Investigation of char strength and expansion properties of an intumescent coating exposed to rapid heating rates

An efficient and space saving method for passive fire protection is the use of intumescent coatings, which swell when exposed to heat, forming an insulating char layer on top of the virgin coating. Although the temperature curves related to so-called cellulosic fires are often referred to as slow heating curves, special cases where the protective char is mechanically damaged and partly removed can cause extremely fast heating of the coating. This situation, for a solvent based intumescent coating, is simulated using direct insertion of free films into a muffle oven. The char formed is evaluated with respect to the mechanical resistance against compression, degree of expansion, and residual mass fraction. Experimental results show that when using this type of shock heating, the mechanical resistance of the char against compression cannot meaningfully be correlated to the expansion factor. In addition, char properties, measured at room temperature, were dependent on the preceding storage conditions (in air or in a desiccator). The char was found to have the highest mechanical strength against compression in the outer crust facing the heat source. For thin (147 μm) free coating films, a tendency to contract in the horizontal plane was observed. The experimental approach is relevant for testing of intumescent coatings used in buildings where moving or falling objects may damage the char during a fire.     

Thermal degradation study of fire resistive coating containing melamine polyphosphate and dipentaerythritol

A melamine polyphosphate (MPP)/dipentaerythritol (DPER) mixture was used as fire retardant additives for preparing waterborne intumescent fire resistive coating. The thermal degradation of the MPP/DPER mixture and of the coating was studied by TGA and FTIR. The resulting char of the coating was investigated by XPS, SEM and energy dispersive spectroscopy (EDS). The results showed that the thermal degradation behavior of the MPP/DPER mixture was similar to that of the coating. They decomposed to nonflammable gases, and formed intumescent char layer containing phosphorus oxide at high temperature. The EDS results proved that the resulting char was gradually oxidized with the temperature increase. The SEM micrographs showed that the average cell size of the char layers became bigger and the cell size distribution became wider as the temperature increased from 500 °C to 800 °C, and this non-uniform char layer could damage the fire protection of the coating.     

氧化石墨烯提高钢结构水性膨胀防火涂料的防火性能研究

以水性丙烯酸树脂为基体,聚磷酸胺、季戊四醇和三聚氰胺为膨胀阻燃体系,加入少量氧化石墨烯制备水性膨胀防火涂料。采用小板燃烧法研究了氧化石墨烯用量对膨胀型防火涂料的阻燃性能的影响。结果表明:加入极少量氧化石墨烯(<0.01%),可提高涂料的阻燃性,当氧化石墨烯含量在0.005%时,涂层的耐燃时间可达432 s,炭层膨胀高度较未加氧化石墨烯涂层增加了13.04%。结合红外光谱(FT-IR)、X射线衍射(XRD)和扫描电子显微镜(SEM)等表征手段对炭层形貌进行分析可知,加入氧化石墨烯后炭层在300~500 ℃范围的热稳定性提高,燃烧炭层完整密实,隔热性能提高,耐燃时间提高。     

氮化硼膨胀型钢结构防火涂料的理论与实验

建立了以四硼酸钠为氧化剂,5-氨基四氮唑发生氧化还原反应生成氮化硼和大量气体的膨胀体系理论。按照这个理论制备了以四硼酸钠、5-氨基四氮唑、磷酸硅为膨胀体系,铝酸盐水泥为硬化剂的钢结构防火涂料。用正交试验方法设计涂料配方,用电热炉测试涂料耐火性能,得到了最优配方,并分析了隔热层的失效机理。结果表明:采用5-氨基四氮唑可以解决四硼酸钠熔化问题;受热膨胀后的氮化硼隔热层具有疏松多孔的海绵状结构;所得最优配方的耐火性能可达1 h;涂料的失效机理是隔热层的龟裂,解决这一问题的关键因素是铝酸盐水泥的种类和含量。     

Thermal degradation study of fire resistive coating containing melamine polyphosphate and dipentaerythritol

A melamine polyphosphate (MPP)/dipentaerythritol (DPER) mixture was used as fire retardant additives for preparing waterborne intumescent fire resistive coating. The thermal degradation of the MPP/DPER mixture and of the coating was studied by TGA and FTIR. The resulting char of the coating was investigated by XPS, SEM and energy dispersive spectroscopy (EDS). The results showed that the thermal degradation behavior of the MPP/DPER mixture was similar to that of the coating. They decomposed to nonflammable gases, and formed intumescent char layer containing phosphorus oxide at high temperature. The EDS results proved that the resulting char was gradually oxidized with the temperature increase. The SEM micrographs showed that the average cell size of the char layers became bigger and the cell size distribution became wider as the temperature increased from 500 °C to 800 °C, and this non-uniform char layer could damage the fire protection of the coating.     

