Flame retardancy and smoke suppression of silicone foams with microcapsulated aluminum hypophosphite and zinc borate

The flame‐retardant microcapsules were successfully fabricated with an aluminum hypophosphite (AHP) core. Fourier transform infrared (FTIR) and X‐ray photoelectron spectroscopy (XPS) were used to verify that AHP was encapsulated in the microcapsules, and thermogravimetry analysis showed that microencapsulated AHP (MAHP) possessed higher thermal stability than that of AHP. Then, a flame‐retardant and smoke suppression system for silicone foams (SiFs) was obtained through a synergistic effect of MAHP and zinc borate (2ZnO·3B₂O₃·3.5H₂O). The mechanical properties, flame retardance, and smoke suppression of SiFs with MAHP and zinc borate were tested using the tensile test, limiting oxygen index (LOI) test, UL‐94 test, and cone calorimeter test. The mechanical properties indicated that the tensile strength and elongation at break of SiFs could evidently improve with the incorporation of MAHP. Compared with pure SiF, SiF8 with 4.5‐wt% MAHP and 1.5‐wt% zinc borate could achieve an LOI value of 30.7 vol% and an UL‐94 V‐0 rating, the time to ignition amplified almost six times, the peak heat release rate and total heat release were 51.10% and 46.00% less than that of pure SiF, respectively, the fire performance index increased nearly 13 times, and the fire growth index value was only 13.18% of pure SiF. Moreover, the partial substitution of zinc borate imparted a substantial improvement in both flame retardancy and smoke suppression. Especially, the peak smoke production rate and total smoke production of SiF8 were merely 38.46% and 38.84% of pure SiF.     

Melamine integrated metal phosphates as non-halogenated flame retardants: Synergism with aluminium phosphinate for flame retardancy in glass fiber reinforced polyamide 66

An integrated multicomponent molecule, Melamine-poly(aluminium phosphate) (Safire^®200), its zinc and magnesium analogues namely Safire^®400 and Safire^®600 respectively were used as flame retardants for glass fiber reinforced polyamide 66 in combination with aluminium phosphinate. Characterisation, thermal stability, combustion properties, glow-wire flammability index and glow-wire ignition temperature and cone calorimetry results are reported. Lower threshold of loading of flame retardants that pass V0 rating in UL-94 vertical burning test have been determined. Effect of Zinc borate (Firebrake^®500 grade) in these formulations was investigated. Influence of additives on endothermic and exothermic transitions of polyamide 66 in these formulations were studied by differential scanning calorimetry. The formulations were evaluated against the properties and fire performances of classical commercial combination of aluminium phosphinate and melamine polyphosphate. All the new formulations down to 15% of additives loading achieve V0 rating according to UL-94 protocol. This synergistic combination of additives significantly reduces the peak of heat release rate (pHRR) and total heat release (THR) in formulations exhibiting various degrees of intumescence.     

Flame retardancy of polyamide 66 nanocomposites with thermally stable organoclay

A thermally stable imidazolium organoclay was synthesized to improve the flame retardancy performance of polyamide 66 (PA 66). To enhance flame retardancy of the PA 66/organoclay nanocomposite, the thermally stable organoclay was coated with monomethylol melamine (MMM) before melt‐compounding with PA 66. Transmission electron microscopy and X‐ray diffraction results confirmed the partial exfoliation of the organoclay in the PA 66 matrix. The use of the thermally stable organoclay did not affect the thermal stability of PA 66. The cone calorimeter results showed that the PA 66/orgnaoclay nanocomposite exhibited a greatly reduced heat release rate and a longer ignition time. However, the PA 66/organoclay binary nanocomposite had no rating in the UL‐94 vertical burning test because it did not extinguish until the entire polymer component was burnt. The PA 66 nanocomposite with 15 wt% of MMM‐coated organoclay performed better in the ignition resistance test than the PA 66/organoclay nanocomposite containing 15 wt% of melamine. Copyright © 2011 John Wiley & Sons, Ltd.     

