Horizontal Flame Spread Research Articles

Disulfide-containing polyamidoamines with remarkable flame retardant activity for cotton fabrics

Bioinspired polyamidoamines containing disulfide-groups in the main chain (SS-PAAs), prepared by Michael polyaddition of 2,2-bis(acrylamido)acetic acid with l-cystine (B-CYSS) and of N,N′-bis(acryloyl-l-cystine) with either glycine or 2-methylpiperazine (BACYSS-GLY and BACYSS-MP), were investigated as intumescent surface-confined flame retardants for cotton textiles. The main purpose was to ascertain if the presence of disulfide functions in the repeat units imparted superior flame retardant properties compared with sulfur-deprived polyamidoamines whose efficacy were previously demonstrated. In horizontal flame spread tests, at 18% add-on both BACYSS-GLY and BACYSS-MP inhibited ignition; at 12% add-on BACYSS-GLY extinguished flame, whereas BACYSS-MP burnt completely leaving substantial carbonaceous residues. In vertical flame spread tests, both BACYSS-GLY and BACYSS-MP burnt completely leaving substantial residues up to at least 18% add-on. At 12% add-on B-CYSS inhibited ignition in both horizontal- and vertical flame spread tests. In the latter test, only limited afterglow was observed. Scanning electron microscopy (SEM), thermogravimetric and cone calorimetric analyses were consistent with these results. In particular, thermogravimetric analyses showed at 750 °C high residues in nitrogen (28–54%) and only moderately lower residues in air (19–48%). In cone calorimetry tests, all tested SS-PAAs increased time to ignition, decreased peak of heat release rate and effective heat of combustion of cotton. All samples remarkably reduced CO and CO2 yields. SEM micrographs of combustion residues of all SS-PAAs treated cotton fabrics presented diffused intumescent bubbles.

Coatings made of proteins adsorbed on TiO2 nanoparticles: a new flame retardant approach for cotton fabrics

A novel durable intumescent flame retardant coating, based on metal oxide nanoparticles (NPs) and biomacromolecules, was designed and applied on cotton fabrics. Specifically, different TiO2 NPs/proteins systems were deposited by dip-pad-dry-cure process and the morphology of the resulting coating were assessed by SEM analysis. Enhancement of durability (i.e. resistance to washing treatments) was verified by release tests carried out in static and dynamic conditions. Flammability and cone calorimetry tests were performed for evaluating the fire behavior of the treated fabrics. More specifically, in horizontal flame spread tests, the different nanoparticle/protein based coatings provided an increase of the total burning time and a decrease of the burning rate. Furthermore, the residues at the end of the test were significantly higher with respect to untreated cotton fabric. In particular, casein-based systems seemed to be more effective as compared to the whey proteins counterparts. Cone calorimetry tests showed better fire performances for the coatings based on TiO2/caseins with respect to TiO2/whey proteins, which did not seem to be so effective in protecting the underlying fabric from the heat flux. Therefore, due to their high char-forming character, casein-based coatings may represent an effective and durable fire-resistant finishing alternative to standard flame retardant treatments for cotton.

Linear polyamidoamines as novel biocompatible phosphorus-free surface-confined intumescent flame retardants for cotton fabrics

Eight linear polyamidoamines (PAAs) prepared by polyaddition of amines to bisacrylamides are investigated as intumescent surface-confined flame retardants for cotton textiles. The structure of the amine-derived subunits governs their performances. In ignitability tests, aminoacid-deriving PAAs exposed to direct flame for 10 s do not burn, but produce carbonaceous crusts sheltering the underneath sample apparently intact. PAAs carrying guanidine pendants partially volatilize without burning. 2-Methylpiperazine-derived PAAs burn completely. Thermogravimetric analyses show that in air at ≥400 °C all PAAs leave substantial char residues that oxidize at >500 °C. Horizontal flame spread tests on PAA-impregnated cotton stripes show flame extinction for add-ons ranging from 4 to 20%, apart from 2-methylpiperazine-deriving PAAs that never extinguish flame but slow down flame propagation leaving a substantial residue. In vertical flame spread tests, no PAA induces flame extinguishment at add-ons up to 20%, but all PAA-treated fabrics leave significant residues. In cone calorimetry tests, all PAAs increase the time to ignition and decrease the peak of heat release rate and the effective heat of combustion. Most PAAs remarkably reduce the release of CO and CO2. After the above tests the combustion residues of PAA-treated cotton fabrics present intumescent bubbles. All results indicate that PAAs warrant potential as effective surface-confined intumescent flame retardants.

