Phosphate urethane block copolymers were made with these phosphorylated oligomers, diisocyanate and a diol as chain extender. Gel permeation chromatography GPC was performed on both the oligomeric materials and on block copolymers. Differential scanning calorimetry DSC shows a glass transition above room temperature and two melting temperatures for hard and soft blocks of these block copolymers. Thermo-gravimetric analysis results show these phosphorylated block copolymers have a tendency to form char when they were heated in nitrogen and air.
Electron scanning microscopy ESM and electron dispersive x-ray spectroscopy EDX do not support the segregation of phosphorus onto the surface as is found with silicone block copolymers in polyurethanes. Oxygen indices of these materials were measured. The results show that even with a low level of phosphorus in the building blocks of the copolymers, some of these block copolymers were resistant to ignition and some had higher OI values compared to control and reference materials.
Based on f1ammability testing OI results these block copolymers were categorized as a ignition resistant, b higher Oxygen Index materials, and c comparable to non-phosphorylated controls. These materials showed less flame retardancy compared to siliconated polyurethane block copolymers previously reported.
Synergistic flame retardant mixtures were successfully tested as halogen-free flame retardants in two prepreg epoxies relevant in printed wired boards PWB. Reactive organophosphorus compounds were incorporated into these resins together with low-priced inorganic substances to give efficient flame-retardant systems. Melamine polyphosphate MPP amplifies the activity of organophosphorus flame retardants, too. Additionally, novel salt-like additives were found to be efficient fire-retardants in the epoxy resins examined. Their flame-retardant efficiencies could be further enhanced by combination with boehmite or MPP.
Using these synergistic mixtures allows the maintainence of the glass transition temperature Tg of the cured samples and to reduce the loading of phosphorus compounds. Such synergistic mixtures surpass the flame retardant efficiency of TBBA.
Flame Retardant Composites
An experimental setup has been constructed to record the real-time melt-dripping behavior in a furnace. All experiments were repeated in a UL set-up to replicate their melt dripping behavior in flaming conditions. The physical and chemical changes occurring during melt dripping have also been studied by conducting thermal analysis and rheology experiments on molten drops and comparing them with those of respective original polymer samples. The results have shown that during melt dripping a polymer degrades to a considerable extent and its viscosity is affected by the action of the flame retardant at that particular temperature range.
Single step and multi-step adsorption processes have been investigated in order to enhance flame retardancy of poly ethylene terephthalate fabrics and their blends with cotton. The first strategy concerns single step nanoparticle adsorption in a finishing-like process upon plasma surface activation.
This approach aims at evaluating the effectiveness of nanoparticle simple adsorption on fabric combustion properties and the enhancement promoted by the plasma surface activation performed at different processing conditions. Subsequently, the layer by layer assembly technique has been investigated as an evolution of the nanoparticle adsorption. This technique, which consists in a multi-step adsorption process, allows the build-up of coatings made of different kinds of nanoparticles and polymers, each one bearing a specific functionality.
By using the multi-step approach, hybrid organic-inorganic or completely inorganic coatings have been deposited on selected fabrics and subjected to flammability and combustion tests. Incorporation of nanoparticles into a polymer can result in enhancement of electrical, thermal and mechanical properties, particularly at high temperatures where the polymer alone might exhibit softening or degradation.
The nanocomposite softening temperature may or may not coincide with the temperature at which the nanoparticle enhances char formation. Different compositions of TPU nanocomposites were prepared on a commercial scale twin-screw extruder using a montmorillonite organo-clay, carbon nanofibers and multiwall carbon nanotubes MWNT. The onset of softening was found to increase with nanoparticle loading tested at 1 Hz.
A gap in reinforcement was noted at certain temperatures as the samples developed char. A correlation can be drawn between crossover of dissipative versus elastic behavior dominance of loss modulus versus storage modulus and dripping in UL 94 tests. Pyrolysis-combustion flow calorimeter is becoming a common and useful tool to study the flammability of materials at a very small scale several milligrams of sample.
Most generally, it is used according to the method A described in the ASTM D standard anaerobic pyrolysis and complete combustion since it is possible to monitor the conditions of pyrolysis and combustion to a large extent. Moreover, combining PCFC with thermogravimetric analysis allows a better understanding of the thermal degradation of materials.
Even if there is no general correlation between PCFC and cone calorimeter or other flammability tests results, it has also been shown that the comparison of the results from both tests could help to identify the modes-of-action of flame retardants. This chapter reviews the multiple uses of PCFC and points out some issues or developments about this tool.
X-ray diffraction, transmission electron microscopy were used to characterize the morpohlogy of composites. Thermal stability and flame retardancy of the composites were evaluated by thermogravimetric analysis TGA , cone calorimetric analysis, limiting oxygen index LOI and the UL94 protocol. The limiting oxygen index of composite increased by 3, from Carbonate LDH, with a Mg:Al molar ratio of , was synthesized by the urea hydrolysis method and external basal surfaces were selectively modified using a siderophilic ligand 3,4-dihydroxybenzo-phenone.
