Reduction In Flammability Research Articles

Polycarbonate nanocomposite with improved fire behavior, physical and psychophysical transparency

Transparent polycarbonate nanocomposites with improved fire behavior were prepared by incorporation of polyhedral oligomeric silsesquioxane (POSS) and resorcinol bis (diphenyl phosphate) (RDP) via melt blending. Flame retardancy performance was characterized using thermogravimetric analysis, pyrolysis combustion flow calorimeter and cone calorimeter. Simultaneous presence of RDP and POSS led to the decrease of the degradation rate and the increase of char residue due to the reaction of the additives with the decomposing polymer. This results in a significant reduction of flammability of polycarbonate. In cone calorimeter, the heat release rate as well as the smoke production rate were shown to strongly decrease due to a condensed phase mechanism that favored the formation of a cohesive char layer. Transparency evaluation was performed in both physical and psychophysical spaces. The two approaches give various assessment of transparency. Considering the perceived optical properties, it could be concluded that flame retarded PC is translucent rather than transparent.

Reduction of flammability of ultrahigh-molecular-weight polyethylene by using triphenyl phosphate additives

The mechanism of reducing the flammability of ultrahigh-molecular-weight polyethylene (UHMWPE) with triphenyl phosphate (TPP) additives was investigated, using the methods of molecular-beam mass spectrometry (MBMS), differential mass spectrometric thermal analysis (DMSTA), thermocouple, thermogravimetry (TGA), and gas chromatography mass spectrometry (GC/MS). Kinetics of thermal degradation of pure UHMWPE and of that mixed with TPP was studied at high (∼150K/s) and low (0.17K/s) heating rates at atmospheric pressure. Effective values of the rate constants of the thermal degradation reaction were determined. Times of ignition delay, the limiting oxygen index, the burning rates of UHMWPE and UHMWPE+TPP and their temperature profiles in the flames were measured. The flame structure was investigated and the composition of the combustion products in the flame zone adjacent to the specimen’s combustion surface. TPP vapors in flame were found. Addition of TPP to UHMWPE was found to result in reduction of polymer flammability. TPP was shown to act as flame retardant both in the condensed and gas phases.

Innovative Approach to Rapid Growth of Highly Clay-Filled Coatings on Porous Polyurethane Foam.

An innovative twist to fabricating layer-by-layer coatings resulted in transparent, high-content clay coatings on porous polyurethane foam. The addition of an anionic poly(acrylic acid) (PAA) monolayer between anionic clay and cationic branched-polyethylenimine (PEI) monolayers resulted in a trilayer nanocomposite structure with an order of magnitude thicker coating using 40% less monolayers than the conventional bilayer approach. The eight trilayer system thoroughly coated all internal and external surfaces of the porous polyurethane foam, creating a clay brick wall barrier that reduced the foam flammability by as much as 17% of the peak heat release rate and 21% of the total burn time. Though the flammability reduction is comparable to common commercial fire retardant polyurethane foam, the clay is used at a 50% lower amount and may be a greener solution as many of the commercial fire retardants (e.g., halogen bases) have potential environmental and health concerns.

Permeability, Viscoelasticity, and Flammability Performances and Their Relationship to Polymer Nanocomposites

Despite abundant studies on gas barrier, viscoelastic, and flammability properties of polymer nanocomposites, comprehensive understandings of these performances and their relationships are still lacking. We herein attempt to gain deep insights into the performances by creating several polymer nanocomposites by incorporating three types of nanoparticles, nanoclay (Clay), carbon nanotubes (CNTs), and reduced graphene nanoplates (RGO), into polypropylene (PP). The oxygen permeability, viscoelasticity, and flammability measurements demonstrate that RGO can lead to much more reduction in the gas permeability (by ∼73%) and flammability (peak heat release rate (PHRR) reduction by ∼78%), as well as a higher storage modulus and melt viscosity of polymer matrix relative to clay and CNTs at the same loading (1.0 wt %) due to its higher aspect ratio. Clay performs better than CNTs in terms of gas barrier property due to its lamellar structure while behaves worse than CNTs in terms of increasing the melt viscosity and reducing flammability of polymers. Most important, there is a nearly line correlation among these properties for all polymer nanocomposites despite some deviations.

