Flame retarding effect of graphite in rotationally molded polyethylene/graphite composites

Linear low‐density polyethylene (LLDPE) compounds containing 10 wt % graphite fillers were rotationally molded into flat sheets. Flame retardancy was studied using cone calorimeter tests conducted at a radiative heat flux of 35 kW/m². Only the expandable graphite, an established flame retardant for polyethylene, significantly reduced the peak heat release rate. Compared with the neat polyethylene, it was easier to ignite the LLDPE composites containing carbon black, expandable graphite, and exfoliated graphite. However, rather unexpectedly, the inclusion of flake graphite increased the time to ignition by up to 80%. Simulations conducted with the ThermaKin numerical pyrolysis software suggest that increased reflectivity was mainly responsible for this effect. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41472.     

EG与IFR复合阻燃ABS协同效应及热失重行为研究

将可膨胀石墨(EG)、P-N型膨胀阻燃(剂IFR)与ABS树脂共混,制作复合阻燃材料。用氧指数(OI)、UL 94测试和锥形量热仪(CONE)探讨了EG与IFR复合阻燃ABS的协同效应。通过热失重分析(TG)研究了阻燃ABS体系的热失重行为。结果表明:EG与IFR协同阻燃ABS,OI达到29%,UL 94为V-0级,热释放速率大幅度降低,EG与IFR复合阻燃ABS具有一定的协同效应;在空气气氛下,EG与IFR可以相互促进成炭,且形成的炭层稳定在,850℃也不会分解。     

A comparison of fire retarded and non‐fire retarded wood‐based wall linings exposed to fire in an enclosure

Full‐scale fire experiments were carried out in an ISO room to study the behaviour of commonly used cellulosic lining materials in real fire conditions. In addition to the temperature measurements recommended by the ISO 9705, temperature recordings were made at each node of grid lines on the wall lining surfaces. Four lining materials were chosen to represent different types of products and the surface spread of classifications determined using the BS 476 Part 7 flame spread test environment. The linings included fire retarded, melamine faced and non‐fire retarded boards which facilitated a comparative study of the behaviour of these materials with respect to ignition, flame spread, heat release rate and time to flashover. Corner fire scenarios were used in all the experiments. A T shape flame spread pattern on the surface of the two adjacent walls was observed prior to flashover. Prior to the onset of flashover conditions, downward opposed flow surface flame spread to the wall/ceiling intersection. For the non‐retarded wood based materials, such as plywood and medium density fibre board, flashover conditions occurred approximately 4 min after the start of the experiment. However, the fire retarded chipboard ignition was delayed by some 11 min 45 s after which flame spread was very rapid with flashover occurring within a further 1 min 45 s. An explanation for this particular behaviour is the considerable pre‐heating which occurred during the pre‐ignition period. For the fire retarded linings, much higher surface temperatures were recorded compared with those for non‐fire retarded linings. It was found that the areas of the fire retarded linings facing the source flame suffered extensive pyrolysis and charring which penetrated to the rear surface of the lining. Copyright © 1999 John Wiley & Sons, Ltd.     

Polyethylene flame retarded with expandable graphite and a novel intumescent additive

A novel intumescent additive was synthesized by neutralizing 3,5‐diaminobenzoic acid hydrochloride salt with ammonium dihydrogen phosphate. This compound, which melts at 257°C, decomposes concurrently to release carbon dioxide gas. The flame retardant performance of this compound as a primary fire retardant and in combination with expandable graphite (EG) was evaluated by cone calorimetry. Cone calorimeter results showed that addition of 10 wt % EG alone lowers peak heat release rate (pHRR) of carbon black‐pigmented polyethylene from 710 ± 109 to 342 ± 15 kW m^?2, whereas addition of 27 wt % of the novel intumescent lowered it to 400 ± 16 kW m^?2. Combinations of these two additives were able to decrease the pHRR even further. Furthermore, the novel intumescent additive reduced the flame out time from 773 ± 307 to 537 ± 69 s although all other EG containing samples increased it. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40493.     