Comparative study on the flammability of polyethylene modified with commercial fire retardants and a zinc aluminum oleate layered double hydroxide

Polyethylene (PE) was modified by the addition of a layered double hydroxide of zinc aluminum oleate (ZnAl) and/or commercial fire retardants. Commercial additives included: melamine polyphosphate (MPP), ammonium polyphosphate (APP), triphenol phosphate (TPP), resorcinol diphosphate (RDP), decabromophenyl oxide (DECA) and antimony oxide (AO). The thermal stability and the combustion behaviors of the new composite polymeric materials are evaluated in TGA experiments and cone calorimetry. At 20% total additive loading, APP and LDH enhance the thermal stability of the PE composites and favor char formation. ZnAl leads to the best reduction in the peak of heat release rate (PHRR), 72%, while the combinations of PE with other additives give reductions in the range 20-40%. The combination of DECA and AO effectively increases the time to ignition and time to PHRR while LDH lowers these two parameters. APP and MPP on the other hand, do not affect the time to ignition, but they effectively increase the time to PHRR relative to the pristine polymer.     

Acrylamide/2-acrylamido-2-methylpropane sulfonic acid and associated sodium salt superabsorbent copolymer nanocomposites with mica as fire retardants

Acrylamide (AM) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS-H⁺) or its sodium salt (AMPS-Na⁺) were copolymerised by free-radical crosslinking polymerization to obtain poly(AM-co-AMPS-H⁺) and poly(AM-co-AMPS-Na⁺) superabsorbent polymers (SAPs). A maximum water absorbency in deionised water of 1200 g g⁻¹ was achieved for poly(AM-co-AMPS-Na⁺) at a 85% mol of AMPS-Na⁺. The inclusion of mica at 5-30% (w w⁻¹) into the preparation of poly(AM-co-AMPS-Na⁺) SAP leads to an intercalated structure, as detected by XRD and TEM analyses. Poly(AM-co-AMPS-Na⁺)/30% (w w⁻¹) mica SAP nanocomposite showed a tap water absorbency of 593 g g⁻¹ with a better thermal stability, compared to the pure SAP. Cone calorimetric analyses revealed that the wood specimens coated with the prepared poly(AM-co-AMPS-Na⁺) SAP or its 30% (w w⁻¹) mica nanocomposite provided excellent protection in delaying the ignition time after exposure to an open flame when compared to that observed with the uncoated specimen. The maximum reduction in the peak heat release rate and the greatest extension of time at peak heat release rate were observed with the nanocomposite-coated surface, but the total heat release rate was increased. The delayed burning mechanism is brought by the intercalating structure of mica in the SAP nanocomposites, which provided a better shielding effect against external heat sources, and the capability of the SAP nanocomposite in holding a large amount of water.     

Synergistic fire retardancy of colemanite, a natural hydrated calcium borate, in high-impact polystyrene containing brominated epoxy and antimony oxide

This study explores for the first time the synergistic fire retardant action of natural hydrated calcium borate, namely the mineral colemanite, which partially replaces antimony oxide in brominated flame retardant high-impact polystyrene compounds. Various antimony oxide to hydrated calcium borate ratios were employed keeping the brominated flame retardant additive at a constant loading level. With partial colemanite substitution for antimony oxide, lower heat release rate, total heat evolved and fire growth index was obtained under forced flaming fire conditions. Synergism was also seen in limiting oxygen index along with maintained V-0 classification in UL-94 tests. Regarding fire behaviour and flammability ratings, a large antimony oxide to calcium borate ratio provided ultimate fire retardant performance whereas magnitudes of synergism in average heat release rate and total heat evolved tend to be higher towards a smaller ratio. Effective heats of combustion and structural/morphological characterization of fire residues ascribed the underlying mechanism demonstrated by hydrated calcium borate to the formation of a consolidated residue that co-operates with the dominant gas phase fire retardancy originating from bromine-antimony synergism. It is thus proposed that coupling is achieved between gas phase and condensed phase modes of action increasing the overall fire retardant effectiveness. Along with enhanced fire retardancy, thermal stability and mechanical properties were satisfactorily maintained with the use of hydrated calcium borate at a variety of loading levels in compounds.     

