Search

A method to estimate the thermo-oxidative stability of chars is proposed using pyrolysis-combustion flow calorimetry. The temperature of char degradation is measured for different oxygen fractions (from 0.01 to 0.4, i.e. from 0 to 40%) into the pyrolyzer. Then the thermo-oxidative stability versus the oxygen fraction is modelled using a simple phenomenological equation. Two parameters have been calculated: the first one predicts the temperature of char degradation in “pure” oxygen and the second one corresponds to the sensitivity of the char degradation temperature to the oxygen fraction. These two parameters allow comparing the chars obtained from different materials after various pyrolysis procedures. Rough relationships between these two parameters and the elemental composition of char are identified. Phosphorus allows improving the thermo-oxidative stability of chars as expected but its effect is nonlinear. Lignocellulosic materials lead to chars with low thermal stability even when the phosphorus content is high. Finally, the obtained results show that the char elemental composition is not the only parameter influencing its thermo-oxidative stability. [ABSTRACT FROM AUTHOR]

Various amounts of a phosphonium ionic liquid (IL169) were used as curing agents as well as flame retardants of epoxy prepolymer in order to prepare epoxy networks with improved fire properties. The flame retardancy of these resins was investigated using thermogravimetric analysis (TGA), pyrolysis-combustion flow calorimetry (PCFC) and cone calorimetry. Phosphonium ionic liquid significantly reduced flammability without further addition of flame retardants due to the high amount of phosphorus (up to 3.69 wt%). The Peak of heat release rate decreases from 1099 kW/m 2 to 300 kW/m 2 in cone calorimeter at 35 kW/m 2 when incorporating 30 phr of IL169. Phosphorus modifies pyrolysis pathway, promotes charring and may act as flame inhibitor. The char layer protects the underlying polymer, leading to a high unburnt polymeric fraction. Char properties were studied using PCFC, Raman spectroscopy and X-ray tomography. Phosphorus improved the graphitization of the char and its thermo-oxidative stability. [ABSTRACT FROM AUTHOR]

The flame retardancy of ethylene-vinyl acetate copolymer filled with metal hydroxides (aluminum hydroxide - ATH and magnesium hydroxide - MDH) and silica was investigated. Several composites containing only metal hydroxides or a combination of metal hydroxides and silica (ratio silica/hydrated filler = 0.18) were prepared and tested using pyrolysis-combustion flow calorimeter, thermogravimetric analysis and cone calorimeter at various heat fluxes. It was observed that silica provides benefits when the amount and other properties of the fillers allow the formation of an insulating mineral layer. In such cases, silica does not modify the first peak of heat release rate in cone calorimeter tests, but reduces or completely suppresses the breakdown of the insulating layer near the end of the combustion (assessed by the intensity of the second peak in the heat release rate as function of time). This effect is particularly obvious at lower heat flux, the insulating layer protects the underlying polymer, which is therefore not completely degraded. [ABSTRACT FROM AUTHOR]

This study presents the use of oedometric compression test in order to evaluate the breakdown of a protective layer acting as a diffusion barrier (“barrier effect”) occurring during cone calorimeter tests for ethylene-vinyl acetate copolymer/aluminium trihydroxide (EVA/ATH) composites. The formation of an alumina layer at the sample surface during burning insulates thermally the underlying material and reduces the heat release rate. The efficiency of this barrier depends on the cohesion of the layer formed. This cohesion depends on the ability of the particles (ATH and synergistic mineral fillers) to self-arrange. During the test, the breakdown of this barrier can lead to an increase in HRR. The oedometric compression test allows assessing the ability of fillers to form a cohesive layer. Results obtained from compression modulus of filler powders are directly related to some aspects of the heat release rate curve of composites measured in cone calorimeter tests. Indeed, the appearance and the intensity of the second pHRR (related to the breakdown of the barrier layer) in cone calorimeter test are related to the slope of oedometric compression curve. [ABSTRACT FROM AUTHOR]