Influences of silicone emulsion on fire protection of waterborne intumescent fire-resistive coating

The combination of self-crosslinking polyacrylate emulsion and silicone emulsion was used as a binder for the preparation of waterborne intumescent fire-resistive coatings. The influences of silicone emulsion on fire protection and char formation of the coatings were investigated in detail by means of TGA, SEM, energy dispersive spectroscopy analysis, rheological measurement, and fire protection tests. The results showed that using silicone emulsion improved thermal stability and antioxidation ability of the coating and increased the residue weights of the char layer at high temperature. Furthermore, an appropriate amount of silicone emulsion could improve the rheological property of the mixed binders and be conducive to the increase of the intumescent factor of the coatings, thus improving the fire protection of the coating significantly. However, an excess amount of silicone emulsion can lead to uneven dispersion of silicone emulsion in the mixed binder and cause an uneven distribution of cell size of the char layer.     

新型阻燃体系对木塑防火涂层阻燃性能的影响

采用隔热性能试验、热失重分析(TG)、傅里叶红外光谱分析(FTIR)以及显微分析等方法,研究了两种改性材料膨胀石墨(EG)和云母对膨胀防火涂层防火性能和热降解行为的影响。结果表明:EG与云母加入后不会改变涂层的基本阻燃进程,且会提高膨胀炭质层的热稳定性,涂层的阻燃效果显著改善。     

钢结构用水性膨胀型防火涂料的制备及性能研究

以高岭土及含锆陶瓷纤维作为增强填料,聚醋酸乙烯酯乳胶和醋叔乳胶的混合液为基料,多聚磷酸铵(APP)、三聚氰胺(MEL)、季戊四醇(PER)为膨胀阻燃体系,开发了一种燃烧后具有高强度膨胀炭层的水性膨胀型防火涂料.研究了乳胶类型、膨胀阻燃体系各组分配比、颜基比、高岭土及含锆陶瓷纤维对水性膨胀型防火涂料性能及炭层强度的影响....     

Experimental study on insulative properties of intumescent coating exposed to standard and nonstandard furnace curves

This paper reports the results of an experimental study on two types of intumescent coating exposed to the ISO834 standard fire and three nonstandard fire curves. The nonstandard fires were all less severe than the standard fire. A total of 72 intumescent coating protected steel specimens were tested. The expanded thickness of intumescent char was measured, and the pore feature was observed. Constant thermal conductivity for each specimen was calculated based on the measured steel plate temperature. Thermogravimetric analysis (TGA) test was carried out, and the results show that more gas is trapped within the coating due to better matching of thermal behaviour between gas evolution and polymer viscosity as the rate of heating increases. The constant effective thermal conductivities for the intumescent coating under the nonstandard fires were 65% (type‐W) and 35% (type‐S) higher than that under the standard fire, which resulted in an overestimation of the coating failure time up to 15 and 11 minutes, respectively. Therefore, it is sometimes insecure to use results from standard fire tests guiding the design of coating thickness for steel elements under nonstandard fire conditions.     

Expandable graphite: A fire retardant additive for polyurethane coatings

The study investigates the mechanism of fire retardancy induced by expandable graphite in a polyurethane coating. A complementary investigation to the spectroscopic study performed previously confirms that little interaction occurs between the matrix and the additive. X‐ray diffraction study demonstrates that the crystalline structure of the graphite is maintained during the intumescent process. The presence of free radicals in the protective shield is then demonstrated but at low concentration compared with classical intumescent systems, such as for example polyurethane/ammonium polyphosphate. Finally, the physical properties of the char are then investigated. Blowing measurement demonstrates the high degree of expansion of the layer which may partially explain the fire retardant performance of expandable graphite in polyurethane. Surface analyses by optical microscopy and optical profilometry also enable a better understanding of the efficiency of expandable graphite. In the absence of a fire retardant additive the coating displays cracks and holes, providing a pathway for oxygen diffusion as well as heat and mass transfer between the flame and the virgin polymer. Both phenomena are limited when expandable graphite is added to polyurethane. Consequently, fire retardancy of expandable graphite results more from a physical than from a chemical action. Copyright © 2003 John Wiley & Sons, Ltd.     