Preparation and characterisation of a novel fire retardant PET/α-zirconium phosphate nanocomposite

The preparation of a novel fire retardant nanocomposite of poly(ethylene terephthalate) (PET) using nanoscopic α-zirconium phosphate (α-ZrP), by in situ polymerisation was investigated. The novel fire retarded PET nanocomposite, PET-co-DDP/α-ZrP, was synthesized by the direct condensation of terephthalic acid, ethylene glycol, 9,10-dihydro-10[2,3-di(hydroxycarbonyl)propyl]-10-phosphaphenanthrene-10-oxide (DDP) and nano α-ZrP. The morphology, thermal stability and burning behaviour of the nanocomposite with 1 wt% α-ZrP loading was investigated. The extent of dispersion of the nanofillers was quantified by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Significant improvements in fire retardant performance were observed for the nanocomposite from limiting oxygen index (increased from 21.2 to 32.6), UL-94 (achieving V-0), and cone calorimetry (reducing both the heat release rate and the total heat released, without reducing the time to ignition).     

Structural and thermal interpretation of the synergy and interactions between the fire retardants magnesium hydroxide and zinc borate

The mechanism of cooperative action of commercial fire retardants is interpreted as resulting from specific chemical reaction and phase changes. This investigation focuses on the thermally initiated interactions between two forms of commercially available fire retardant compounds. The fire performance of a polyolefin with a metal hydroxide fire retardant, magnesium hydroxide, can significantly reduce the heat release rate through absorption of heat during conversion to its metal oxide. Formation of water, followed by vaporisation, decreases heat and dilutes volatiles from polymer degradation. The second form of fire retardant compounds are zinc borates (2ZnO·3B₂O₃·3H₂O and 4ZnO·B₂O₃·H₂O), that undergo dehydration with increasing temperature. Differential thermal analysis and wide-angle X-ray spectroscopy indicated that various structural changes occurred during heating. Endothermic transitions were observed for all components, while zinc borate (2ZnO·3B₂O₃·3H₂O) showed an exothermic crystallisation transition at relatively high temperature. The exotherm was modified by the development of a new crystalline phase, magnesium orthoborate (3MgO·B₂O₃) that formed on reaction with magnesium oxide (MgO) at temperatures greater than 500 °C. Formation of crystalline zinc oxide (ZnO) was also detected. From zinc borate (4ZnO·B₂O₃·H₂O), ZnO was primarily formed. No new crystalline phases were observed in the presence of MgO over the temperature range investigated.     

MPP/PER/APP系统阻燃的PA6/OMMT纳米复合材料的燃烧特性

以聚磷酸蜜胺(MPP)／季戊四醇(PER)／聚磷酸铵(APP)三元膨胀型阻燃剂(IFR)(其中P／PER／三聚氰胺(MA)的摩尔比为4．1／1．0／1．1)对聚酰胺6(PA6)／有机蒙脱土(OMMT)纳米复合材料(wOMMT=0．03)进行阻燃，测定了阻燃PA6／OMMT的极限氧指数(LOI)及垂直燃烧阻燃性(UL94)，以锥形量热仪(CONE)测定了材料诸多与火灾安全性有关的阻燃参数，包括释热速率、有效燃烧热、总释热量、质量损失速率、比消光面积及引燃时间等，并与PA6、阻燃PA6及PA6／OMMT进行了比较，用扫描电镜(SEM)观察了由CONE测试所得残炭的形态。     

Synergistic effects of organo‐sepiolite and zinc borate on the fire retardancy of polypropylene