Influence of graphite and wood-based fillers on the flammability of flexible polyurethane foams

The aim of this work was to verify the influence of graphite and wood-based fillers on the flammability of flexible polyurethane foams (FPF). Expandable graphite (EG) and cellulose (C) fillers were added to FPFs to improve their thermal stability and reduce their flammability. Four types of foams have been compared: FPF, FPF with the addition of EG, FPF with the addition of C and FPF with the addition of both fillers. Linear flammability tests and pyrolysis combustion flow calorimetry (PCFC) were performed to assess the flammability of these materials. It was found that the addition of cellulose does not improve the fire reaction, but a combination of both the EG and C fillers mixed together was able to achieve a small reduction in flammability, as confirmed by a linear flammability test and PCFC. The best properties observed by PCFC were from FPFs with EG. Usage of cellulose filler separately is not a good method for the assessment of higher thermal stability and lower flammability of FPFs. Thermal properties were measured by thermogravimetric analysis and dynamic mechanical analysis. These results showed that especially EG addition allows to achieve a positive effect on the thermal stability of the tested materials. Mechanical and physical tests (density, hardness, flexibility and irreversible strain) showed that the presence of graphite or cellulose filler results in changes in the properties of the FPFs, but these changes are not extensive. Fourier transform infrared spectroscopy analysis showed that only small changes exist in the chemical structure with the addition of the fillers. The introduction of EG and EG+C fillers into an FPF may reduce its flammability.

Synthesis and flame retardant testing of new boronated and phosphonated aromatic compounds

The present report describes the preparation and use of some dimethyl terephthalate derivatives in transition metal-catalyzed coupling reactions to produce new reactive flame retardants. Dimethyl iodoterephthalate and dimethyl 2,5-diiodoterephthalate were successfully employed in the preparation of phosphonic and boronic esters and acids. The latter were tested for heat release with a microcombustion calorimeter (ASTM D7309) to determine the potential for heat release reduction of these flame retardant molecules. The results showed that the addition of boronic or phosphonic acids greatly lowered the heat release, due to a condensed phase (char formation) mechanism. Adding ester groups to the boronic acids or phosphonic acids could either completely remove all flame retardant effects or make the molecule act more like a vapor phase flame retardant. Finally, the various potential flame retardants were solvent blended with a thermoplastic polyurethane to assess their flammability reduction effects by microcombustion calorimetry. The results of these experiments found that the molecules that reduced heat release the most by themselves showed the greatest reduction in heat release in a polyurethane as well, with the boronic acids yielding the greatest reduction in heat release.

The synthesis and properties of a reactive flame‐retardant unsaturated polyester resin from a phosphorus‐containing diacid

AbstractA transparent flame‐retardant unsaturated polyester resin (FR‐UPR) was obtained by reacting propylene glycol (PG) with maleic anhydride (MA), phthalic anhydride (PA), and 9,10‐dihydro‐10[2,3‐di(hydroxy carbonyl)propyl]‐10‐phosphaphenanthrene‐10‐oxide (DDP) synthesized from 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide (DOPO) and itaconic acid (ITA). The chemical structure of the resulting FR‐UPR was confirmed by FTIR, 1H‐NMR and 31P‐NMR. The average molecular weight and viscosity of the FR‐UPR were determined by gel permeation chromatography (GPC) and viscometer, respectively. Thermal stability was studied by thermogravimetric analysis (TGA) both in air and nitrogen to determine the thermal decomposition mechanism, and the apparent activation energy (Ea) was calculated by both the Kissinger and Ozawa methods. Compared to unsaturated polyester resin (UPR), the higher Ea of FR‐UPR3 implied an improved thermal stability. According to variations of the limited oxygen index (LOI) values, the UL 94 rating of vertical burning test and scanning electron microscopy (SEM) photographs of char residues, the flame retardance of cured FR‐UPR was enhanced with increasing DDP content. The study of fire reaction tests, using a cone calorimeter, suggested that there was a significant reduction of flammability in the FR‐UPR. Copyright © 2010 John Wiley & Sons, Ltd.

