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International audience; Owing to the strong public concerns about environmental protection and potential energy crisis (fossil fuels), there is a global trend of substitution of petrochemical-based polymers towards biopolymers. Polybutylene succinate (PBS), as an emerging biobased and biodegradable polymer, has drawn a great deal of interest in a number of fields. However, high flammability of PBS constitutes a major obstacle for its potential application. In this study, based on the available literature, the approaches used for the flame retardancy of PBS are systematically reviewed. Those approaches include inorganic (nano)particles, lignin, and intumescent flame retardant systems. This comprehensive review aims to outline the recent research advances in the field of flame retardancy of PBS, focusing on the preparation, properties, and mechanisms. Finally, a brief summary and perspective in flame retarding PBS is also given, which may be able to inspire the development of future research and application. more...

Silica-epoxy nanocomposites were prepared via an “in-situ” sol-gel synthesis process and a phosphorus (P) flame-retardant i.e. 6H-dibenz[c,e][1,2]oxaphosphorin,6-[(1-oxido-2,6,7-trioxa-1-phosphabicyclo[2.2.2]oct-4-yl)methoxy]-, 6-oxide (DP) and melamine (Mel) were further added to the matrix to improve its fire performance. The main components of epoxy resin were bisphenol A diglycidyl ether (DGEBA) and isophorone diamine (IPDA) hardener. The addition of DP as well as silica alone into the epoxy system stopped the melt dripping phenomena in the vertical fire test (UL 94), however, the addition of melamine was crucial for achieving the highest fire classification (UL 94-V0 rating). The presence of DP and Mel in the silica-epoxy nanocomposite promoted a large reduction (ranging from 53% up to 80%) in the heat release rate (HRR) and a delay (up to 31%) in the ignition time in the cone calorimetry experiments. Improved fire performance of the epoxy system was attributed to i) a condensed phase activity of silica, DP and melamine to form a protective thermal barrier during combustion and ii) a minor gas phase flame inhibition activity of DOPO component of DP. The mechanical characterization of the epoxy nanocomposites through tensile tests showed that the addition of DP increases the stiffness of the epoxy resin, resulting in a strong increase of Young modulus (up to 32%) and in a slight decrease of fracture strength, elongation at break and toughness. An increased glass transition temperature (up to 8%) of the epoxy system possibly due to hydrogen bonds and polar interactions of DP with the matrix was also observed. more...

International audience; The paper deals with intumescent polypropylene (PP) undergoing extreme fire (burn-through test with heat flux higher than 100 kW/m2). The purpose of this unusual approach is to explore the possibility to design intumescent plastic (here PP) resisting to burn-through test. A combination of commercial intumescent flame retardants (ammonium polyphosphate-based compounds containing a char former; AP766 (AP) and FlameOff (FO) of the companies Clariant and FlameOff Inc) with zinc borate (supplied by US Borax, ZB) or Kemgard (combination of ZB and molybdate supplied by Huber, KZ) was incorporated in PP. Use of ZB and KZ as synergists in FO formulations increases dramatically the time of piercing (formation of hole through the plaque of polymer at 80 s without ZB or KZ vs. 280 s with KZ) at the burn-through test (heat flux ¼ 116 kW/m2, propane burner) while the combination with AP does not show any benefit. Analyses of the residues obtained at different times of combustion by solid state nuclear magnetic resonance (NMR) of 31P, 11B and 13C shows the formation of borophosphates creating a glass reinforcing the intumescent char: it acts as a ‘glue’ providing flexibility and cohesion to the char. more...

The performance of commercial intumescent coatings is assessed by industrial norms and standards with clearly defined experimental conditions. In contrast, academic research on intumescent coatings is much more diverse and there are no clear guidelines on how such coatings should be characterised. Some researchers transfer the conditions defined in the industrial standards to laboratory-scale setups while others rely on cone calorimeters or Bunsen burners. This might not be an issue when comparing different coating formulations within one study. However, it significantly complicates the comparison of coatings characterised with different experimental approaches and usually provides little insight into the coating performance under industrial fire test conditions. This review article gives an overview over different experimental approaches reported in the academic literature for the performance evaluation of intumescent coatings. The heating conditions in these different groups of setups, ranging from furnaces and ovens over radiative heaters to impinging flames, are elaborated in a tutorial style fashion. Besides the sample heating, in-situ characterisation techniques, such as measurements of char expansion, temperature, and mechanical strength will be discussed. The aim is to aid researchers in evaluating literature reports as well as stimulate the development of new and the optimisation of existing experimental approaches. more...