Fire risks of burning asphalt

Eyewitnesses describe burning pavement surfaces in extreme fire scenarios. However, it was believed that the pavement plays a negligible role in comparison to other items feeding such an extreme fire at the same time. The asphalt mixtures used differ widely, thus raising the question as to whether this conclusion holds for all kinds of such materials. Three different kinds of asphalt mixtures were investigated with the aim of benchmarking the fire risks. Cone calorimeter tests are performed at an irradiance of 70kWm^?2. All three investigated asphalts burn in extreme fire scenarios. The fire response (fire load, time to ignition, maximum heat release rate and smoke production) is quite different and varies by factors of up to 10 when compared to each other. The fire load per mass is always very low due to the high content of inert minerals, whereas the effective heat of combustion of the volatiles is quite typical of non‐flame retarded organics. The heat release rate and fire growth indices are strongly dependent on the fire residue and thus the kind of mineral filler used. Comparing with polymeric materials, the investigated Mastic Asphalt and Stone Mastic Asphalt may be called intrinsically flame resistant, whereas the investigated Special Asphalt showed a pronouncedly greater fire risk with respect to causing fire growth and smoke. Thus the question is raised as to whether the use of certain kinds of asphalts in tunnels must be reconsidered. Apart from the binder used, the study also indicates varying the kind of aggregate as a possible route to eliminate the problem. Copyright © 2010 John Wiley & Sons, Ltd.     

聚磷酸蜜胺系膨胀型阻燃剂阻燃PA6的燃烧行为及热裂解研究

采用以聚磷酸蜜胺(MPP)为基的三元膨胀型阻燃剂阻燃聚酰胺6(PA6)，测定了阻燃PA6的氧指数(LOI)、UL94V阻燃性及热稳定性，以傅立叶变换红外光谱(FT—IR)分析了阻燃PA6的热分解残余物，以锥形量热仪(CONE)测定了阻燃PA6的诸多与火灾有关的阻燃参数(包括释热速度、质量损失速度、有效燃烧热、比消光面积等)，并以光电子能谱(XPS)测定了阻燃PA6残炭表面的元素组成及XPS曲线拟合数据。     

硼烷合乙二胺的点火、燃烧及热解特性

为探索高氢含量硼烷合乙二胺储氢材料在空气中的燃烧性能,使用气相合成方法制备了硼烷合乙二胺(EDAB)微米颗粒。通过连续激光点火实验,测试了其点火和燃烧参数;通过在氮气和空气中的热解实验,研究了其燃烧过程机理。结果表明,硼烷合乙二胺的燃烧具有点火延迟时间短、点火能量低的特点,在常温常压静止空气流中,点火功率密度为10~9 W/m~2量级时,微米级硼烷合乙二胺的点火延迟时间为0.000 2~0.000 9s,最小点火能量仅0.000 1J;其连续激光点火燃烧过程分为两个阶段,分别产生亮蓝色与黄色火焰。结合材料在氮气及空气中的热解行为,推测该材料燃烧第1阶段蓝色火焰对应其热解释放氢气的燃烧,第2阶段的黄色火焰对应其骨架高温裂解所生成挥发物的燃烧。     

Development of halogen‐free flame‐retardant thermoplastic elastomer polymer blend

Ethylene‐propylene diene rubber (EPDM) and isotactic polypropylene (iPP) blends have widest industrial applications that require a degree of flame retardancy. Halogen‐free intumescent technology based on phosphorous salt is a significantly advanced approach to make the polymer flame‐retardant. Both ammonium polyphosphate and ethylenediamine phosphate are important intumescent compounds. Their combination with carbonific and spumific agents were studied in binary blends of EPDM/PP. The polymer system was vulcanized online during melt mixing. Intumescent flame‐retardant polymer systems exhibit good flame‐retardancy with optimum comparable physiomechanical, electrical, and fluid resistance properties, including lower smoke emission, which is essential to protect people because the visibility remains unaffected in the event of fire. Pronounced charring and intumescent effect appear to enhance the flame‐retardancy of the polymers. Possible expected intumescent mechanism is proposed based on the nonpyrolysis mechanism for the flame‐retarded polymer and the intumescent components. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 407–415, 2004     

The Accumulation of Flammable Gases in Cone Calorimeter Tests is Responsible for Flash Ignition of Wool and Cotton Samples

In this paper a possible explanation is presented for the differences found between the fire behaviour of materials in small-scale cone calorimeter tests and the large-scale furniture calorimeter. The results obtained with cone calorimeter/FTIR equipment at 35 kW m⁻² will show that the early flash ignitions of typical materials like cotton and wool are due to the liberation of flammable gases during the pyrolysis phase and the typical ignition situation on the cone calorimeter, that is, the presence of a sparking igniter above the sample. This fast flash ignition and the early heat release behaviour on the cone calorimeter may be in contradiction to the early fire growth in other fire tests where the ignition conditions are clearly different from pyrolysis circumstances, that is, ignition via a burning newspaper, match, gas flame, etc.     