Nanostructure of montmorillonite barrier layers: A new insight into the mechanism of flammability reduction in polymer nanocomposites

This study describes the mechanism of flammability reduction in flame-retarded polymer matrix organo-montmorillonite reinforced nanocomposites. Morphologies of untested polymer nanocomposites and char residues formed by combustion in the mass loss calorimeter are characterized by XRD and TEM techniques. It is postulated that a combination of well-dispersed montmorillonite platelets and flame retardants in the polymer matrix provides nano-structured char formation. Initial montmorillonite dispersion in flame-retarded nanocomposites is found to be a major controlling factor on formed char nanostructures. An initially intercalated structure is invariantly converted to complete montmorillonite collapse whereas an initially exfoliated structure transforms to nano-structured chars demonstrating retained exfoliation or a new state of intercalation via incomplete collapse of montmorillonite layers. It is proposed that nano-structured char formation is the effective mechanism of flammability reduction, i.e. reduction in rate of heat release during combustion, in flame-retarded polymer nanocomposites.

Modeling impacts of fire severity on successional trajectories and future fire behavior in Alaskan boreal forests

Much of the boreal forest in western North America and Alaska experiences frequent, stand-replacing wildfires. Secondary succession after fire initiates most forest stands and variations in fire characteristics can have strong effects on pathways of succession. Variations in surface fire severity that influence whether regenerating forests are dominated by coniferous or deciduous species can feedback to influence future fire behaviour because of differences in forest flammability. We used a landscape model of fire and forest dynamics to explore the effects of different scenarios of surface fire severity on subsequent forest succession and potential fire activity in interior Alaska. Model simulations indicated that high levels of surface fire severity leading to a prolonged phase of deciduous forest dominance caused a reduction in landscape flammability and fewer large fire events. Under low surface fire severity, larger patches of contiguous conifer forest promoted fire spread and resulted in landscapes with shorter fire return intervals compared to scenarios of high surface severity. Nevertheless, these negative feedbacks between fire severity, deciduous forest cover, and landscape flammability were unable to fully compensate for greater fire activity under scenarios of severe climate warming. Model simulations suggest that the effects of climate warming on fire activity in Alaska’s boreal forests may be partially but not completely mitigated by changes in fire severity that alter landscape patterns of forest composition and subsequent fire behaviour.

Flammability of thermoplastic carbon nanofiber nanocomposites

AbstractFive commodity thermoplastics (polyethylene, polypropylene, thermoplastic polyurethane, poly(butylene terephthalate), and poly(amide 6)) were melt compounded with vapor grown carbon nanofibers via twin screw extrusion. These materials were then analyzed for flammability behavior by cone calorimeter to determine how the nanofibers would reduce flammability of the polymers. It was found by cone calorimeter that the nanofibers greatly reduced peak heat release rate and improved many other flammability parameters of the samples. However, smoke release was increased in all samples, which may be one drawback of using these materials. Interestingly, the amount of flammability reduction was not uniform across all samples, with nanofiber reducing flammability the most in the thermoplastic polyurethane sample. The mechanism of flammability reduction in the polymers tested in this paper is shown again to be a mass loss rate reduction induced by the formation of thick tangled networks of carbon nanofibers during polymer decomposition. This mechanism was confirmed by studying the mass loss rate curves and electron microscopy analysis of the final chars collected from the cone calorimeter experiments. Copyright © 2010 John Wiley & Sons, Ltd.

