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High loadings of carbon black (CB) are usually used to achieve the properties demanded of rubber compounds. In recent years, distinct nanoparticles have been investigated to replace CB in whole or in part, in order to reduce the necessary filler content or to improve performance. Multilayer graphene (MLG) is a nanoparticle made of just 10 graphene sheets and has recently become commercially available for mass-product nanocomposites. Three phr (part for hundred rubbers) of MLG are added to chlorine isobutyl isoprene rubber (CIIR)/CB composites in order to replace part of the CB. The incorporation of just 3 phr MLG triples the Young’s modulus of CIIR; the same effect is obtained with 20 phr CB. The simultaneous presence of three MLG and CB also delivers remarkable properties, e.g. adding three MLG and 20 phr CB increased the hardness as much as adding 40 phr CB. A comprehensive study is presented, showing the influence on a variety of mechanical properties. The potential of the MLG/CB combination is illustrated to reduce the filler content or to boost performance, respectively. Apart from the remarkable mechanical properties, the CIIR/CB/MLG nanocomposites showed an increase in weathering resistance.
The fire behaviour of light-weight material used in structural applications is regarded as the main challenge to be solved for mass transportation. The task is to perform realistic experiments, including a mechanical test scenario under fully developed fires, to improve the material's reliability in structural applications. Our approach utilises an intermediate-scale test set-up (specimen size 500 × 500 mm) to apply realistic compressive loads and fully developed fires directly to one side of a carbon-fibre-reinforced sandwich composite. Three different intumescent coatings were applied to sandwich structures and compared to a bench-scale study. The results emphasise intumescent coatings as a promising method to sustain fire resistance, multiplying the time to failure. Nevertheless, the realistic intermediate-scale test using severe direct flame application underlines the extremely short failure times when the actual composite components are tested without any additional insulation.
Elastomers are usually reinforced and employed in different applications. Various different nanoparticles, including layered silicates, carbon nanotubes, and expanded graphite, are currently being used as nanofiller. Multilayer Graphene (MLG) is proposed as promising nanofiller to improve the functional properties of Chlorine-Isobutylene-Isoprene Rubber (CIIR), Nitrile-Butadiene Rubber (NBR), Natural Rubber (NR) and Styrene–Butadiene Rubber (SBR) at low concentrations. MLG is constituted by only approximately 10 graphene sheets. Nanocomposites with extremely low MLG content (3 phr) showed evident improvement in rheological, mechanical and curing properties. The Young's modulus of the nanocomposites increased more than twice in comparison with the unfilled rubbers. MLG also improved the weathering resistance of the different rubbers. The nanocomposites conserved their initial mechanical properties against weathering exposure.
The presentation gives an overview of actual research adtivities in the field of flame retardant polymers. Details are selected illuminating the scientific topic beyond the state of the art. Different concepts are illustrated with own results obtained in different Research projects over the last 15 years.
Hydroliquefaction is a possible pathway to produce liquid transportation fuels from solid feedstocks like coal or biomass. Though much effort has been put into the investigation of maximizing the oil yield using expensive catalysts and pasting oils in batch setups, little is known about how to commercialize the process. This work aims at the demonstration of lignin hydroliquefaction under conditions interesting for commercial operation. The results from hydroliquefaction experiments of two different lignin types using a cheap iron-based catalyst and anthracene oil as the pasting oil in a semibatch system are presented here. Oil yields of above 50% are reached without observing coke formation. Extensive analyses of the feedstocks and product oils were performed. The process supplies high-quality oil, while differences in the decomposition path of both lignin types are observed. An high heating value of 39 400 J/g and H/C and O/C ratios of up to 1.6 and 0.1, respectively, are detected for the produced bio-oils.
Das Brandverhalten stellt wie das ausgezeichnete elektrische Isolationsverhalten, die geringen elektrischen Verluste, die Verarbeitbarkeit und Formbarkeit eine der wesentlichen Schlüsseleigenschaften im Eigenschaftsprofil von Polymerwerkstoffen in der Elektronik und der Elektrotechnik dar. Dabei bedarf es einer Ausrüstung der Polymerwerkstoffe mit Flammschutzmittel. Die Entwicklung von immer effizienteren, synergistischen und multifunktionalen Multikomponentensystemen ist dabei eine herausragende Quelle für Innovation. Die Entwicklung und Verbesserung der werkstoff- und anwendungsspezifischen Flammschutzlösungen bestimmen die aktuellen und zukünftigen Polymermaterialien in der Elektronik und Elektrotechnik mit. Der Vortrag stellt anhand von Beispielen einige der erfolgreichen Konzepte dar. Es wird versucht, über das wissenschaftlich-systematische Verständnis Grundprinzipien und vielversprechende Lösungsstrategien zu verdeutlichen.
Ethylene propylene diene monomer (EPDM) Rubbers with the flame retardants tris(2-ethylhexyl)phosphate, ammonium polyphosphate, polyaniline, and aluminum trihydroxide were prepared and analyzed in this study. The homogenous dispersion of the fillers in the rubber matrix was confirmed by scanning electron microscope. To investigate the interplay of the different flame retardants, the flame retardants were varied systematically. The comprehensive study sought combinations of flame retardants that allow high loadings of flame retardants without deterioration of the physical and mechanical properties of the EPDM rubber. The eight EPDM rubbers were investigated via thermogravimetric analysis and pyrolysis gas chromatography coupled with a mass spectrometer (Py GC/MS) to investigate the potential synergistic effects. In the Py-GC/MS experiments, 27 pyrolysis products were identified. Furthermore, UL 94, limiting oxygen index, FMVSS 302, glow wire tests, and cone calorimeter tests were carried out. In the cone calorimeter test the EPDM rubbers R-1AP and R-1/2P achieved an increase in residue at flameout of 76% and a reduction in total heat evolved of about 35%. Furthermore, the compounds R-1AP and R-1/2P achieved a reduction in MARHE to about 150 kW m−1, a reduction of over 50% compared to the unprotected rubber R.
Polyurethanes (PU) represent one of the most versatile classes of plastics. They are processed and used as thermoplastic, elastomer, and thermoset. The requirements regarding flammability are correspondingly versatile. Depending on the material and the field of application, specific fire tests have to be fulfilled. This paper describes the different concepts used to fulfil these requirements by choosing the right raw materials and flame retardants.
Natural keratin fibres derived from Mexican tannery waste and coconut fibres from coconut processing waste were used as fillers in commercially available, biodegradable thermoplastic starch-polyester blend to obtain sustainable biocomposites. The morphology, rheological and mechanical properties as well as pyrolysis, flammability and forced flaming combustion behaviour of those biocomposites were investigated. In order to open up new application areas for these Kinds of biocomposites, ammonium polyphosphate (APP) was added as a flame retardant. Extensive flammability and cone calorimeter studies revealed a good flame retardance effect with natural fibres alone and improved effectiveness with the addition of APP. In fact, it was shown that replacing 20 of 30 wt. % of APP with keratin fibres achieved the same effectiveness. In the case of coconut fibres, a synergistic effect led to an even lower heat release rate and total heat evolved due to reinforced char residue. This was confirmed via scanning electron microscopy of the char structure. All in all, these results constitute a good approach towards sustainable and biodegradable fibre reinforced biocomposites with improved flame retardant properties.
Wood products are often treated by different techniques to improve their longevity when used as building materials. Most of the time, the goal is to increase their resistance to weathering effects, deformations in material dimensions or biotic decomposition. These wood treatment techniques have a significant impact on pyrolysis and burning behavior. The general effects of three different common wood treatments on flame retardancy were investigated by comparing treated woods with their untreated counterparts and with other kinds of wood. While the acetylation of beech leads to a slightly increased fire hazard, the thermal treatment of wood and crosslinking of cellulose microfibrils dimethyloldihydroxy-ethyleneurea show a limited flame retarding effect. Switching to woods with a higher lignin content, and thus higher char yield, however, results in a more pronounced improvement in flame retardancy performance. This article delivers a comprehensive and balanced assessment of the general impact of different wood modifications on the fire behavior. Further, it is a valuable benchmark for assessing the flame retardancy effect of other wood modifications.
In this work, a series of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivative salts containing phosphorus and nitrogen were synthesized, and their effects on mechanical properties, thermal stability and flame retardancy of flexible polyurethane foam (FPUF) were investigated. Studies have shown that the addition of DOPO derivatives will increase the tensile strength, compression set, and compression hardness of FPUF, but it will lead to a decrease in elongation at break. Thermogravimetric analysis showed that the initial decomposition temperature of FPUF containing DOPO derivatives was reduecd, but the char reside was significantly improved. A series of combustion tests indicated that the addition of DOPO derivative salts can improve the flame retardancy of FPUF, of which 10-hydroxy-9,10-dihydro-9-oxa-10 phosphaphenanthrene-10-oxide dicyandiamide salt (D-DICY) exhibited the best flame retardancy. When the load of D-DICY was 20 phr, the limiting oxygen index (LOI) of foam reached 24.5%, and the peak heat release rate and total heat release were decreased by 55.7% and 52.9%, respectively. Furthermore, based on the analysis of the gas phase combustion products and the char residue of the condensed phase, the possible flame retardant mechanism was proposed.