Melamine poly(metal phosphates) as flame retardant in epoxy resin: Performance,modes of action,and synergy

Melamine poly(metal phosphates) (MPMeP) are halogen‐free flame retardants commercialized under the brand name Safire. Melamine poly(aluminum phosphate) (MPAlP), melamine poly(zinc phosphate) (MPZnP), and melamine poly(magnesium phosphate) (MPMgP) were compared in an epoxy resin (EP). The thermal decomposition, flammability, burning behavior, and glass transition temperature were investigated using thermogravimetric analysis, pyrolysis combustion flow calorimeter, UL 94 testing, cone calorimeter, and differential scanning calorimetry. While the materials exhibited similarities in their pyrolysis, EP + MPZnP and EP + MPMgP showed better fire behavior than EP + MPAlP due to superior protective properties of the fire residues. Maintaining the 20 wt % loading, MPZnP was combined with various other flame retardants. A synergistic effect was evident for melamine polyphosphate (MPP), boehmite, and a derivative of 6H‐Dibenzo[c,e][1,2]oxaphosphinine‐6‐oxide. The best overall performance was observed for EP + (MPZnP + MPP) because of the best protection effectiveness of the fire residue. EP + (MPZnP + MPP) achieved V1/V0 in UL 94, and an 80% reduction in the peak heat release rate. This study evaluates the efficiency of MPMeP in EP, alone and in combination with other flame retardants. MPMeP is a suitable flame retardant for epoxy resin, depending on its kind and synergists. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43549.     

Investigation of fire behavior of rigid polyurethane foams containing fly ash and intumescent flame retardant by using a cone calorimeter

Cone calorimeter is one of the most useful bench‐scale equipment which can simulate real‐world fire conditions. Therefore, cone calorimeter tests have been the most important and widely used tests for research and development of fire behavior of polymeric materials. In this study, fire behavior of rigid polyurethane foams containing fly ash (up to 5 wt %) and intumescent flame retardant (up to 5 wt %) composed of ammonium polyphosphate/pentaerythritol was investigated by using a cone calorimeter. In addition, thermogravimetric analysis of the additives and the foams were also carried out to explain the effects of fly ash and intumescent flame retardant on fire behavior of the foams. Experimental results indicated that rigid polyurethane foam containing fly ash and the intumescent flame retardant in comparison with pure rigid polyurethane foam shows significantly enhanced fire resistance and thermal stability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

反应型磷氮阻燃剂/可膨胀石墨复配阻燃聚氨酯泡沫

将反应型阻燃剂六(4-磷酸二乙酯羟甲基苯氧基)环三磷腈(HPHPCP)和可膨胀石墨(EG)复配,制备了阻燃聚氨酯泡沫,详细研究了复配阻燃剂对聚氨酯泡沫的物理力学性能、热稳定性以及阻燃性能的影响。结果表明,阻燃聚氨酯泡沫的密度和热导率随着复配阻燃剂中EG含量的增加而升高;压缩强度随着EG含量的增加呈现先增加后降低的趋势。热失重表明复配阻燃剂大大提高了聚氨酯泡沫的热稳定性。聚氨酯泡沫的初始分解温度(T_10%)从212.9℃,分别提高到222.0、231.2和243.2℃;700℃残炭量从7.6%分别提高到26.3%、31.6%和37.9%。聚氨酯泡沫的阻燃性能随着复配阻燃剂中EG含量的增加而提高。阻燃聚氨酯泡沫的极限氧指数从19%提高到29%,均能通过UL-94水平燃烧HF-1等级和垂直燃烧V-0等级。     

The application of organophosphorus flame‐retardants in epoxy resin

The influence of two novel aryl phosphate mixtures on fire retardancy and the thermal stability of epoxy resin were studied. Combustion behavior, decomposition pathway, and thermal and thermo‐oxidative degradation of the epoxy resin were examined by using the limiting oxygen index, vertical burning test (UL‐94), cone calorimeter test, thermogravimetric analysis, and thermogravimetry coupled with Fourier‐transform infrared spectroscopy. The morphology of the residues from the degradation of flame‐retarded epoxy resins was investigated by using scanning electron microscopy. Data from the cone calorimeter test demonstrated that the total heat evolved, heat release rate, and peak heat release rate decreased significantly when the epoxy resin contained these retardants. Moreover, a 20 wt% of both phosphate mixtures in the epoxy resin allowed for a satisfactory oxygen index (30–33%) and for UL‐94 V2 to be achieved. The condensed‐phase and gas‐phase actions of these aryl phosphate flame‐retardants are proposed as the mode of flame‐retardancy in epoxy resins. J. VINYL ADDIT. TECHNOL., 23:142–151, 2017. © 2015 Society of Plastics Engineers     

