Reduction In Heat Release Rate Research Articles

Castor‐oil derived nonhalogenated reactive flame‐retardant‐based polyurethane foams with significant reduced heat release rate

ABSTRACTNational Fire Protection Association encounters one structural fire every 66 s. Rigid polyurethane foam is one of the principal components used in constructional and household applications. In this work, a reactive flame retardant (FR) was synthesized using a facile one‐step thiol–ene reaction by reacting mercaptenized castor oil (MCO) and diethyl allyl phosphonate (DEAP). The obtained MCO–DEAP polyol was used for the preparation of polyurethanes having different weight percentages of phosphorus (P). Addition of FR polyol showed no adverse effect on the cellular structure of the foams and maintained the compressive strength. All the foams showed closed cell content greater than 95%. Horizontal burning test (HBT) was performed before and after the migration test to understand the stability of the FR within the foams. Foams showed no relative weight loss before and after the migration test and maintained equivalent results for HBT. For 1.5 wt % P foams, low extinguishing time of 3 s and weight loss of 4% was observed. The cone calorimeter test showed a reduction in the peak heat release rate from 313 to 158 kW m−3, the total heat release from 18 to 8 MJ m−2, and O2 consumption from 12 to 6 g. Our results suggest that MCO–DEAP polyol could act as an essential FR for rigid PU foam ensuring fire safety. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47276.

Impact of expandable graphite on flame retardancy and mechanical properties of rigid polyurethane foam

Flame retardant (FR) and mechanical performance properties of two different rigid polyurethane foams (RPUFs) containing expandable graphite (EG) as FR additive were studied. The impact of EG on the foam properties were evaluated. Cellular structures were less homogeneous in foams containing EG. Thermal conductivities of RPUF increased slightly with EG addition. FR properties of the foams were evaluated by limiting oxygen index (LOI) test, vertical burning test (UL94), and cone calorimeter test. The addition of EG improved the FR performance and increased the density of the foams. For example, LOI value was increased from 18.4 to 25.2 in EG10PU1, whereas for EG10PU2, LOI increased from 19.2 to 29.8. In UL94 test, EG10PU1 reached V‐1 rating, while EG8PU2 passed V‐0 rating. Results from cone calorimeter test showed that the EG in the RPUF effectively reduced heat release rate, total heat released, total smoke production, and mass loss rate with increase in EG. This improvement was more efficient for the higher density foam. In addition, low loading of EG in PU1 increased the compression performance but decreased as the amount of EG was further increased. POLYM. COMPOS., 40:E1705–E1715, 2019. © 2018 Society of Plastics Engineers

Flammability and thermal properties of modified carbon nanotubes in poly(lactic acid)

The multi-walled carbon nanotubes (CNTs) were modified using phosphaphenanthrene compounds (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)) and vinyl triethoxy silane (VTES) by covalent bond. The DOPO- and VTES-treated CNTs were named DVCNT, and the structure was characterized by Fourier transform infrared, thermogravimetric analysis, and transmission electron microscopy. Nanocomposites were prepared by adding CNTs or DVCNT to poly(lactic acid) (PLA), and the flame retardancy was examined by determination of limiting oxygen index (LOI), vertical burning (UL94), and cone calorimetry. Results reveal that the LOI of PLA/DVCNT_4% composites was increased to 26.6 and prevents dripping of PLA in some level, and DVCNT can significantly reduce heat release rate and mass loss rate during combustion, which indicate that DVCNT can improve the dispersibility of the CNTs in the polymer composites and hence enhance the flame retardancy simultaneously.