Polypropylene (PP)/sepiolite/zinc borate (BZn) composites were prepared by melt extrusion after pre‐modification of sepiolite with cetyltrimethylammonium bromide. The synergistic effects of organo‐sepiolite (OSEP) and BZn on the fire retardancy of PP were studied. X‐ray diffraction and transmission electron microscopy were used to characterize the morphology of the composite. Thermogravimetric analysis, cone calorimetric analysis, limiting oxygen index, and the UL‐94 protocol (Demaisheng technology Co. Ltd.,Shenzhen,China) were used to assess the thermal stability and fire retardancy of the composites. The fire retardancy of PP was greatly improved by introducing OSEP and BZn. The reduction in peak heat release rate for PP/BZn composites at 10% BZn loading is 62% compared with pristine PP, but increased to 78% for PP/10%BZn/10%OSEP composite. Other fire retardant parameters were also improved. The fire performance index of PP/10%BZn/10%OSEP composite was 0.045 sm²/kW compared with 0.014 sm²/kW of pristine PP. The average mass loss rate was 12.1 g/sec/m² for the composite with both additives compared with 30.1 g/sec/m² for pristine PP; the smoke production rate decreased by 37% from 0.117 m²/s of pristine PP to 0.074 m²/s of PP/OSEP/BZn. The char residue of composite increased from 0.6% in pristine PP to 12.19% in the composite. The limiting oxygen index increased from 17.1 in pristine PP to 20.8 in the composite: all the samples could obtain a UL‐94 horizontal burn rating. Copyright © 2013 John Wiley & Sons, Ltd.     

Comparative study of boron compounds and aluminum trihydroxide as flame retardant additives in epoxy resin

The aim of this study was to investigate and compare the flame retardant properties of boron compounds with respect to aluminum trihydroxide (ATH) in an epoxy system based on bisphenol A epichlorohydrin‐based epoxy resin and cycloaliphatic polyamine‐based hardener. Six different boron compounds including colemanite (C), ulexite (U), boric acid (BA), boric oxide (BO), melamine borate (MB) and guanidinium nonaborate (GB) were used as flame retardant additive. The flame retardant properties of epoxy‐based composites were investigated using limiting oxygen index (LOI), UL 94 standards both in vertical and horizontal position, thermogravimetric analysis, cone calorimeter and scanning electron microscopy. According to flammability test results, boron compounds except for C and U showed better performance than ATH. According to the LOI results, 40% BA containing sample had the highest LOI value of 28.5, while 30% MB, 35% GB and 40% BA containing samples had the highest UL 94V rating (V0). According to the cone calorimeter test results, all boron containing samples had better fire performances than ATH containing sample; 40 wt% BO containing sample showed the lowest peak heat release rate, average heat release rate and total heat release values. Copyright © 2014 John Wiley & Sons, Ltd.     

Melamine,silica, and ionic liquid as a novel flame retardant for rigid polyurethane foams with enhanced flame retardancy and mechanical properties

Rigid polyurethane (PU) foams were successfully filled with different weight ratios of melamine (1 wt%, 5 wt%, 10 wt%), silica (0.1 wt%) and ionic liquid, 1-Ethyl-3-methylimidazolium chloride, [EMIM]Cl (0.3 wt%). The aim of this study was to improve the flame retardancy of PU foams and to develop the synergistic effect between melamine, silica and ionic liquid on the flame-retardant PU foams. The influence of different loadings of the fillers was examined. The results showed that in comparison with unfilled foam, all modified compositions are characterized by higher density (41–46 kg m⁻³), greater compression strength (134–148 kPa), and comparable thermal conductivity (0.023–0.026 W m⁻¹ K⁻¹). Moreover, the reaction to fire of the PU composites has been investigated by the cone calorimeter test. The results showed that the fire resistance of PU foams containing as little as 1 wt% of melamine is significantly improved. For example, the results from the cone calorimeter test showed that the incorporation of the melamine, silica and ionic liquid significantly reduced the peak of heat release rate (pHRR) by ca. 84% compared with that of unmodified PU foam. SEM results showed that incorporated fillers can form an intumescent char layer during combustion which improves the reaction to fire of the composite foams.     

Characterization of ignition and combustion characteristics of phenolic fiber-reinforced plastic with different thicknesses