Effects of variations in incident heat flux when using cone calorimeter test data for prediction of full‐scale heat release rates of polyurethane foam

The development of methods to predict full‐scale fire behaviour using small‐scale test data is of great interest to the fire community. This study evaluated the ability of one model, originally developed during the European Combustion Behaviour of Upholstered Furniture (CBUF) project, to predict heat release rates. Polyurethane foam specimens were tested in the furniture calorimeter using both centre and edge ignition locations. Input data were obtained using cone calorimeter tests and infrared video‐based flame area measurements. Two particular issues were investigated: how variations in incident heat flux in cone calorimeter tests impact heat release rate predictions, and the ability of the model to predict results for different foam thicknesses. Heat release rate predictions showed good agreement with experimental results, particularly during the growth phase of the fire. The model was more successful in predicting results for edge ignition tests than for centre ignition tests and in predicting results for thinner foams. Results indicated that because of sensitivity of the burning behaviour to foam specimen geometry and ignition location, a single incident heat flux could not be specified for generating input for the CBUF model. Potential methods to determine appropriate cone calorimeter input for various geometries and ignition locations are discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

环境气体氧含量对NEPE推进剂激光点火过程的影响

为研究环境气体氧含量对硝酸酯增塑聚醚(NEPE)推进剂激光点火过程的影响,采用CO2激光辐射点火并利用高速摄影仪记录NEPE推进剂的点火过程,讨论了环境气体氧含量对NEPE推进剂初焰位置与点火延迟时间的影响。结果表明,当环境气体氧含量小于NEPE推进剂热解产物中氧化性气体含量时,NEPE推进剂点火的气相反应发生在推进剂热解产物的分散区,初焰紧靠NEPE推进剂表面,环境气体氧含量变化不影响NEPE推进剂的点火延迟时间;当环境气体氧含量大于NEPE推进剂热解产物中氧化性气体含量时,NEPE推进剂点火的气相反应发生在推进剂热解产物与环境气体的扩散区,初焰远离NEPE推进剂表面,此时由于扩散区氧含量高于NEPE推进剂热解产物分散区氧含量,NEPE推进剂的点火延迟时间减小。     

Correlations between pyrolysis combustion flow calorimetry and conventional flammability tests with halogen‐free flame retardant polyolefin compounds

Seven halogen‐free flame retardant (FR) compounds were evaluated using pyrolysis combustion flow calorimetry (PCFC) and cone calorimetry. Performance of wires coated with the compounds was evaluated using industry standard flame tests. The results suggest that time to peak heat release rate (PHRR) and total heat released (THR) in cone calorimetry (and THR and temperature at PHRR in PCFC) be given more attention in FR compound evaluation. Results were analyzed using flame spread theory. As predicted, the lateral flame spread velocity was independent of PHRR and heat release capacity. However, no angular dependence of flame spread velocity was observed. Thus, the thermal theory of ignition and flame spread, which assumes that ignition at the flame front occurs at a particular flame and ignition temperature, provides little insight into the performance of the compounds. However, results are consistent with a heat release rate greater than about 66kW/m² during flame propagation for sustained ignition of insulated wires containing mineral fillers, in agreement with a critical heat release rate criterion for burning. Mineral fillers can reduce heat release rate below the threshold value by lowering the flaming combustion efficiency and fuel content. A rapid screening procedure using PCFC is suggested by logistic regression of the binary (burn/no‐burn) results. Copyright © 2008 John Wiley & Sons, Ltd.     

Fire retardancy effect of phosphorus‐modified halloysite on polyamide‐11 nanocomposites

Halloysite nanotubes (HNTs) were successfully incorporated as flame retardants in polyamide‐11 (PA11) after their modification with methyl phosphonic acid. Fourier transform infrared spectroscopy, thermal gravimetric analysis (TGA) and pyrolysis–gas chromatography–mass spectrometry were used to evidence the functionalization of the clay. Raw and modified HNTs were then incorporated by melt mixing in PA11 at 20 wt%. Compositions containing both ammonium polyphosphate (APP) and HNTs were also prepared. TGA and pyrolysis combustion flow calorimeter exhibited enhancement in thermal stability upon incorporation of both raw and modified halloysite nanotubes while APP causes degradation at lower temperature. Cone calorimeter data showed that modified halloysite acts by forming an insulating barrier during the combustion, which limits heat and mass transfers. Moreover, elemental analysis of sample residues after cone test evidenced that a part of the phosphorus of the modified halloysite was transferred to the gaseous phase. These results suggest the full potential of halloysite as fire retardant agent for polyamides. POLYM. ENG. SCI., 59:526–534, 2019. © 2018 Society of Plastics Engineers     

