Reduced Heat Release Research Articles

Preparation and studies of new phosphorus‐containing diols as potential flame retardants

SummarySeveral new phosphorus‐containing potential flame retardants (FRs) were prepared and evaluated for heat release reduction potential, by incorporation of the molecules into polyurethane samples, generated from methylene diphenyl diisocyanate and 1,3‐propane diol. The potential FRs were all prepared from commercial diisocyanates, with the phosphorus‐containing substructure introduced as a semicarbazone. All of the target structures were diols, to facilitate their incorporation into a polyurethane main chain. The polyurethane samples were prepared via copolymerization, and analysis clearly demonstrated that the potential FRs were chemically incorporated, prior to heat release testing. The heat‐release reduction potential of these substances was evaluated using the microcombustion calorimeter. Results demonstrated that both heat release reduction potential and char formation were structure dependent. Some of the compounds containing an aromatic core had more effect on char formation (higher char yields) and peak heat‐release rate (lowered heat release) than just phosphorus content alone.

Nano-architectured mesoporous silica decorated with ultrafine Co3O4 toward an efficient way to delaying ignition and improving fire retardancy of polystyrene

Aiming to impart polystyrene (PS) with delayed ignition and improved fire retardancy, mesoporous silica SBA-15 decorated with Co3O4 ultrafine nanoparticles (SBA-15@Co3O4) was nano-architectured successfully via multi-step microwave radiation approach. The design principles included: 1) SBA-15 offered the absorbing and labyrinth effect of volatiles 2) the homogeneous and ultrafine dispersion of Co3O4 on SBA-15 interior walls endowed more interacting sites to volatiles. In detail, the obtained SBA-15@Co3O4 was firstly verified using FTIR, Raman, XRD, SEM, TEM and N2 sorption measurement. Compared with neat PS and PS/SBA-15 composites, PS composites with SBA-15@Co3O4 demonstrated significantly enhanced thermal and thermo-oxidation stability. Meanwhile, PS composite with 2wt% SBA-15@Co3O4 (PS/2SBA-15@Co3O4) had a notably better fire retardancy with time to ignition (TTI) value of 116±2s, which was obviously higher than those of PS (98±1s) and PS/2SBA-15 (106±1s). Thermogravimetric analysis coupled with FTIR (TG-FTIR) and mass spectrometry (TG-MS) measurement revealed the probable mechanism of reduced heat release and delayed TTI, which was involved in the adsorption-desorption-combustion mode. Moreover, tensile test illustrated that SBA-15@Co3O4 notably improved the mechanical property of PS. Through this study, nano-architecture of functionalized hybrid offered a novel idea to delay ignition, decrease flammability while improve the mechanical properties for polymeric materials.

Functional organoclay with high thermal stability and its synergistic effect on intumescent flame retardant polypropylene

In this work a novel functional modifier for clay with increased thermal stability and synergistic effect on the flame retardancy of intumescent flame retardant polypropylene (IFR PP) composites was developed. First, triphenyl(undec-10-enyl)phosphonium bromide (TPB) was synthesized and characterized by FT-IR and 1H NMR spectroscopy. TPB has a high thermal stability with an initial decomposition temperature of about 270°C. Subsequently, TPB was used to prepare functional organoclay (OC) by cation exchange reaction. OC was characterized by thermogravimetric analysis (TGA) and wide-angle X-ray scattering (WAXS). The interlayer distance of novel OC increased to 1.85nm. OC was used in IFR PP nanocomposites prepared by melt mixing. The morphology, thermal stability and fire behavior of these IFR PP nanocomposites were investigated by SEM, TEM, TGA, limiting oxygen index (LOI), vertical burning test (UL94), and cone calorimeter (CC) test. In comparison to IFR (18wt%) PP composites, IFR (16wt%)+OC (2wt%) PP nanocomposites passed the UL94 V-0 rating and showed no dripping. The LOI value decreased from 30.5 to 28.8 due to the use of low molar mass TBP. It was shown by cone calorimeter tests that the additional used of 1 or 2wt% OC leads to a reduced heat release rate, smoke production rate and total smoke production. All these experimental results showed that this novel OC provided an excellent synergistic effect on the flame retardancy of IFR PP composites. Finally, electron beam treatment was used to enhance the thermal stability of flame retardant nanocomposites.