Polyurethane (PU) bilden eine der vielseitigsten Klassen der Polymerwerkstoffe. Kein anderer Kunststoff wird sowohl als Thermoplast, als Elastomer wie auch als Duroplast verarbeitet und eingesetzt. Entsprechend vielfältig sind auch die Anforderungen an den Flammschutz. Je nach Material und Anwendung müssen spezifische Brandnormen erfüllt werden. Der vorliegende Aufsatz gibt einen Überblick über die verfügbaren Ansätze, um durch geeignete Auswahl der Rohstoffe und der Flammschutzmittel diese verschiedensten Anforderungen an das Brandverhalten zu erfüllen.
Flame-retarded biocomposites of thermoplastic starch and natural fibres are successfully processed according to state-of-the-art extrusion and injection moulding. Using agave fibres and henequen fibres recovered from local industrial waste is a convincing contribution to sustainability. A systematically varied set of biocomposites is investigated comprehensively, e.g. electron microscopy is used for characterizing the morphology, rheology for the melt viscosity, tensile and impact resistance for the mechanical properties, thermal analysis for the pyrolysis, UL 94 burning chamber and oxygen index for the flammability, and cone calorimeter for the fire behaviour. Achieving sufficient mechanical properties was not the goal in our pre-competitive study but may be tackled by adding compatibilizer in future. The combination of well-dispersed natural fibres, aluminium diethylphosphinate (AlPi) and a special silicone synergist (Si) is proposed as promising innovative route for V-classified biocomposites. The flame-retardancy modes of action in the gas phase (fuel dilution and flame inhibition) and in the condensed phase (charring, protective layer formation) are discussed in detail, as is the role of combining the ingredients. This work is a convincing proof of principle of how to prepare industrial-waste fibres biocomposites, to apply the synergistic combination of AlPi and Si for future flame-retarded technical polymer materials that are based on renewable resources and compostable.
Whereas the degradation of flame retardant polymers has been discussed since decades, only more recently, the lifetime of the flame retardancy itself becomes an important factor, e.g. for cables used as building products. In this work, several kinds of accelerated artificial ageing tests are performed simulating different environmental exposures and thus highlighting different degradation mechanisms: artificial accelerated weathering, climatic chamber, water immersion, salt spray chamber, and autoclave test. The durability is expected to be different for different flame-retardant materials. Thus, various sets of halogen-free fire-retarded polymers were investigated: ethylene vinyl acetate (EVA) with aluminum hydroxide (ATH), boehmite and synergists, ester-based and ether-based thermoplastic polyurethane (TPU) with melamine cyanurate (MC), aluminum diethylphosphinate (AlPi), and boehmite, and glass fiber reinforced polyamide 66 (PA66) with AlPi-based mixtures.
Intensive degradation of the surface was observed, e.g. yielding discoloration and yellowing, EVA showed cracking when weathered. Changes in chemical structure was investigated by ATR-FTIR. The flammability was investigated with the cone calorimeter, UL-94 classification, and oxygen index (LOI). The flame retardancy of most of the materials studied degraded only slightly for the investigated exposure times. EVA/ATH achieved an improved LOI due to flame retardants agglomeration at the surface. Sets of materials, based on EVA and TPU, were also investigated as cable jackets. While flame retarded EVA exhibited no dripping during burning, TPU flame-retarded with MC cables showed pronounced melt-dripping. Cone calorimeter tests were carried out using cable rafts as well as our self-made cable module test, simulating a vertical bundle of cables at the bench scale. The comparison of different fire tests, different exposure conditions, and different materials carved out the specific degradation phenomena with respect to each of these parameters.
Most of this work was supported by the IGF Project (18926 N) of the Fördergemeinschaft für das Süddeutsche Kunststoff-Zentrum e.V., supported by the AiF within the framework of the program “Förderung der Industriellen Gemeinschaftsforschung (IGF)” of the German Federal Ministry for Economic Affairs and Energy based on a decision of the Deutschen Bundestag.
We successfully synthesized multifunctional P-based hyperbranched polymeric flame retardants (hb-FRs) with varying oxygen-to-nitrogen (O : N) content and characterized them via 1H and 31P NMR and GPC. Their miscibility in epoxy resins (EP) and impact on glass-transition temperatures (Tg) were determined via differential scanning calorimetry (DSC). Using thermogravimetric and evolved gas Analysis (TGA, TG-FTIR), pyrolysis gas chromatography/mass spectrometry (Py-GC-MS), hot stage FTIR, flammability tests UL-94 and LOI, fire testing via cone calorimetry, residue analysis via scanning electron microscopy (SEM) and elemental analysis, detailed decomposition mechanisms and modes of action are proposed. hb-polymeric FRs have improved miscibility and thermal stability, leading to high FR performance even at low loadings. Polymeric, complex FRs increase flame retardancy, mitigate negative effects of low molecular weight variants, and can compete with commercial aromatic FRs. The results illustrate the role played by the chemical structure in flame retardancy and highlight the potential of hb-FRs as multifunctional additives.
This paper is based mainly on the results of two different projects performed in the group of the author recently (2016-2019). The three external partners involved in these two projects are competent in the preparation of FPUF (ICL IP America), RPUF (Department of Industrial Engineering, Padova University), and TPU (Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF, Darmstadt) as well as for the specimen preparation. Systematically varied sets of materials were prepared as the key basic for scientific discussion, varying the kind and combination of flame retardant, PUR structure, density, and blowing agent.
A multimethodical approach based on thermogravimetry (TGA), TGA coupled with evolved gas analysis (TGA-FTIR) and pyrolysis GC-MS was used for investigating the pyrolysis. The flammability was addressed using oxygen index (OI) and testing in UL 94 burning chamber in vertical and horizontal set-up. The fire behaviour was addressed by using a cone calorimeter. Beyond these methods according to the state of the art, key experiments were performed. We addressed the dripping and the two-stage burning of TPU using a self-designed apparatus and specific data evaluation, the foam burning through quenching burning samples, using different special sample holders, and measuring temperature profiles within the burning foams. The investigation is made round by intensive analysis of the fire residues, such as comprehensive investigation of the morphology.
Result on the pyrolysis (TGA-FTIR, Pyrolysis-GC/MS), flammability (UL 94, LOI), and fire behaviour (cone calorimeter) of TPU and flame retardant TPUs are shown. We discuss in detail the characteristic of PUR decomposition: the low tendency to char, and the specific two step decomposition and how these characteristics control the regimes in fire behaviour. We demonstrate that the different burning regimes are controlled by different pyrolysis products and effective heat of combustions. The resulting formation of pool fires as well as the formation of dripping is discussed in detail. The latter quite important to understand the flame retardancy applied with respect to achieve the UL 94 classification V0 nondripping or V0 non-flaming dripping.
Rigid and flexible PUR foams and their flame retarded versions are investigated for different densities. Water and pentane-blown foams are compared as well as PUR and polyisocyanurate-polyurethane (PIR) foams. Horizontal testing in the cone calorimeter is used and the vertical foam specimen holder as well. Self-designed set-ups within the cone calorimeter enable a better inside in the pyrolysis front running through the foam samples as well as the development of the temperature gradient inside the foam during the fire test. The morphology change during burning was characterised by the means of quenching burning foams with liquid nitrogen and investigating the cross sections with scanning electron microscope. In sum, a rather comprehensive study was performed to work out the principle fire phenomena controlling the fire behaviour of PUR foams in a very systematic and significant way.
Promising flame retardancy approaches are discussed. The importance of either combining the drain of fuel and flame inhibition or charring into an effective protection layer/multicellular structure is underlined.
This contribution focusses the general conclusions and trends. It tries to increase the understanding of the specific and demanding challenge to develop flame retardant PUR materials.
A series of new flame retardants (FR) based on dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO) incorporating acrylates and benzoquinone were developed previously. In this study, we examine the fire behavior of the new flame retardants in polyisocyanurate (PIR) foams. The foam characteristics, thermal decomposition, and fire behavior are investigated. The fire properties of the foams containing BPPO-based derivatives were found to depend on the chemical structure of the substituents. We also compare our results to state-of-the-art non-halogenated FR such as triphenylphosphate and chemically similar phosphinate, i.e. 9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide (DOPO), based derivatives to discuss the role of the phosphorus oxidation state.