膨胀炭质层物相结构的X射线衍射研究

采用Ｘ射线衍射技术，对膨胀型防火涂料经过大板燃烧后所形成的炭质层的物相结构进行了系统研究。研究结果表明，在膨胀炭质层中，除灰在无定形炭以外，还存在一种对基材的防火起较大作用的化合物－焦磷酸钛。     

Experimental and numerical study of burning behaviors of flaxboard with intumescent coating and nanoparticles in the cone calorimeter and single burning item tests

This paper presents an experimental and numerical investigation of the effects of intumescent coating and nanoparticles on the burning behaviors of flaxboard. Virgin flaxboard samples and those coated with intumescent coatings (with/without nanoparticles) were tested in the cone calorimeter and single burning item (SBI) test. Experimental results show a significant increase in the time to ignition and also a reduction in the heat release rate by the intumescent coatings. In order to explain quantitatively and predict the effects of the intumescent coating, a global fractional factor (the ratio of the heat flux at the interface of the intumescent surface and the char layer of flaxboard to the surface heat flux when there is no intumescent coating layer) was introduced based on analytical solutions for charring materials. The fractional factor for the intumescent coatings was found by comparing predictions to the experimental data in the cone calorimeter test and, subsequently, was incorporated in an upward flame spread model, along with the ignition and thermal properties deduced from the ignition tests, to predict the burning rates in the SBI tests. Copyright © 2011 John Wiley & Sons, Ltd.     

Influence of heat-stable filler on the thermal shielding performance of water-based intumescent fire-resistive coating for structural steel applications

Intumescent coatings are the newest passive fireproofing materials which maintain structural integrity of high-rise buildings in fire events. The present work focuses on the influence of zirconium silicate as a heat-stable filler in intumescent coatings. Different coatings were formulated by varying the zirconium silicate concentration from 1, 3, 5, 8, and 10 on parts per hundred basis (phr). Fire performance of the coatings was then determined by fire test using a Bunsen burner fire flame at 950°C for 1 h. The degradation of coatings was examined by thermogravimetric analysis (TGA). The morphology of the intumescent chars was analyzed by environmental scanning electron microscopy. The char was also examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy. XRD confirmed the inertness of zirconium silicate with intumescent ingredients at high temperatures. TGA showed an increase in the weight residue of char at high temperature. The incorporation of zirconium silicate into intumescent coating forms a thermally stable char with better substrate adhesion. EDS analysis confirmed an increase in the antioxidation property of the char, and the fire test also confirmed an increase in char strength of coatings by the incorporation of zirconium silicate.     

Effects of inorganic fillers on the performance of the water-based intumescent fire-retardant coating

The purpose of this research was to evaluate the influences of filler type and its content on the performance of a water-based intumescent fire-retardant coating. Three fillers (vermiculite, celite, and aluminum hydroxide) were added to the intumescent paint formulation. The thermal and fire protective properties were studied with thermogravimetric analysis (TGA), torch test, electrical furnace, scanning electron microscopy (SEM), and Fourier transform infrared analysis (FTIR). The results showed that adding fillers into coatings up to 3% could improve the intumescent coating's behavior and increase its endurance against flames. Of the three fillers used, vermiculite showed a better performance in the torch test, attributed to its chemical and physical structure. Vermiculite has low thermal conductivity and is considered an appropriate filler for heat-insulation. The final back-plate temperatures in the torch test for the vermiculite-containing samples were around 100°C–150°C lower than that of other samples. Moreover, vermiculite's addition improved the coating's expansion by 10% compared with the control sample's. The vermiculite sample's char layer morphology showed a uniform cell size distribution, indicating structural robustness. The coating samples successfully transformed polypropylene flammability from highly flammable to V0 level in the UL 94 vertical burning test standard. The results showed that vermiculite could improve intumescent paint's fire resistance and be used as an enhancer in intumescent coating formulations.     

Exfoliated and functionalized boron nitride nanosheets towards improved fire resistance and water tolerance of intumescent fire retardant coating

In this work, the exfoliated and functionalized boron nitride (f-BN) nanosheets were prepared via facile treatment and used in the intumescent fire retardant (IFR) coatings, which offer passive fire protection to the steel. To acquire the best fire resistance, the formula of the coating was optimized using response surface methodology (RSM) based on central composite design. According to the result, the optimal sample, with 36.2 wt% ammonium polyphosphate (APP), 27.4 wt% pentaerythritol (PER), 16.8 wt% melamine (MEL), and 7.9 wt% f-BN, was prepared and its fire resistance was tested in our lab. At the end of fire resistance test, the backside temperature of optimal sample was only 185.2°C, which was very close to the RSM-predicted result, indicating satisfactory fire resistance. During the test, the coating decomposed to form an intumescent char layer with high graphitization degree and compactness, thus suppressing the transfer of heat and protecting the underlying steel. In addition, the optimal coating possessed great water tolerance and thermal stability, and its water contact angle and char yield reached up to 66.7° and 40.5%, respectively. Hence, this IFR coating with satisfied fire retardancy and water tolerance has broad practical future in the fire safety of steel structure.     