Development of waste based biochar/wool hybrid biocomposites: Flammability characteristics and mechanical properties

Due to the realisation of the reinforcement potential of waste based biochar and wool in polymeric composites, in the recent past, their individual flammability, thermal and mechanical properties were determined. Composites were manufactured with biochar and with both biochar and wool in conjunction with the halogen free flame retardant, which was followed by their characterisation through cone calorimeter, limiting oxygen index (LOI), thermogravimetry, tension/flexural tests, and scanning electron microscopy (SEM). Biochar exhibited a high resistance to heat without being ignited and possessed very low heat release and smoke production rates. Wool, although, had relatively high peak heat release rate (PHRR), its advantageous charring ability enabled a gradual reduction in heat release until flameout. The hardness and modulus of biochar were 4.3 GPa and 26 GPa, respectively. The tensile strength and modulus of wool were 160 MPa and 4.8 GPa, respectively. Composites containing biochar and wool significantly reduced the PHRR, smoke production, and elevated the mass loss rate (compared to neat polypropylene/PP). Hybridisation with wool proved to be beneficial for enhancing the LOI. Certain mechanical properties, such as flexural strength and tensile/flexural moduli, were preserved and enhanced, respectively, due to biochar pore infiltration by PP as seen in SEM.

Flame-retardant-wrapped polyphosphazene nanotubes: A novel strategy for enhancing the flame retardancy and smoke toxicity suppression of epoxy resins

The structure of polyphosphazene nanotubes (PZS) is similar to that of carbon nanotubes (CNTs) before modification. For applications of CNTs in polymer composites, surface wrapping is an economically attractive route to achieve functionalized nanotubes. Based on this idea, functionalized polyphosphazene nanotubes (FR@PZS) wrapped with a cross-linked DOPO-based flame retardant (FR) were synthesized via one-step strategy and well characterized. Then, the obtained FR@PZS was introduced into epoxy resin (EP) to investigate flame retardancy and smoke toxicity suppression performance. Thermogravimetric analysis indicated that FR@PZS significantly enhanced the thermal stability of EP composites. Cone calorimeter results revealed that incorporation of FR@PZS obviously improved flame retardant performance of EP, for example, 46.0% decrease in peak heat release rate and 27.1% reduction in total heat release were observed in the case of epoxy composite with 3wt% FR@PZS. The evolution of toxic CO and other volatile products from the EP decomposition was significantly suppressed after the introduction of FR@PZS, Therefore, the smoke toxicity associates with burning EP was reduced. The presence of both PZS and a DOPO-based flame retardant was probably responsible for this substantial diminishment of fire hazard.

Enhanced flame retardancy of flax bio-composites for the construction market

Bio-composites made of natural fibres are an attractive alternative to conventional composites with synthetic fibres such as glass or carbon fibres not only because of their intrinsic properties but also because of their contribution to sustainability. However, natural fibres are flammable, and bio-composites need to be protected against fire for safety reasons but also to meet the strictest EU regulations for the transportation and construction sectors. Thermosetting composites need high loadings of flame retardant additives to achieve satisfactory results in terms of flammability which may lead to significant deterioration in their mechanical properties. This work explores the possibility of reducing the flammability of flax bio-polyester composites with potential use in the transportation and construction sectors through the combination of several novel fire retardant additives, which are halogen-free and considered environmentally friendly. Cone calorimeter tests indicate that proper combinations of fire retardant additives such as alumina trihydrate, ammo- nium polyphosphate and Exolite 740 reduced heat release rate and flammability up to a 60%; delaying the ignition time with respect to the unfilled material. These results were achieved at concentrations much lower than those with tradi- tional solutions. However, the addition of dimethyl propyl phosphonate to the resin formulation with alumina trihydrate and ammonium polyphosphate failed to demonstrate any significant synergistic effect at reducing the heat release rate.