Improving the Flame Retardancy and Smoke Suppression of Poly(Lactic Acid) with a SiO2@ammonium Molybdate Core-Shell Nanotubes

ABSTRACTDesign and fabrication of SiO2@ammonium molybdate(AM) core-shell nanotubes are important for polylactic acid (PLA), these two components form a well-defined core-shell configuration that is distinct from simple core-shell or hybrid structures. The PLA was investigated by limiting oxygen index, vertical burning test and smoke density, cone calorimeter test, SEM and TGA. The results showed that SiO2@AM nanotube can effectively increase the flame retardancy and smoke suppression properties, and that it can apparently reduce heat release rate, total heat release and total smoke release. Furthermore, the addition of SiO2@AM nanotube brings better mechanical properties than the sample contain SiO2 nanotube. Here, SiO2@AM nanotube was considered to be an effective flame retardant in PLA.

Synthesis of an organic-inorganic hybrid strontium hydroxystannate nanorod and application as novel flame retardant

A novel sulfonyldiphenol-containing polyphosphazene derivative (PZS) wrapped strontium hydroxystannate (PZS-SrSn(OH)6) nanorods with rich N, P, Sr, Sn elements was prepared and used as an efficient flame retardant. PZS-SrSn(OH)6 exhibited high flame retardant efficiency and smoke suppression to the epoxy (EP) composites. Compared with EP, under merely 3% of addition of PZS-SrSn(OH)6 nanorods, the LOI value was increased to 29.6% from 26.2%. Furthermore, the combustion properties of treated EP were assessed by cone calorimeter (CONE) and it demonstrated that the EP/PZS-SrSn(OH)6 obtained better flame retardancy which was confirmed by the reduction of heat release rate (HRR) and total smoke release (TSR). The peak HRR values and TSR for EP/PZS-SrSn(OH)6 were reduced by 30.2% and 23.1%, respectively. It was confirmed that the core/shell structured PZS-SrSn(OH)6 could significantly enhance the synergistic effect between PZS and SrSn(OH)6, and thereby resulting higher flame retardant efficiency.

Comparative Studies on Thermal, Mechanical, and Flame Retardant Properties of PBT Nanocomposites via Different Oxidation State Phosphorus-Containing Agents Modified Amino-CNTs.

High-performance poly(1,4-butylene terephthalate) (PBT) nanocomposites have been developed via the consideration of phosphorus-containing agents and amino-carbon nanotube (A-CNT). One-pot functionalization method has been adopted to prepare functionalized CNTs via the reaction between A-CNT and different oxidation state phosphorus-containing agents, including chlorodiphenylphosphine (DPP-Cl), diphenylphosphinic chloride (DPP(O)-Cl), and diphenyl phosphoryl chloride (DPP(O3)-Cl). These functionalized CNTs, DPP(Ox)-A-CNTs (x = 0, 1, 3), were, respectively, mixed with PBT to obtain the CNT-based polymer nanocomposites through a melt blending method. Scanning electron microscope observations demonstrated that DPP(Ox)-A-CNT nanoadditives were homogeneously distributed within PBT matrix compared to A-CNT. The incorporation of DPP(Ox)-A-CNT improved the thermal stability of PBT. Moreover, PBT/DPP(O3)-A-CNT showed the highest crystallization temperature and tensile strength, due to the superior dispersion and interfacial interactions between DPP(O3)-A-CNT and PBT. PBT/DPP(O)-A-CNT exhibited the best flame retardancy resulting from the excellent carbonization effect. The radicals generated from decomposed polymer were effectively trapped by DPP(O)-A-CNT, leading to the reduction of heat release rate, smoke production rate, carbon dioxide and carbon monoxide release during cone calorimeter tests.