可膨胀石墨在膨胀型钢结构防火涂料中的应用

为了改善钢结构防火涂料膨胀炭质层蓬松易脱落和易开裂的缺点,将可膨胀石墨(EG)添加到防火涂料中,通过耐火实验来研究EG对炭质层形貌和钢结构耐火极限的影响。结果表明,EG膨胀后成“蠕虫”状穿插于膨胀炭质层中,起到增强作用,使炭质层结构更致密。热分析结果表明,w(EG) =6 7%时,防火涂料在600℃时的热失重减少了7%;w(EG) =0 5%时,钢结构耐火极限延长了10min。     

Flame retardancy and crack resistance of transparent intumescent fire‐resistive coatings

In this article, dihydroxy polydimethylsiloxane (n = 5–10) was introduced into the structure of polyphosphate (PPE) to get siloxane‐modified polyphosphate (SiPPE). Five kinds of SiPPEs with different Si contents were obtained. FTIR (Fourier Transform Infrared spectroscopy) ICP (Inductively Coupled Plasma Emission Spectroscopy), ³¹P NMR (Nuclear Magnetic Resonance Spectroscopy) and TGA (Thermogravimetric Analysis) were used to characterize the composition and structure of PPE and SiPPEs. Six kinds of transparent fire‐resistive coatings were prepared by the mixing of amino resin with PPE and five kinds of SiPPEs. The results of the fire protection test showed that both the fire‐resistive time of coatings and intumescent factor of char layers increased with the increase in content of Si. The results of TGA demonstrated that the carbonaceous residue of coating also increased regularly. The hardness, flexibility, digital photos, SEM (Scanning Electronic Microscopy) and other testing results showed that the introduction of silicon oxygen segment can effectively improve the crack resistance. The charcoal layer structure was more solid than before and collapse was not obvious after long time flame shock. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42423.     

水性钢结构防火涂料的制备及其耐火性能研究

以水性树脂为基体,聚磷酸铵(APP)、三聚氰胺(MEL)、季戊四醇(PER)为膨胀阻燃体系,可膨胀石墨(EG)和绢云母为填料制备了水性膨胀型钢结构防火涂料;研究了基体拼合、膨胀阻燃体系、EG与绢云母配比对钢结构防火涂料性能的影响。结果表明:氯偏乳液与纯丙AC261P乳液质量比为22:3,APP、MEL、PER的质量比为4:3:3,可膨胀石墨和绢云母的质量比为5:3时,制备的防火涂料涂层受热膨胀倍率为5.68倍,形成了"蜂窝状"结构的膨胀炭质层,孔洞均匀致密,与钢板粘附性好、强度高,耐火性能好,耐火极限高达2 997 s。     

聚丙烯膨胀成炭行为对裂解燃烧过程的影响

对膨胀阻燃聚丙烯材料在锥形量热仪试验条件下的燃烧过程进行了研究，分析了材料膨胀成炭行为对裂解燃烧过程的影响。测量了纯聚丙烯及膨胀阻燃聚丙烯在膨胀燃烧过程中的质量损失速率、热释放速率和炭层膨胀高度随时间变化规律。分析了膨胀高度、膨胀速度、炭层结构对裂解燃烧的影响。结果表明，随着膨胀阻燃剂添加量的增加，膨胀升高的速度有加快的趋势；随着外部辐射功率的加大，膨胀速度加快。聚丙烯材料的炭层整体性越强，炭层结构越致密，阻隔效果越好，热释放速率越低。通过对材料膨胀成炭过程的理论分析也验证了膨胀高度（或膨胀速度）和炭层的结构都对裂解燃烧过程有很大的影响。     

Engineering model for intumescent coating behavior in a pilot‐scale gas‐fired furnace

In the event of a fire, intumescent fire protective coatings expand and form a thermally insulating char that protects the underlying substrate from heat and subsequent structural failure. The intumescence includes several rate phenomena, which have been investigated and quantified in the literature for several decades. However, various challenges still exist. The most important one concerns mathematical model validation under realistic exposure conditions and/or time scales. Another is the simplification of advanced models to overcome the often‐seen lack of a complete set of input and adjustable model parameters for a given coating, thereby providing models for industrial applications. In this work, these two challenges are addressed. Three experimental series, with an intumescent coating inside a 0.65 m³ gas‐fired furnace, heating up according to so‐called cellulosic fire conditions, were conducted and a very good repeatability was evident. The experiments were run for almost 3 h, reaching a final gas temperature of about 1100°C. Measurements include transient temperature developments inside the expanding char, at the steel substrate, and in the mineral wool insulation placed behind the substrate. A mathematical model, describing the intumescent coating behavior and temperatures in the furnace using a single overall reaction was developed and validated against experimental data. By including a decomposition front movement through the char, a good qualitative agreement was obtained. After further validation against experiments with other coating formulations, it has potential to become a practical engineering tool. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3947–3962, 2016