The efficiency of this surface modification was investigated by studying the sedimentation kinetics in an organic solvent.
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Cone calorimeter measurements showed little influence of specific surface areas but a pronounced influence of aspect ratio on flame retardancy. Interestingly, at this loading an unusual increase of tign could be observed. The improved material properties are also mainly influenced by morphology of the blends. In addition, a novel approach to increase not only compatibility but also flame retardancy of the biodegradable polymer blends is reviewed.
In this method, an aryl phosphate flame retardant, resorcinol di phenyl phosphate RDP , is adsorbed onto the added particles. This is shown to have the following advantages; a it can act as a surfactant on either starch or clays, leading to better dispersion in the polymer matrices, b enhance compatibilization of PLA and ECOFLEX by localizing the particles at the blend interfaces, and c segregated to the blend surface when heated, and reacted with both polymer and starch.
The reactive properties allowed the formation of a shell like layer whose modulus was much higher than the interior polymer, and which dissipated the heat of the approaching front. Analysis of the chars formed after combustion in a cone calorimeter, indicated that addition of the RDP soaked clays did not affect the ductility of the chars or their ability to encase the combustion products which sustained internal pressures from the decomposition gases allowing the release at a steady rate.
To speed up the development of new flame-retardant chemistries for polyurethane foam, there is a strong need for small-scale flammability tests, especially those which work at the milligram scale. In this paper we discuss current results using the only standard milligram heat release test Pyrolysis combustion flow calorimetry — ASTM D to study how some commercial flame retardants work in flexible polyurethane.
Flexible polyurethane foams formulated to pass small flame ignition regulatory tests showed only small reductions in measured heat release when compared to non-flame retardant foams. This suggests that reductions in heat release are not the primary mechanism by which these additives pass these regulatory tests FMVSS , TB and additional testing in combination with ASTM D may be needed to understand performance and further develop this technique for future flame retardant polyurethane chemistries.
Flexible polyurethane foams with different cell morphology cell size and fraction of open cells were prepared. The effect of foam morphology on smoldering was assessed. Cell-size, in combination with air permeability, appeared to be a good indicator for smoldering propensity in the range of formulations investigated here. Fiber-reinforced polymers FRP have been used widely in building, construction and mass transit applications in many parts of the world.
Although some efforts towards the harmonization of fire performance standards are taking place like EN in the European train industry most countries continue to have their own requirements to qualify materials for specific applications. As the economy becomes more global, it would be helpful for composite fabricators and end users to predict how materials perform in the different tests.
A study was undertaken to test 10 different materials from the United States and Europe to see how they perform in a range of North American and European fire performance tests. The results will be discussed. The most important code requirements on reaction-to-fire safety for building products involve interior finish testing.
In terms of interior wall and ceiling interior finish, traditionally this testing was conducted in the U. In recent years there has been abundant work designed to revise and improve the ASTM E84 standard, because it did not describe how materials or products need to be mounted for testing in enough detail. Thus misleading tests are often conducted, and some corresponding materials or products are being approved without the proper associated fire safety. In order to improve the fire safety of materials or products tested in the Steiner tunnel for interior finish applications, two strategies are being employed: a modification of the wording in the standard and b issuance of standard practices for specimen preparation and mounting of specific materials and products, which are then referenced in the base standard.
Key changes to the ASTM E84 test address details of specimen width and thickness, incorporation of requirements to use the standard practices and special clarifications. However, increasingly regulatory and research testing is conducted to assess heat and smoke release rate with room-corner tests and now the de-facto default test for interior wall and ceiling finish is the NFPA room-corner test.
In both Steiner tunnel testing and room-corner testing, significant differences in fire test results can be obtained by variations in specimen preparation techniques and mounting methods. This work will present an update and indicate areas where additional work is still needed.
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A global shift in chemical regulations and regulatory programs has been actively underway over the past two decades. It impacts many different materials, including flame retardants. Emerging chemical regulations are focusing on characterizing the environmental and human health impacts of all substances.
Industry is responding to market driven and regulatory challenges to ensure that flame retardants are safe, effective, sustainable, and meet evolving marketplace demands. A crucial aspect of sustainability is to understand the life-cycle implications of chemicals and even polymer formulations.
Life-Cycle Assessments can determine if the substitution of one flame retardant or technology for another can result in unforeseen consequences that can impact society or the ecosystem. Programs are in place to drive all members of the supply chain to reduce or eliminate chemical emissions to the environment, understand human health and environmental characteristics, and make transitions to more environmentally preferred products that are sustainable.
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Flame retardant - Wikipedia
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