Effects of a phosphorus compound on the morphology, thermal properties, and flammability of polystyrene/MgAl‐layered double hydroxide nanocomposites

AbstractPhosphorus, nitrogen‐containing monomer, acryloxyethyl phenoxy phosphorodiethyl amidate (AEPPA), was synthesized and copolymerized with styrene (St). Nanocomposites of polystyrene and poly(St‐co‐AEPPA) with various amounts of Mg‐Al layered double hydroxide (LDH) were then prepared by in situ bulk polymerization. Structure and morphology of the nanocomposites were investigated by Fourier transform infrared (FTIR), X‐ray diffraction (XRD), and transmission electron microscopy (TEM). The nanocomposites were also examined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and microscale combustion calorimeter (MCC) to evaluate the thermal properties and flammability. Intercalated or exfoliated structures were obtained for all the nanocomposites. The results from XRD and TEM showed the LDH layers dispersed better in poly(St‐co‐AEPPA) than those in PS matrix. Decrease in thermal stability and enhancement in char residues were observed for poly(St‐co‐AEPPA) nanocomposites compared with PS nanocomposites at the same LDH loading. The addition of LDH can obviously reduce the heat release capacity (HRC) and total heat release (THR) of PS. Moreover, further reductions in HRC and THR were found in poly(St‐co‐AEPPA) nanocomposites. The reduction in flammability was attributed to the lower maximum mass loss rate (MMLR) and higher char residues of the nanocomposites. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers

Use of inorganic materials to enhance thermal stability and flammability behavior of a polyimide

While a great variety of high temperature polyimide materials exist, these materials are being subjected to higher and higher use temperatures in oxidative and environmentally aggressive environments. There is a limit to the extent one can take a polyimide before it will oxidize and subsequently suffer property degradation, thermal decomposition, and structural failure. Therefore, we instead sought to use materials which do not oxidize (inorganic materials) to enhance the polyimide composition and perhaps move the properties of the organic polymer more into the realm of ceramics while maintaining polyimide composite weights and processing advantages. In this paper we present results of the combination of inorganic micron sized particles with and without carbon nanofibers to produce a variety of highly inorganic particle filled polyimides. These polyimides were tested for thermal stability and flammability in resin pellet form and as a protective coating for a carbon–fiber composite structure. Our results demonstrate that the resin with inorganic particles exhibited significant reductions in flammability by themselves, but minimal flammability reduction when used as a thin coating to protect a carbon–fiber composite. Further, the gains in thermal stability are limited by the thermal stability of the polyimide matrix, suggesting that more work is needed in measuring the limits of inorganic fillers to improve thermal stability. Still, the results are promising and may yield polyimide systems useful for providing resistance to damage from high heat flux exposures/fire risk scenarios.

Modification of polyester binders for glass fiber-reinforced plastics with phosphorus-containing metacrylates for reduction of composite flammability

Synthetic procedures for methacrylic derivatives of phosphorus acids are developed. Their copolymerization with unsaturated polyesters gives binders for low-flammable composite materials. Novel fiberglass plastics for shipbuilding are presented.

Organo-montmorillonite barrier layers formed by combustion: Nanostructure and permeability

Self-assembly of nanoparticles into barrier layers has been the most cited theoretical explanation for the significant reduction in flammability often noted for polymer/montmorillonite nanocomposites. Both mass and heat transport reductions have been credited for such improvements, and in most cases a coupled mechanism is expected. To provide validation for early transport models, the structure of model barrier layers was investigated, these being produced by combustion of a homologous series of organo-montmorillonites. One model barrier layer was subjected to novel permeability analysis to obtain a flux, which will be useful in the evaluation of transport models. The effects of compatibilizer structure, temperature and pressure on barrier layer structure were examined. XRD versus TGA results suggest that the onset of chemical degradation and the onset of physical collapse on heating are correlated. Addition of pressure as low as 7 kPa affected the onset of structural collapse; for the case of a “two-tailed” dimethyl dialkyl quaternary ammonium ion compatibilized organo-montmorillonite this meant expansion of the basal spacing rather than the expected densification. Permeability of Ar through the ash was found to be a sensitive measure of structural change of high aspect ratio MMT nanoparticles. Actual fluxes ranged from 0.139 to 0.151 mol (m 2 s) − 1 for 0.5 mm thick samples.