The present study focuses on ignition and combustion characteristics of phenolic fiber-reinforced plastic (FRP) with different thicknesses under different external heat fluxes using cone calorimeter, which receives little attention to date. A series of parameters including ignition time, thermal thickness, mass loss factor, mass loss rate (MLR), heat release rate (HRR), total heat release (THR), fire performance index (FPI) and fire growth index (FGI) are measured or calculated. Results indicate that the ignition time increases with the thickness, but decreases with the external heat flux. Phenolic FRP with thickness of 3 mm may be considered as thermally thin material. However, phenolic FRP with thickness of 5 and 8 mm is prone to be thermally thick material. The critical heat flux, minimum heat flux and ignition temperature are deduced and validated. The thermal thickness increases with the external heat flux. Linear correlations of the thermal thickness with the ratio of specimen density and external heat flux are demonstrated and presented. The mass loss factor decreases with the thickness. Three and two peak MLRs occur in the cases of low and high external heat fluxes, respectively. The average MLR increases with the external heat flux and thickness. The average and maximum HRR increases with the external heat flux. The FGI for the maximum HRR increases with the external heat flux. Linear correlations of the average MLR, the average and maximum HRR and the FGI for the maximum HRR with the external heat flux are demonstrated and presented.

     

Study of the fire resistant behavior of unfilled and carbon nanofibers reinforced polybenzimidazole coating for structural applications

With increasing interest in epoxy‐based carbon fiber composites for structural applications, it is important to improve the fire resistant properties of these materials. The fire resistant performance of these materials can be improved either by using high performance epoxy resin for manufacturing carbon fiber composite or by protecting the previously used epoxy‐based composite with some fire resistant coating. In this context, work is carried out to evaluate the fire resistance performance of recently emerged high performance polybenzimidazole (PBI) when used as a coating material. Furthermore, the effect of carbon nanofibers (CNFs) on fire resistant properties of inherently flame retardant PBI coating was studied. Thermogravimetric analysis of carbon/epoxy composite, unfilled PBI and nano‐filled PBI shows that the carbon/epoxy composite maintained its thermal stability up to a temperature of 400°C and afterwards showed a large decrease in mass, while both unfilled PBI and nano‐filled PBI have shown thermal stability up to a temperature of 575°C corresponding to only 11% weight loss. Cone calorimeter test results show that unfilled PBI coating did not improve the fire retardant performance of carbon/epoxy composite. Conversely, nano‐filled PBI coating has shown a significant improvement in fire retardant performance of the carbon/epoxy composite in terms of increased ignition time, reduced average and peak heat release rate and reduced smoke and carbon monoxide emission. These results indicate that addition of carbon nanofibers to inherently flame retardant coating can significantly be helpful for improving the fire resistance performance of composite materials even with low coating thickness. Copyright © 2013 John Wiley & Sons, Ltd.     

Durability of Flame-Retarded,Co-Extruded Profiles Based on High-Density Polyethylene and Wheat Straw Residues

At present, little information is available in the scientific literature related to the durability (weathering resistance) of fire-retarded wood and natural fiber-reinforced thermoplastics. In this work, thermoplastic profiles for façade applications based on high-density polyethylene, wheat straw particles, and fire-retardants were extruded and their reaction-to-fire performance before and after artificial weathering evaluated. Profile geometries were either solid or hollow-core profiles, and fire-retardants (FR) were added either in the co-extruded layer or in the bulk. Various FR for inclusion in the co-extruded layer were screened based on UL-94 tests. For profile extrusion, two types of FR were chosen: a coated intumescent combination based on ammonium polyphosphate (APP) and an APP coated with melamine and without formaldehyde. Before weathering, the peak heat release rate (pHRR) and the total heat release (THR), which were determined using cone calorimeter measurements, were reduced by up to 64% and 67% due to the FR. However, even before weathering, pHRR of the profiles was relatively high, with best (lowest) values between 230 and 250 kW/m² under the test conditions. After 28 days of artificial weathering, changes in reaction-to-fire performance and color were evaluated. Use of the APP in the co-extruded layer worsened color change compared to the formulation without APP but the pHRR was not significantly changed. The influence of weathering on the fire behavior was small compared to the difference between fire-retarded and non-fire-retarded materials. Results from the cone calorimeter were analyzed with regard to ETAG 028, which provides requirements related to the durability of fire performance of building products. In many formulations, increase in THR was less than 20% compared to before weathering, which would place some of the profiles in class C or better (EN 13501-1). However, due to the high pHRR, at best, class D was obtained under the conditions of this study. In addition to cone calorimeter measurements, results from the single flame source test, limiting oxygen index determination and thermogravimetric analysis, are shown and discussed. Strength properties, water uptake and swelling of the profiles, thermal conductivity, and energy dispersive X-ray data are also presented.     

