Liquid Flame Retardants Research Articles

Synthesis of P/Si liquid flame retardant via the covalent modification and in-situ dispersion strategies for improving comprehensive performance of epoxy resin

Maintaining the balance between thermal stability, smoke suppression and mechanical properties of flame retardant epoxy resin (EP) systems has been very challenging in industry and academia. Herein, we prepared a P/Si flame retardant fluid (KHDOPO) to modify expandable graphite (EG) through covalent modification strategy for flame retardant EP. The comprehensive performance of EP/KEG was further enhanced via the in-situ dispersion strategy. The covalent modification strategy provided a synergistic P/Si flame retardant effect for EG. The in-situ dispersion strategy further improved the dispersion properties of KEG in EP. Surprisingly, EP/KEG exhibits a UL-94 V-0 rating, limit oxygen index (LOI) value of 30.9 % and total smoke production (TSP) value of 15.5 m2 with an ultralow loading of 4 wt% KEG. Besides, EP/KEG maintains superior thermal stability and mechanical properties due to ultra-low addition and better dispersion of KEG.

A DOPO-eugenol linear siloxane as a highly effective liquid flame retardant also imparting improved mechanical properties to an epoxy amine network

A liquid bio-derived eugenol-containing phosphorus silicone hybrid molecule (EGDS-DOPO) that endows excellent flame-retardancy and enhanced mechanical performance to an epoxy amine network at low levels of addition was successfully synthesized and characterised. The EGDS-DOPO significantly improved the flame retardancy requiring only 5 wt% of EGDS-DOPO to achieve a limiting oxygen index (LOI) of 34.9 % and a UL 94 V-0 rating. Cone calorimetry measurements reveal a reduction of the peak heat release rate, the total heat release, and total smoke production by 62.2 %, 34.0 % and 47.5 %, respectively when EGDS-DOPO concentration was 20 wt%, compared to the unmodified epoxy network. Viscosity remained low throughout cure, and despite some retardation of reactivity, the epoxy amine resin remains fast curing and suitable for liquid moulding composite fabrication technologies. Moreover, the modified EGDS-DOPO epoxy networks display a glass transition temperature (Tg) between 218.5 °C and 174.1 °C, a hydrophobic surface with water contact angle of 97.5°–106.6°, a low moisture ingress of 2.35 %–2.91 %, and improved overall mechanical properties in flexure (maximum 39.8 % increase in flexural strength and 27.0 % in flexural modulus), compression (maximum 24.5 % and 35.0 % increase in compressive strength and modulus, respectively), and fracture toughness (maximum 28.0 %).

A DOPO modified cyclosiloxane reactive diluent as an effective flame retardant for a high-performance epoxy network

A novel phosphorus-siloxane containing liquid flame retardant epoxy resin was synthesized and incorporated into an epoxy amine network, maintaining low viscosity and rapid cure characteristics, good mechanical and thermal properties, and affording excellent flame retardancy at low concentration. The synthesized flame retardant incorporated a tetra-functional glycidyl ether cyclosiloxane substructure which was substituted with two DOPO segments to obtain a liquid bi-functional flame-retardant epoxy resin (BGTS-DOPO). At only 10 wt% BGTS-DOPO, the modified epoxy amine resin had a viscosity of less than 210 mPa s at 90 °C, gelled rapidly at 150 °C, (9.3 min at 150 °C), exhibited a Tg of 198.7 (extrapolated onset of E’) and 233.0 °C (tan δ max), and possessed improved flexural strength (4.5 %), modulus (4.1 %), strain (7.7 %) and fracture toughness (26.1 %). The self-extinguishing behaviour easily achieved a UL-94 V0 rating, exhibited a maximum limiting oxygen index of 36.7 %, while cone calorimetry produced a 24 % improvement in combustion behaviour of the carbon fibre composite. Presented here therefore is a new highly fire-retardant epoxy resin system that exhibited fast cure, low viscosity and excellent mechanical and thermal properties.