Flax fabrics were modified by radiation grafting method to improve their flame retardancy. Several phosphonated monomers with different carbon-carbon double bond reactivity were grafted. According to 1H NMR carried out on irradiated monomers solubilized in water, the reactivity is the highest for (acryloyloxy)methyl phosphonic acid (hPAAPC1), and the lowest for allyl phosphonic acid (APA). Nevertheless, grafting yield on flax, assessed by X-ray fluorescence and scanning electron microscopy showed a different tendency. Especially (methacryloyloxy)methyl phosphonic acid (hPMAPC1) and vinyl phosphonic acid (VPA) appear to be highly grafted. In all cases, diffusion of the molecules into the flax elementary fibers bulk was observed. The choice of the solvent in washing step after the irradiation step showed to be effective to control the final phosphorus content in flax fabrics. The effect of phosphorus grafting on thermal properties and fire behavior was studied using thermogravimetric analysis, pyrolysis combustion flow calorimetry and a preliminary fire test. According to the latter, self-extinguishing and non-flammable fabrics were obtained for phosphorus content of 0.5 wt% and 1.2 wt% respectively. Correlations with flammability at microscale were pointed out. Additional cone calorimeter tests highlight the influence of flame retardant treatment on flammability under forced flaming conditions. • Phosphorus FR molecules were radiation grafted onto flax fabrics. • Reactivity of these FR molecules under radiation was assessed. • Two competitive phenomena occurred: grafting and homopolymerization. • Flame retardancy was improved and depended mainly on phosphorus content. [ABSTRACT FROM AUTHOR]

Flax fabrics were modified through two grafting methods in order to improve their flame retardancy. Vinyl phosphonic acid was used to treat flax fabrics via a condensation reaction between phosphonic acid function and flax hydroxyl groups. It was also grafted under radiation conditions taking advantage of its carbon-carbon double bond. Grafting efficiency of each method was assessed by X-ray fluorescence and scanning electron microscopy. The effect of the phosphorus grafting on fire behavior was studied using thermogravimetric analysis, pyrolysis combustion flow calorimetry and a preliminary fire test. In all cases, the diffusion of the phosphorus molecules into the elementary fibers bulk was observed. Phosphorus content reached 1.4 wt% using radiation grafting, leading to self-extinguishing fabrics. [ABSTRACT FROM AUTHOR]

The fireproofing study of polyamide 11 (PA11), a bio-based polyamide synthesized from castor oil and marketed under the trade name Rilsan ® is presented. As an interesting perspective, FR can be chemically linked to the PA backbone. In this way, we achieved the synthesis of a dicarboxylic acid from DOPO cycle (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide). This phosphorus diacid derivative was able to react by polycondensation to give rise of new copolyamides (coPA) bearing phosphorus moieties attached to the PA backbone with 15,000–30,000 g/mol as molar masses. The amount of phosphorus and the viscosity of the final PA were optimized. Thermal properties such as thermogravimetry analysis (TGA) or differential scanning calorimetry (DSC) were evaluated and were shown crystallinity and degradation typical of linear PA11. UL94-V0 ranking coupled with high Oxygen Limit Indexes (LOI = 40) were also obtained. Pyrolysis-combustion flow calorimeter (PCFC) and cone calorimeter were performed to understand the mode-of-action of the new phosphorus-containing FR used to obtain self-extinguishing bio-based PA11. Lastly, the preserving of mechanical properties was highlighted. [ABSTRACT FROM AUTHOR]

In this study the influence of surface modification of kaolinite with trisilanolisooctyl Polyhedral OligoSilSesquioxane (POSS) in polypropylene composites was evaluated in terms of thermal stability and fire retardancy and compared with talc. Thermogravimetric analysis showed that incorporating 30 wt% of kaolinite enhanced the thermal stability by ca. 20 °C compared to neat polymer. Cone calorimeter results demonstrated that kaolinite can greatly reduce the pHRR but not unmodified kaolinite. Rheological measurements showed that surface treatment of kaolinite leads to a decrease in viscosity, which could enhance processability. Finally, a correlation between viscosity and pHRR was found and the fire behavior of PP containing modified kaolinite could be explained. [ABSTRACT FROM AUTHOR]

In the present work, diatomite was used as co-filler in aluminium hydroxide/ethylene-vinyl acetate composites (ATH/EVA). This silica-based marine sediment acts as a synergistic agent with ATH, to increase the flame retardant properties of EVA composites. When diatomite was used with ATH the formation of an expanded layer during cone calorimetry tests was observed. This layer presents a complex structure which better insulates the sample and reduces the heat release rate (HRR). Rheological measurements, such as complex viscosity obtained with an ARES apparatus, suggest an influence of the viscosity of the sample melt. We assume that the viscosity of the EVA composites is influenced by the porosity of the diatomite. Better residue cohesion was also obtained in presence of diatomite. [ABSTRACT FROM AUTHOR]