Model polymer poly(vinyl acetate) (PVAc) was combined with melamine isocyanurate (MIC) as intumescent flame retardant composite. This work emphasises on the study of the decomposition mechanism and compared with a single fire test in order to show its performance as flame retarded composite. As such, mass loss cone calorimetry tests were performed and compared with it inert and oxidative decompositions in lab tests. PVAc/MIC composites cannot be ignited with high loadings MIC. Difference curves in oxidative conditions revealed that the composites with MIC show only positive differences, indicating a high stabilisation, especially in the temperature region of a mild flame (500–700 °C). Experiments performed with TG coupled with mass spectroscopy and analyses on partially degraded residues with solid-state 13C-NMR enabled the construction of the complete decomposition mechanism. MIC has both a heat-sink FR activity as well as a crosslinking role in the stabilization of the polymer. The latter then creates a highly stabilised char at elevated temperatures in oxidative environments. The formed char starts to degrade only 100 °C higher than the pure polymer within a heating. The degradation of formed char of pure PVAc is autocatalytic; this behaviour disappears upon addition of sufficient amount of MIC. Therefore, the transport of fuel towards the gaseous phase is limited, creating an efficient flame retardant system. more...

The objective of this study is to assess the efficiency of biobased carbonization agent in intumescent formulations (IFRs) to examine the flame retardant properties of polylactic acid (PLA) composites and to investigate their melt-spinnability. We used phosphorous-based halogen free flame retardant (FR) and kraft lignin (KL) as bio-based carbonization agent. After melt compounding and molding into sheets by hot pressing various fire related characteristics of IFR composites were inspected and were characterized by different characterization methods. It was fascinating to discover that the introduction of 5&minus, 20 wt% FR increased the limiting oxygen index (LOI) of PLA composites from 20.1% to 23.2&minus, 33.5%. The addition of KL with content of 3&minus, 5 wt% further increased the LOI up to 36.6&minus, 37.8% and also endowed PLA/FR/KL composites with improved anti-dripping properties. Cone calorimetry revealed a 50% reduction in the peak heat release rate of the IFR composites in comparison to 100% PLA and confirmed the development of an intumescent char structure containing residue up to 40%. For comparative study, IFR composites containing pentaerythritol (PER) as a carbonization agent were also prepared and their FR properties were compared. IFR composites were melt spun and mechanical properties of multifilament yarns were tested. The analysis of char residues by energy dispersive X-ray spectrometry (EDS) and SEM images confirmed that PLA/FR/KL composites developed a thicker and more homogeneous char layer with better flame retardant properties confirming that the fire properties of PLA can be enhanced by using KL as a carbonization agent. more...

International audience; The concept of intumescence was applied to make flame retarded polypropylene (PP). This paper examines two types of intumescence in PP based on expandable graphite (EG, physical expansion) and on modified ammonium polyphosphate (AP760, chemical expansion). Reaction to fire of PP containing EG and AP760 was first evaluated by cone calorimetry. The incorporation of intumescent additives at relatively low loading (10 wt%) in PP permits the reduction by 70% of peak of heat release rate (pHRR). The mode of action occurs via the formation of an expanded carbonaceous layer in all cases. The protective coating acts mainly as heat barrier in the case of the formulations containing AP760 or as heat dissipater with EG. The incorporation of small amount of EG in PP-AP760 modifies heat transfer in the coating creating a strong anisotropy. Upon expansion, graphite worms align normal to the surface increasing the transverse heat conductivity (lower efficiency of the heat barrier) and hence, decreasing the fire performance (decrease by only 30% of pHRR). Kinetic analysis was then performed to quantify the thermal stability of the intumescent systems. It reveals that the intumescent additives do not modify the reactional scheme of the PP thermal decomposition but they increase slightly the thermal stability of the intumescent systems. For all materials, the decomposition model follows a reactional scheme at two successive reactions. This model was determined in dynamic conditions (conditions of thermogravimetry with linear heating rates) but it is able to simulate the decomposition of the materials in isothermal conditions (excellent agreement between the simulated and experimental curves). more...