An experimental study of horizontal flame spread over PMMA surface in still air

The paper presents a comprehensive experimental study of flame spread over the surface of horizontally placed slabs of four types of PMMA specimens in still air. Temperature distributions in the gas phase near the solid fuel surface and in the condensed phase were measured using microthermocouples. Spatial variation of the species concentration in the gas-phase flame near the solid fuel surface was measured using probing mass spectrometry. Also flame spread rate over the polymer surface was measured. The experiments revealed differences in the combustion character of the specimens investigated. At the flame spread over surface of two (out of the four) specimens boiling and formation of large bubbles were discovered. The main flame components including ММА, О2, СО2, Н2О, N2, С2Н4 (ethylene), С3Н6 (propylene) have been first identified, and their concentration profiles at different distances from the flame front have been measured. The data on the chemical flame structure have been shown to be in good agreement with the data on its thermal flame structure. The size of the “dark zone” of the flame, in which the temperature near the polymer surface is minimal, correlates well with the size of the oxygen-free zone, which is adjacent to the burning surface. Conductive heat feedback from the flames to the condensed fuel surface was estimated on the basis of the experimental results. The conductive heat flux averaged over the burning surface was estimated to be approximately 13.2 kW/m2. It has been established that it is maximal in the flame front and decreases as the specimen burns out. The data obtained may be used for developing and validating a numerical model of flame spread over PMMA surface.

Transition condition and control mechanism of subatmospheric flame spread rate over horizontal thin paper sample

The horizontal flame spread over paper samples was investigated using a subatmospheric cabin with varied O2 concentration. The 25 kPa is found to be a clear turning point for the flame illumination and structure, radiative heat flux and flame spread rate (FSR), which leads to the transition boundary between the extinction limits and power law regions. In the extinction limits (non-linear) region below 25 kPa, the oxygen partial pressure is low with a small Da number. Consequently, the flame spread is gas phase kinetics controlled, resulting in low burning rate, low radiative heat loss and weak buoyancy, and thus the FSR is more sensitive to the oxygen concentration while less sensitive to the ambient pressure. In the power law (linear) region above 25 kPa, in contrast, the oxygen partial pressure is high and the Da number is large, and the flame spread is heat transfer controlled, which weakens the dependence of FSR on oxygen concentration and enhances the dependence on air pressure.

Intumescent flame retardant properties of graft copolymerized vinyl monomers onto cotton fabric

In this paper, an intumescent flame retardant treatment, obtained by a combination of vinylphosphonic acid (VPA) and methacrylamide (MAA), was applied to cotton fabrics. In order to improve the cross-linking degree onto cellulose polymers, potassium persulfate was used as initiator of a radical polymerization technique. The application on cotton was carried out by padding, followed by drying and a curing treatment. The treated samples were characterized by SEM, TGA and FTIR-ATR analyses and tested in terms of flammability and washing fastness. The thermal and fire behavior of the treated fabrics was thoroughly investigated. The results clearly showed that the VPA/MAA coating was able to exert a protective action, giving rise to the formation of a stable char on the surface of textile fibers upon heating, hence improving the flame retardant performance of cotton. Horizontal flame spread tests confirmed that the coated fabrics achieved self-extinction, and the residues well preserved the original weave structure and fiber morphology; at variance, the uncoated fabric left only ashes. A remarkable weight loss was observed only after the first washing cycle, then the samples did not show any significant weight loss, hence confirming the durability of the self-extinguishing treatment, even after five laundering cycles.