Experimental investigation and numerical modelling of the fire performance for epoxy resin carbon fibre composites of variable thicknesses

This paper applies a unique integrated approach to determine the flammability properties of a composite material (epoxy with carbon fibre) and compares its fire behaviour at two different thicknesses (2.1 and 4.2 mm) by performing small scale (thermo‐gravimetric analysis (TGA)/Fourier transform infrared radiation) and meso‐scale tests (cone calorimeter). For small‐scale tests, experiments were conducted in nitrogen using TGA coupled to gas analysis by Fourier transform infrared radiation. These results allow the determination of thermal stability, main degradation temperature and main gaseous emissions released during the thermal degradation. For meso‐scale tests, experiments were carried out using a cone calorimeter with sample dimensions of 100 × 100 mm at five heat fluxes (30, 40, 50, 60 and 70 kW/m²). The results show that the ignition time increases with an increase in the thickness of the material. Relative hazard classification of the fire performance of the current composites has also been compared with other materials using parameters obtained elsewhere. In addition, the effective ignition, thermal and pyrolysis properties obtained from the ignition and mass loss rate experiments for the 4.2‐mm thick samples were used in a numerical model for pyrolysis to predict well ignition times, back‐surface temperatures and mass pyrolysis rates for all heat fluxes as well as for the 2.1‐mm thick samples. Note that the ignition temperature obtained in the cone agrees with the main degradation temperature in the TGA. The flammability properties deduced here can be used to predict the heat release rate for real fire situations using CFD modelling. Copyright © 2016 John Wiley & Sons, Ltd.     

Flame retardation and thermal stability of novel phosphoramide/expandable graphite in rigid polyurethane foam

A novel flame retardant named diethylene N,N',N''‐tri (diethoxy)phosphoramide (DTP) was synthesized using diethyl phosphate and diethylenetriamine via Atherton–Todd reaction. Then, series of flame‐retardant water‐blown rigid polyurethane foams (RPUFs) with expandable graphite (EG) and DTP were prepared through box‐foaming. The results of thermogravimetric analysis showed that DTP/EG changed thermal degradation process of RPUF and promoted enhancing char residues. The complex flame‐retardant system (EG/DTP) endowed RPUF higher limiting oxygen index (LOI) values (29.1%–30.2%) and lower heat release rate peak (PHRR) values according to LOI and microscale combustion calorimeter tests. More importantly, the synergistic flame‐retardant effect between EG and DTP in RPUF was proved by the analysis of synergistic effectivity values. Based on the analysis of cone calorimetric tests, EG/DTP revealed remarkable effects to inhibit the fire intensity and smoke release of RPUF with decreased PHRR and total smoke production due to good char‐forming action. To further investigate the char‐residues of the foams after combustion, scanning electron microscope and energy dispersive X‐ray spectroscopy analyses were conducted. The results suggested that EG/DTP flame‐retardant system promoted RPUF forming a compact, continuous and phosphorus‐rich char layer as a good fire barrier in combustion. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46434.     

Flame retardants and heat release: review of data on individual polymers

This is part of a project considering whether flame retardants affect polymer heat release, a critical issue to assess whether adding flame retardants decreases fire hazard. The work investigated the following. (1) Fire properties affecting fire hazard, confirming that heat release rate is the key fire property most strongly influencing fire hazard. (2) Ways to assess heat release and whether full‐scale fire heat release rate can be predicted from small‐scale test results, confirming that cone calorimeter and Ohio State University data are adequate to predict full‐scale heat release. (3) Analysis of key 1988 NBS/NIST study comparing the fire hazard of flame retarded products versus non‐flame retarded products for the same application. This confirmed that the study demonstrated that flame retardants lower fire hazard and that the levels of additives in the flame retarded products used were not excessive. (4) Review of studies investigating effects of flame retardants on various polymeric systems. The overall conclusion is that flame retardants does indeed improve fire safety (when used appropriately) primarily because they decrease heat release. Part 2 of the project (separately) considers the key polymers that need to be potentially flame retarded and reviews recent studies on effects of flame retardants on heat released by such polymers. Copyright © 2014 John Wiley & Sons, Ltd.