Although the main flame retardant modes of action are known, in practise the detailed scientific understanding usually falls short, when it comes to modern multicomponent systems, the important tiny optimizations, or quantifying in terms of specific fire properties. The description of the flame retardant modes of action remains usually vague and fragmentary. This talk tries to deliver thought-provoking impulses how the understanding of the fire behaviour and flame retardancy can be utilized to direct the development of future flame retardant polymer products. Some overseen details are picked up as well as rethinking of concepts memorised long ago is encouraged to discover something new. Furthermore, the talk tries to fill the gap between flame retardant modes of action and fire performance constituting a product. This talk promotes the evidence-based development of flame retardant polymers
The current trend for future flame retardants (FRs) goes to novel efficient halogen-free materials, due to the ban of several halogenated FRs. Among the most promising alternatives are phosphorus-based FRs, and of those, polymeric materials with complex shape have been recently reported. Herein, we present novel halogen-free aromatic and aliphatic hyperbranched polyphosphoesters (hbPPEs), which were synthesized by olefin Metathesis polymerization and investigated them as a FR in epoxy resins. We compare their efficiency (aliphatic vs. aromatic) and further assess the differences between the monomeric compounds and the hbPPEs. The decomposition and vaporizing behavior of a compound is an important factor in its flame-retardant behavior, but also the interaction with the pyrolyzing matrix has a significant influence on the performance. Therefore, the challenge in designing a FR is to optimize the chemical structure and its decomposition pathway to the matrix, with regards to time and temperature. This behavior becomes obvious in this study, and explains the superior gas phase activity of the aliphatic FRs.
We synthesized a library of phosphorus-based flame retardants (phosphates and phosphoramides of low and high molar mass) and investigated their behavior in two epoxy resins (one aliphatic and one aromatic).
The pyrolytic and burning behavior of the two resins (via TGA, TG-FTIR, Hot stage FTIR, Py-GC/MS, PCFC, DSC, LOI, UL-94, Cone calorimeter) are analyzed and compared to the results of flame retardant (FR)-containing composites. A decomposition pathway incorporating the identified modes of action and known chemical mechanisms is proposed. The overlap of decomposition temperature (Tdec) ranges of matrix and FR determines the efficacy of the system. Low molar mass FRs strongly impact material properties like Tg but are very reactive, and high molar mass variants are more thermally stable. Varying PeO and PeN content of the FR affects decomposition, but the chemical structure of the matrix also guides FR behavior. Thus, phosphates afford lower fire load and heat release in aliphatic epoxy resins, and phosphoramides can act as additives in an aromatic matrix or a reactive FRs in aliphatic ones. The chemical structure and the structure-property relationship of both FR and matrix are central to FR performance and must be viewed not as two separate but as one codependent system.
Rigid polyurethane foams (RPUFs) exhibit short times to ignition as well as rapid flame spread and are therefore considered to be hazardous materials. This paper focuses on the fire phenomena of RPUFs, which were investigated through a multimethodological approach. Water-blown polyurethane (PUR) foams without flame retardants (FRs) as well as waterblown PUR foams containing triethyl phosphate as a gas phase-active FR were examined. The aim of this study is to clarify the influence of the FR on the fire phenomena during combustion of the foams. Additionally, materials’ densitieswere varied to range from 30 to 100 kg/m3. Thermophysical properties were studied bymeans of thermogravimetry; fire behavior and flammability were investigated via cone calorimeter and limiting Oxygen index, respectively. During the cone calorimeter test, the temperature development inside the burning specimens was monitored with thermocouples, and cross sections of quenched specimens were examined visually, giving insight into the morphological changes during combustion.
The present paper delivers a comprehensive study, illuminating phenomena occurring during foam combustion and the influence of a FR active in the gas phase. The superior fire performance of flameretarded PUR foams was found to be based on flame inhibition, and on increased char yield leading to a more effective protective layer. It was proven that in-depth absorption of radiation is a significant factor for estimation of time to ignition. Cross sections investigated with the electron scanning microscope exhibited a pyrolysis front with an intact foam structure underneath. The measurement of temperature development inside burning specimens implied a shift of burning behavior towards that of non-cellular materials with rising foam density.
Microplastic particles are currently detected in almost all environmental compartments. The results of detection vary widely, as a multitude of very different methods are used with very different requirements for analytical validity.
In this work four thermoanalytical methods are compared and their advantages and limitations are discussed. One of them is thermal extraction-desorption gas chromatography mass spectrometry (TED-GC/MS), an analysis method for microplastic detection that has become established in recent years. In addition, thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy (TGA-FTIR) and mass spectrometry (TGA-MS) were applied, two methods that are less common in this field but are still used in other research areas. Finally, microscale combustion calorimeter (MCC) was applied, a method not yet used for microplastic detection.
The presented results are taken from a recently published interlaboratory comparison test by Becker et al. (2020). Here a reference material consisting of suspended matter and specified added polymer masses was examined, and only the results of the recoveries were presented. In the present paper, however, the results for the individual polymers are discussed in detail and individual perspectives for all instruments are shown.
It was found that TED-GC/MS is the most suitable method for samples with unknown matrix and unknown, variable kinds and contents of microplastic. TGA-FTIR is a robust method for samples with known matrix and with defined kinds of microplastic. TGA-MS may offer a solution for the detection of PVC particles in the future. MCC can be used as a very fast and simple screening method for the identification of a potential microplastic load of standard polymers in unknown samples.
First phosphorus AB2 monomer for flame-retardant hyperbranched polyphosphoesters: AB2vs. A2 + B3
(2019)
Branched polymers are an important class of polymers with a high number of terminal groups, lower viscosity compared to their linear analogs and higher miscibility, which makes them especially interesting for flame retardant applications, where the flame retardants (FR) are blended with another polymer matrix. Hyperbranched polyphosphoesters (hbPPEs) are gaining more and more interest in the field of flame retardancy, as low molar mass FRs often have the disadvantage of blooming out or leaching, which is not desired in consumer products. Here, we present the first phosphorus-based AB2 monomer for the synthesis of hbPPEs and assess its flame-retardant performance in an epoxy resin compared to a hbPPE synthesized by an A2 + B3 approach. The hbPPE synthesized from an AB2 monomer exhibited a slightly higher performance compared to a similar hbPPE, which was prepared by A2 + B3 polyaddition, probably due to its higher phosphorus content.
The main flame retardant modes of action are known, nevertheless in practise the detailed scientific understanding usually falls short, when it comes to modern multicomponent systems, the important tiny optimizations, or quantifying in terms of specific fire properties. The description of the flame retardant modes of action remains usually vague and fragmentary. This talk tries to deliver thought-provoking impulses how the understanding of the fire behaviour and flame retardancy can be utilized to direct the development of future flame retardant polymer products. Some overseen details are picked up as well as rethinking of concepts memorised long ago is encouraged to discover something new. Furthermore, the talk tries to fill the gap between flame retardant modes of action and fire performance constituting a product. This talk promotes the evidence-based development of flame retardant polymers.
Flame retarded polymeric materials are used in various applications in which a certain fire behavior is demanded. Protection goals are defined, such as limited flammability in terms of hindered sustained ignition or limited contribution to a fire, and these protection levels are tested with defined specimens or components in defined fire scenarios, that is to say, different fire tests. Passing a specific fire test by meeting whatever its demands is often the most important development goal, so the parameters of the different fire tests vary widely to emphasize different fire properties. Some fire tests are used to screen or provide a general assessment of flame retardant polymers during development, while other fire tests and tailored experiments are performed to address special phenomena or understand the flame retardancy modes of action. For all fire testing, the devil is in the details – demanding know-how and crucial efforts to manage the quality of investigations and advanced interpretation. This chapter aims to offer a structured overview of all these aspects.
Scientific publications addressing the durability of the flame retardance of cables during their long-term application are rare and our understanding lacks. Three commercial flame retardants, aluminum hydroxide, aluminum diethyl phosphinate (AlPi-Et), and intumescent flame retardant based on ammonium polyphosphate, applied in ethylene-vinyl acetate copolymer (EVA) model cables, are investigated. Different artificial aging scenarios were applied: accelerated weathering (UV-irradiation/temperature/rain phases), humidity exposure (elevated temperature/humidity), and salt spray exposure. The deterioration of cables’ surface and flame retardancy were monitored through imaging, color measurements, attenuated total reflectance Fourier transform infrared spectroscopy, and cone calorimeter investigations. Significant degradation of the materials’ surface occurred. The flame retardant EVA cables are most sensitive to humidity exposure; the cable with AlPi-Et is the most sensitive to the artificial aging scenarios. Nevertheless, substantial flame retardance persisted after being subjected for 2000 h, which indicates that the equivalent influence of natural exposure is limited for several years, but less so for long-term use.
Hyperbranched polyphosphoesters are promising multifunctional flame retardants for epoxy resins. These polymers were prepared via thiol-ene polyaddition reactions. While key chemical transformations and modes of actions were elucidated, the role of sulfur in the chemical composition remains an open question. In this study, the FR-performance of a series of phosphorus-based flame retardant additives with and without sulfur (thioethers or sulfones) in their structure are compared. The successful synthesis of thio-ether or sulfone-containing variants is described and verified by 1H and 31P NMR, also FTIR and MALDI-TOF. A decomposition process is proposed from pyrolytic evolved gas analysis (TG-FTIR, Py-GC/MS), and flame retardancy effect on epoxy resins is investigated under pyrolytic conditions and via fire testing in the cone calorimeter. The presence of sulfur increased thermal stability of the flame retardants and introduced added condensed phase action. Likely, Sulfur radical generation plays a key role in the flame-retardant mode of action, and sulfones released incombustible SO2. The results highlight the multifunctionality of the hyperbranched polymer, which displays better fire performance than its low molar mass thio-ether analogue due to the presence of vinyl groups and higher stability than its monomer due to the presence of thio-ether groups.
