Studying smoldering to flaming transition in polyurethane furniture subassemblies: Effects of fabrics,flame retardants,and material type

The transition from smoldering to flaming was studied on fabric, batting, and foam assemblies via an electric spot ignition source of similar intensity to a cigarette. The materials studied included four different fabrics (cotton, polyester, cotton/polyester blend, flame retardant cotton/polyester blend), two types of batting (cotton, polyester), and three types of polyurethane foam (nonflame retardant, flame retardant by FMVSS 302 testing, flame retardant by BS5852 testing). The results from testing found that materials highly prone to smoldering could propagate smoldering into foams and lead to ignition, whereas materials that tended to melt back from the ignition source did not. Flame retardant fabrics or foam can and do prevent the transition from smoldering to flaming provided sufficient levels of flame retardants are incorporated in the upholstery fabric or foam. The transition from smoldering to flaming of cotton fabric/nonflame retardant foam assembly was also studied using temperature measurements and evolved gas analysis. It was determined that the transition takes place when the oxygen consumption by accelerating smoldering front exceeds the oxygen supply. At this point, the solid fuel gasification becomes driven by thermal decomposition rather than by surface oxidation which leads to high enough concentrations of fuel for flaming combustion to occur.     

Effect of particle granularity on smoldering fire in wood chips made from wood waste: An experimental study

Fires in wood waste storages cause financial losses, are difficult to extinguish, and emit large amounts of fire effluents. The mechanisms related to fires in wood chip piles are not well elucidated. To find suitable preventive measures for handling such fires in wood waste, a better understanding of the physical properties of wood waste is needed. The present study investigates how granularity affects mechanisms of smoldering fire and transition to flaming in wood chip piles. Eighteen experiments with samples inside a top-ventilated, vertical cylinder were conducted. Heating from underneath the cylinder induced auto-ignition and smoldering fire, and temperatures and mass loss of the sample were measured. The results showed that granularity significantly affects the smoldering fire dynamics. Material containing larger wood chips (length 4-100 mm) demonstrated more irregular temperature development, higher temperatures, faster combustion, and higher mass losses than material of smaller wood chips (length <4 mm). The larger wood chips also underwent transition to flaming fires. Flaming fires were not observed for small wood chips, which instead demonstrated prolonged and steady smoldering propagation. The differences are assumed to be partly due to the different bulk densities of the samples of large and small wood chips affecting the ventilation conditions. Increased knowledge about these combustion processes and transition to flaming is vital to develop risk-reducing measures when storing wood chips made from wood waste in piles.     

An experimental setup for observation of smoldering‐to‐flaming transition on flexible foam/fabric assemblies

Fires that involve upholstered furniture frequently begin as a smoldering combustion and, with time, transition to a flaming combustion, which sharply increases the level of hazard. Therefore, understanding how the compositions of the primary flammable components of the furniture, ie, flexible foam and upholstery fabric, affect this transition is important for fire safety considerations. In the current study, an experiment was designed to observe this transition using a sample consisting of 30 × 15 × 6 cm³ rectangular foam block covered with 30 × 15 cm² piece of fabric. For a representative system of 1.8 lb/ft³ (29 kg/m³) flexible polyurethane foam and 11 oz (0.37 kg/m²) cotton fabric, 0.69 transition probability was measured. This probability decreased by a factor of 4 when a small amount of phosphorus‐based flame retardant, Fyrol® HF‐9, was added to the foam. The transition to flaming was speculated to be associated with the formation of adjacent pyrolysis and smoldering regions within the foam. The pyrolysis region, dominated by anaerobic decomposition, provided gaseous fuel, the ignition of which resulted in the transition. The smoldering region, dominated by oxidation reactions at the solid‐gas interface, generated the heat necessary to maintain the pyrolysis process and ignite the gaseous fuel.     