Preparation of modified hollow glass microspheres using Fe2O3 and its flame retardant properties in thermoplastic polyurethane

In this paper, the hollow glass microspheres coated with Fe2O3 (HGM-Fe2O3) were synthesized and characterized by scanning electron microscopy (SEM–EDS) and X-ray photoemission spectroscopy, respectively. Then, the flame retardant and smoke suppression properties of HGM-Fe2O3 in thermoplastic polyurethane (TPU) composites have been investigated intensively using several methods, including cone calorimeter test (CCT), smoke density test (SDT), scanning electron microscopy, and thermogravimetric analysis/infrared spectrometry. The CCT results showed that HGM-Fe2O3 can greatly enhance the flame retardance of polymer matrix materials compared with TPU. For example, HGM-Fe2O3 can reduce heat release rate, total heat release, and smoke release of TPU composites in the combustion process. The SDT results showed that HGM-Fe2O3 can effectively decrease the amount of smoke production in the test. Furthermore, the TG results indicate that HGM-Fe2O3 can decrease the initial decomposition temperature, and change the structure of char residue layer.

Effects of iso-octane/ethanol blend ratios on the observance of negative temperature coefficient behavior within the Ignition Quality Tester

An ignition delay study investigating the reduction in low temperature heat release (LTHR) and negative temperature coefficient (NTC) region with increasing ethanol concentration in binary blends of ethanol/isooctane was conducted in the Ignition Quality Tester (IQT). The IQT is advantageous for studying multi-component fuels such as iso-octane/ethanol which are difficult to study at lower temperatures covering the NTC region in traditional systems (e.g., shock tubes, rapid compression machines, etc.). The high octane numbers and concomitant long ignition delay times of ethanol and iso-octane are ideal for study in the IQT allowing the system to reach a quasi-homogeneous mixture; allowing the effect of fuel chemistry on ignition delay to be investigated with minimal impact from the fuel spray due to the relatively long ignition times. NTC behavior from iso-octane/ethanol blends was observed for the first time using an IQT. Temperature sweeps of iso-octane/ethanol volumetric blends (100/0, 90/10, 80/20, 50/50, and 0/100) were conducted from 623 to 993K at 0.5, 1.0 and 1.5MPa and global equivalence ratios ranging from 0.7 to 1.0. Ignition of the iso-octane/ethanol blends in the IQT was also modeled using a 0-D homogeneous batch reactor model. Significant observations include: (1) NTC behavior was observed for ethanol/iso-octane fuel blends up to 20% ethanol. (2) Ethanol produced shorter ignition delay times than iso-octane in the high temperature region. (3) The initial increase in ethanol from 0% to 10% had a lesser impact on ignition delay than increasing ethanol from 10% to 20%. (4) The 0-D model predicts that at 0.5 and 1.0MPa ethanol produces the shortest ignition time in the high-temperature regime, as seen experimentally.

Integrated effect of supramolecular self-assembled sandwich-like melamine cyanurate/MoS2 hybrid sheets on reducing fire hazards of polyamide 6 composites

A novel strategy of using supramolecular self-assembly for preparing sandwich-like melamine cyanurate/MoS2 sheets as the hybrid flame retardants for polyamide 6 (PA6) is reported for the first time. The introduction of MoS2 sheets function not only as a template to induce the formation of two-dimensional melamine cyanurate capping layers but also as a synergist to generate integrated flame-retarding effect of hybrid sheets, as well as a high-performance smoke suppressor to reduce fire hazards of PA6 materials. Once incorporating this well-designed structures (4wt%) into PA6 matrix, there resulted in a remarkable drop (40%) in the peak heat release rate and a 25% reduction in total heat release. Moreover, the smoke production and pyrolysis gaseous products were efficiently suppressed by the addition of sandwich-like hybrid sheets. The integrated functions consisting of inherent flame retarding effect, physical barrier performance and catalytic activity are believed to the crucial guarantee for the reduced fire hazards of PA6 nanocomposites. Furthermore, this novel strategy with facile and scalable features may provide reference for developing various kinds of MoS2 based hybrid sheets for diverse applications.