Morphologies and thermal properties of flame-retardant polystyrene/α-zirconium phosphate nanocomposites

Abstract The phosphorus- and nitrogen-containing monomer, acryloxyethyl phenoxy phosphorodiethyl amidate (AEPPA), was synthesized and characterized. Poly(St-co-AEPPA)/α-zirconium phosphate (α-ZrP) nanocomposites with different amounts of α-ZrP were then prepared by in situ radical bulk copolymerization. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that the α-ZrP layers were exfoliated in the polymer matrix. Improvements in thermal stability and char residues of the copolymer and nanocomposites were observed by thermogravimetric analysis (TGA). The incorporation of AEPPA can reduce the flammability of polystyrene (PS). Moreover, further reductions were observed when α-ZrP was added. The reduction in flammability was attributed to a lower maximum mass loss rate and more char residues of the nanocomposites involved in thermal degradation.

Mild processing and characterization of silica epoxy hybrid nanocomposite

Previous research has shown that the inclusion of the spherical silica (SiO 2) nanoparticles into epoxy resin can achieve simultaneous improvement of fracture toughness and modulus. However, the glass transition temperature of the nanocomposite was significantly decreased when loading the nanosilica was higher than 5 wt.%. This perhaps was caused by utilization of the ultrasonication probe in the processing of these materials. In this paper, milder processing procedures were applied to make spherical silica epoxy nanocomposites while investigating if the homogeneous dispersion and morphology of the individual silica nanoparticle dispersed in the epoxy matrix could still be achieved. The results show that even at high loading of the silica nanoparticle, such as 30 wt.% silica, the perfect morphology of the nanocomposite could still be achieved with these milder processing conditions which indicates that ultrasonication is not needed. With the use of milder processing conditions, the glass transition temperature of the nanocomposite of 5 wt.% silica loading did not change, and the drop in the T g was minimal for silica loading up to 15%, but some effects of self-polymerization of the epoxy were noted on T g up to 30 wt.% loading of silica. Thermal analysis and flammability testing of the resulting materials suggest that nanosilica has only an inert filler effect (dilution of fuel) on flammability reduction and char yield increase, not a synergistic decrease in heat release as is often observed for clays and carbon nanotubes/nanofibers. So the mild and easy processing procedure only achieved uniform nanoscale morphology with excellent dispersion in the final nanocomposite, but also the effect on the change in the T g can be minimized as nanosilica loading was increased.

Graphite Oxide Flame-Retardant Polymer Nanocomposites

Graphite oxide (GO) polymer nanocomposites were developed at 1, 5, and 10 wt % GO with polycarbonate (PC), acrylonitrile butadiene styrene, and high-impact polystyrene for the purpose of evaluating the flammability reduction and material properties of the resulting systems. The overall morphology and dispersion of GO within the polymer nanocomposites were studied by scanning electron microscopy and optical microscopy; GO was found to be well-dispersed throughout the matrix without the formation of large aggregates. Mechanical testing was performed using dynamic mechanical analysis to measure the storage modulus, which increased for all polymer systems with increased GO loading. Microscale oxygen consumption calorimetry revealed that the addition of GO reduced the total heat release and peak heat release rates in all systems, and GO-PC composites demonstrated very fast self-extinguishing times in vertical open flame tests, which are important to some regulatory fire safety applications.