Graphene and poly(ionic liquid) modified polyurethane sponges with enhanced flame‐retardant properties

ABSTRACTGraphene (Gr) and poly(ionic liquid) (PIL) modified polyurethane (PU) sponges with enhanced flame‐retardant properties were prepared by the direct dip coating of Gr and ionic liquid (IL) monomers onto a PU sponge followed by the polymerization of IL monomers under thermal initiation. With a content of 1.5% Gr in IL, the limiting oxygen index (LOI) of PU–PIL–Gr was 26.1%, whereas the neat PU sponge showed an LOI of only 17.9%. The horizontal flame test results indicate that PIL–Gr prevented horizontal flame spread and eliminated melt dripping. Compared with that of the neat PU sponge, the peak heat release rate of PU–PIL–Gr decreased about 22.0%. These improvements on flame retardancy might have been due to a hybrid flame retardant originating from Gr (which acted as carbon source) and PIL (which contained the flame‐retardant elements) in the PU sponge and the formation of protective layers, which isolated the oxygen and heat more effectively. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45477.

Improving the Flame Retardant Efficiency of Layer by Layer Coatings Containing Deoxyribonucleic Acid by Post-Diffusion of Hydrotalcite Nanoparticles.

This work deals with the use of hydrotalcite nanoparticle post-diffusion in layer by layer (LbL) coatings with the aim of improving their flame retardant action on cotton. The selected LbL components, which encompass polydiallyldimethylammonium chloride and deoxyribonucleic acid, aim at the deposition of an intumescent coating. Infrared spectra pointed out a super-linear growth of the investigated assembly, indicating the ability to deposit thick coatings while maintaining a relatively low deposition number. A post-diffusion process, performed by exposing the LbL-treated fabrics to two different concentrations of hydrotalcite water suspensions (0.1 or 1 wt %), was carried out to improve the fireproofing efficiency of these coatings. Coatings treated with the lowest concentration suspension partially swelled as a consequence of their structural rearrangements while the use of the highest concentration led to nanoparticle aggregates. Horizontal flame spread tests were used for assessing the achieved flame retardant properties. The post-diffusion performed at the lowest hydrotalcite concentration lowers the minimum number of Bi-Layers required for obtaining cotton self-extinguishment while samples treated with the highest concentration showed detrimental effects on the performances of treated fabrics. This behavior is ascribed to the effects of hydrotalcite particles on the intumescence of LbL coatings, as evidenced by the morphological analyses of post-combustion residues.

Experimental analysis of high oxygen concentration influences on horizontal flame spread over PA6 and epoxy

The combustion characteristic of material in high oxygen concentration is directly related to the safety of elevated oxygen environment similar to oxygen bombs and future spacecraft. In this study, flame front and flame spread rate in high oxygen concentration are discussed. Thermoplastic material polyamide (PA6) and thermosetting material epoxy are selected as comparison material. The variation of flame front over epoxy is more stable than PA6 which has dripping phenomenon during the flame spread process. The flame spread rate of both PA6 and epoxy have a power law with the increasing oxygen concentration.

Vinylphosphonic acid/methacrylamide system as a durable intumescent flame retardant for cotton fabric

A novel intumescent flame retardant treatment, consisting of vinylphosphonic acid (VPA) as the acid source and methacrylamide (MAA) as blowing agent, was designed and applied onto cotton fabrics. The grafting of reactive monomers onto cellulose chains was carried out using potassium persulfate as initiator of a radical polymerization technique. The thermal and fire behaviour of the treated fabrics was thoroughly investigated: in particular, the VPA/MAA coating was able to exert a protective action, giving rise to the formation of a stable swollen char on the surface of textile fibers upon heating, hence improving the flame retardancy of cotton. In addition, the treated fabric achieved self-extinction as assessed by horizontal flame spread tests. Finally, a remarkable weight loss was observed only after the first washing cycle, then the samples did not show any significant weight loss, hence confirming the durability of the self-extinguishing treatment, even after five laundering cycles.