Thermal degradation and flammability of nanocomposites composed of silica cross-linked to poly(methyl methacrylate)

The effect of polymer cross-linkages on thermal degradation of silica/poly (methyl methacrylate) (PMMA) nanocomposites is investigated using a single novel nanoparticle. Nanosilica surface treated with KH570, an organic surface treatment capable of free-radical polymerisation, was used to cross-link PMMA via an in situ method. Scanning electron microscopy was used to characterise nanosilica before use, while X-ray diffraction confirmed silica was well dispersed in PMMA. Thermogravimetric analysis (TGA) results showed that thermal degradation of silica cross-linked nanocomposites was significantly stabilised compared to PMMA, with a 30% reduction in the peak mass loss rate. Kinetic studies revealed the degradation of nanocomposites in this work abide by first-order kinetics, with an increase in the degradation activation energy of approximately 100 kJ mol−1. This is nearly double the improvement compared to conventional PMMA-silica nanocomposites in literature, showing dramatic enhancements to thermal stability. Analysis of high-temperature residuals from TGA tests suggest that cross-linked silica have increased char yields when compared with both PMMA and traditional silica nanocomposites. Cone Calorimetry results showed the materials in this work have reduced heat release rates compared to PMMA and traditional silica-PMMA nanocomposites.

Graphene-based flame retardants: a review

Graphene and its derivatives are potential flame retardant materials with good flame retardant performance; in particular, graphene as an adjuvant in combination with inorganic nanomaterials may be a promising candidate of flame retardant. This review describes the flame retardant mechanism, the development trend, and the classification of graphene-based flame retardants. It points out that graphene has attracted intensive interests in the fields of electronics, energy, and information, due to its excellent properties such as high thermal conductivity, good electron transport ability, and large specific surface area. In the meantime, graphene can change the pyrolysis as well as the thermal conductivity, heat absorption, viscosity and dripping of polymer during the combustion process. In other words, graphene can improve the thermal stability of polymer and delay its ignition, and it can also inhibit fire from spreading and reduce heat release rate.

Sustainable, Biobased Silicone with Layered Double Hydroxide Hybrid and Their Application in Natural-Fiber Reinforced Phenolic Composites with Enhanced Performance

With wide application of natural fibers in polymer composites, improvements in their flame retardancy, water absorption, and electrical resistance become an urgent need. To this end, 4.5 wt % of layered double hydroxide (LDH) is introduced into sisal fiber reinforced biobased silicone modified phenolic composites. The modified composites optimally shows 60% reduction in total heat release (20.2 MJ/m2) compared to the composites without LDH. In addition, the biobased silicone modifier TDS is incorporated into phenolic resins (SPF), to further reduce water absorption rate to 6 wt %, and increase volume electrical resistance up to 4.6 × 1016 Ω m. The SPF-SF-SDBSLDH exhibits a high impact strength of 4.2 kJ/m2, over 50% higher than the unmodified PF-SF composites. The SEM observations show that the SPF composites exhibit better interfacial interaction with sisal fiber than normal phenolic (PF) composites. All these flame retardant, impact strength and electrical resistance properties are compatible with the r...

Combustion characteristics and thermal properties of high-density polyethylene/ethylene vinyl-acetate copolymer blends containing magnesium hydroxide

Magnesium hydroxide (MH) was added into high-density polyethylene (HDPE)/ethylene vinyl-acetate (EVA) copolymer blends with various MH contents (30–60 wt%) to improve the flame retardancy of HDPE/EVA blends. The flammability, morphology of charred residues, thermal stability, crystallization, and mechanical properties of HDPE/EVA/MH composites were investigated by UL-94 test, limiting oxygen index (LOI), cone calorimeter test (CCT), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and tensile test. The data obtained from LOI, UL-94 test, and CCT revealed that the addition of MH provided improvements in flame retardancy by increasing the LOI values, UL-94 rating, and reducing heat release, carbon monoxide and carbon dioxide emissions along with delayed ignition with increasing the content of MH. The UL-94 V-0 rating and high LOI value were achieved with the incorporation of MH at a loading level higher than 50 wt% in HDPE/EVA blends, which suggested that the formation of intact, consolidated, and thick residue structures on the surfaces of MH-filled composites prevented the underlying polymer materials from burning. DSC results showed that the crystallinity of HDPE/EVA blends increased with increasing the content of MH, resulting in the enhancement of the strength of HDPE/EVA/MH composites. The thermal stability of HDPE/EVA blends decreased due to the addition of MH.