A quantitative understanding of an intumescent material’s reaction to fire remains largely an unsolved challenge. More specifically, the relationship between thermal transport and the resulting char structure is not well understood. Improved pyrolysis models for intumescent materials are necessary to advance the fields of fire modeling and material development. To aid in this endeavor, a systematic methodology to parameterize comprehensive pyrolysis models for charring and intumescent materials is presented. Rigid poly(vinyl chloride), flexible poly(vinyl chloride), Bisphenol A poly(carbonate), poly(ether ether ketone), and poly(vinylidene fluoride) were analyzed in this work. First, thermogravimetric analysis and differential scanning calorimetry were employed simultaneously to characterize the kinetics and thermodynamics of thermal decomposition. Microscale combustion calorimetry was utilized to parameterize the heats of complete combustion of gaseous pyrolyzates. ThermaKin, a numerical pyrolysis solver, was employed to inversely analyze all milligram-scale tests. A multi-step reaction mechanism, consisting of sequential steps, was constructed to capture all observed physical changes and chemical reactions. Gasification tests were conducted on 0.07 m diameter disk-shaped samples using the newly developed Controlled Atmosphere Pyrolysis Apparatus II to parameterize the thermal transport within the undecomposed material and developing char layer. A recently expanded version of ThermaKin, ThermaKin2Ds, was employed to inversely model the gasification experimental results. The model accounted for spatially non-uniform swelling of the sample and the ensuing changes within the thermal boundary conditions. The resulting two-dimensional models were shown to reproduce the experimental sample shape profiles, unexposed surface temperatures, and mass loss rates with excellent accuracy. An analysis of the char pore structure was also conducted to determine the pore size distribution and char porosity. Further analysis enabled the mean, median, and volume-weighted mean pore diameters to be computed from pore size distributions. Quantitative relationships were subsequently developed between relevant thermal transport quantities and the char’s physical structure. It was determined that the thermal insulating potential of the fully developed char was related to the number of pore walls positioned perpendicular to the direction of heat flow. Therefore, designing charring polymers capable of producing many small pores will aid in the development of intumescent materials with an enhanced thermal insulating potential. more...

International audience; The concept of intumescence was applied to make flame retarded polypropylene (PP). This paper examines two types of intumescence in PP) based on expandable graphite (EG, physical expansion) and on modified ammonium polyphosphate (AP760, chemical expansion). Reaction to fire of PP containing EG and AP760 was first evaluated by cone calorimetry. The incorporation of intumescent additives at relatively low loading (10 wt%) in PP permits the reduction by 70% of pHRR. The mode of action occurs via the formation of an expandedcarbonaceous layer in all cases. The protective coating acts mainly as heat barrier in the case of the formulations containing AP760 or as heat dissipater with EG. The incorporation of small amount of EG in PP-AP760 modifies heat transfer in the coating creating a strong anisotropy. Upon expansion graphite worms align normal to the surface increasing the transverse heat conductivity (lower efficiency of the heat barrier) and hence, decreasing the fire performance (decrease by only 30% of pHRR). Kinetic analysis was then performed to quantify thethermal stability of the intumescent systems. It reveals that the intumescent additives do not modify the reactional scheme of the PP thermal decomposition but they increase slightly the thermal stability of the intumescent systems. more...

The objective of current research on intumescent formulations is on consolidated approaches for conferring flame retardancy properties to polymers and polymer blends. Numerous academic and industrial efforts have been carried out in the last fifteen years, by revisiting the traditional concept of intumescence on the basis of the new chemical synthesis or novel nano-technological developments. The main concepts of intumescence are reviewed in this report, highlighting the novelties as well as the most significant results achieved in the flame retardancy of polymeric materials in the last 10–15 years. Although the basic aspects of intumescence such as the chemical components, thermal and rheological aspects are well-known, the modeling and simulation of these systems are completely new and never reviewed. Analogously, the traditional chemical compositions will be compared with the novel systems, most of them based on the nanotechnology and synergistic aspects. Thus, the results collected up-to-now by using these new intumescent formulations will be dealt with the different polymer families. The use of current intumescent coatings for metals, steel, wood and plastics as well as the application of novel intumescent coatings deposited on fabrics, films and foams through layer-by-layer assembly are reviewed. Although the latter technique is not new, its use to confer flame retardancy properties to polymers is a recent development. more...