Evaluate the flammability of a PU foam with double-scale analysis

Two-scale tests, microscale and bench scale, are conducted to analyze the flammability of a flexible polyurethane foam. Microscale tests include simultaneous thermal analysis coupled to Fourier transform infrared spectroscopy, and microscale combustion calorimeter (MCC). Evolved gas components, heat release rate per unit mass, total heat release, derived heat release capacity, and minimum ignition temperature are obtained. Bench scale tests are performed on cone calorimeter. Peak heat release rate per unit area, effective heat of combustion, minimum incident heat flux for ignition, and total heat release per unit area of different incident heat fluxes are obtained. FO-category of the PU foam is estimated by multiple discriminant function analysis based on the results of cone calorimeter test. The relationship between the two-scale tests is analyzed. The minimum ignition temperatures derived from multi heating rate MCC tests are used to predict the time to ignition and compared with the results from cone calorimeter tests. This PU foam is evaluated as a high fire hazard polymer having low heat release capacity, low ignition temperature, and short ignition time.

     

Layered double hydroxides intercalated with borate anions: Fire and thermal properties in ethylene vinyl acetate copolymer

Fire and thermal properties of ethylene vinyl acetate (EVA) composites prepared by melt blending with layered double hydroxides (LDH) have been studied. Two types of LDHs intercalated with borate anion were prepared using the coprecipitation method and the metals Mg²⁺, Zn²⁺ and Al³⁺. Characterization of the LDHs and the EVA composites was performed using X-ray diffraction, thermogravimetric analysis, and cone calorimetry. Thermal analyses show that the addition of LDHs improves the thermal stability of EVA. Fire properties evaluated using the cone calorimeter were significantly improved in the EVA/LDH composites. The peak heat release rate was reduced by about 40% when only 3% by weight of the LDH was added to the copolymer. Comparison of the fire properties of the LDHs with those of aluminum trihydrate (ATH), magnesium hydroxides (MDH), zinc hydroxide (ZH) and their combinations at 40% loading, reveal that the LDHs were more effective than when MDH and ZH are used alone.     

Thermal stability and flammability of silicone polymer composites

Silicone polymer composites filled with mica, glass frit, ferric oxide and/or a combination of these were developed as part of a ceramifiable polymer range for electrical power cables and other high temperature applications. This paper reports on the thermal stability of polymer composites as determined by thermogravimetric techniques, thermal conductivity and heat release rate as measured by cone calorimetry. The effects of fillers on thermal stability and flammability of silicone polymer are investigated. Of the fillers studied, mica and ferric oxide were found to have a stabilising effect on the thermal stability of silicone polymer. Additionally, mica and ferric oxide were found to lower heat release rates during combustion, but only mica was found to increase time to ignition.     

A model for the prediction of the thermal degradation and ignition of wood under constant and variable heat flux

The ignition of combustible materials is an important aspect of the processes taking place in an unwanted fire. In this work, an experimental and theoretical study of the ignition process of wood has been carried out. Experiments of both spontaneous and piloted ignition have been performed. Constant and decreasing variable heat fluxes have been tested. A mathematical model has been used to predict the time to ignition of wood for the different operating conditions used. The solution of the model provides the temperature at each point of the solid, the local solid conversion and the time to ignition of the material. In general, a good agreement between experimental and theoretical results is obtained.     

Experimental study of woods under external heat flux by autoignition

Piloted ignition of woods has been commonly investigated, which is accelerated by a spark plug. Autoignition is a complex phenomenon that combustible materials are ignited by internal heating, without the spark plug. Compared with piloted ignition, process of autoignition is closer to the development of real fire. Very few studies have focused on the prediction of ignition time and average mass loss rate by autoignition. Therefore, ignition time and mass loss rate on six species of commonly used wood samples, namely pine, beech, cherry, oak, maple, and ash, were studied under external heat flux by autoignition in a cone calorimeter. Three mass loss stages of woods under external heat flux was observed. Empirical models of ignition time and average mass loss rate for woods under external heat flux were developed. These empirical models can be used not only for fire risk evaluation, but also for modeling input and validation.