Synergistic effects of a novel silicon‐containing triazine charring agent on the flame‐retardant properties of poly(ethylene terephthalate)/hexakis (4‐phenoxy)cyclotriphosphazene composites

A novel triazine oligoimides containing silicone charring agent (TSCA) was prepared and used as charring agents in poly(ethylene terephthalate) (PET)/hexakis (4‐phenoxy) cyclotriphosphazene (PNCP) flame retardant system. Limited oxygen index, microscale combustion calorimetry, thermogravimetric analyses, and environment scanning electron microscopy tests were used to study the flame retardance and mechanism of samples. The results revealed that there was a good synergistic effect between TSCA and PNCP in flame retardant PET. The new flame retardant system induced the acid catalytic charring at higher temperature range, enhanced the formation of the integrity and stable char layer, and significantly reduced heat release capacity. Moreover, the prepared PET/PNC/TSCA composites exhibited improved thermal stability and desirable mechanic properties. POLYM. COMPOS., 39:858–868, 2018. © 2016 Society of Plastics Engineers

Radiative shielding effect due to different water sprays used in a real scale application

Thermal radiation attenuation is a well-known positive effect of water sprays applied to firefighting. It was studied here to quantify its real effect on the whole process of fire mitigation. For the demonstration, three different real scale spraying devices were used: a water mist nozzle operating at 85 bars, a sprinkler operating at low pressure (0.3 bars at the nozzle) and a sprinkler operating at a higher pressure (1.3 bars at the nozzle). The radiation attenuation was specifically studied, separately from other actions of the sprays on the fire, using an experimental configuration where water was injected between the radiation source and a detector, but not directly onto the actual fire. Hence, the radiation flux reduction could only be attributed to mixing of water droplets and smoke, not to any reduction in heat release due to water directly cooling the fire area nor to inerting effects occurring simultaneously. The flux was measured using an infrared device combining a Fourier transform infrared spectrometer and a multispectral infrared camera. Two radiative sources were used: a high-temperature blackbody for quantification of the radiation transmission with a calibrated source, and a 200 kW heptane pool fire for an application to a realistic radiation source involved in fires. When using a blackbody source for radiation generation, the radiation attenuation of the incident fluxes was 89% for the high-pressure water mist, 62% for the sprinkler at the higher operating pressure and 20% for the sprinkler at the lower pressure. These differences were easily explained by a sensitivity study conducted coupling the Mie theory for the prediction of droplet radiative properties to the Monte Carlo method for radiative transfer simulation. This showed the sensitivity of the radiation attenuation to droplet size and concentration. When the blackbody source was replaced by a pool fire, the flux reduction was even higher for the low pressure sprinkler, i.e. 45%, while being almost unchanged for the water mist. In the present configuration, where smoke stratification was observed before spray activation, this was mainly attributed to the fact that a mixing of droplets and smoke was produced in the measurement area due to the drag effect. The smoke and spray mixing resulted in a stronger attenuation capacity with the sprinkler device. This increased attenuation was not observed through the transmission data for the water mist, perhaps because of compensating effects related to evaporation and the surrounding temperature, or a smoke flow that was highly penalized by the spray activation.

Superior flame retardant by combining high aspect ratio layered double hydroxide and graphene oxide

By combining two platy nano-additives with high aspect ratio, a layered double hydroxide (LDH) and graphene oxide (GO), remarkable flame retardancy in polystyrene nanocomposite was observed. Surprisingly, the effect is superior to nanocomposites made with either of the two types of fillers. The nanocomposites were prepared via solution blending from tetrahydrofuran utilizing a three-roll mill for improved compounding. A highly stable suspension of a mixture of the two nano-additives in THF was achieved by sophisticated surface modifications of LDH and GO using 3,4-dihydroxybenzophenone (DBP) and 1-dodecylamine (DDA), respectively. Forced sedimentation tests and particle size distribution confirmed the good suspension and suggested that heterocoagulation between the two types of oppositely charged colloids could be prevented by the appropriate combination of surface modificators. Cone calorimetry revealed a significant reduction of the peak of heat release rate of 47% at a very low loading (5.5 wt%). Most interestingly, after formation of a protective layer, combustion occurred at a much reduced heat release rate, and consequently, the related burn out time was prolonged by 154%. While, as usual, these platy inorganic fillers fail to reduce time of ignition or improve limiting oxygen index, the pronounced push of the burn out time underlines the great potential resting in the combination of different types of adjuvant fillers. The remarkably reduced heat release rate for longer burning times is superior to other published nanocomposites. When combining this system with flame retardants decreasing total heat evolved and reducing the initial peak of heat release rate, very efficient flame retardant systems will be obtained.