Interfacial Interactions and Flammability of Flame-Retarded and Short Fiber-Reinforced Polyamides

Interfacial properties, crystallinity and flammability of short fiber reinforced and flame retarded polyamide 6 and polyamide 66 compounds are investigated, emphasizing the influence of flame retardant fillers on the resistance of fiber/matrix interface to shear. Interfacial shear strengths are derived through a micromechanical approach by determining the tensile properties and residual fiber length distributions. Validated by fracture morphologies, interfacial strengths are found to be governed by filler – induced apparent crystallinities and fractional occurrence of polyamide polymorphs, obtained via peak deconvolution of X-Ray diffraction patterns. Although flame retardant additives based on Br/Sb synergism are found to impart excellent flammability reductions regarding oxygen index and UL94 classifications (V-0 rating), degree of crystallinity; thus, interfacial properties are deteriorated due to lowered thermal expansion and increased cooling rates. Red phosphorus as a flame retardant also induces a UL94 V-0 and significant reduction in flammability together with the facts that crystallinity is not altered and a strong fiber/matrix interface is maintained. Use of melamine cyanurate in an unreinforced polyamide improves the limiting oxygen index considerably; however, the UL94 rating remains unchanged as V-2 as a consequence of increased level of melt dripping. Melamine cyanurate additionally increases the degree of crystallinity through promotion of heterogeneous nucleation.

Negative fire feedback in a transitional forest of southeastern Amazonia

AbstractAnthropogenic understory fires affect large areas of tropical forest, particularly during severe droughts. Yet, the mechanisms that control tropical forests' susceptibility to fire remain ambiguous. We tested the widely accepted hypothesis that Amazon forest fires increase susceptibility to further burning by conducting a 150 ha fire experiment in a closed‐canopy forest near the southeastern Amazon forest–savanna boundary. Forest flammability and its possible determinants were measured in adjacent 50 ha forest plots that were burned annually for 3 consecutive years (B3), once (B1), and not at all (B0). Contrary to expectation, an annual burning regime led to a decline in forest flammability during the third burn. Microclimate conditions were more favorable compared with the first burn (i.e. vapor pressure deficit increased and litter moisture decreased), yet flame heights declined and burned area halved. A slight decline in fine fuels after the second burn appears to have limited fire spread and intensity. Supporting this conclusion, fire spread rates doubled and burned area increased fivefold in B3 subplots that received fine fuel additions. Slow replacement of surface fine fuels in this forest may be explained by (i) low leaf litter production (4.3 Mg ha−1 yr−1), half that of other Amazon forests; and (ii) low fire‐induced tree and liana mortality (5.5±0.5% yr−1, SE, in B3), the lowest measured in closed‐canopy Amazonian forests. In this transitional forest, where severe seasonal drought removed moisture constraints on fire propagation, a lack of fine fuels inhibited the intensity and spread of recurrent fire in a negative feedback. This reduction in flammability, however, may be short‐lived if delayed tree mortality or treefall increases surface fuels in future years. This study highlights that understanding fuel input rate and timing relative to fire frequency is fundamental to predicting transitional forest flammability – which has important implications for carbon emissions and potential replacement by scrub vegetation.

Relation between the viscoelastic and flammability properties of polymer nanocomposites

Previous work has shown that the formation of a network structure of nanoparticles within a polymer matrix can significantly reduce nanocomposite flammability and that viscoelastic properties could be utilized to predict their flammability reduction. The present work extends this type of investigation to the study of clay and carbon nanotube nanocomposites. In particular, we study PS/clay, PS/MWNT, PMMA/clay, and PMMA/SWNT nanocomposites. At a clay level of about 10% by mass, the network structure is formed for the PS and the PMMA clay nanocomposites; it requires a level of about 0.5% with the SWNT and 2% with the MWNT. These samples showed significantly reduced mass loss rates of PS and PMMA. However, the solid residues collected from radiative gasification tests of PS/clay and PMMA/clay showed many small cracks, despite the network formation within the initial sample. This is in contrast to the smooth, continuous residues (no cracks or openings) for PS/MWNT and PMMA/SWNT nanocomposites. The cracks in the clay samples are probably formed due to weaker network at elevated temperatures due to weaker bridging interaction between clay platelets as compared to stronger network resulting from dense entanglement and bridging of carbon nanotubes.