Manipulating the melt dripping of thermoplastics makes a fire scenario more or less dangerous. Yet, a detailed understanding of this phenomenon has remained a question mark in studies of the flammability of plastics. In this work, the individual and collective impacts of additives on the dripping behaviour of polyamide 6 (PA6) were studied. A set of materials compounded with melamine cyanurate (MCA) and glass fibre (GF) was investigated. Under UL 94 vertical test conditions, the dripping during first and second ignition was quantified and investigated in detail. The number, size and temperature of the drops were addressed, and the materials and their drops evaluated with respect to such aspects as their averaged molecular weight, thermal decomposition and rheological properties. PA6 with V-2 classification improved to V-0 with the addition of MCA, and achieved HB in the presence of GF. PA6/GF/MCA achieved V-2. Non-flaming drops of PA6/MCA consisted of oligomeric fragments. Flaming drops of PA6/GF showed a more pronounced decomposition of PA6 and an increased GF content. The dripping behaviour of PA6/GF/MCA can be understood as a combination of the influence of both additives. The results showed nicely that dripping under fire is neither a straightforward material property nor a simple additive influence, but the complex response of the material influenced by the interaction and competition of different phenomena.
Nowadays there are intumescent coatings available for diverse applications. There is no established assessment of their protection performance besides the standard time-temperature curve, but natural fire scenarios often play an important role. A reliable straightforward performance-based assessment is presented. The effective thermal conductivity per thickness is calculated based on intermediate-scale fire tests. The optimum thermal insulation, the time to reach it, and the time until contingent failure of the coating are used for an assessment independent of the heating curve. The procedure was conducted on four different commercially intumescent coatings for steel construction, one solvent-based, one waterborne, one epoxy-based, and a bandage impregnated with a waterborne coating. The performance was studied under four different but similar shaped heating curves with different maximum temperatures (standard time-temperature curve, hydrocarbon curve and two self-designed curves with reduced temperature). The thermal protection performance is crucially affected by the residue morphology. Therefore, a comprehensive morphology analysis, including micro-computed tomography and scanning electron microscopy, was conducted on small-scale residues (7.5 x 7.5 cm2). Two different types of inner structures and the residue surface after different heat exposures were discussed in terms of their influence on thermal protection performance.
The durability of flame retardancy is a challenge for cables over long lifetimes. The degradation of flame retardance is investigated in two kinds of exposures, artificial weathering and humidity. In this basic study, typical mineral flame retardants in two polymers frequently used in cable jackets are investigated to get the fundamental picture. Aluminum hydroxide (ATH) and magnesium hydroxide (MDH) are compared in ethylene‐vinyl acetate (EVA), and further in EVA and linear low‐density polyethylene (LLDPE) cables containing the same ATH. The changes in chemical structure at the surface are studied through attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR), the formation of cracks, and changes in color are investigated. The cone calorimeter and a bench scale fire testing cable module are utilized to evaluate the fire behavior of the cables. Although the flame retardancy deteriorated slightly, it survived harsh exposure conditions for 2000 h. Compared to EVA/MDH and LLDPE/ATH, the fire behavior of EVA/ATH is the least sensitive. Taken together, all of the results converge to estimate that there will be no problem with flame retardancy performance, for materials subjected to natural exposure for several years; the durability of fire retardancy is questionable for longer periods, and thus requires further investigation.
A systematic approach was used to investigate the weathering-induced degradation of a common water–based intumescent coating. In this study, the coatings are intended for humid indoor applications on steel substrates. The coating contains ammonium polyphosphate, pentaerythritol, melamine, and polyvinyl acetate. By replacing each ingredient with a less water-soluble substance, the most vulnerable substances, polyvinyl acetate and pentaerythritol, were identified. Furthermore, the weathering resistance of the system was improved by exchanging the ingredients. The coatings were stressed by artificial weathering tests and evaluated by fire tests. Thermogravimetry and Fourier-transform infrared spectroscopy were used to study the thermal decomposition. This study lays the foundation for the development of a new generation of water-based intumescent coatings.
To curtail flammability risks and improve material properties, flame retardants (FRs) and fillers are mixed into rubbers. High loadings of aluminum trihydroxide (ATH) and carbon black (CB) are the most used FRs and reinforcing additive, respectively, in rubbers. To reduce loading without losing mechanical properties, partial substitution of ATH as well as CB by low amounts of multilayer graphene (MLG) nanoparticles is investigated. The high aspect ratio MLG is made of ten graphene sheets. In polybutadiene/chloroprene (BR/CR) nanocomposites 3 phr MLG replaced 15 phr CB and/or 3 phr ATH. Material and mechanical properties as well as fire behavior of the nanocomposites are compared to BR/CR with 20 phr CB both with and without 50 phr ATH. MLG appears as a promising nanofiller to improve the functional properties: replacement of CB improved rheological, curing, and mechanical properties; substitution of ATH improved nanocomposite properties without affecting flame retardancy.
Phosphorus-based flame retardants were incorporated into different, easily preparable matrices, such as polymeric thermoset resins and paraffin as a proposed model for polyolefins and investigated for their flame retardancy performance. The favored mode of action of each flame retardant was identified in each respective system and at each respective concentration. Thermogravimetric analysis was used in combination with infrared spectroscopy of the evolved gas to determine the pyrolysis behavior, residue formation and the release of phosphorus species. Forced flaming tests in the cone calorimeter provided insight into burning behavior and macroscopic residue effects. The results were put into relation to the phosphorus content to reveal correlations between phosphorus concentration in the gas phase and flame inhibition performance, as well as phosphorus concentration in the residue and condensed phase activity. Total heat evolved (fire load) and peak heat release rate were calculated based on changes in the effective heat of combustion and residue, and then compared with the measured values to address the modes of action of the flame retardants quantitatively. The quantification of flame inhibition, charring, and the protective layer effect measure the non-linear flame retardancy effects as functions of the phosphorus concentration. Overall, this screening approach using easily preparable polymer systems provides great insight into the effect of phosphorus in different flame retarded polymers, with regard to polymer structure, phosphorus concentration, and phosphorus species.
Carbon fibre (CF) and glass fibre (GF) reinforced polymers are used for diverse applications demaning flame and fire retardancy in the fire scenarios ignition, developing fire and fully developed fire. The fire behaviour of composites differs from polymers, since fibres behave often inert with respect to pyrolysis, change the melt flow / dripping behaviour, the heat absorption and transfer, the amount and properties of the fire residue. Concepts are needed suitable for the different fire protection goals, but also tailored for composites. The field is illuminated by examples carried out in the group of the author in the recent years. Approaches to halogen-free flame retardancy in GF reinforced thermoplastics and CF reinforced thermosets are presented as well as building up a bench and intermediate scale testing of composites in fire applying mechanical load and direct flame exposure simultaneously. The understanding of fire behaviour and flame retardancy modes of action in composites is a promising basis for target-oriented development.
The main flame retardant modes of action are well known, but in practise the detailed scientific understanding usually falls short, when it comes to modern multicomponent systems, the important tiny optimizations, or quantifying in terms of specific fire properties. This talk delivers thought-provoking impulses, picking up some overseen details as well as raising basic questions. A detailed scientific insight in flame retardant modes of action much more than an overview is presented.
Melt flow and dripping of polymeric materials can be both beneficial and detrimental during fire. It reduces flame spread and result in extinction, as mass and heat are removed from the actual pyrolysis zone. In contrast, melt flow and dripping can provide an additional ignition source, additional process of flame spread and has the potential to start a pool fire. In the vertical UL 94 test, a well adjusted dripping behaviour of flame retarded polypropylene (PP-FR) resulted in a non-flaming dripping V-0 classification. For the polymer samples and their drops collected in UL 94, the decomposition and viscosity was investigated. Particle finite element method (PFEM) was successfully used to simulate the material behaviour in the UL 94 test and increased the understanding of the complex behaviour of polymeric materials during fire.
Der Vortrag gibt einen Überblick über die Thematik der flammgeschützten Polyurethanwerkstoffe, d.h. thermoplastisches und elastomeres Polyurethan (TPU, PUR), PUR Hard- und Weichschäume, PUR Coatings. Die Werkstoffcharakteristika wie Pyrolyse, effektive Verbrennungswärme, Rückstandsausbeute, Verarbeitungsparameter und kg-Preis definieren die Anforderungen an Flammschutzlösungen. Der Flammschutz ist spezifisch für das Material ausgelegt, aber auch für die verschiedenen Anwendungen (Automobilbau, Schienenfahrzeuge, Bauwesen, Elektrotechnik, usw.), d.h. um verschiedene Brandtests zu bestehen. Die Pyrolyse und das Brandverhalten von PUR und PUR-Schäumen sowie der flammgeschützten Varianten wird diskutiert. Die gängigen Flammschutzmittel(-kombinationen) für PUR Hard- und Weichschaum sowie thermoplastisches und elastomeres PUR werden zusammengefasst.