Selective dispersion of 10 phr of magnesium dihydroxide nanoplatelets into 80/20 HDPE/PBT blends was successfully achieved by adjusting the processing temperatures, without any surface modification of the MDH nanoparticles. Three morphologies were achieved where nanoplatelets of MDH are dispersed only in the PBT dispersed phase (M1), only in the HDPE matrix (M2) or in both polymers (M3). An original extraction method (coupled with TGA results) allowed confirming the microstructures obtained by SEM and determining the amount of nanoplatelets in each phase. At microscale, the flame retardancy is somewhat dependent on the morphology. The first degradation peak assigned to early PBT degradation by water released from MDH is slightly shifted to higher temperature for M2. Moreover, a significant decrease of peak of heat release rate in cone calorimeter is observed for M2 associated to a more efficient barrier effect. This is due to the structure of the mineral residue which is thicker and more cohesive for this morphology than for M1 and M3, leading to a more insulating layer. This work emphasizes the strategy consisting in optimizing the morphology to improve the flame retardancy at low or moderate flame retardant amounts. [ABSTRACT FROM AUTHOR]

• A new flame-retardant curing agent was prepared via aza-michael addition. • The prepared flame-retardant compound was successfully integrated into an epoxy resin matrix. • The thermal stability, fire reaction and mechanical properties of the epoxy resin were improved. • Peak of Heat Release Rate is closely related to the delay to intumescence • The fire performances depend not only on phosphorus content but also on crosslinking. A novel reactive flame-retardant (FR), phosphorus-modified tetraethylenepentamine (TEPA-m-MVP), was prepared via aza-Michael addition process, using dimethyl vinylphosphonate (MVP). TEPA-m-MVP was successfully covalently introduced into the structure of the epoxy system, into the epoxy resin matrix synthesised from tetraethylenepentamine (TEPA) and diglycidyl ether bisphenol A (DGEBA) reaction, leading to the development of a flame-retardant epoxy resin (FR-EP). The curing behaviour, mechanical properties, thermal stability and flame-retardant behaviour of FR-EP samples were investigated and compared to the behaviour of the neat epoxy resin (EP). FR-EPs showed an increase in glass transition temperature (T g), from 120 to 147 °C upon integrating TEPA-m-MVP into the epoxy resin structure, while the value of the E modulus remained unaffected. Furthermore, FR-EP-2%P sample with the optimal P content, approximately 2 wt%, displayed excellent flame-retardant properties. In comparison to EP, total heat release (THR) and peak heat release rate (pHRR) for FR-EP-2%P decreased from 22.6 to 15.3 kJ.g−1 and from 1557 to 572 kW.m−2, respectively. In addition, an interesting impact of the crosslinking density of FR-EP samples on the fire behaviour was observed. This work presents a new strategy for the simultaneous modification of the flame retardancy and mechanical properties of epoxy systems. [Display omitted] [ABSTRACT FROM AUTHOR]

• Original DOPO-containing cyclocarbonate monomers. • First synthesis of PolyHydroxyUrethane foams containing phosphorus-based flame retardants. • Development of PHU foams with various flexibilities. • High reduction in total heat release of DOPO-PHU foam compared to the DOPO-free foam. Polyurethane (PU) foams are widely used for many applications, however the use of toxic isocyanate monomers for their synthesis has recently led researchers to non-isocyanate PU foams. The most promising alternative is the aminolysis of cyclic carbonate which yields polyhydroxyurethanes (PHU). Nevertheless, the obtained foams suffer from significant flammability and require the introduction of flame retardants to improve their flame retardant properties. Hence, this article demonstrates the first synthesis of PHUs foams containing phosphorus-based flame retardants. The flame retardant were allowed to react with the monomers to prevent any leaching from the foams. Moreover, several structures of cyclic carbonates were analyzed in order to determine the influence of aromatic rings on both thermal stability and mechanical properties of foams by thermogravimetric analyses, differential scanning calorimetry and dynamic mechanical analyses. The flame retardant properties were studied with a cone calorimeter and pyrolysis combustion flow calorimeter. The best results were obtained by the foam containing 2 wt% of phosphorus and two aromatic rings in the cyclic carbonate structure. Cone calorimeter analysis showed a total heat release of 13.1 KJ.g−1 versus 19.1 KJ.g−1 for the DOPO-free foam. [Display omitted] [ABSTRACT FROM AUTHOR]