Experimental study on the width and pressure effect on the horizontal flame spread of insulation material

Organic insulation materials such as polyurethane foams are widely used as buildings' façade wall insulation materials in China. However, they are highly flammable and of great fire hazard by the chemical nature. In this paper, a series of laboratory scale experiments using rigid polyurethane foam were conducted and theoretical analysis was applied to evaluate the real fire performance of such materials under different situations. Temperature profiles in both solid and gas phases were obtained. This work provides basic correlations of flame spread characteristic of polyurethane foams regarding to width and pressure changes. Theoretical analysis on heat transfer of width and pressure effects was also provided. Good agreement of changing trends was found between experimental results and theoretical calculation.

All-Inorganic Intumescent Nanocoating Containing Montmorillonite Nanoplatelets in Ammonium Polyphosphate Matrix Capable of Preventing Cotton Ignition.

In the present manuscript a new concept of completely inorganic intumescent flame retardant nanocoating comprised of sodium montmorillonite nanoplatelets embedded in an ammonium polyphosphate matrix has been investigated using cotton as model substrate. The coating, deposited by multistep adsorption from diluted water-based suspensions/solutions, homogenously cover each cotton fibers with average thicknesses below 50 nm and add-on up to 5% in weight. Combustion characterization evidences the interesting properties: indeed, the so-treated fabrics reached self-extinguishing during horizontal flame spread tests. Furthermore, when the coating add-on reaches 5%, no ignition has been observed during cone calorimetry tests under 35 kW/m2 heat flux. Residue analyses pointed out the formation of an expanded all-inorganic coating capable of greatly improving char formation by exerting barrier function towards volatile release and heat transfer.

Sample width and thickness effects on horizontal flame spread over a thin PMMA surface

In previous studies, it was found that there exists a minimum flame spread rate under a certain range of sample widths for steady burning horizontal flame spread. While this was hypothesized to occur due to a transition between convectively-dominated to radiation-dominated flame spread, no measurements were performed to quantify this process. This paper presents a detailed experimental study investigating sample width and thickness effects on steady horizontal flame spread, including detailed measurements of the components of radiation, convection, and conduction. Water-cooled heat flux gauges, R-type micro-thermocouples traversed through the gas phase, and K-type thermocouples embedded in the solid phase were all used to deduce these heat transfer components. Results show that convective heat transfer decreases with increasing sample width as the shape of the flame front is on average farther from the fuel surface, while radiation increases as the view factor from the fire to unignited fuel increases with larger sample size. Conduction measured within the fuel sample is, as expected, confirmed to be negligible. Comparing a combination of these components, the total heat flux first decreases as the competition between radiation and convection changes, followed by steadily increasing heat fluxes as the width of the sample increases. Heat feedback also influences the sample pyrolysis rate, so there was a coupled response following this trend. The apparent dip followed by an increase in total heat flux can now explain why a period of minimum flame spread rate exists. Modification of an existing theory also matches experimental results very closely. Finally, a dimensionless heat-release rate for different sample configurations is used to scale the dimensionless flame heights with a power-law correlation having exponents 0.39 for Q* >1 and 0.6 for Q* <1, closely resembling the 2/5 and 2/3 predicted by Zukoski's model.