Thermal oxidative degradation of wood modified with aminophenylborates

Comparative thermal analysis in the presence of oxygen was carried out for samples of native pine wood and wood samples modified with aminophenylborates. Significant decrease in the amount of heat released during thermal decomposition of the modified samples was established, which is due to the increase of carbonaceous residues on the surface. Reduction of heat release during decomposition of the modified samples may be explained by the lower yield of combustible volatile products as well as by thin film of boron oxide, formed on the surface of the modified wood, that partially reflects heat flow. Produced upon the modifier decomposition water vapor and inert nitrogen oxides dilute gaseous mixture near the wood surface and isolate it from oxygen. This enhances fire-resistance of wood modified with mono- and diethanolamine(N→B)phenylborates. Hydroxyl group at the sixth carbon atom of the glucopyranose ring of cellulose participates in reactions of cellulose modification, which prevents formation of flammable levoglucosan and, consequently, improves the fire-resistance of the modified wood.

Water-soluble polyelectrolyte complex nanocoating for flame retardant nylon-cotton fabric

Blends of cotton with synthetic fibers are widely used for various military and industrial applications. Nylon-cotton (NYCO) blends offer high durability and strength from nylon and the softness of cotton, but both fiber types are highly flammable. Previously reported flame retardant coatings for cotton fabric, comprised of a complex of polyethylenimine and a polyphosphate, are not able to protect NYCO textiles, so a new generation of water-soluble polyelectrolyte complex coating is needed. The basis of this new treatment is an aqueous complex of polyethylenimine and ammonium polyphosphate that forms melamine polyphosphate in-situ during exposure to a melamine-containing solution. NYCO fabric was rendered self-extinguishing in a vertical flame test and pyrolysis combustion flow calorimetry showed a 28% reduction in total heat release, and a 65% reduction of cotton's peak heat release, with less than 20 wt% coating. The effectiveness of this halogen-free, flame retardant coating is due to condensed phase activity that includes cooling effects and charring. The ease of this coating procedure and the use of more environmentally benign chemicals deposited from aqueous solutions make this an industrially feasible alternative to current treatments.

Influence of Plasticizer Amount on Rheological and Hydration Properties of CEM II Type Portland Cements

The article analyzes the effect of plasticizer (based on polycarboxilates) amount (0.3 - 1.2% wt. of cement) on the rheological and hydration properties of two Portland cements pastes: CEM II/A-S 42.5N and CEM II/A-LL 42.5N. Increase of plasticizer amount reduces viscosity of CEM II/A-LL 42.5N cement paste from 3 to 12 times, where viscosity of CEM II/A-S 42.5N cement paste reduces from 5 to 20 times. The optimum plasticizer dose (0.3%) in case of CEM II/A-S 42.5N and (1.2%) in case of CEM II/A-LL 42.5N was established. Calorimetry studies have shown that plasticizer reduces the wetting heat release rate in CEM II/A-LL 42.5N cement twice and in CEM II/A-S 42.5N cement - by 25%. Plasticizer prolongs the maximum heat release rate time by 16 h in CEM II/A-LL 42.5N samples and reduces heat release rate by 19%. In CEM II/A-S 42.5N cement samples plasticizer prolongs maximum heat release rate time by 14.5 h and increases heat release rate by 15%. The goal of this study is to analyze the effect of the dosage of the most widely used plasticizer on solubility characteristics, rheological and hydration properties of two cements CEM II/A-S 42.5N and CEM II/A-LL 42.5N to establish the optimum dose of plasticizer in cements pastes.

A survey of drag and heat reduction in supersonic flows by a counterflowing jet and its combinations

Drag reduction and thermal protection is very important for hypersonic vehicles, and a counterflowing jet and its combinations is one of the most promising drag and heat release reduction strategies. In the current survey, research progress on the drag and heat release reduction induced by a counterflowing jet and its combinations is summarized. Three combinatorial configurations are considered, namely the combination of the counterflowing jet and a forward-facing cavity, the combination of the counterflowing jet and an aerospike, and the combination of the counterflowing jet and energy deposition. In conclusion, some recommendations are provided, especially for jet instability protection, for the tradeoff between drag and heat release reductions, and for the critical points for the operational and geometric parameters in the flow mode transition.