• A new method to recycle silicone elastomer waste. • SIOC ceramic as original filler in silicone materials. • Enhanced isothermal properties. • Improved fire resistance by shielding effect. Two types of fillers were prepared by controlled pyrolysis of a commercial silicone elastomer. An aerobic process led to the formation of a silica powder while an anaerobic pyrolysis generated a silicon-carbon-oxide (SiOC) ceramic. Each filler was incorporated into a silicone gum and thus-prepared obtained formulations were further crosslinked with peroxide to prepare new silicone materials. Silica powder allowed controlling the mechanical properties of the materials whereas enhanced thermal stability was brought by the ceramic; mixing both fillers generated materials with joint properties (tensile strength of about 2 MPa, elongation at break of 300%, onset of degradation at 470 °C). The flame resistance behavior of these silicone materials was tested by cone calorimetry. Early formation of an insulating layer on the heat-exposed surface moderated the heat release (total heat release of 16.4 kJ/g PDMS) and increased final residue (above 50%) compared to commercial silica-filled elastomers. This work opens new possibilities to transform silicone waste into useful inorganic fillers and produce new performant thermal-resistant silicone materials. [ABSTRACT FROM AUTHOR]

Flame retardancy of EVA copolymers using three new synthesized and two commercial hydrated mineral aluminum-based fillers having different aspect ratio was studied. It was shown that the peak of heat release rate (pHRR) in cone calorimeter test significantly decreased in presence of lamellar-shaped pseudoboehmites compared to that observed in presence of aluminum trihydroxyde and boehmite. On the opposite, thermogravimetric analysis (TGA) and Pyrolysis Combustion Flow Calorimeter analysis (PCFC) did not show any significant modification between the five formulations indicating that the pHRR decrease is related to barrier effect and not to endothermic effect or to improvement of thermal stability. No relationship was found between the pHRR decrease and the melt viscosity. ESEM and EDX analyses have confirmed that the efficiency of the barrier effect in presence of the two lamellar pseudoboehmites is assigned to migration phenomena of particles which led to the quick formation of a homogeneous and cohesive insulating layer. [ABSTRACT FROM AUTHOR]

Abstract: The flame retardant effect of ultrafine kaolinite in Ethylene Vinyl Acetate copolymer (EVA) was studied and compared to that conferred by aluminum trihydrate (ATH). The thermal degradation and flammability of EVA composites were evaluated up to 60 wt% filler loading. Thermogravimetric (TG) and cone calorimeter analyses showed a higher decomposition temperature range and an improved FR performance for EVA/kaolinite composites in comparison to EVA/ATH composites. For a loading of 35 wt%, the peak of heat release rate (pHRR) of EVA/kaolinite was reduced by 55% compared to EVA/ATH. Moreover, we observed that kaolinite leads to a significant intumescent behavior during cone calorimeter tests. Finally, the rheology in the molten state of the different samples was studied and viscosity seems to play an important role on the fire retardancy of EVA/kaolinite composites. [Copyright &y& Elsevier]

Abstract: The flame retardancy of silicone composites containing calcium- and aluminum-based fillers has been investigated using several methods including cone calorimeter, Pyrolysis Combustion Flow Calorimeter (PCFC), thermogravimetric analysis and pyrolysis-gas chromatography-mass spectrometry analysis (Py-GC/MS). The fire reaction of precipitated calcium carbonate, calcite, calcium hydroxide, aluminum trihydrate, boehmite and alumina-based composites was correlated mainly with their thermal stability, while for mica and wollastonite-based composites, a barrier effect was also evidenced. The endothermic effect was not established as an efficient flame retardancy mechanism for the silicone composites containing hydrated fillers. Mica composite exhibited the best flame retardancy, in terms of depressed HRR, among all investigated formulations. Finally, a unique behavior was observed during the cone calorimeter test of calcium hydroxide-based composite, which co-crystallization with silica occurs exclusively at high heat flux. [Copyright &y& Elsevier]