Heat release rate of wooden cribs with water application for fire suppression

A series of experiments was conducted in order to measure the maximum heat release rate of a wood crib ignited at the center of its base after water applications which were not sufficient to extinguish the wood crib fire. The novelty of the present experiments lies in distributing the water uniformly just above the top surface thus ensuring what the exact delivery density is. Uniform water distribution was produced by a system of pipes with holes 5 cm above the wood crib. The variable experimental parameters were the number of layers of wood cribs (6, 9, 12), the water delivered density, and the water activation time. The size of the wood sticks is fixed and they are layered in a fixed staggered way alternating at 9 or 10 sticks per layer. Regardless of the number of wood crib layers, the reduction of the maximum heat release rate by water supplication was proportional to the total water flow rate W˙. The constant of proportionality is approximately 12 kJ/g in these experiments for all water delivered densities and all numbers of layers of wood cribs where water was applied either earlier or just when the maximum heat release rate was reached in the free burning wood crib fires. The proportionality factor 12 kJ/g is explained by noting that the heat removed per unit time by the completely evaporated water is proportional to the water application rate times the heat of evaporation and that this leads to the reduction of mass loss rate to be proportional to the water application rate multiplied by the heat of evaporation and divided by the heat of pyrolysis of wood. Therefore, the reduction of heat release rate is equal to the reduction of the mass loss rate multiplied by the heat of combustion of wood. In addition, data for the total heat released and the total mass loss also support the proposition that the reduction in the total heat release is due to the extinction of the wood crib burning area being proportional to the water supply rate. We expect that these results to be applicable as long as the burning of wood crib is fuel controlled.

Synergistic effect of halloysite nanotubes on flame resistance of intumescent flame retardant poly(butylene succinate) composites

A novel intumescent flame retardant poly(butylene succinate) (IFR‐PBS) with antidripping property was prepared using halloysite nanotubes (HNTs) as the synergistic agent. Ammonium polyphosphate (APP), melamine (MA), pentaerythritol (PER), and halloysite nanotubes (HNTs) were added in PBS via melt blending. The effects of HNTs as the synergistic agent on the flame retardancy property, thermal property, and mechanical property of IFR‐PBS composites were investigated. Cone calorimetry revealed that partial substitution of IFR by HNTs (1.5 wt%) substantially improved the flame retardancy of IFR‐PBS with a reduction of heat release rate (HRR), total heat release (THR), and total smoke production (TSP). In addition, the limiting oxygen index value was increased from 42.1 to 58.2 with only 1.5 wt% addition of HNTs. The incorporation of HNTs also enhanced the thermal stability of the IFR‐PBS composites and reinforced the composites. Scanning electron microscopy (SEM) results showed that the composite containing HNTs had a tighter protective char layer after cone calorimeter test, which protected the underlying polymer from the external heating. Overall, the results indicated that suitable amounts of HNTs had a noticeable synergistic effect on the flame retardancy property of IFR‐PBS composites. POLYM. COMPOS., 40:202–209, 2019. © 2017 Society of Plastics Engineers

Nanostructured Wood Hybrids for Fire-Retardancy Prepared by Clay Impregnation into the Cell Wall.

Eco-friendly materials need "green" fire-retardancy treatments, which offer opportunity for new wood nanotechnologies. Balsa wood (Ochroma pyramidale) was delignified to form a hierarchically structured and nanoporous scaffold mainly composed of cellulose nanofibrils. This nanocellulosic wood scaffold was impregnated with colloidal montmorillonite clay to form a nanostructured wood hybrid with high flame-retardancy. The nanoporous scaffold was characterized by scanning electron microscopy and gas adsorption. Flame-retardancy was evaluated by cone calorimetry, whereas thermal and thermo-oxidative stabilities were assessed by thermogravimetry. The location of well-distributed clay nanoplatelets inside the cell walls was confirmed by energy-dispersive X-ray analysis. This unique nanostructure dramatically increased the thermal stability because of thermal insulation, oxygen depletion, and catalytic charring effects. A coherent organic/inorganic charred residue was formed during combustion, leading to a strongly reduced heat release rate peak and reduced smoke generation.

