Reduction In Peak Heat Release Rate Research Articles

Effects of carbon nanotubes and its functionalization on the thermal and flammability properties of polypropylene/wood flour composites

In this article, pristine carbon nanotubes (CNTs) and hydroxylated CNTs (CNT-OH) were employed to enhance the thermal stability and flame retardancy of polypropylene (PP)/wood flour composites (WPC) compatibilzed by maleic anhydride-grafted polypropylene (PP-g-MA). Incorporating 10 wt% PP-g-MA only enhanced the mechanical and thermal properties to some extent, but did not improve the flame retardancy of WPC. Thermogravimetric analysis (TGA) showed that the thermal stability of WPC was further increased with the addition of CNTs or CNT-OH and the increase of their loading level. Cone calorimeter measurements suggested that CNTs and CNT-OH could effectively reduce the peak heat release rate (PHRR) of WPC, and the flame retardancy properties reached the optimum value when both of their loading was 1.0 wt%, for instance, a reduction in PHRR by 16.7% and 25% for CNTs and CNT-OH, respectively. In addition, CNT-OH conferred better flame retardancy on WPC relative to pristine CNTs due to the better interfacial adhesion with wood flour and PP matrix, which was evidenced by scanning electron microscopy (SEM) observations.

Synergistic effect of carbon nanotubes and decabromodiphenyl oxide/Sb 2O 3 in improving the flame retardancy of polystyrene

Brominated flame retardant polystyrene composites were prepared by melt blending polystyrene, decabromodiphenyl oxide, antimony oxide, multi-wall carbon nanotubes and montmorillonite clay. Synergy between carbon nanotubes and clay and the brominated fire retardant was studied by thermogravimetric analysis, microscale combustion calorimetry and cone calorimetry. Nanotubes are more efficient than clay in improving the flame retardancy of the materials and promoting carbonization in the polystyrene matrix. Comparison of the results from the microscale combustion calorimeter and the cone calorimeter indicate that the rate of change of the peak heat release rate reduction in the microscale combustion calorimeter was slower than that in the cone. Both heat release capacity and reduction in the peak heat release rate in the microscale combustion calorimeter are important for screening the flame retardant materials; they show good correlations with the cone parameters, peak heat release rate and total heat released.

Flame retardancy mechanisms of bisphenol A bis(diphenyl phosphate) in combination with zinc borate in bisphenol A polycarbonate/acrylonitrile–butadiene–styrene blends

Bisphenol A polycarbonate/acrylonitrile–butadiene–styrene (PC/ABS) with and without bisphenol A bis(diphenyl phosphate) (BDP) and 5 wt.% zinc borate (Znb) were investigated. The pyrolysis was studied by thermogravimetry (TG), TG-FTIR and NMR, the fire behaviour with a cone calorimeter applying different heat fluxes, LOI and UL 94. Fire residues were examined with NMR. BDP affects the decomposition of PC/ABS and acts as a flame retardant in the gas and condensed phases. The addition of Znb results in an additional hydrolysis of PC. The fire behaviour is similar to PC/ABS, aside from a slightly increased LOI and a reduced peak heat release rate, both caused by borates improving the barrier properties of the char. In PC/ABS + BDP + Znb, the addition of Znb yields a borate network and amorphous phosphates. Znb also reacts with BDP to form alpha-zinc phosphate and borophosphates that suppress the original flame retardancy mechanisms of BDP. The inorganic–organic residue formed provides more effective flame retardancy, in particular at low irradiation in the cone calorimeter, and a clear synergy in LOI, whereas for more developed fires BDP + Znb become less effective than BDP in PC/ABS with respect to the total heat evolved.

Polymer nanocomposites using zinc aluminum and magnesium aluminum oleate layered double hydroxides: Effects of the polymeric compatibilizer and of composition on the thermal and fire properties of PP/LDH nanocomposites

A series of five oleate-containing layered double hydroxides with varied ratios of zinc to magnesium, i.e., with the general formula Zn 2− y Mg y Al(OH) 6 [CH 3(CH 2) 7CH CH(CH 2) 7COO]· nH 2O, were synthesized and used to prepare nanocomposites of polypropylene (PP). The nanomaterials were characterized by elemental analysis, attenuated total reflection-infrared spectroscopy (ATR-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA), while the composites were characterized by XRD, TGA, transmission electron microscopy (TEM) and cone calorimetry. The zinc-containing LDH showed better dispersion in the polymer at the micrometer level than did the magnesium-containing LDH while both are equally well-dispersed at the nanometer level. The magnesium-containing composites led to more thermally stable systems in TGA experiments, while the zinc systems gave greater reductions in heat release rate during combustion. Dispersion was also affected by the amount of PP- g-MA which was present. More PP- g-MA gave better dispersion and a significantly reduced peak heat release rate, i.e., enhanced fire performance.