Synergy in flame-retarded epoxy resin - Identification of chemical interactions by solid-state NMR
(2017)
The potential synergists aluminium diethylphosphinate (AlPi), boehmite (AlO(OH)) and melamine polyphosphate (MPP) were compared in flame-retardant epoxy resin (EP)/melamine poly(magnesium phosphate) (S600). The pyrolysis, the fire behaviour as well as the chemical interactions in the gas and condensed phases were investigated by various methods. Flammability was investigated by cone calorimeter and oxygen index (OI). The thermal and thermo-oxidative decomposition were studied by thermogravimetric analysis coupled with FTIR spectrometer. The special focus was on the Investigation of structural changes in the condensed phase via solid-state NMR of 27Al and 31P nuclei. By the comparison of epoxy resin with only one additive or with S600 in combination with AlPi, AlO(OH) or MPP, it was possible to calculate the synergy index. The best performance in terms of fire behaviour was observed for EP/S600/MPP with a PHRR (Peak heat release rate) of 208 kW m-2 due to slight synergy. In the case of THE (total heat evolved), clear synergy occurred for EP/S600/AlPi and EP/S600/AlO(OH). By solid-state NMR, different phosphates and aluminates were identified, indicating the chemical interactions between S600 and AlPi, AlO(OH) or MPP. The systematic multi-methodical approach yielded insight into the synergistic effects in the flame-retarded epoxy resin.
In den letzten Jahren werden zunehmend Nanopartikel als Füllstoff für Polymere vorgeschlagen und auch erfolgreich in Elastomer-Nanocomposites eingesetzt. In dieser Arbeit wird Multilayergraphen (MLG) als Nanofüllstoff näher untersucht, der sich bereits bei geringen Konzentrationen als effizient erweist. MLG besteht aus nur etwa zehn Graphenlagen.
Chlorbutylkautschuk (CIIR)/MLG-Nanocomposites mit verschiedenen MLG-Gehalten wurden mit Hilfe eines ultraschallunterstützen Mischverfahrens in Lösung hergestellt und auf einem Walzwerk weiterverarbeitet. Das Einmischen von MLG führt zu einer deutlichen Verbesserung der rheologischen und mechanischen Eigenschaften, des Vernetzungsverhaltens sowie der Barrierewirkung gegenüber Gasen. Bereits der Zusatz von 3 phr MLG zu CIIR führt zu einem mehr als zweifach höheren E-Modul und zu einer Reduktion der Permeabilität von O2 und CO2 um 30 %. Höhere Konzentrationen an Nanofüllstoff resultieren in einer weiteren Verbesserung der Eigenschaften der Nanocomposites. Weiterhin zeigten die CIIR/MLG-Nanocomposites auch eine geringere Entflammbarkeit.
A mono-component intumescent flame retardant named ethylenediamine-modified ammonium polyphosphate (MAPP) is used in polyethylene-octene elastomer (POE). Insight into the flame-retardant mechanisms of the MAPP is provided from a new perspective. The fire performance of POE/MAPP composites is investigated by oxygen index (OI) and vertical burning (UL-94) tests. POE Composite containing 35 wt% MAPP achieves a V-0 rating, and its OI is 29.3 vol%. The thermogravimetric Analysis (TGA) and Fourier transform infrared spectra (FTIR) confirm that the incorporation of ethylenediamine changes the thermal decomposition of APP, mainly resulting in the formation of char layer with a thermally stable structure. Cone calorimeter analysis revealed the flame-retardant modes of action of MAPP in POE under forced-flaming conditions. Quantitative analysis illustrates that both the residue due to charring and the fuel dilution/flame Inhibition resulting from the release of incombustible products/ phosphorus species decrease the total heat release (fire load) by 20e28%. The residue increases linearly with increasing MAPP content, whereas the reduction in effective heat of combustion levels off. Moreover, the flame-retardant effect resulting from the protective properties of the char is discovered to be the dominant mode of action (up to 85% reduction) with respect to the peak heat release rate, leading to the excellent flame retardancy of POE/MAPP.
Several expandable graphites (EGs), differing in Expansion volume but with the same mean size, are compared as flame retardants in polyurethane (PUR) foams. Not only common sulfur-intercalated graphites are investigated but also a new one intercalated with phosphorus. The main aim of this article is to understand which properties of EG are important for its flame retardancy effectiveness in PUR foams. Thermal stability, flammability, and fire behavior are analyzed through limiting oxygen index and cone calorimeter tests. Detailed characterization of the phosphorus-intercalated graphite is also provided as well as physical–mechanical characterization. The results show that the well-known sulfur-intercalated graphites and the one with phosphorus both enhance the residue yield, induce a protective layer, and thus efficiently flame-retard PUR foams. While the expansion volume of the EGs had a surprisingly limited influence on the performance of the foams, at least in the range tested, the most important feature Controlling the effectiveness of EG in terms of flame retardant PUR foams was the type of intercalant. The presence of EG affected the physical–mechanical properties of the foams; however, no significant effect of the expansion volume or intercalant type has been revealed on the physical–mechanical properties of the foams.
The rapid mass calorimeter (RMC) was used as a screening tool based on accelerated fire testing to assess flame-retarded thermoplastic polyurethane (TPU). The reliability of RMC results was proven with the cone calorimeter as reference fire test. The influence of melamine cyanurate (MC) concentration on the fire performance of TPU was investigated, along with some flame-retardant combinations such as MC with aluminium diethylphosphinate (AlPi), aluminium trihydrate (ATH), and melamine polyphosphate (MPP). The two-stage burning behaviour of TPU was investigated in detail; the first stage corresponds mainly to the hard segments' decomposition and has a much lower effective heat of combustion (EHC) than the second stage, in which mainly the soft segments decompose and an intensive liquid pool fire is observed in the cone calorimeter set-up. In addition to fire testing with the cone calorimeter, RMC, and UL 94 flammability tests, the decomposition of the materials was investigated using thermogravimetric analysis coupled with infrared spectrometry (TGeFTIR). TPU/MC/AlPi shows the most promising results, achieving V-0 classification in UL 94 and reducing the extreme peak heat release rate (PHRR) of the liquid pool fire from 3154 kW/m2 to 635 kW/m2. Using MC/AlPi/MPP enhances the latter PHRR reduction further. The decomposition products identified in the gas phase via TGeFTIR reveal specific MCeAlPi eMPP interactions, as they differ from products seen in systems with MC/AlPi or MC/MPP. Correlations between RMC and cone calorimeter results were examined and presented in the final part of the paper. Several characteristics correlate strongly, pointing out that RMC is a reliable high-throughput fire testing method to screen multicomponent flame-retardant solutions in TPU.
The ubiquity of polymeric materials in daily life Comes with an increased fire risk, and sustained research into efficient flame retardants is key to ensuring the safety of the populace and material goods from accidental fires. Phosphorus, a versatile and effective element for use in flame retardants, has the potential to supersede the halogenated variants that are still widely used today: current formulations employ a variety of modes of action and methods of implementation, as additives or as reactants, to solve the task of developing flameretarding polymeric materials. Phosphorus-based flame retardants can act in both the gas and condensed phase during a fire. This Review investigates how current phosphorus chemistry helps in reducing the flammability of polymers, and addresses the future of sustainable, efficient, and safe phosphorus-based flame-retardants from renewable sources.
Natural keratin fibres derived from Mexican tannery waste and coconut fibres from coconut processing waste were used as fillers in commercially available, biodegradable thermoplastic starch-polyester blend to obtain sustainable biocomposites. The morphology, rheological and mechanical properties as well as pyrolysis, flammability and forced flaming combustion behaviour of those biocomposites were investigated. In order to open up new application areas for these kinds of biocomposites, ammonium polyphosphate (APP) was added as a flame retardant. Extensive flammability and cone calorimeter studies revealed a good flame retardance effect with natural fibres alone and improved effectiveness with the addition of APP. In fact, it was shown that replacing 20 of 30 wt. % of APP with keratin fibres achieved the same effectiveness. In the case of coconut fibres, a synergistic effect led to an even lower heat release rate
and total heat evolved due to reinforced char residue. This was confirmed via scanning electron microscopy of the char structure. All in all, these results constitute a good approach towards sustainable and biodegradable fibre reinforced biocomposites with improved flame retardant properties.