S-Triazine phosphonates as flame retardants for polyurethane and polyisocyanurate rigid foams

The liquid flame retardant tris(2‑chloro-isopropyl) phosphate (TCPP) is widely used in polyurethane and polyisocyanurate rigid foams. However, TCPP is currently under assessment by the European Chemicals Agency ECHA and National Toxicology Program NTP, USA. For this reason, there is a high demand for new flame retardants with similarly good processing and application properties. This paper examines the influence of low-molecular liquid s-triazine phosphonates on the foaming behaviour and flame retardancy of polyurethane and polyisocyanurate rigid foams for building applications. The flame retardant investigations consisted of thermogravimetric analysis of the components and flame retardancy tests performed on the foams: limiting oxygen index, EN 13501 class E, and cone calorimetry. The newly developed class of s-triazine phosphonates are promising flame-retardant candidates with good processing and application properties.

The effect of flame retardants on the fire technical characteristics of recycled textiles

The paper deals with the fire technical characteristics of insulation panels made of recycled technical textiles from the automotive industry. The introductory part focuse an of the use of recycled textiles, a description and division of technical textiles, a description of the examined material and its composition, combustion processes, and the method of handling waste textiles. The monitored characteristics were the determination of the ignitability of the material, the gross calorific value as well as the radiant heat resistance. The measurements were carried out on samples from recycled technical textiles before and after their treatment with flame retardants (Isonem Anti-fire Solution, Ecogard B45, HR Prof, woven carbon foil, non-woven carbon foil). The best results in the ignitability test after treatment with liquid flame retardants were obtained after treatment with Ecogard B45. The results show that when flame retardants are used, the released heat during the combustion of the monitored materials treated through the dipping method is significantly lower from 13.7 MJ/kg to 23.7 MJ/kg. The lowest gross calorific values were achieved when using liquid flame retardant HR Prof when applied by dipping. The proportion of material that did not burn was very low (4.61 to 5.63%). After exposure to radiant heat for 10 min, the highest mass loss was 13.6% (dipping in Ecogard B45) and the smallest 1.8% (non-woven carbon foil). Based on results, it shows that flame retardant ECOGARD® B45 for the insulation material Senizol AT XX2 TL60 made from recycled technical textiles is the most suitable fire protection.

Forest Fire Spread Simulation and Fire Extinguishing Visualization Research

There are three main types of forest fires: surface fires, tree crown fires, and underground fires. The frequency of surface fires and tree crown fires accounts for more than 90% of the overall frequency of forest fires. In order to construct an immersive three-dimensional visualization simulation of forest fires, various forest fire ignition methods, forest fire spread, and fire extinguishing simulation exercises are studied. This paper proposes a lightweight forest fire spread method based on cellular automata applied to the virtual 3D world. By building a plant model library using cells to express different plants, and by building a 3D geometric model of plants to truly capture the combustion process of a single plant, we can further simulate forest-scale fire propagation and analyze the factors that affect forest fire spread. In addition, based on the constructed immersive forest scene, this study explored various forms of fire extinguishing methods in the virtual environment, mainly liquid flame retardants such as water guns, helicopter-dropped flame retardants, or simulated rainfall. Therefore, the forest fire occurrence, spread, and fire extinguishing process can be visualized after the interactive simulation is designed and implemented. Finally, this study greatly enhanced the immersion and realism of the 3D forest fire scene by simulating the changes in plant materials during the spread of a forest fire.