International audience; 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. more...

The effect of six halogen-free flame retardant (FR) formulations was investigated on the thermal stability of two low-density polyethylenes (LDPE) and one linear low-density polyethylene (LLDPE), by means of thermogravimetric analysis (TGA) under nitrogen and air atmosphere. The relative data were combined with flammability properties and the overall performance of the FRs was correlated with the type of branching in the polyethylene grades and to their processing behavior. The thermal degradation kinetics was further determined based on the Kissinger and Coats-Redfern methods. In terms of flammability, the addition of a triazine derivative and ammonium polyphosphate at a loading of 35 wt. %. was found to be the most efficient, leading to UL 94 V0 ranking in the case of the LDPE grade produced in an autoclave reactor. - 2019 by the authors. Funding: This publication was made possible by the NPRP award [NPRP 9-161-1-030] from the Qatar National Research Fund (a member of The Qatar Foundation). The statements made herein are solely the responsibility of the author(s). Scopus more...

International audience; Many circumstances can lead to an electrical fire. It is then helpful to reproduce those circumstances in laboratory conditions to duplicate fire scenarios in order to increase knowledge and to develop safer and flame-retarded materials and electrical systems. Our approach was to develop specific bench scale tests. The mass loss cone calorimeter coupled with Fourier transform infrared was used to mimic a fire scenario on simulated low voltage cable (flame-retarded polymer molded around copper wire) and to characterize the gas phase. The electric current creates an additional heating condition (Joule effect) which can modify the decomposition of the flammable material (e.g. the cable jacket made in thermoplastic), and so its fire behavior in case of fire. It is the reason why we performed the experiments mimicking different fire scenarios with and without electric current. Specific test was also developed to investigate the flame spread and the delamination of the polymer around the wire. The bench scale tests presented in this article were applied on intumescent polymers (ethylene-vinyl acetate containing commercial intumescent additive). The results were discussed with a special emphasis on the influence of electric current on the fire behavior. more...

The flame retardant synergism between highly stretched polymer fibres and intumescent flame retardant systems was investigated in self-reinforced polypropylene composites. It was found that the structure of reinforcement, such as degree of molecular orientation, fibre alignment and weave type, has a particular effect on the fire performance of the intumescent system. As little as 7.2 wt % additive content, one third of the amount needed in non-reinforced polypropylene matrix, was sufficient to reach a UL-94 V-0 rating. The best result was found in self-reinforced polypropylene composites reinforced with unidirectional fibres. In addition to the fire retardant performance, the mechanical properties were also evaluated. The maximum was found at optimal consolidation temperature, while the flame retardant additive in the matrix did not influence the mechanical performance up to the investigated 13 wt % concentration. more...

The problem of thermal protection is explored for two idiosyncratic reactive systems, namely a sacrificial heat-sink material and an intumescent system where a dynamically evolving insulation layer is produced from an initially thin coating. Relatively simple mathematical models of both systems are proposed that encompass the important physical characteristics of each situation and these models are analysed using a mixture of numerical and analytical techniques. Important dimensionless parameter groups are identified and domains of parameter space where thermal performance is particularly good- or particularly bad- are identified. more...

International audience; The mechanical properties and fire resistance of a recycled poly(ethylene terephthalate) were improved by using a specific treatment of the waste material and the incorporation of encapsulated red phosphorus in combination with co-additives. The use of red phosphorus has to be limited due to a negative influence on impact resistance and rate of heat release. Among several metal oxides, Al2O3 acts as a good co-synergist at a total loading of 5 wt.% due to its reactivity, high specific surface area and aluminium phosphate formation. The complementary use of glass fibres can also generate intumescence by improving the mechanical stability of the char layer. more...