Optical study on combustion characteristics of hydrotreated vegetable oil and blends under simulated CI engine conditions and various EGR

Soot and NOx emissions are the inherent combustion characteristics of diesel engines. The modification of fuel property makes for an interesting study of methods for elimination of soot and NOx emissions. HVO and blends of 20 %, 50 %, 80 % by mass of HVO with commercial diesel fuel (mixed 7 % FAME), in combination with various EGR conditions were carried out to evaluate soot and NOx formation, as well as combustion characteristics of HVO blends in RCEM. The obtained results revealed that ignition delay, flame temperature, NOx and soot concentration decreased as HVO percentage increased. Mixing ratios of HVO with diesel showed a similar flame profile at baseline condition, higher flame temperature and darker soot density-KL regions were distributed on the upstream of spray flame. HVO displayed a slightly lower in-flame temperature and KL density, which led to a decrease of 33 % and 15.9 % of NOx and soot concentration, respectively, compared to diesel. By applying higher EGR levels, a reduction of heat release rate, flame temperature and NOx emissions were recorded. Also observed was an increase in ignition delay and soot concentration. Notably, soot at 10 % O2 concentration was lower than that of 15 % O2 concentration.

Incorporation of cellulose with adsorbed phosphates into poly (lactic acid) for enhanced mechanical and flame retardant properties

We have engineered an environmentally sustainable, biodegradable, and flame retardant poly (lactic acid) (PLA) based composite by introducing resorcinol bis (diphenyl phosphate) (RDP) coated cellulose fibers at a mass fraction of only 8%. Mechanical testing showed that formation of the composite significantly improved the impact strength, dynamic and elastic moduli, and tensile strength relative to neat PLA. The composite self-extinguished in less than 2 s and had greatly reduced dripping, hence easily passing the UL-94 V0 criteria. Fourier Transform Infrared Spectroscopy (FTIR) was used to elucidate the chemical mechanism responsible for these effects, which were interpreted in terms of a dehydration process of cellulose in the presence of RDP. This has an overall cooling effect and reduction of the combustion, which can be observed in the reduction of heat release rate (HRR) by cone calorimetry and increase in limiting oxygen index (LOI) value.

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.

Thermal degradation and flammability of polyamide 11 filled with nanoboehmite

The flame-retardant effect of rod-like nanoboehmite was evaluated in biobased polyamide 11. Thermal analysis reveals that hydrated nanofillers modify the degradation pathway of polyamide 11 turning from a two-step to a single-step mechanism. The polymer thermal stability is increased due to interactions between polar groups and filler surface hydroxyl groups. Despite this improved thermal stability, polyamide 11/nanoboehmite composites exhibit shorter times to ignition in cone calorimeter. The phenomenon was attributed to changes in thermoradiative properties leading to a faster heating of the polymer surface. The most significant flame-retardant action is a reduction in heat release rate that was related to a barrier effect while endothermic water release seems to play a minor role.

Synergistic effect of lanthanum oxide on the flame retardant properties and mechanism of an intumescent flame retardant PLA composites

The synergistic effect of lanthanum oxide (La2O3) on the flame retardant properties and mechanism of a novel intumescent flame retardant polylactide composites (PLA/IFR) was investigated by the means of limited oxygen index (LOI), catalytic effectivity analysis (CAT-EFF), vertical burning test (UL-94), microscale combustion calorimetry (MCC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), Laser Raman spectroscopy (LRS) and X-ray photoelectron spectroscopy (XPS). La2O3 enhanced the LOI value of the PLA/IFR composite dramatically and all the composites passed the UL-94 V-0 rating test. PLA/IFR/1% La2O3 had the highest CAT-EFF, and the LOI value of the composite increased from 32.8 to 42.2% according to catalytic affectivity (CAT-EFF) analysis. 1%La2O3 enhanced the fire retardant performance of PLA/IFR, resulting consequently in reduction of heat release rate (HRR), total heat release (THR), heat release capacity (HRC) and degree of flammability (Findex) of the PLA/IFR. The TGA test revealed that La2O3 changed the degradation behavior of the PLA/IFR, enhanced the thermal stability of the PLA/IFR at high temperature and increased the char residue. The morphological structures observed by SEM demonstrated that La2O3 effectively help to form more continuous and compact intumescent char layer on the surface. The LRS results indicated that higher graphitization degree of the residue char was formed. The EDS and XPS results illustrated that the existence of La2O3 promoted to remain more P and O in the char layer to form more crosslinking structure to improve barrier properties of the char layer.