Heat release and burning behaviour of foam and foam/Basofil fabric combination

A comprehensive characterization of the heat release rate and burning behaviour of foam and foam/Basofil fabric combination has been carried out at different levels of heat flux varying from 10 to 70 kW/m 2 using cone calorimetry. Peak heat release rate (PHRR) was found to increase for foam and foam/fabric combination with the increase in the level of heat flux. However, considerable reduction in PHRR was noted for foam/fabric combination vis-à-vis that of foam alone. Foam/fabric combination was found to exhibit two-step decomposition behaviour at heat flux levels of 40 kW/m 2 and above due to the cracking of the char formed from the cover fabric. Flashover potential of the foam was considerably reduced by the fabric covering the foam. Carbon dioxide and carbon monoxide yields were found to be lower for foam/fabric combination. Smoke toxicity, as indicated by the index of combustion completeness, was found to be lower for the foam/fabric combination.

The bonding of a hydroxy-functional organophosphorus oligomer to nylon fabric using the formaldehyde derivatives of urea and melamine as the bonding agents

In this research, we studied the mechanism of bonding a hydroxy-functional organophosphorus oligomer (HFPO) to nylon 6.6 fabric using the formaldehyde derivatives of urea and melamine, including dimethyloldihydroxyethyleneurea (DMDHEU) and trimethylolmelamine (TMM), as the bonding agents. The nylon fabric treated with HFPO/DMDHEU or HFPO/TMM retained significant amount of phosphorus after multiple launderings. The laundering durability of the HFPO applied to nylon was probably attributed to the formation of a crosslinked polymeric network on the nylon fiber. The nylon fabric treated with HFPO/DMDHEU showed higher percent phosphorus retention than that treated with HFPO/TMM. The percent phosphorus retention of the treated nylon increased as the DMDHEU or TMM concentration was increased, and the nylon fabric's stiffness follows the same trend. The micro-scale combustion calorimetry and thermal analysis data indicate that the HFPO bound to nylon reduced peak heat release rate and heat release capacity of the nylon fabric, decreased decomposition temperature and promoted the char formation of the treated fabric. The nylon/cotton blend military fabric treated with HFPO/DMDHEO or HFPO/TMM demonstrated flame retardant performance after 10 laundering cycles.

C60 reduces the flammability of polypropylene nanocomposites by in situ forming a gelled-ballnetwork

The thermal and flame retardancy properties of polypropylene/fullerene(PP/C60) nanocomposites were investigated by thermogravimetric analysis (TGA),differential scanning calorimetry (DSC) and cone calorimetry with theC60 loading varied from 0.5 to 2% by weight. Dispersion ofC60 in the PP matrix was characterized by transmission electron microscopy (TEM) andoptical microscopy (OM). TGA and DSC results showed that the presence ofC60 could remarkably enhance the thermal property and cone calorimeter measurements suggested thatC60 could to some extent reduce the flammability of PP, with a significant reduction in peak heatrelease rate and a much longer time to ignition. Furthermore, the larger the loading level ofC60, the better the flame retardancy property ofPP/C60 nanocomposites. The flame retardation mechanism and corresponding model wereproposed with the help of rheological measurements, TEM and x-ray diffraction.C60 reduced the flammability of PP by trapping free radicals in the gas phase and in situforming a gelled-ball crosslink network to improve the flame retardancy of PP in thecondensed phase. Finally, this suggested mechanism was supported by the results ofadvanced rheological extended systems (ARES), gel content, infrared spectrum, OM, andatomic force microscopy (AFM) measurements.

Effect of heat flux on the burning behaviour of foam and foam/Nomex III fabric combination in the cone calorimeter

A comprehensive characterization of the burning behaviour of foam and foam/fabric combination has been carried out at different levels of heat flux varying from 10 to 70 kW/m 2 using cone calorimetry. Peak heat release rate (PHRR) was found to increase for foam and foam/fabric combination with increase in the level of heat flux. However, considerable reduction in PHRR was noted for foam/fabric combination vis-à-vis that of foam alone. Foam/fabric combination was found to exhibit two-step decomposition behaviour at heat flux levels of 50 kW/m 2 and above. Carbon dioxide and carbon monoxide yields were found to be lower for foam/fabric combination. Smoke toxicity, as indicated by the index of combustion completeness, was found to be lower for the foam/fabric combination.

Fire retardancy of polyethylene‐alumina trihydrate containing clay as a synergist

AbstractThe fire behavior of polyethylene combined with alumina trihydrate (ATH) and an oligomerically‐modified clay has been studied. The combination of polyethylene with 2.5% inorganic clay and 20% ATH gives a 73% reduction in the peak heat release rate (PHRR), which is the same as that obtained when 40% ATH is used alone. A further increase in the clay loading does not improve the fire properties. Mechanical properties, such as elongation at break, can be improved in comparing compounds with or without clay at the same reduction in PHRR. The oligomerically‐modified clay can also facilitate the melt blending process. Copyright © 2005 John Wiley & Sons, Ltd.