Thermally reduced graphite oxide (TRGO), containing only four single carbon layers on average, was combined with ammonium polyphosphate (APP) and magnesium hydroxide (MH), respectively, in polypropylene (PP). The nanoparticle’s influence on different flame-retarding systems and possible synergisms in pyrolysis, reaction to small flame, fire behavior and mechanical properties were determined. TRGO has a positive effect on the yield stress, which is decreased by both flame-retardants and acts as a synergist with regard to Young’s modulus. The applicability and effects of TRGO as an adjuvant in combination with conventional flame-retardants depends strongly on the particular flame-retardancy mechanism. In the intumescent system, even small concentrations of TRGO change the viscosity of the pyrolysing melt crucially. In case of oxygen index (OI) and UL 94 test, the addition of increasing amounts of TRGO to PP/APP had a negative impact on the oxygen index and the UL 94 classification. Nevertheless, systems with only low amounts (≤1 wt%) of TRGO achieved V-0 classification in the UL 94 test and high oxygen indices (&gt, 31 vol%). TRGO strengthens the residue structure of MH and therefore functions as a strong synergist in terms of OI and UL 94 classification (from HB to V-0). more...

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. more...

International audience; This study investigates the effects of the incorporation of nanoparticles on the reaction to fire of an epoxy resin containing a conventional intumescent flame retardant. Two types of nanoparticles are considered: OctaMethylOligomericSilsesquioxanes (OMPOSS) and Carbon NanoTubes (CNTs). The combination of an intumescent phosphorus-based flame-retardant (APP) and CNTs provides no enhancement of the reaction to fire of this system. In contrast, using OMPOSS in combination with APP provides a large synergistic effect via an intumescence phenomenon. The study of the thermal degradation of these systems shows that the interactions between these fillers modify the viscosity of the degraded matrix. The trapping of degradation gases is enhanced in the case of APP/OMPOSS, which results in the creation of anintumescent protective layer earlier than with the reference system containing APP alone. Furthermore,the presence of OMPOSS permits the creation of silicophosphates which reinforce the residue. In contrast, the residue of the formulation containing carbon nanotubes is excessively stiff and it cracks during combustion, hindering the proper formation of the protective layer. more...

Different kinds of additive and reactive flame retardants containing phosphorus are increasingly successful as halogen-free alternatives for various polymeric materials and applications. Phosphorus can act in the condensed phase by enhancing charring, yielding intumescence, or through inorganic glass formation; and in the gas phase through flame inhibition. Occurrence and efficiency depend, not only on the flame retardant itself, but also on its interaction with pyrolysing polymeric material and additives. Flame retardancy is sensitive to modification of the flame retardant, the use of synergists/adjuvants, and changes to the polymeric material. A detailed understanding facilitates the launch of tailored and targeted development. more...

International audience; The present work focuses on the fire retarding behaviour of (ethylene–vinyl acetate (EVA) copolymer/magnesium hydroxide (MH)/talc) composites. Talc particles of different lamellarity and specific surface area have been tested, leading to the conclusion that for highly lamellar talc particles, the fire retarding behaviour becomes similar to that of (EVA/MH/organomodified montmorillonite (oMMT)) composites, with a significant intumescence.This intumescence, which occurs during the pre-ignition period in cone calorimeter tests, seems to be related to three phenomena caused by the presence of the lamellar particles (oMMT or talc): heterogeneous bubble nucleation, increased viscosity and charring promotion. more...

International audience; This study deals with the effect resulting from the association of pentaerythritol with flax fibres in an intumescent PP/Fibre/ ammonium polyphosphate/pentaerythritol/melamine system. This consists only in a preliminary to prove the efficiency of inturnescent additives systems in polyolefin/flax composites considering the fire behaviour and the thermal stability of the material. The study confirms the Fire Retardance performances of a PP/flax/ammonium polyphosphate composite considering cone calorimeter data. Moreover, it shows that charring of the flax fibers in this composite does not give an interesting material in term of dynamic property. Using an inturnescent model additive, we show that association of charring of the cellulosic material and of the intumescent system allows to obtain an optimized FR formulation. more...

This paper is a compendium on intumescent paint and its main features regarding chemical composition, thermophysical properties and performance as a fire-retardant material. Some of the main technical publications and lines of research on the subject are presented herein. The purpose of this paper is to show the current stage of the technical research being conducted on the topic and enable a better understanding of this fire-retardant material. Resumo O presente trabalho é um compêndio sobre tintas intumescentes, apresentando as principais características a respeito de sua composição química, propriedades termo físicas e desempenho como material de proteção contra incêndio. São apresentadas algumas das principais publicações técnicas e linhas de pesquisas sobre a intumescência. Objetiva-se, assim, elucidar o atual estágio técnico de pesquisas e possibilitar uma melhor compreensão sobre este material de proteção contra incêndio. more...