A flame‐retardant composite foam: foaming polyurethane in melamine formaldehyde foam skeleton

A composite foam, polyurethane–melamine formaldehyde (PU/MF) foam, was prepared through foaming PU resins in the three‐dimensional netlike skeleton of MF foam. The chemical structure, morphology, cell size and distribution, flame retardancy, thermal properties and mechanical properties of such composite foam were systematically investigated. It was found that the PU/MF foam possessed better fire retardancy than pristine PU foam and achieved self‐extinguishment. Moreover, no melt dripping occurred due to the contribution of the carbonized MF skeleton network. In order to further improve the flame retardancy of the composite foam, a small amount of a phosphorus flame retardant (ammonium polyphosphate) and a char‐forming agent (pentaerythritol) were incorporated into the foam, together with the nitrogen‐rich MF, thus constituting an intumescent flame‐retardant (IFR) system. Owing to the IFR system, the flame‐retardant PU/MF foam can generate a large bulk of expanded char acting as an efficient shielding layer to hold back the diffusion of heat and oxygen. As a result, the flame‐retardant PU/MF foam achieved a higher limiting oxygen index of 31.2% and exhibited immediate self‐extinguishment. It exhibited significantly reduced peak heat release rate and total heat release, as well as higher char residual ratio compared to PU foam. Furthermore, the composite foam also showed obviously improved mechanical performance in comparison with PU foam. Overall, the present investigation provided a new approach for fabricating a polymer composite foam with satisfactory flame retardancy and good comprehensive properties. © 2018 Society of Chemical Industry     

Nanoclay filled soy‐based polyurethane foam

Polyurethane foam was fabricated from polymeric diphenylmethane diisocyanate (pMDI) and soy‐based polyol. Nanoclay Cloisite 30B was incorporated into the foam systems to improve their thermal stabilities and mechanical properties. Neat polyurethane was used as a control. Soy‐based polyurethane foams with 0.5–3 parts per hundred of polyols by weight (php) of nanoclay were prepared. The distribution of nanoclay in the composites was analyzed by X‐ray diffraction (XRD), and the morphology of the composites was analyzed through scanning electron microscopy (SEM). The thermal properties were evaluated through dynamic mechanical thermal analysis (DMTA). Compression and three‐point bending tests were conducted on the composites. The densities of nanoclay soy‐based polyurethane foams were higher than that of the neat soy‐based polyurethane foam. At a loading of 0.5 php nanoclay, the compressive, flexural strength, and modulus of the soy‐based polyurethane foam were increased by 98%, 26%, 22%, and 65%, respectively, as compared to those of the neat soy‐based polyurethane foam. The storage modulus of the soy‐based polyurethane foam was improved by the incorporation of nanoclay. The glass transition temperature of the foam was increased as the nanoclay loading was increased. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Role of two stage pyrolysis in fire growth on flexible polyurethane foam slabs

A series of experiments designed to characterize fire behavior on flat 1.2 m × 1.2 m samples of commercial non‐fire‐retarded flexible polyurethane foam were performed. Time‐resolved heat release and mass loss rates were measured. Experimental parameters varied, including foam thickness (5.1 and 10.2 cm) and burning angle (+25°, +12.5°, 0°, ?12.5°, and ?25°). Polyurethane foam is typically produced by reacting a multifunctional isocyanate with a polyol. The foam used here was formed by reacting toluene diisocyanate and a polyol based on a condensed polyether of polypropylene oxide. Earlier cone calorimeter studies of this foam had revealed a clear two stage pyrolysis behavior in which the heated foam first released a gaseous fuel derived from the isocyanate component, while leaving behind a liquid produced primarily from the polyol, which only gasified and burned following additional heating. The subsequent burning behavior of the polyol‐derived liquid is shown in this work to play a crucial role in the maximum heat release rate and total heat released by the fires spreading across the foam slabs. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Physical properties of garnet‐filled polyurethane foam composite

Garnet‐filled polyurethane foam composite was prepared by solvent‐free reaction. Density, hardness, and compression strength were measured to study its basic physical properties. Percent volume loss and arithmetical mean surface roughness were investigated as an abrasion property to determine its potentiality as an abrasive and establish a relationship between basic properties and abrasion properties. These properties were measured as functions of blowing agent content, and garnet was used as filler. The particle size of the garnet and the polyol mixing ratio were also changed to investigate the dependence of properties on formulation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1336–1343, 2001     

Ignition and combustion of low‐density polyimide foam

The ignition, flaming and smoldering combustion of low‐density polyimide foam have been studied using a cone calorimeter. Low‐density polyimide foam exhibits a high ignition resistance. The minimum heat flux for the ignition of flaming combustion ranges from 48 to 54 kW/m². This minimum heat flux also indicates the heat flux for transition from smoldering to flaming combustion. The flaming combustion results show that the heat release rate of low‐density polyimide foam is very low even at a high incident heat flux of 75 kW/m². The smoldering combustion results show that the smoldering of low‐density polyimide foam becomes significant when the incident heat flux is greater than 30 kW/m². The smoldering combustion of low‐density polyimide foam cannot be self‐sustaining when the external heat source is removed. Copyright © 2003 John Wiley & Sons, Ltd.     