Flammability of Polymer-Clay and Polymer-Silica Nanocomposites

A comprehensive discussion on the flammability of organic-inorganic nano-composites is presented based on different fire testing methods. Based on various flammability tests, reduced peak heat release rate, an increased oxygen index, and an enhanced thermal stability were observed, while faster burning rates were found when the nanocomposites underwent horizontal and vertical burning tests. Moreover, it has also been found that when traditional flame-retardant additives were added to the nanocomposites, less additive was required to achieve the same level of flame retardancy.

Synergy between nanocomposite formation and low levels of bromine on fire retardancy in polystyrenes

An organically-modified clay has been prepared using ammonium salts which contain an oligomeric material consisting of vinylbenzyl chloride, styrene and dibromostyrene. The presence of dibromostyrene enhances the flame retardancy of polystyrene nanocomposites compared to both the virgin polymer and polystyrene nanocomposites prepared from non-halogen-containing organically-modified clays. The nanocomposites were prepared both by bulk polymerization and melt blending and they were evaluated by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis and cone calorimetry measurements. Bulk polymerization produced nanocomposites with reduced peak heat release rate, reduced total heat release and improved thermal stability. It is noteworthy that all these improvements were obtained with clay loading as low as 3% and bromine content less than 4%.

Thermal stability and flammability of polypropylene/montmorillonite composites

Smectite clays, such as montmorillonite, are of great industrial value because of their high aspect ratio, plate morphology, intercalative capacity, natural abundance and low cost. In the present work, polypropylene/montmorillonite (PP/MMT) composites have been prepared and their thermal stability and flammability have been investigated. Although the composites are not nano-dispersed, they exhibit higher thermal stability and considerably reduced peak heat release rate (PHRR). This is probably due to physico-chemical adsorption of the volatile degradation products on the silicates. On the other hand, the addition of MMT can catalyse the initial decomposition of PP matrix and accelerate its ignition in combustion. It has been observed that a ceramic-like char formed on the surface of the composites during the combustion test. The characterization of the char surface prior to ignition indicates that it is an inorganic-rich surface, leading to improvement of the thermal stability and reduction of flammability of the composites because of its better barrier properties.

Flame retardancy of polystyrene nanocomposites based on an oligomeric organically-modified clay containing phosphate

Novel modified clays, which may enable the formation of flame retarded polystyrene nanocomposites by melt or solution blending, have been prepared using an ammonium salt which contains an oligomeric material consisting of vinylbenzyl chloride, styrene and vinyl phosphate reacting with dimethylhexadecylamine. These nanocomposites have been characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, cone calorimetry and the evaluation of mechanical properties. Melt blending is an effective, economical way to produce intercalated nanocomposites with greatly reduced peak heat release rate and a decreased total heat release; the polymer does not all undergo thermal degradation.

A Cone Calorimetric Study of Flame Retardant Elastomeric Polyurethanes Modified with Siloxanes and Commercial Flame Retardant Additives

Polyurethanes are the single most versatile family of polymers with a wide range of applications. There is a substantial need for the development of polyurethane materials with low heat release rate and low smoke release rate. In this study, an extensive series of elastomeric polyurethanes based on diphenylmethane-4,4'-diisocyanate (MDI) prepolymers were prepared and fur ther modified with fluid and powered siloxanes and conventional flame retardant additives. The flame retardant behavior of these polymers was studied using the Cone Calorimeter (ASTM E-1354), the instrument that has emerged as an impor tant tool for the analytical testing of materials for their fire properties. ** All pow dered siloxane additives used in this study, even at 5% loading level, gave a 70-80% reduction in peak heat release rates compared to standard materials.The reductions of peak HRR of fluid siloxane-modified materials compared to the base material were in the range of 49-78%. The conventional flame retardant addi tives used in this study also reduced peak heat release rate dramatically. The syn ergistic effect of conventional flame retardant additives with siloxane powders is discussed.

Cotton in roads

In this research, we studied the mechanism of bonding a hydroxy-functional organophosphorus oligomer (HFPO) to nylon 6.6 fabric using the formaldehyde derivatives of urea and melamine, including dimethyloldihydroxyethyleneurea (DMDHEU) and trimethylolmelamine (TMM), as the bonding agents. The nylon fabric treated with HFPO/DMDHEU or HFPO/TMM retained significant amount of phosphorus after multiple launderings. The laundering durability of the HFPO applied to nylon was probably attributed to the formation of a crosslinked polymeric network on the nylon fiber. The nylon fabric treated with HFPO/DMDHEU showed higher percent phosphorus retention than that treated with HFPO/TMM. The percent phosphorus retention of the treated nylon increased as the DMDHEU or TMM concentration was increased, and the nylon fabric's stiffness follows the same trend. The micro-scale combustion calorimetry and thermal analysis data indicate that the HFPO bound to nylon reduced peak heat release rate and heat release capacity of the nylon fabric, decreased decomposition temperature and promoted the char formation of the treated fabric. The nylon/cotton blend military fabric treated with HFPO/DMDHEO or HFPO/TMM demonstrated flame retardant performance after 10 laundering cycles.