Multi-functional solvent-free SiO2 nanofluid simultaneously improve major properties and fluidity of epoxy resin: A new strategy beyond nanofillers

High flowability and good wettability are the key advantages of liquid thermoset resin applied in high performance fiber reinforced composites. However, the adverse effects of powder flame retardants on processing stability of epoxy resin limits its application in vacuum assisted resin transfer molding (VARTM) process. A novel solvent-free SiO2 nanofluid (SiO2NPES-P) was synthesized by ion exchange method, and the simultaneously improved flowability and higher glass transition temperature (Tg) of EP/SiO2NPES-P composites was obtained. The results showed that the nanofluid played a role as an accelerator of EP polymerization, which not only leaded to the decrease of curing temperature, but also improved the monodispersion of SiO2 nanoparticles and the compatibility between EP and nanofiller. This successful design results in EP composites with better thermal stability, Tg and mechanical properties than pure EP, which was hardly obtained by adding traditional nanofiller or liquid flame retardants. Moreover, EP/SiO2NPES-P composites possessed better flame retardancy and smoke and heat suppression effects. With 5 wt% SiO2NPES-P addition, LOI was increased to 28.5% from 22.0%, the peak heat release rate and total smoke product were reduced by 33.8% and 52.4%. The transparency of the EP was well preserved, indicating the successful avoidance of nanoparticle agglomeration. This work provides a new idea for low carbon manufacturing of flame-retardant EP composites.

Investigation of the Flame Retardant Properties of High-Strength Microcellular Flame Retardant/Polyurethane Composite Elastomers.

Flame retardants (FRs) often reduce the mechanical properties of polymer materials, and FR/microcellular polyurethane elastomer (MPUE) composite materials have not been systemically studied. Hence, we conducted this study on FR/MPUE composites by using multiple liquid FRs and/or expandable graphite (EG). Compared with liquid flame retardants, the LOI of an expandable graphite/dimethyl methylphosphonate (EG/DMMP) (3:1) combination was significantly increased (~36.1%), and the vertical combustion grade reached V-0 without a dripping phenomenon. However, the corresponding tensile strength was decreased by 17.5%. With the incorporation of EG alone, although the corresponding LOI was not a match with that of DMMP/EG, there was no droplet phenomenon. In addition, even with 15 wt% of EG, there was no significant decline in the tensile strength. Cone calorimeter test results showed that PHRR, THR, PSPR, and TSR were significantly reduced, compared to the neat MPUE, when the EG content surpassed 10 wt%. The combustion process became more stable and thus the fire risk was highly reduced. It was found that flame retardancy and mechanical properties could be well balanced by adding EG alone. Our proposed strategy for synthesizing FR/MPUE composites with excellent flame retardancy and mechanical properties was easy, effective, low-cost and universal, which could have great practical significance in expanding the potential application fields of MPUEs.

Fabrication of dimethyl methylphosphonate-loaded mesoporous silica nano fire extinguisher and flame retarding unsaturated polyester

A novel nano fire extinguisher is constructed by loading the guest molecule (dimethyl methylphosphonate, DMMP) into the host material (mesoporous silica, m-SiO2) by a vacuum-assisted immersion method. SiO2-DMMP can avoid the excessive plasticization caused by the high addition of DMMP; under a relatively high addition amount (20 phr), the unsaturated polyester (UP) can normally be cured. 20 phr SiO2-DMMP imparts excellent flame retardancy to UP, i.e., 49.8% reduction in peak heat release rate and passing the UL-94 V-0 rating. Moreover, through the mesoporous confinement of m-SiO2, the thermal stability of DMMP is improved. In addition, easy migration of DMMP in UP is also solved; the UP can pass the UL-94 V-0 rating after soaking in water for 72 h. The flame retardant mechanism is the quenching mechanism. This strategy will be a universal method for loading liquid flame retardants to construct SiO2-based composite flame retardants.

Influence of Flame Retardant Impregnation on Acoustic and Thermophysical Properties of Recycled Technical Textiles with the Potential for Use in Wooden Buildings.