The effect of the trimerization catalyst on the thermal stability and the fire performance of the polyisocyanurate‐polyurethane foam

In this work, 3 currently used trimerization catalysts, TMR‐2 (quaternary ammonium), K‐15 (potassium octoate), and PU‐1792 (potassium acetate) were used to produce rigid polyisocyanurate (PIR) foams with certain amounts of isocyanurate contents. The results from Fourier transform infrared (FTIR) quantitative analysis showed that PU‐1792 had the highest catalytic efficiency in isocyanurate formation. Then, the effect of different amounts of PU‐1792 catalyst on isocyanurate ring output was further investigated, and the result showed that the highest amount of isocyanurate ring formation could be attained by the 5 pphp of PU‐1792 catalyst. It was also found that the increased amount of isocyanurate ring could result in reduced cell size, improved compressive strength, and lowered thermal conductivity of PIR foam. The results from thermogravimetric analysis (TGA) and cone calorimeter (CONE) test revealed that the thermal stability and fire performance of PIR foam could be improved with the increased amount of isocyanurate ring. Furthermore, the CONE test indicated that the smoke production of PIR foam decreased approximately 51.7% in comparison to the reference polyurethane (PU) foam, and the SEM image of char morphology showed that the char of PIR foam was more compact than PU foam.     

Cone calorimeter study of inorganic salts as flame retardants in polyurethane adhesive with limestone filler

A cone calorimeter was used to test inorganic water‐releasing and low‐melting compounds as flame retardants in polyurethane adhesive samples. Sodium metasilicate pentahydrate, potassium carbonate mixed with silica gel, sodium hydrogen carbonate, calcium oxalate monohydrate, zinc and magnesium chloride mixed with potassium chloride, aluminium and magnesium hydroxides, ammonium polyphosphate (APP), sodium and potassium phosphates were tested. These additives were used to partially (10–20%) replace the limestone used as a filler in the adhesive. Thermogravimetric analysis was used to study decomposition and melting of the inorganic compounds. The results showed that sodium metasilicate monohydrate formed a protective layer of sodium silicate on the sample surface, significantly delaying the time to ignition. Addition of APP resulted in the lowest overall heat release rate curve. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis of aminophosphonate polyols and polyurethane foams with improved fire retardant properties

Aminophosphonated polyols with flame retardant properties are synthesized by ring opening polymerization using diethyl-N,N-bis(2-hydroxyethyl) aminomethyl phosphonate (Fyrol-6) as initiator. The influence of the catalyst type and its concentration on the polymerization rate are studied. The catalyst system formed by potassium methoxide (MeOK) in DMSO as a solvent presents the highest polymerization rate and allows reducing the polydispersity. The thermal resistance of the synthesized polyols is confirmed by the char residues formation. Finally, PU foams are synthesized containing up to a 50 pph of PFyCs[1:1], preserving good cellular structure up to a 25 pph content and improving the fire resistance by increasing the char residue from 7.79 to 22.13 wt % and decreasing the PHRR and the smoke production according to TGA and cone calorimeter tests, respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47780.     

Effects of variations in incident heat flux when using cone calorimeter test data for prediction of full‐scale heat release rates of polyurethane foam

The development of methods to predict full‐scale fire behaviour using small‐scale test data is of great interest to the fire community. This study evaluated the ability of one model, originally developed during the European Combustion Behaviour of Upholstered Furniture (CBUF) project, to predict heat release rates. Polyurethane foam specimens were tested in the furniture calorimeter using both centre and edge ignition locations. Input data were obtained using cone calorimeter tests and infrared video‐based flame area measurements. Two particular issues were investigated: how variations in incident heat flux in cone calorimeter tests impact heat release rate predictions, and the ability of the model to predict results for different foam thicknesses. Heat release rate predictions showed good agreement with experimental results, particularly during the growth phase of the fire. The model was more successful in predicting results for edge ignition tests than for centre ignition tests and in predicting results for thinner foams. Results indicated that because of sensitivity of the burning behaviour to foam specimen geometry and ignition location, a single incident heat flux could not be specified for generating input for the CBUF model. Potential methods to determine appropriate cone calorimeter input for various geometries and ignition locations are discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Revisiting flexible polyurethane foam flammability in furniture and bedding in the United States