The multicomponent flame retardant system of melamine polyphosphate (MPP), melamine cyanurate (MC) and aluminum diethylphosphinate (AlPi) is proposed and investigated for thermoplastic polyurethane (TPU). The synergy between those additives and the resulting superior fire performance are discussed. Systematically varied sets of flame retarded TPU with various MPP/MC/AlPi ratios were investigated in terms of fire behavior, pyrolysis products and mechanical properties. The total amount of the additives was always 30 wt.-%. Further, the influence of various AlPi concentrations was investigated. The optimal MPP:MC ratio was determined while keeping the amount of AlPi constant. The combination of 8 wt.-% MPP, 12 wt.-% MC and 10 wt.-% is proposed as the most promising halogen free flame retardant formulation for TPU, because it yielded a reduction in PHRR from 2660 kW/m2 (TPU) to 452 kW/m2 and enabled V-0 classification in the UL 94 test. Combinations of MPP and MC as well a high concentration of AlPi are beneficial for the mechanical properties e.g. tensile strength and elongation at break of the formulations and could be a strong competitor to commercial flame retarded TPUs.
High-throughput fire tests and weathering-induced degradation behaviour of intumescent coatings
(2018)
In this work, the weathering-induced degradation of intumescent coatings was investigated by a systematic and comprehensive approach. A mechanism is revealed that is proposed to be responsible for the loss of function of intumescent coatings induced by weathering.
First, the thermal decomposition of artificially weathered intumescent coatings was examined. To get a better understanding of the weathering and ageing phenomena, the degradation behaviour of the single ingredients during the weathering process was investigated, as well as their chemical and physical interactions. For the systematic approach, the materials that are essential for intumescence (ammonium polyphosphate, pentaerythritol, titanium dioxide, melamine and the binder) are treated with moisture, elevated temperature and UV radiation.
Thermogravimetry (TG) and IR spectroscopy were used to compare the initial samples with their different grades of weathering. We demonstrate that ammonium polyphosphate, melamine and the binder are mainly responsible for the ageing process. Further, it was demonstrated that TG and IR spectroscopy are suitable measuring methods to detect the effects of weathering on intumescent coatings.
Finally, a small-scale fire test procedure is introduced. Based on the reduction of the sample size, up to 50 samples can be tested in a single fire test. The results of this fire test have the same quality as the results from standard intermediate fire tests corresponding to DIN 4102-8.
Elastomers are usually reinforced by large amount of fillers like carbon black (CB) or silica in order to improve various mechanical properties, such as Young’s modulus, hardness, tear resistance, abrasion resistance, and gas barrier properties. In recent years, such improvements were also obtained by using nanoparticles at significantly lower filler loadings. Graphene is a twodimensional (2D) sheet of a thickness in the atomic scale, composed of a honeycomb structure of sp2 carbon atoms. Besides significant mechanical reinforcement, graphene harbors the potential to be used as a multifunctional filler, as it can also increase the conductivity and weathering stability of elastomer matrices. Ultraviolet (UV) irradiation and oxidative agents can lead to the degradation of elastomers due to a multistep photooxidative process, including the formation of radicals. Carbon-based fillers have an influence on these reactions, as they can absorb UV radiation and act as radical scavengers.
This chapter summarizes the results of our larger project on multilayer graphene (MLG)/elastomer nanocomposites, previously published, which present a comprehensive case study of MLG as a multifunctional nanofiller in elastomer/graphene nanocomposites. Different elastomeric matrices are compared in order to demonstrate the outstanding impact of MLG as a general benefit. The dependency of this effect on concentration is discussed in detail. Taking into account the key role of dispersion, different mixing procedures are compared, evaluating a facile implementation of graphene nanocomposites into conventional rubber processing. Finally, the most probable commercial uses of MLG nanofillers in combination with conventional CB are studied. The nanocomposites were prepared in the kg scale in order to obtain enough specimens to investigate various properties of the uncured and vulcanized rubbers at the highest quality level, including rheology, curing, morphology, several mechanical properties, abrasion, conductivity, gas permeation, burning behavior, and weathering stability. The structure property relationships are asserted and questioned, for example, by investigating the radical scavenging ability or aspect ratio of the MLG. This chapter illustrates the state of the art of graphene/rubber nanocomposites targeted for commercial mass applications.
Intumescent coatings are used for decades to increase the fire resistance of steel or wood constructions. Intermediate and full scale tests are used to assess their protection performance. For the product development and screening, cheaper and faster bench-scale tests are demanded that provide information about thermal protection, foaming dynamics and mechanical resistance. In the recent years, we have developed several bench-scale fire resistance tests and used them in different research and developing projects. The influence of distinct binders and fillers, respectively, was studied in intumescent coatings using the Standard Time Temperature modified muffle furnace (STT Mufu+). This bench-scale test evaluates the fire resistance (by means of temperature measurements) and the foaming behaviour (by means of a high-temperature endoscope) during a standard time-temperature exposure. The fire residues were suitable for advance residue analysing techniques like nondestructive μ-computed tomography (μ-CT). Also, scanning electron microscopy was used to investigate the microscopic structure of the surface and inside of the residues. The mechanical resistance of the residues was tested by an impact resistance experiment.
The binder influence on the insulation of the coating was small for the investigated systems. Nevertheless, it was interestingly noted, that coatings with high expansion did not provide the best protection. The great influence of the binder material on the inner structure of the foamed residues was revealed by the μ-CT images. Clear differing morphologies were observed. These led to distinct mechanical resistance properties of the tested coatings. Also the change of a low amount of fillers, such as fibres and clay was investigated with similar effects. What is more, a transition of the residue from black, carbonaceous foam with closed cells into an inorganic, residual open cell sponge occurs at high temperatures during the test. This transition is due to the loss of carbon; the change in microstructure is analysed by scanning electron microscopy.
The bench-scale tool presented outreaches screening; the investigation based on the STT Mufu+ delivers a deeper understanding of the phenomena controlling the performance of intumescent coatings.
Low amounts (<7.5 wt%) of organically modified layered silicate (LS) as well as large amounts (>10 wt%) of spherical amorphous SiO2 (sSiO2) has been used successfully as adjuvants in commercial polymeric materials flame retarded with metal hydroxide. The combination of LS and SiO2 is investigated in different thermoplastics with respect to their fire behavior, particular to overcome the restrictions in maximum and minimum filler contents know for the single additives. The aim was to check the potential of combinations of the inert fillers in absence of a real fire retardant. The combination of LS and sSiO2 harbors the potential for flame retardancy effects close to superposition or even synergy, due to an improved structure of the fire residue. LS-sSiO2 combinations are proposed to work as adjuvants superior to LS and sSiO2 in flame retarded polymeric materials.
The fire stability of carbon fiber reinforced polymer (CFRP) shell structures was investigated using an intermediate-scale test setup. The shell specimens are representative of typical load-bearing CFRPs in modern civil aviation. The CFRP shell specimens were exposed to a fully developed fire with direct flame impingement to one side at a heat flux of 182 kW/m2. Specimens were simultaneously loaded with constant compressive force equal to 40% of the ultimate failure load. CFRP shells and four different fire retarding configurations, using integrated protective layers, were investigated. Unprotected CFRP specimens failed after just 27 s. Specimens with integrated protective layers with low heat conductivity and high burn-through resistance showed the most promising results. An integrated titanium foil decelerated the decomposition of the epoxy matrix and increased the time to failure by 68% compared to the unprotected CFRP shell.
Intumescent coatings have been used for fire protection of steel for decades, but there is still a need for improvement and adaptation. The key parameters of such coatings in a fire Scenario are thermal insulation, foaming dynamics, and cohesion. The fire resistance tests, large furnaces applying the standard time temperature (STT) curve, demand coated full‐scale components or intermediate‐scale specimen. The STT Mufu+ (standard time temperature muffle furnace+) approach is presented. It is a recently developed bench‐scale testing method to analyze the performance of intumescent coatings. The STT Mufu+ provides vertical testing of specimens with reduced specimen size according to the STT curve. During the experiment, the foaming process is observed with a high‐temperature endoscope. Characteristics of this technique like reproducibility and resolution are presented and discussed. The STT Mufu+ test is highly efficient in comparison to common tests because of the reduced sample size. Its potential is extended to a superior research tool by combining it with advanced residue analysis (μ‐computed tomography and scanning electron microscopy) and mechanical testing. The benefits of this combination are demonstrated by a case study on 4 intumescent coatings. The evaluation of all collected data is used to create performance‐based rankings of the tested coatings.
In addition to the acid source, charring agent, and blowing agent, the binder is a crucial part of an intumescent coating. Its primary task is to bind all compounds, but it also acts as a carbon source and influences the foaming process. A series of intumescent coatings based on five different binders was investigated in terms of insulation, foaming, mechanical impact resistance, and residue morphology. The Standard Time-Temperature modified Muffle Furnace (STT MuFu+ ) was used for the bench-scale fire resistance tests and provided data on temperature and residue thickness as well as well-defined residues. The residue morphology was analyzed by nondestructive m-computed tomography and scanning electron microscopy. A moderate influence of the binder on insulation performance was detected in the set of coatings investigated, whereas the foaming dynamics and thickness achieved were affected strongly. In addition, the inner structure of the residues showed a rich variety. High expansion alone did not guarantee good insulation. Furthermore, attention was paid to the relation between the microstructure transition induced by carbon loss due to thermo-oxidation of the char and the development of the thermal conductivity and thickness of the coatings during the fire test.