This article presents the results of an investigation of acoustic and thermophysical properties of insulation panels made from recycled technical textiles originating from the automotive industry. Measurements were performed on the samples of insulation panels (Senizol AT XX2 TL60), which were modified with liquid flame retardants (ISONEM® ANTI-FIRE SOLUTION, ECOGARD® B45, HR Prof). Another method of treatment was carried out by surface application of non-flammable facing (woven carbon fibre, nonwoven carbon fibre). Retardants were applied to the samples by surface spraying and soaking. The results showed a high ability of material to absorb sound in the frequency range 350 Hz–2 kHz. The sound absorption coefficient ranged from 0.82 to 0.9 in the frequency range 500 Hz–2 kHz. The noise reduction coefficient is 0.75. After material modification with the flame retardants, there was no significant change of sound absorption. The thermal conductivity coefficient of material before modification was 0.038 W⋅m−1⋅K−1. After application of the flame retardants, the thermal conductivity coefficient increased depending on type and method of retardant application in the range of 2.6–105.3%. The smallest change was detected after modification of material with ECOGARD® B45.

The Effect of Multilevel Carbon Reinforcements on the Fire Performance, Conductivity, and Mechanical Properties of Epoxy Composites.

We studied the effect of a multilevel presence of carbon-based reinforcements—a combination of conventional load-bearing unidirectional carbon fiber (CF) with multiwalled carbon nanotubes (CNT) and conductive CNT-containing nonwoven carbon nanofabric (CNF(CNT))—on the fire performance, thermal conductivity, and mechanical properties of reference and flame-retarded epoxy resin (EP) composites. The inclusion of carbon fibers and flame retardant reduced the peak heat release rate (pHRR) of the epoxy resins. The extent to which the nanoreinforcements reduced the pHRR depended on their influence on thermal conductivity. Specifically, high thermal conductivity is advantageous at the early stages of degradation, but after ignition it may lead to more intensive degradation and a higher pHRR; especially in the reference samples without flame retardant. The lowest pHRR (130 kW/m2) and self-extinguishing V-0 UL-94 rating was achieved in the flame-retarded composite containing all three levels of carbon reinforcement (EP + CNF(CNT) + CNT + CF FR). The plasticizing effect of the liquid flame retardant impaired both the tensile and flexural properties; however, it significantly enhanced the impact resistance of the epoxy resin and its composites.

Synthesis and properties of rigid polyurethane foams synthesized from modified urea-formaldehyde resin

In this study, ethylene glycol modified urea formaldehyde resin (EUF) was synthesized from urea, paraformaldehyde and ethylene glycol, and then incorporated into rigid polyurethane foams (RPUFs) as a reactive-type liquid flame retardant. The structure of EUF was characterized by Fourier transform infrared spectroscopy, and the thermal degradation properties and fire behaviors of RPUFs were characterized by limiting oxygen index (LOI), cone calorimetry test and thermogravimetry analysis. The results show that the incorporation of EUF results in an increase in the thermal stability and LOI of RPUFs. As the EUF loading increases, the peak heat release rate, total smoke release and CO/CO2 weight ratio of RPUFs decrease significantly. This is because EUF can release non-flammable gases during the initial degradation of polyurethane foams and promote the formation of the compact char layer, which can serve as an effective shield against heat, oxygen and combustible volatiles during the combustion. However, EUF shows negative effect on the cell morphology and mechanical properties of RPUFs. In conclusion, EUF has excellent performance in flame retardancy and smoke suppression for RPUFs.

Preparation and fire behavior of rigid polyurethane foams synthesized from modified urea-melamine-formaldehyde resins.

In this study, a series of ethylene glycol modified urea–melamine–formaldehyde resins (EUMFs) were synthesized from urea, melamine, paraformaldehyde and ethylene glycol, and then incorporated into rigid polyurethane foams (RPUFs) as a reactive-type liquid flame retardant. The structure of EUMFs was characterized by Fourier transform infrared spectrometry; the morphology of the foams was characterized by scanning electron microscopy; and the thermal degradation and fire behavior of RPUFs were characterized by limiting oxygen index (LOI), cone calorimetry test and thermogravimetry analysis. The results show that the incorporation of EUMFs results in an increase in thermal stability, smoke suppression and LOI of RPUFs. As the melamine loading in EUMFs increases, the peak heat release rate and the total heat release of RPUFs decrease significantly, but the LOI increases slightly. Compared with the original foam, the cells of RPUFs become less regular with nonuniform diameters. In general, EUMFs show excellent flame retardancy and smoke suppression for RPUFs.