The influence of low air pressure on horizontal flame spread over flexible polyurethane foam and correlative smoke productions

Pressure effects on quasi two-dimensional flexible polyurethane (FPU) foam flame spreading behavior, typical product concentrations, and smoke detector responses were investigated by comparative experiments under different ambient pressures of 99.8 kPa (in Hefei) and 66.5 kPa (in Lhasa), respectively. First, significant decreases of flame spreading velocity and burning rate were observed under low pressure condition. Averaged global burning rate was found to be dependent on pressure, with an exponential factor of 4/3 theoretically based on pressure modeling. Second, the maximum temperature at a given position in axial thermal plume showed insensitivity to pressure, yet the maximum temperature in ceiling jet was obviously higher. Third, the low pressure was shown to have no effect on soot particles size distribution by scan electron microscopy (SEM) imaging. However, the soot number concentration decreased with reduced pressure attributed to the much slower soot formation rate under low pressure. This result would further have an interesting influence on the response signals of photoelectric detector and ionization detector. Finally, the pressure effects on variation of CO and O2 volume concentration were discussed. Considering the relatively small heat release rate for FPU foam selected, the CO concentration in the far-field ceiling jet low under low pressure was found to be lower for the enhanced diffusive effect.

How much the fabric grammage may affect cotton combustion?

The present article is addressed to investigating the effect of different fabric grammages (mass per area unit) on cotton combustion. To this aim, 100, 200 and 400 g/m2 cotton fabrics were tested when exposed to (1) two different heat fluxes (25 and 35 kW/m2) under a cone calorimeter, (2) a methane flame in horizontal or vertical flame spread tests or (3) a propane flame in Limiting Oxygen Index tests, and (4) when pyrolysed and further oxidised in pyrolysis-combustion flow calorimetry (PCFC). The collected results demonstrated a precise relationship between fabric grammage and cotton combustion behaviour. Indeed, when exposed to a 35-kW/m2 heat flux, the higher the fabric grammage, the higher the total heat release during combustion was; the opposite trend was observed when the same fabrics were pyrolysed and further oxidised in PCFC. This finding was ascribed to the different scenarios described by these instrumentations; indeed, the cone calorimeter was able to reproduce cotton combustion in a well-ventilated context in the presence of air (thus, oxygen), while PCFC only represented the combustion of pyrolysis products. However, both techniques indirectly evidenced a linear dependence of char formation as a function of fabric grammage: the higher the fabric grammage, the larger the amount of char formed was. The same trend was also observed during horizontal and vertical flame spread tests. In conclusion, the present article is intended to show how cotton combustion may be affected by fabric grammage as well as how such behaviour is influenced by the experimental conditions in which it is investigated.

Effects of altitude and inclination on the flame structure over the insulation material PS based on heat and mass transfer

Experiments were conducted on the insulation materials of EPS and XPS in a small-scale flame spread experimental bench in the Tibetan plateau area of Lhasa (with an altitude of 3658m) and the plain area of Hefei (with an altitude of 50m), respectively. The detailed flame structure including flame angle, flame length and maximum length of pool fire over EPS and XPS with thicknesses of 2cm, 3cm, 4cm and 5cm inclined at the angles of −30° to 30° was investigated. It is found that for the same thickness of EPS and XPS inclined at the same angle, the flame length is longer and the flame angle is smaller in Hefei than those in Lhasa in the wall fire zone, which is in good agreement with the predictions. The preheating length δf is correspondingly longer in plain due to smaller flame angle and longer flame length and the flame heat flux q̇f″ increases with air pressure, which make the flame convective and radiative heat (q̇f″)2δf larger leading to promote flame spread. For the horizontal flame spread over EPS and XPS, the maximum length of pool fire is significantly smaller than that in other incline angles in Lhasa, which can be attributed to the smallest heat transfer to the residue pool fire zone during flame spread making PS in the residue pool fire zone extinguish more easily.