Developing flame retarded thermoplastic elastomers (TPES) based on styrene−ethylene−butylene−styrene, polypropylene, and mineral oil is a challenging task because of their very high fire loads and flammability. A promising approach is the synergistic combination of expandable graphite (EG) and ammonium polyphosphate (APP). Cone calorimetry, oxygen index, and UL 94 classification were applied. The optimal EG:APP ratio is 3:1, due to the most effective fire residue morphology. Exchanging APP with melamine-coated APPm yielded crucial improvement in fire properties, whereas replacing EG/APP with melamine polyphosphate did not. Adjuvants, such as aluminum diethyl phosphinate (AlPi), zinc borate, melamine cyanurate, titanium dioxide, dipentaerylthritol, diphenyl-2-ethyl phosphate, boehmite, SiO2, chalk, and talcum, were tested. All flame retardants reinforced the TPE-S. The combination with AlPi is proposed, because with 30 wt % flame retardants a maximum averaged rate of heat emission below 200 kW m−2 and a V-0 rating was achieved. Multicomponent EG/APP/adjuvants systems are proposed as a suitable route to achieve efficient halogen-free flame retarded TPE-S.
The rapid mass calorimeter based on reduced‐size specimens is proposed for accelerated fire
testing and put up for discussion, particularly for flame retarded polymeric materials. A mass loss
calorimeter is combined with a semiautomatic sample changer. Experiments on specimens of
reduced size were conducted on poly(methyl methacrylate), poly(propylene), polyamide 66,
poly(ether ether ketone), and pine sapwood square samples with edge lengths of 100, 75, 50,
25, 20, and 10 mm. Specimens of 20 × 20 mm2 were selected to achieve a crucial reduction in
specimen size and a measuring protocol developed. A total of 71 different polymeric materials
were investigated in the rapid mass calorimeter and cone calorimeter for comparison and several
materials with different heat release rate characteristics in the pyrolysis combustion flow calorimeter to test this additional screening method as well. The important fire properties obtained in the rapid mass calorimeter show reasonable correlation with the cone calorimeter results but also with the oxygen index. All in all, the rapid mass calorimeter produces reliable and meaningful results and, despite acceleration and size reduction, still allows for a certain degree of burning behavior interpretation. Material savings of 96% and time savings of around 60%‐70% are achieved compared to measure cone calorimeter.
The fire behaviour of carbon fibre (CF) reinforced polymers differs in comparison to polymers. Fibres behave often inert with respect to pyrolysis, they change the melt flow and dripping behaviour, the heat absorption and transfer, the amount and properties of the fire residue and so on. Flame and fire retardancy concepts are needed not only suitable for the different fire protection goals typical for each application, but also tailored for composites. This field is illuminated by examples taken from different projects carried out in the group of the author in the recent years. The examples target on different applications through achieving reduction in reaction to fire controlling the fire risks (flammability, heat release) in the beginning and development of a fire and investigating the fire stability, when a severe flame is directly applied (key property in fully developed fires). Approaches to halogen-free flame retardancy in CF reinforced thermosets are presented as well as building up a bench and an intermediate scale testing of composites in fire applying mechanical load (up to 1 MN compression) and direct flame exposure (180 kW/m2) simultaneously. Indeed, e.g. we have investigated the fire stability of stringer reinforced shell components taken out from the fuselage of an aircraft.
The understanding of fire behaviour, fire resistance, and fire retardant modes of action in composites is a promising basis for target-oriented development. The role of flame inhibition, charring, and protective layer formation is discussed. Successful concepts are presented for fire retardancy tailored for different application as well as general guidelines for future development. Different phosphorus flame retardants are proposed to achieve halogen-free flame retardancy with respect to ignition and developing fires. Different protective approaches are sketched for addressing the fire stability of composites that is the most important fire risk for the fire resistance in structural applications.
Basic paths towards fully green flame retarded kenaf fiber reinforced polylactic acid (K-PLA) biocomposites are compared. Multicomponent flame retardant Systems are investigated using an amount of 20 wt% such as Mg(OH)2 (MH), ammonium polyphosphate (APP) and expandable graphite (EG), and combinations with Silicon dioxide or layered silicate (LS) nanofillers. Adding Kenaf fibers and flame retardants increases the E modulus up to a factor 2, although no compatibilizer was used at all. Thus, in particular adding EG and MH decreases the strength at maximum elongation, and kenaf fibers, MH, and EG are crucial for reducing the elongation to break. The Oxygen index is improved by up to 33 vol% compared to 17 vol% for K-PLA. The HB classification of K-PLA in the UL 94 test is outperformed. All flame retarded biocomposites show somewhat lower thermal stability and increased amounts of residue. MH decreases the fire load significantly, and the greatest reduction in peak heat release rate is obtained for K-PLA/15MH/5LS. Synergistic effects are observed between EG and APP (ratio 2:1) in flammability and fire properties. Synergistic multicomponent systems containing EG and APP, or MH with adjuvants offer a promising route to green flame retarded natural fiber reinforced PLA biocomposites.
A siloxane compound (MVC) and a bi-group phosphaphenanthrene/triazine compound (TGD) were employed in epoxy thermosets to explore high-efficiency flame retardant systems. With only 1wt% MVC and 3wt% TGD, an epoxy thermoset passed UL 94 V-0 rating test and achieved a limiting oxygen index value of 34.0%, exhibiting an excellent flame retardant effect. The MVC/TGD system not only decreased the peak value of heat release rate and effective heat of combustion but also imparted an improved charring ability to thermosets, thereby outstandingly reducing the flammability of 1%MVC/3%TGD/EP. Compared with the fire performance of 4%TGD/EP and 4%MVC/EP, the MVC/TGD system showed an obvious flame retardant synergistic effect, mainly depending on the general improvement of flame inhibition, charring and barrier effects of the thermoset during combustion. Evolved gas analysis combinedwith condensed-phase pyrolysis product Analysis jointly revealed the details of the changed pyrolysis mode.
The Role of Decomposition Temperature for Flame Redartancy Mode of Action in the Condensed Phase
(2018)
Condensed-phase mechanisms play a major role in fire-retardant polymers. Generations of development have followed the concept of charring to improve fire properties. Whereas the principal reactions are believed to be known, the specific description for multicomponent systems is lacking, as is the picture across different systems. One important aspect in achieving, adjusting and optimising flame retardancy in the condensed phase is exploiting chemical reactions between the pyrolysing polymer and flame retardant at the right place, time and temperature. It is the aim of this contribution to address the role of the decomposition temperature of both flame retardant and polymer by the means of two examples: First, aryl phosphates in Polycarbonate/ Acrylonitrile-Butadiene-Styrene (PC/ABS) blends, where the reaction with the early stage decomposition products of PC is controlling the flame retardancy mechanism in the condensed phase. Second, a comprehensive set of phosphorus flame retardants in thermosets and their corresponding carbon fibre reinforced composites based on two different epoxy systems. Both examples show that key reactions between intermediate decomposition products only occur when the decomposition temperature ranges correspond to each other. The systems can be shifted towards condensed phase activity such as charring or inorganic glass formation as well as towards phosphorus release and thus flame inhibition in the gas phase. Changing the role of flame retardancy mechanisms also influence the efficiency in the achieved flame retardancy.
Flexible polyurethane foams with densities of 40 ± 2 kg m−3 were prepared by combining different ecofriendly fillers such as layered double hydroxides (LDH) and kraft lignin (a byproduct of the pulp and paper industry) with a phosphorous polyol (E560) in order to study their effect on the mechanical performance and fire behavior of the foams. Two series of foams were prepared, some containing lignin or LDH separately, and some with a combination of both: one of the series was prepared without E560 (0E foam series) and the other with 5 parts per hundred of E560 polyol (5E series). The use of fillers resulted in increased viscosity of the reactive mixture, requiring higher blowing agent content in order to hold the density of the foams constant. It was observed that urea phase segregation was favored in the series of 0E foams due to their lower viscosity than the 5E series. This had consequent effects on the resilience, compression force deflection and compression set of these foams. In terms of fire behavior it was observed that while the limiting oxygen index decreased, cone calorimeter results showed that the combination of lignin, LDH and E560 decreased the heat release of the foams. In addition, the combination of fillers and E560 contributed to increase the viscosity of the pyrolysis products, preventing the dripping of the molten polymer, which is a key factor in flame propagation towards adjacent objects in fire scenarios.