Unique liquid multi-maleimide terminated branched polysiloxane and its flame retarding bismaleimide resin with outstanding thermal and mechanical properties

Developing halogen-free and phosphorus-free flame retardants with good processing characteristic for heat-resistant polymers is still a great challenge. A unique multi-maleimide terminated branched polysiloxane (PMI-HSi) was synthesized, which is liquid, reactive and does not volatilize, overcoming the disadvantages of available liquid flame retardants. PMI-HSi was added into bismaleimide/diallyl bisphenol A (BD) resins to prepare a series of modified resins (PMI-HSi/BD), which were found to have desirable flame retardancy and remarkably increased mechanical properties while maintaining outstanding thermal resistance. For the PMI-HSi/BD resin with 15 wt% PMI-HSi, its impact and flexural strengths are more than 1.8 and 1.3 times of those of BD resin, respectively, while the initial decomposition and glass transition temperatures are severally as high as 399 °C and 316 °C. Attractively, a small addition of PMI-HSi effectively increases limited oxygen index, greatly reduces the risk of catching fire and combustion intensity, and remarkably decreases the smoke production, demonstrating that PMI-HSi is a multi-functional flame retardant. The origin behind these attractive properties was revealed.

Flame retardancy of bitumen: A calorimetry study

The article investigates the flame retardancy of bitumen for roofing applications using the mass loss calorimeter. Screening of the solid flame retardants, including expandable graphite, boron-based compounds, and silsesquioxanes, shows that they can provide high fire performance. Nevertheless, the settling of these compounds during hot storage stability tests does not permit using them for large-scale application (transportation of bitumen at high temperature). On the contrary, the incorporation of the commercial liquid flame retardant OP 920 (phosphoric acid alkyl ester) in bitumen enhances the reaction to fire of the bitumen, and the mixture is stable during hot storage test. Nanoparticles (organoclay and multiwall carbon nanotubes) have not been found to be appropriate flame retardants for bitumen, but they can be used as synergist with OP 920. Nevertheless, they are not suitable for practical applications because organoclay settles during hot storage tests. Only OP 920 among the evaluated flame retardants can be considered for roofing applications. It provides a very promising fire performance in polymer-modified bitumen and in roofing felts.

Preparation and Characterization of Excellent Flame Retarded Rigid Polyurethane Foams

Rigid polyurethane foams were excellent thermal insulation materials with widely used, which was highly flammable at the same time. In order to obtain safe application, flame retarded polyurethane foams were needed. In this paper, series flame retarded rigid polyurethane foams were prepared with loading different flame retardants such as ammonium polyphosphate, expandable graphite, red phosphorus, Tri (2-chloroethyl) phosphate and dimethyl methylphosphonate. The effects of flame retardants on the foaming-process and flame retardant property of the rigid polyurethane foams were investigated by otary viscometer and limiting oxygen index. The results showed that the combination of solid and liquid flame retardants was necessary to improve the flame retardant and different flame retardants played synergistic roles in rigid polyurethane foams. The limiting oxygen indexes of the foams could be up to 30wt% and 29.6% with 25wt% solid flame retardants and 10wt% liquid retardants, respectively.

Flexible Polyurethane Foams: Flammability

Polyurethane flexible foam is a very versatile, high quality cushioning material. By its chemical nature, polyurethane foam is a combustible material. Test methods have been progressively introduced to classify the fire behaviour of foam and legislation based on these tests has been introduced in various countries to ensure that the foam complies with these fire standards. A notable example of this is British Standard 5852 on which the United Kingdom bedding and furniture legislation is based. The influence of formulation variables such as the type and particle size of the filler, the foam density, the air flow (openness) are some of the well documented parameters. Another important variable is the liquid flame retardant (halogenated phosphate type) which is the objective of the present study. This paper provides a basic understanding of foam combustibility based on the British Standard 5852 test method. Dynamic weight loss made with two types of liquid flame retardants with and without melamine is used to provide this understanding. Thermogravimetric analysis and cone calorimeter have been used to support the discussion. In melamine free foams, our study has shown that the decomposition temperature of the liquid flame retardant is a key parameter, which governs the foam combustion. In melamine containing foams, the overall combustion behavior is dependant on the type of liquid flame retardant used. However, intrinsic differences do exist and synergy is seen between melamine and liquid flame retardant under specific conditions. Applying this basic understanding and the actual combustion standards, foam producers can attain flexibility in designing cost effective foam formulations.