The flammability of flexible polyurethane foam has been well studied to date, via smoldering and flaming ignition. Its contribution to fire loss in the United States has also been well documented, as the flammability of this material will contribute to large fire events when not protected from ignition and heat sources. Despite this known fire risk, fire protection approaches for polyurethane foam are being questioned in regards to fire protection performance, as well as proven and hypothesized concerns over health impacts before and after fire events. The flammability of flexible polyurethane foam in furniture and bedding is a clear and present danger that must be addressed, and this article discusses the current available technologies for fire protection, with pros and cons of these approaches. Known physical and chemical behavior of these foams in fires is discussed, as well as how this behavior contributes to large fire events. Finally, issues that still need further research and information to definitively address the polyurethane foam flammability in the United States is discussed.     

Flame retardancy of different‐sized expandable graphite particles for high‐density rigid polyurethane foams

The effects of expandable graphite (EG) of different particle sizes, on the fire‐retardant properties of high‐density rigid polyurethane foam (RPUF) (0.45 g cm^?3) were studied. Samples of EG with different particle sizes were obtained by pulverization in an ultra‐high‐speed mixer for 4 and 13 min, respectively. It was shown that as received (EG0) and 4 min pulverized EG (EG4) efficiently improved the fire‐retardant properties of RPUF composites, while 13 min pulverized EG (EG13) did not. The char of the burned composites filled with EG0 and EG4 covered the whole surface of the samples and formed a complete physical barrier. This barrier material prevented combustible gases from feeding the flame and also isolated oxygen efficiently from the burning material. EG13 did not produce enough char to cover the whole surface of the burning sample, resulting in poor fire‐retardant property of the RPUF composites. Thermal degradation tests of the foams by thermogravimetric analysis indicated that EG showed negligible effects on the thermal stability of the RPUFs. Copyright © 2006 Society of Chemical Industry     

Morphology development of high‐density rigid polyurethane foam upon compression by on‐line scanning electronic microscope

The high‐density rigid polyurethane foam (RPUF) was obtained by airtight cast molding. The morphology development during the compressive fracture process of RPUF was observed on‐line by a scanning electronic microscope (SEM). In the early stage of loading, the deformation of samples came from the tiny shape change in the cells' windows. As the load increases, some creases were formed in some cell windows in the vertical direction of loading, and the creases enlarged and resulted in the cracks across the whole cells. Moreover, during the deformation process, a failure band was formed in the weakest position. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Dependence of flame‐retardant properties on density of expandable graphite filled rigid polyurethane foam

Different density rigid polyurethane foams (RPUF) filled with various expandable graphite loadings were fabricated by cast molding. The flame retardant properties of these composites were assessed by limiting oxygen index and horizontal and vertical burning tests. The results showed that the flame retardant efficiency got better with increase in the foam density at the fixed EG weight percent or with increase in the EG weight percent at the fixed foam density. After burning, the low density (0.065 g/cm³) pure burned RPUF produced the highly collapsed and carbonized material, while the high density (0.510 g/cm³) pure RPUF had little change in size and had reduced destruction of the material. Moreover, the scanning electronic microscope (SEM) observation showed that the higher density EG/RPUF composites had a more compact outer layer (burned layer) after burned, in which more wormlike materials composed of expanded graphite particles appeared. In addition, higher foam density led to less plastic deformation in the interface layer between the burned and the inside layers. These results indicated that a weight percent of a flame retardant additive that achieves satisfactory flame retardancy for a certain density foam cannot effectively be applied for another density foam. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

CFD modeling approach of smoke toxicity and opacity for flaming and non‐flaming combustion processes

Current engineer's methods of fire safety design include various approaches to calculate the fire propagation and smoke spread in buildings by means of computational fluid dynamics (CFD). Because of the increased computational capacity, CFD is commonly used for prediction of time‐dependent safety parameters such as critical temperature, smoke layer height, rescue times, distributions of chemical products, and smoke toxicity and visibility. The analysis of smoke components with CFD is particularly complex, because the composition of the fire gases and also the smoke quantities depends on material properties and also on ambient and burning conditions. Oxygen concentrations and the temperature distribution in the compartment affect smoke production and smoke gas toxicity qualitatively and quantitatively. For safety designs, it can be necessary to take these influences into account. Current smoke models in CFD often use a constant smoke yield that does not vary with different fire conditions. If smoke gas toxicity is considered, a simple approach with the focus on carbon monoxide is often used. On the basis of a large set of experimental data, a numerical smoke model has been developed. The developed numerical smoke model includes optical properties, production, and toxic potential of smoke under different conditions. For the setup of the numerical model, experimental data were used for calculation of chemical components and evaluation of smoke toxicity under different combustion conditions. Therefore, averaged reaction equations were developed from experimental measurements and implemented in ANSYS CFX 14.0. Copyright © 2015 John Wiley & Sons, Ltd.     

