was first evaluated by cone calorimetry. The incorporation of intumescent additives at relatively low loading (10 wt%) in PP permits the reduction by 70% of peak of heat release rate (pHRR). The mode of action occurs via the formation of an expanded carbonaceous layer in all cases. The protective coating acts mainly as heat barrier in the case of the formulations containing AP760 or as heat dissipater with EG. The incorporation of small amount of EG in PP-AP760 modifies heat transfer in the coating creating a strong anisotropy. Upon expansion, graphite worms align normal to the surface increasing the transverse heat conductivity (lower efficiency of the heat barrier) and hence, decreasing the fire performance (decrease by only 30% of pHRR). Kinetic analysis was then performed to quantify the thermal stability of the intumescent systems. It reveals that the intumescent additives do not modify the reactional scheme of the PP thermal decomposition but they increase slightly the thermal stability of the intumescent systems. For all materials, the decomposition model follows a reactional scheme at two successive reactions. This model was determined in dynamic conditions (conditions of thermogravimetry with linear heating rates) but it is able to simulate the decomposition of the materials in isothermal conditions (excellent agreement between the simulated and experimental curves).
Flexible PVC flame retarded with expandable graphite
Polymer Degradation and Stability, 2014
The utility of expandable graphite as a flame retardant for PVC, plasticized with 60 phr of a phosphate ester, was investigated. Cone calorimeter results, at a radiant flux of 35 kW m À2 , revealed that adding only 5 wt.% expandable graphite lowered the peak heat release rate from 325 AE 11 kW m À2 to 63 AE 23 kW m À2 and the total heat release from 55 AE 11 MJ m À2 to only 10.7 AE 0.3 MJ m À2 . All samples containing expandable graphite ignited and burned only very briefly before flame out. The remarkable effectiveness of the expandable graphite is attributed to an excellent match between the exfoliation onset temperature of the graphite and the onset of decomposition of the PVC. This means that the exfoliation of the graphite forms a protective barrier layer at the right place at the right time. In addition, the simultaneous release of halogen species by the polymer matrix and the exfoliating graphite prevents the formation of a flammable air fuel mixture.
Influence of physical properties on polymer flammability in the cone calorimeter
Polymers for Advanced Technologies, 2011
The relationship between physical properties and fire performance as measured in the cone calorimeter is not well understood. A number of studies have identified relationships between the physical and chemical properties of polymeric materials and their gasification behaviour which can be determined through numerical pyrolysis models. ThermaKin, a one-dimensional pyrolysis model, has recently been employed to predict the burning behaviour in fire calorimetry experiments. The range of thermal, chemical and optical properties of various polymers have been utilised to simulate the processes occurring within a polymer exposed to a uniform heat flux, such as in a cone calorimeter. ThermaKin uses these material properties to predict the mass flux history in a cone calorimeter. Multiplying the mass flux history by the heat of combustion of the fuel gases gives the HRR history and these have been calculated for cone calorimeter experiments at 50 kW m-2 incident heat flux for the lowest, average and highest values of physical parameters exhibited by common polymers. In contrast with actual experiments in fire retardancy, where several parameters change on incorporation of an additive, this study allows for the effect of each parameter to be seen in isolation. The parameters used in this study are grouped into physical properties (density, heat capacity and thermal conductivity), optical properties (absorption and reflectivity), and chemical properties (heat of decomposition, kinetic parameter and heat of combustion). The study shows how the thermal decomposition kinetic parameters effect the surface burning (pyrolysis) temperature and resulting heat release rate history, as well as the relative importance of other properties directly related to the chemical composition. It also illustrates the effect of thermal inertia (the product of density, heat capacity and thermal conductivity) and of the samples' ability to absorb radiant heat.
Thermal characteristics of expandable graphite as a burning rate enhancer in hybrid propulsion
Propellants, Explosives, Pyrotechnics, 2023
According to the Fire Statistics Yearbook of the National Fire Agency of the Republic of Korea, the total number of fires in 2018 was 42,338, which resulted in 2500 victims and amounted to property damages of approximately 560 billion KRW. The number of fires in buildings where wood was used as a finishing material was 28,013 (66%) in that period. To minimize human and property damage, composite materials were prepared by mixing wood particles with expandable graphite. The physical and thermal properties of the composite materials were investigated. It was observed that the expansion rate increased by 341.7% according to the expandable graphite content. Additionally, the total heat released and the thermal conductivity decreased from 38.63 to 2.5 MJ/m 2 and from 24.62 to 7.8 W/m•K. The time to inactivity of white mouse in the smoke toxicity test was 14.9 min and exceeded the toxicity standard for flame retardant performance. The expandable graphite added to composite materials adopted worm-like shapes as a result of combustion, and it formed a fine lattice layer structure with 16-22 µm gaps that could reduce thermal conductivity. In addition, we can minimize the damage to people and property in the event of a fire.
Thermal Measurements on Polymeric Epoxy-Expandable Graphite Material
International Journal of Polymer Science, 2016
Combustion measurements, such as heat release rate, critical flux, time-to-ignition, ignition temperature, thermal inertia, and kinematics—activation energy as well as preexponential factor—on epoxy polymer (Prime™20LV) with expandable graphite (EG) inorganic filler of different weight percentage composites, are conducted using the Dual Cone Calorimeter, the thermogravimetric analysis (TGA), and Linseis (Germany) THB100 Transient Hot Bridge thermal conductivity analyser. The results indicate that increasing the amount of EG in polymer composite leads to reduction in the critical flux, the time-to-ignition, the ignition temperature, the thermal inertia, the average thermal conductivity, and the activation energy (from 159.1 ± 2.3 to 145.9 ± 3.1 kJ/mol for neat epoxy to 3 wt.% EG-epoxy) of the composite samples. There is, however, an increase in the heat of gasification with increasing EG content.
Fire behaviors of polymers under autoignition conditions in a cone calorimeter
Fire Safety Journal, 2013
Besides piloted ignition, autoignition is also an important aspect to real fire development as combustible materials may be ignited without independent flame. Fire behaviors of non-charring and charring polymers were then investigated in a cone calorimeter under autoignition conditions. Fire risk of non-charring polymers are higher than those of charring polymers because of high heat release, and the increase of heat release rate is much obvious with a higher heat flux or thickness. Charring polymers seem to have a higher CO yield, while non-charring polymers have a higher CO2 yield. Ignition methods have influences to combustion efficiency of non-charring polymers as effective heat of combustion under autoignition are observed lower than those reference data under piloted ignition conditions. Its influences to charring polymers are not obvious. Both CO and CO2 yields under flaming combustion are higher than those under non-flaming combustion, but mass percent of carbon seem to has limited effect. Experimental data in this study can provide a guidance to fire risk evaluation of non-charring and charring polymers.
Prediction of the burning rates of non-charring polymers☆
Combustion and Flame, 2009
This study provides a thorough examination of whether a numerical pyrolysis model, which describes transient energy transport and chemical reactions taking place in a one-dimensional object, can be used as a practical tool for prediction and/or extrapolation of the results of fire calorimetry tests. The focus is on non-charring polymers, in particular-poly(methylmethacrylate), high-impact polystyrene, and highdensity polyethylene. First, relevant properties of these materials were measured and/or obtained from the literature. Subsequently, the values of these properties were used to simulate gasification and cone calorimetry experiments, which were performed under a broad range of conditions. A comparison with the experimental results indicates that the model gives reasonably good predictions of the mass loss and heat release histories. It also predicts the evolution of temperature inside the material samples.