Fire Behavior of Polyurethane Foams

Combustibility of polyurethane foam is an important industry issue. Many test methods are in place to characterize foam combustion, and legislation exists to ensure that the foam complies with specified standards. This paper provides a basic understanding of foam combustibility based on the British Standard BS5852 test method. Dynamic weight loss of foams made with two types of liquid flame retardants with and without melamine is used to provide this understanding. Thermogravimetric analysis and cone calorimeter have been used to support the discussions. In melamine free foams, our study has shown that the decomposition temperature of the liquid flame retardant is a key parameter, which governs the foam combustion. In the melamine containing foams, the overall combustion behavior is independent of the type of liquid flame retardant used. However, intrinsic differences do exist, and synergy is seen between melamine and liquid flame retardant under specific conditions. Applying this basic understanding and the actual combustion standards, foam producers can attain flexibility in designing cost effective foam formulations.

Formation of a flame retardant-cyclodextrin inclusion compound and its application as a flame retardant for poly(ethylene terephthalate)

We report the formation of an inclusion compound (IC) between a commercial flame retardant (FR) and beta-cyclodextrin (CD). The FR-CD-IC was melt-processed into PET films which were tested for flammability. The flammabilities of pure PET films, PET films containing pure CD, and PET films containing FR applied from a bath and then oven-cured, were also observed. Flammabilities, as measured using a modified AATCC Test Method 34, demonstrated that all but the PET films embedded with FR-CD-IC were either completely or substantially consumed when ignited on a single edge with a 3.8 cm flame applied for 3 s. To our knowledge this is the first demonstration of flame retardance achieved by means of delivering a FR to a polymer in the form of its inclusion compound. The high temperature stability of the FR-CD-IC crystals make them suitable for embedding in a variety of polymers that melt below 300°C. Our results suggest that incorporation of FR-CD-IC directly into polymer films or fibers during their melt-processing may be a means to protect them from burning that is superior to post-fabrication application of FRs. In addition, liquid FRs, which are difficult to incorporate and retain in solid polymers, may be included in their high-melting ICs formed with CDs and embedded directly into polymer samples. More broadly, we would expect that a host of other polymer additives may be more effectively delivered in the form of their CD-ICs.

New High Resilience Slabstock Technologies Based on High Performance Polyols

The Dow Chemical Company has developed a new proprietary technology that makes it possible to produce high molecular weight polyether polyols with reduced by-products. This paper reviews the use of this new generation of High Performance Polyols (HPPs) in the flexible slabstock field. It demonstrates how they make it possible to significantly expand the quality and grade versatility of the current all-water blown High Resilience (HR) technologies. In the TDI field, it was shown that the morphology of the polymer plays a key role. The absence of the polyurea precipitates explains the extreme softness achievable even at very high water levels. In these formulations, foams based on High Performance Polyols feature very high physical properties as expressed by comfort factor, resilience and fatigue properties. Enhanced mechanical properties make it possible to use HPPs over a wider range of isocyanate indices which increases the overall versatility of the system. They also help to reduce foam discoloration that is often observed at low density in the presence of liquid flame retardants. In the MDI field, HPPs also allow a certain level of physical property improvement of foams. Using polyols of various molecular weights, the fell of the foam can be improved to get even closer to latex foams. The use of a new parameter, the Comfort Aspect (CA) is described to express numerically the improvement in the foam touch.