• Synthesis of a new phosphorus containing polyhydroxyurethane oligomer. • Alkyd resin with good thixotropic properties and alkali resistance. • Excellent flame retardant efficiency with only 1.5% w of phosphorus. A novel phosphorus containing polyhydroxyurethane (PHU) oligomer (DGGDAC-MXDA-DOPO), has been synthetized and grafted onto the remaining acid groups of alkyd resins in order to obtain hybrid poly(alkyd hydroxyurethane) (PAHU) resins with flame retardant properties. PAHU resins have demonstrated better alkali resistance than pure alkyd resins without PHU oligomer. Moreover, the grafting of PHU onto alkyd resin through the formation of amide bonds has exhibited thixotropic properties. The thermal and flame retardancy properties have been investigated through differential scanning calorimeter, thermogravimetric analysis and pyrolysis-combustion flow calorimeter. The alkyd resins were applied as a coating on a wood surface and fire behavior was tested by cone calorimeter analysis. The most effective coating, by taking into account, the film properties and the flame retardant behavior contains 24 wt% of PHU (1.5 wt% P) and exhibited a 40% reduction in peak of Heat Release Rate (pHRR) compared to the resins without PHU. [Display omitted] [ABSTRACT FROM AUTHOR]

This work seeks to address the effect of simultaneous use of three flame retardants, having three different modes of action, (magnesium hydroxide, expanded and expandable graphite) on the thermal degradation and flame retardancy of poly(ethylene-co-vinyl acetate). Thermal conductivity of samples was measured in order to investigate the effect of the use of expanded and expandable graphite on the time-to-ignition and the peak of heat release rate in cone calorimeter test. Thermal shielding performances of chars were studied as well. It was found that there is an optimum ratio between expanded and expandable graphite in order to control thermal conductivity and therefore fire properties. Some correlations were also found between the char thickness and the first peak of heat release rate. [ABSTRACT FROM AUTHOR]

The effect of silica treatment by three phosphorous compounds (phosphoric acid, dihydrogen ammonium phosphate and diammonium phosphate) on the thermal and fire behaviour of polybutylene terephthalate (PBT) composites was investigated using Thermogravimetric analysis (TGA), Pyrolysis Combustion Flow Calorimeter (PCFC) and cone calorimeter. It was found that with only 10 wt% of treated silica incorporated into PBT, which corresponds to only 0.2 wt% of phosphorus in composites, the fire behaviour of materials was dramatically improved with a 60% decrease of peak of Heat Release Rate (pHRR). The incorporation of modified silica also leads to a fire growth rate index of 4.3 kW/(m 2 .s) (i.e. a 40% decrease). Those phenomena were related to the expansion of composites during their combustion and to their rheological behaviour. Indeed, the higher the viscosity at low frequencies is, the better the fire behaviour is, due to the induced barrier effect. A decrease of time to ignition (TTI) was also observed with the addition of the various silicas (up to 18s with 10 wt% of neat silica), which was explained by the appearance of bubbles after the PBT melting during cone calorimeter tests leading to a fast increase of the surface temperature. [ABSTRACT FROM AUTHOR]

This study presents a two-steps synthesis of novel additive or reactive phosphorus-and-sulfur-containing flame retardants (P-FR) for epoxy thermosets. The first step consists in totally epoxydizing the phloroglucinol. Then, the epoxy functions grafted are partially or totally open by a thiol bearing a phosphonate group to obtain a reactive P-FR and an additive P-FR respectively. The two synthesized P-FR are then incorporated into a DGEBA-IPDA matrix according to an appropriate approach. The impact of these P-FR on glass transition temperature (Tg) is assessed by DSC. Tg values exhibit the plasticizing effect of the additive P-FR and the loss of epoxy functionality due to the incorporation of the reactive P-FR. The thermal properties of the prepared thermosets are characterized by TGA, showing the more efficient action of the reactive P-FR in condensed phase (charring). TGA-FTIR coupling show the presence of phosphorus-containing gases released during the thermal degradation but these P-containing gases have no radical scavenging action in the gas phase. PCFC analyses prove the similar flame retardant properties of the two P-FR by reducing significantly the pHRR, the THR and the EHC. The cone calorimeter tests exhibit a strong intumescent effect of the residue brought by the two P-FR, leading to insulating expanded residue. [ABSTRACT FROM AUTHOR]