DNA coatings on cotton fabrics: Effect of molecular size and pH on flame retardancy

Deoxyribonucleic acid (DNA) has been mostly considered as a carrier of genetic information and gene expression. Recently, we have demonstrated that this biomacromolecule is very effective in providing cellulosic fabrics with flame retardant features, thanks to its intrinsic intumescent-like behaviour. Here, we have investigated the role played by different parameters on the overall flame retardant features: DNA molecular size, pH of the DNA aqueous solutions, and number of impregnations. For this purpose, herring DNA, at three different molecular sizes, low (100–200 base pairs, bp), medium (400–800bp) and high (2000–10,000bp), has been selected as model biomacromolecule; its effect as fire protective coating on cotton fabrics has been assessed in terms of resistance to a flame application (through horizontal flame spread tests) and to an irradiative heat flux of 35kW/m2 (by cone calorimetry). Furthermore, thermogravimetric analyses have been exploited for evaluating thermal and thermo-oxidative stability of the treated fabrics.The results clearly indicate that, despite a similar composition, the coatings containing low molecular size DNA exert a superior fire protection on the fabric substrate, as clearly indicated by horizontal flame spread and cone calorimetry tests. Multiple impregnation treatment turned out to be more performing than the single one, being equal the final add-on achieved. More specifically, the use of multiple impregnations at pH=4 and 8 allowed achieving self-extinction for 86 and 74% of the tested samples; in addition, 45 and 25% reductions of total heat release and heat release rate peak under 35kW/m2 have been found with respect to untreated cotton. These findings may be attributed to themorphology of the low molecular size DNA coating, which shows a greater penetration into the microfibrillar surfaces of the component fibres within the fabric and to its higher thermal stability in air.

Experimental study of the channel effect on the flame spread over thin solid fuels

We experimentally burn thin solid fuels and obtain the speed of the flame front when it propagates (1) within a narrow channel (closed cross section), (2) within a channel with lateral walls only and (3) through a free cross section (plain case). The latter configuration is the classical one and it has been extensively studied with analytical, numerical and experimental methods by other authors. Our experiments have been carried out at different geometrical configurations and angles of inclination of the sample and also at several values of oxygen molar fraction. All experiments are restricted to purely buoyant flow. Our main results are as follows: (1) sidewalls reduce the flame spread rate in a non-monotonous trend when varying its height; (2) in horizontal flame spread, two simultaneous flame fronts that propagate at different velocities may arise in the channel case at high oxygen levels. The fastest flame front speed may be higher than that obtained in the plain case; (3) in upward flame spread, the channel effect configuration produces the highest flame front speed. We finally analyze the correlation of the downward flame front speed data in terms of the Damkohler number.

Horizontal Flame Spread Characteristics of Rigid Polyurethane and Molded Polystyrene Foams Under Externally Applied Radiation at Two Different Altitudes

To investigate the characteristics of horizontal flame spread over two kinds of typical insulation materials (rigid polyurethane and molded polystyrene foams) under externally applied radiant flux, a series of laboratory-scale experiments are conducted on the Tibetan plateau (at an altitude of 3,658 m) and in the Hefei plain (at an altitude of 30 m) in China for comparisons. The external radiation intensity ranges from 1.0 kW/m2 to 4.5 kW/m2. The temperature distribution in the solid and gaseous phase and the flame spread rate under different external radiations are examined. The different flame spread behaviors of rigid polyurethane and molded polystyrene foams are scrutinized. The rates of flame spread over the two different materials in the plain are larger than those on the plateau at the same external radiant flux. At both altitudes, the flame spread rate increases with the increasing external radiation intensity. And the square root of the reciprocal of flame spread rate vf−1/2 has a negative linear relation with the external radiation intensity, which is consistent with the predictions of prior theory. The calculation of theoretical value of parameter C is 0.039, which is nearly the same as the slope of fitting line. The mechanism of heat transfer during the flame spread process is analyzed in detail, and the simplified expressions of flame spread rate of the two insulation materials under external applied radiation are achieved.

수평화염전파에 대한 매커니즘(ISO 12949에 따른 침대 매트리스 화염성상을 중심으로)

수평화염전파에 대한 매커니즘(ISO 12949에 따른 침대 매트리스 화염성상을 중심으로)