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.

Flame Retardance and Smoke Suppression of CFA/APP/LDHs/EVA Composite

A new intumescent flame-retardants (IFR) system including the charing-foaming agent (CFA), ammonium polyphosphate (APP) and modified-layered double hydroxides (LDHs) with different transition metals (Ni, Co, Cu) were used in the ethylene vinyl acetate (EVA) matrix. Both the limiting oxygen index and the vertical burning tests indicate that the CFA/APP system and LDHs have significant synergistic flame retardant effects. The morphology of combustion residues indicates that the many pores of residues can prevent the melt dripping. The thermal analysis shows that the flame retardants obviously enhanced the thermal degradation temperature of ethylene-based chains of the composites. The cone calorimeter test reveals that the CO2 and combustion residues have an important influence on the reduction of heat release rate (HRR), the smoke production rate (SPR), the production rate and the mean release yield of CO. The composite containing Cu (ELDH-Cu) delivers an 82% reduction in peak heat release rate, while ELDH-Ni has the best CO suppression among all composites. This work not only confirms the flame retardance and smoke suppression of CFA/APP/LDH/EVA, but also provides an effective method for producing new flame retardants and smoke suppressants.

Construction of β-FeOOH nanorod-filled layer-by-layer coating with effective structure to reduce flammability of flexible polyurethane foam

The β-FeOOH nanorod-filled coatings were deposited onto flexible polyurethane foam by layer-by-layer assembly technique to reduce its flammability. The coatings were constructed by two assembly systems: one was bilayer system, which was comprised of polyethylenimine and β-FeOOH nanorods; other one was trilayer system, which was comprised of polyethylenimine, β-FeOOH nanorods, and sodium alginate. Scanning electron microscopy images indicated that the randomly oriented and entangled network structure can only be observed for the coating that assembled by trilayer system. Cone calorimetry test revealed that the coating assembled by trilayer system can lead to significant reduction in peak heat release rate compared with those of control foam, 61.8% peak heat release rate reduction ever occurred to the eight trilayers coated sample, but the coating assembled by bilayer system has slight reduction (<20%). The result is attributed to trilayer approach being beneficial to fabricate coating with sufficient thickness to protect the underlying foams during burning. Copyright © 2016 John Wiley & Sons, Ltd.

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.

Synergistic effect of Ni-based bimetallic catalyst with intumescent flame retardant on flame retardancy and thermal stability of polypropylene

Ni-based bimetallic catalysts were prepared and used as catalysts and synergistic agents to improve the flame retardancy of intumescent flame retardants (IFR) systems based on ammonium polyphosphate (APP) and pentaerythritol (PER) in polypropylene (PP). The synergistic effects of Ni-based bimetallic catalysts were evaluated by limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), fourier transform infrared (FTIR), energy dispersive spectrometer (EDS). It was found that the addition of Ni-based bimetallic catalysts could dramatically enhance LOI value and improve UL-94 rating. Among all the bimetallic catalysts, NiMg catalyst exhibited the best synergistic effect. Only 2 wt% of NiMg catalyst could promote the LOI value of PP/IFR composite from 29.0% to 38.1%. What's more, the introduction of Ni-based catalysts led to great reduction in heat release rate (HRR), total heat release (THR), rate of smoke release (RSR), total smoke release (TSR), with a simultaneous increase in residual char. The TGA curves showed that the presence of Ni-based catalysts could also improve the stability of the char in high temperature. The FTIR curves and EDS analysis indicated that Ni-based bimetallic catalysts could promote the formation of POP and POC, leaving more P, N and O in the condensed phase, and thus giving rise to more crosslinks of the char. SEM observations further confirmed Ni-based bimetallic catalyst could help to form a more compact and homogeneous char layer and effectively reduce the heat and oxygen transfer, resulting in better flame retardancy of PP/IFR composites.