Surface modification of various silicas by phosphorous agents was carried out with the aim to use these particles as flame retardant additive in a polypropylene matrice (PP) at low content (10 wt%). Thermal and flammability properties of PP/modified silica (PP-Tm-10%, PP-Zm-10%) were studied using TGA, PCFC and cone calorimeter and compared to those conferred by pure silica (PP-T-10%, PP-Z-10%). Quite surprisingly the untreated fillers induce the most significant reduction of peak of Heat Release Rate (50% decrease) while the surface modification by phosphorous agents does not lead to the expected effect on the fire behavior of PP composite. This phenomenon was related to the morphology and rheological behavior of the various PP composites. Indeed, the higher the storage modulus at low frequencies is, the better the fire behavior is, because of the induced barrier effect. Moreover, the addition of non modified silicas leads to a decrease of 10 s of the TTI. This phenomenon was related to the formation of bubbles after the PP melting during cone calorimeter test. [ABSTRACT FROM AUTHOR]

In this study, expanded graphite (EG) was investigated as flame retardant for epoxy resin based on DGEBA. Various amounts of EG (up to 50 wt%) were incorporated into the epoxy and the composites were studied using X-ray diffractometer, scanning electronic microscopy, cone calorimeter, pyrolysis-combustion flow calorimeter, thermogravimetric analysis, instrumented epiradiator and laser-flash method. Quite unexpectedly, EG leads to a significant increase in pHRR in cone calorimeter tests. Nevertheless, EG also allows delaying strongly the time-to-ignition. Such behavior was assigned mainly to the increase in thermal diffusivity which allows transferring heat faster from the surface to the bulk. [ABSTRACT FROM AUTHOR]

Abstract: The thermal and fire-resistance properties of the ternary system ammonium polyphosphate/melamine polyphosphate/titanium dioxide (APP/MPP/TiO2) was studied in poly(methyl methacrylate) (PMMA). PMMA-7.5%APP/7.5%TiO2 showed an interesting thermal stability and synergy effects on the peak of heat released rate (pHRR). Mechanisms were investigated following the analysis of residues and gas phase. Residues were analyzed by Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscope (SEM). Gases emitted during degradation were analyzed by Pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS). Comparison between cone calorimetry and pyrolysis–combustion flow calorimetry (PCFC) tests was a helpful tool for determining whether fire-retardancy mainly occurred by a physical or chemical pathway and for explaining the obtained results. [Copyright &y& Elsevier]

• A method is proposed to calculate the action θ in condensed phase of flame retardants. • PE/EVA and ABS formulations were prepared containing mineral, phosphorus and brominated FRs. • Θ was calculated for LOI and cone calorimeter tests. • Antagonistic, synergistic or additive effects between FRs can be highlighted. The assessment of the modes of action of flame retardants (FRs) and their quantification is a challenging issue. This study highlights that the condensed phase efficiency θ can be assessed by combining different flammability tests (pyrolysis-combustion flow calorimeter PCFC, Limiting Oxygen Index LOI, cone calorimeter). Relations were proposed to calculate LOI and pHRR in cone calorimeter from several parameters including θ. A satisfying agreement between experimental values and calculated ones were found for a set of several dozens of FR-free polymers assuming that θ = 1 (i.e. no action in condensed phase).Then, θ was evaluated for EVA/PE blends containing Aluminium TriHydroxyde (ATH) and/or Magnesium DiHydroxyde (MDH) and for ABS containing Ammonium PolyPhosphate (APP) and/or DecaBromoDiPhenylOxide (DBDPO) assuming that LOI and pHRR of flame-retardant compositions follow the same relationships as those of unfilled polymers. The evolution of θ (as well as χ, i.e. the combustion efficiency) highlights the modes of action of FRs and can contribute to the discussion about possible synergy or antagonism between FRs. Especially, an apparent synergism between APP/DBDPO is observed in cone calorimeter from a performance point of view. Nevertheless, the calculation of χ and θ challenges this conclusion. [ABSTRACT FROM AUTHOR]