A comparison of fire retarded and non‐fire retarded wood‐based wall linings exposed to fire in an enclosure

Full‐scale fire experiments were carried out in an ISO room to study the behaviour of commonly used cellulosic lining materials in real fire conditions. In addition to the temperature measurements recommended by the ISO 9705, temperature recordings were made at each node of grid lines on the wall lining surfaces. Four lining materials were chosen to represent different types of products and the surface spread of classifications determined using the BS 476 Part 7 flame spread test environment. The linings included fire retarded, melamine faced and non‐fire retarded boards which facilitated a comparative study of the behaviour of these materials with respect to ignition, flame spread, heat release rate and time to flashover. Corner fire scenarios were used in all the experiments. A T shape flame spread pattern on the surface of the two adjacent walls was observed prior to flashover. Prior to the onset of flashover conditions, downward opposed flow surface flame spread to the wall/ceiling intersection. For the non‐retarded wood based materials, such as plywood and medium density fibre board, flashover conditions occurred approximately 4 min after the start of the experiment. However, the fire retarded chipboard ignition was delayed by some 11 min 45 s after which flame spread was very rapid with flashover occurring within a further 1 min 45 s. An explanation for this particular behaviour is the considerable pre‐heating which occurred during the pre‐ignition period. For the fire retarded linings, much higher surface temperatures were recorded compared with those for non‐fire retarded linings. It was found that the areas of the fire retarded linings facing the source flame suffered extensive pyrolysis and charring which penetrated to the rear surface of the lining. Copyright © 1999 John Wiley & Sons, Ltd.     

Mechanical and thermal properties of phenolic/glass fiber foam modified with phosphorus‐containing polyurethane prepolymer

Phenolic foam exhibits outstanding flame, smoke and toxicity properties, good insulation properties and low production costs. However, the brittleness and pulverization of phenolic foam have severely limited its application in many fields. In this study, a novel phosphorus‐containing polyurethane prepolymer (DOPU) modifier was firstly synthesized, and then the foaming formula and processing of toughening phenolic foam modified with DOPU and glass fiber were explored. The structure and reactive behavior of prepolymer and phenolic resin were investigated using Fourier transform infrared spectroscopy. The effects of DOPU and glass fiber on the apparent density, compressive strength, bending strength and water absorption were investigated. The results suggested that the apparent density, compressive strength and bending strength of modified phenolic foam tended to increase irregularly with increasing content of DOPU. The addition of DOPU led to lower water absorption of glass fiber‐filled foam. Thermal stability and flame retardancy were examined using thermogravimetric analysis and limiting oxygen index (LOI) tests. It was found that foam with 3% DOPU and 0.5% glass fiber added exhibited good thermal stability and high char yields. The LOI value of modified phenolic foams decreased with increasing DOPU content, but it still remained at 41.0% even if the amount of modifier loaded was 10 wt%. © 2012 Society of Chemical Industry     

Mechanical properties and fire retardant behavior of polyurethane foam reinforced with oil palm empty fruit bunch

The objective of this study was to investigate the effects of isocyanate/hydroxyl ratio and ammonium polyphosphate (APP) content on the properties of polyurethane foam. Polyurethane (PU) foam was prepared from polymeric diphenylmethane diisocyanate and polyethylene glycol with molecular weight of 200, reinforced with oil palm empty fruit bunch (EFB) using one shot process. The effect of EFB content on the properties of PU foam was also studied. It was noticed that EFB enhanced the properties of the PU foam. This was due to EFB acting as hard segment in PU foam system. The NCO/OH ratio played an important role in determining the properties of the PU foam produced. However, since EFB is a highly flammable material, APP was introduced to the PU foam system. From the results, APP improved the fire retardant behavior of the PU foam. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012