Rigid polyurethane foams (RPUFs) typically exhibit low thermal inertia, resulting in short ignition times and rapid flame spread. In this study, the fire phenomena of RPUFs were investigated using a multi-methodological approach to gain detailed insight into the fire behaviour of pentaneand water-blown polyurethane (PUR) as well as pentane-blown polyisocyanurate Polyurethane (PIR) foams with densities ranging from 30 to 100 kg/m3. Thermophysical properties were studied using thermogravimetry (TG); flammability and fire behaviour were investigated by means of the limiting oxygen index (LOI) and a cone calorimeter. Temperature development in burning cone calorimeter specimens was monitored with thermocouples inside the foam samples and visual investigation of quenched specimens’ cross sections gave insight into the morphological changes during burning. A comprehensive investigation is presented, illuminating the processes taking place during foam combustion. Cone calorimeter tests revealed that in-depth absorption of radiation is a significant factor in estimating the time to ignition. Cross sections examined with an electron scanning microscope (SEM) revealed a pyrolysis front with an intact foam structure underneath, and temperature measurement inside burning specimens indicated that, as foam density increased, their burning behaviour shifted towards that of solid materials. The superior fire performance of PIR foams was found to be based on the cellular structure, which is retained in the residue to some extent.
Assessing the structural integrity of carbon-fibre sandwich panels in fire: Bench-scale approach
(2019)
The fire resistance of lightweight sandwich panels (SW) with carbon fibre/epoxy skins and a poly(methacryl imide) (PMI) foam core is investigated in compression under direct application of a severe flame (heat flux=200 kW m−2). A bench-scale test procedure was used, with the sample held vertically. The epoxy decomposition temperature was quickly exceeded, with rapid flash-over and progressive core softening and decomposition.
There is a change in failure mode depending on whether the load is greater or less than 50% of the unexposed failure load, or in other words if one or two skins carry the load. At high loads, failure involved both skins with a single clear linear separation across each face. There is an inflection in the failure time relationship in the ∼50% load region, corresponding to the time taken for heat to be transmitted to the rear face, along with a change in the rear skin failure mode from separation to the formation of a plastic hinge. The integrity of the carbon front face, even with the resin burnt out, and the low thermal diffusivity of the core, both play key roles in prolonging rear face integrity, something to be borne in mind for future panel design. Intumescent coatings prolong the period before failure occurs. The ratio of times to failure with and without protection is proposed as a measure of their effectiveness. Apart from insulation properties, their adhesion and stability under severe fire impact play a key role.
Developing halogen‐free flame retardants with reasonably high efficiency, which thus function at limited loadings in polypropylene‐based wood/plastic composites (WPC), is still a challenge. Cost‐effective flame‐retarded WPC have been identified as a way to open the door to an interesting, broader spectrum of application in the building and transportation sectors. This work imparts a systematic comprehensive understanding and assessment of different basic routes to halogen‐free flame‐retarded WPC, taking into account economic and environmental considerations. Cheap, halogen‐free single‐component flame retardants and their multicomponent systems are investigated at reasonable filling grades of 20 wt%. The basic routes of promising synergistic multicomponent systems are discussed, and their potential and Limits assessed. Optimizing the consistency of fire residue; closing the surface of inorganic‐organic residual layers; the thermal stabilization and design of the residue, eg, synergistic combination of ammonium polyphosphate and expandable graphite; and the combination of different flame‐retardant mechanisms, eg, intumescence and flame inhibition, are proposed as promising routes to boost the flame‐retardant efficiency.
Der Beitrag versucht sich an der Herausforderung, trotz beschränktem zeitlichen Rahmen einen ansprechenden Spagat zwischen umfangreichem Überblick und wissenschaftlichem Verständnis und so eine unabhängige und unparteiliche Einführung in Thematik flammgeschützte PUR-Schäume zu geben. Er kann sicherlich nicht individuelle Antworten oder konkrete Entwicklungsziele wie neue Rezepturvorschläge liefern, aber hofft zum Hintergrund und als Handwerkzeugs für das Aufstellen und Überdenken von Entwicklungsstrategien beizutragen.
The recently approved EU Construction Products Regulation (CPR) applies to cables as construction products.
The difficulty of predicting the fire performance of cables with respect to propagation of flame and contribution to fire hazards is well known. The new standard EN 50399 describes a full-scale test method for the classification of vertically mounted bunched cables according to CPR. Consideration of the material, time, and thus cost requires an alternative bench-scale fire test, which finds strong demand for Screening and development purposes. The development of such a bench-scale fire test to assess the fire Performance of multiple vertically mounted cables is described. A practical module for the cone calorimeter is proposed, simulating the fire scenario of the EN 50399 on the bench scale. The efficacy of this module in predicting full-scale CPR test results is shown for a set of 20 different optical cables. Key properties such as peak heat release rate (PHRR), fire growth rate (FIGRA), and flame spread are linked to each other by factors of around 5. In a case study, the bench-scale test designed was used to investigate the influence of the main components on the fire behaviour of a complex optical cable.
Thermal insulation and mechanical resistance play a crucial role for the performance of an intumescent coating. Both properties depend strongly on the morphology and morphological development of the foamed residue. Small amounts (4 wt%) of fiberglass, clay and a copper salt, respectively, are incorporated into an intumescent coating to study their influence on the morphology and Performance of the residues. The bench scale fire tests were performed on 75 x 75 x 2 mm³ coated steel plates according to the standard time–temperature curve in the Standard Time Temperature Muffle Furnace+ (STT Mufu+). It provided information about foaming dynamics (expansion rates) and thermal insulation. Adding the copper salt halved the expansion height, whereas the clay and fiberglass Change the height of the residue only moderately. The time to reach 500 °C was improved by 31% for clay and 15% for the other two fillers. Nondestructive micro computed tomography is used to assess the inner structure of the residues. A transition of the residue from a black, carbonaceous foam with closed cells into an inorganic, residual open cell sponge occurs at high temperatures. This transition is due to a loss of carbon; the change in microstructure is analyzed by scanning electron microscopy. Additional mechanical tests are performed and interpreted with respect to the results of the morphology analysis. Adding clay or copper salt improved the mechanical resistance tested by a factor 4. The additives significantly influence the thickness and foaming Dynamics as well as the inner structure of the residues, whereas their influence on insulation Performance is moderate. In conclusion, different modes of action are observed to achieve similar insulation performance during the fire test.
Although the main flame retardant modes of action are known, in practise the detailed scientific understanding usually falls short, when it comes to modern multicomponent systems, the important tiny optimizations, or quantifying in terms of specific fire properties. Thus instead of a textbook-like overview of different flame retardant modes of action, this talk tries to deliver thought-provoking impulses. Some overseen details are picked up as well as basic questions raised. Rethinking of concepts memorised long ago is encouraged to discover something new. Furthermore, the talk tries to fill the gap between flame retardant modes of action and fire performance.
The fire resistance of load-bearing composite components, e.g. sandwich panels in transportation or stringer reinforced shells used for fuselages, differs in comparison to metal systems. Fibres behave rather inert with respect to pyrolysis reducing burn-through phenomena. The fire stability becomes the main task, because it already breaks down when reaching the softening temperature of the matrix. Fire protection concepts are needed based on efficient thermal insulation and tailored for composite structures.
The fire behaviour of fibre reinforced polymeric composites differs in comparison to polymers. Fibres behave often inert with respect to pyrolysis, they change dripping behaviour, the heat absorption and transfer, the amount and properties of the fire residue and so on. Their fire behaviour becomes somewhat singular. The fire resistance of load-bearing composite components, e.g. sandwich panels for transportation or stringer reinforced shells used for fuselages in aviation, differs in comparison to metal systems. Not burn-through, but the fire stability is typical critical mode of failure. The mechanical failure in fully developed fires can not be explained by the mechanical properties at room temperature, but are controlled by the decomposition and even more important by the softening of the matrix. Fire retardancy concepts are needed based on efficient thermal insulation and tailored for composites. This field is illuminated by examples taken from different projects carried out in the group of the presenting author in the recent years,[1-5] and still running unpublished activities as well. The fire stability is investigated for realistic compression loads, when a severe flame is directly applied (key property in fully developed fires). A bench scale specimen (specimen 150 mm x 150 mm, plates, sandwich, shells) and an intermediate scale (specimen 500 mm x 500 mm, plates, sandwich, shells) fire stability testing was performed. Indeed, e.g. we have investigated the fire stability of stringer reinforced shell components taken out from the fuselage of an aircraft. We applied mechanical load up to 233 kN and 1 MN in the bench-scale and intermediate-scale testing, respectively, and direct flame exposure using burners (180 kW/m2) simultaneously.
The understanding of the fire resistance and fire protection modes of action in composite and composite components is a promising basis for target-oriented development. The role of the fire residue, protective layer formation, and the design of the components is discussed. Successful concepts are presented for increasing the fire resistance of load-bearing composite components as well as general guidelines for future development.
The passive fire protection of steel structures and other load-bearing components will continue to gain importance in future years. In the present contribution, novel intumescent aluminosilicate (geopolymer-bound) composites are proposed as fire-protective coatings on steel. Steel plates coated with these materials were exposed to the standard temperature-time curve as defined in ISO 834 – 1:1999. The coatings partially foamed during curing and expanded further during thermal exposure, demonstrating their intumescent characteristic.Thermogravimetryandoscillatory rheometry determined that the intumescent behavior is attributed to a transition to a viscous state (loss factor > 1) in the temperature range of major water release, differing from conventional geopolymers. XRD and SEM images showed that the coatings had characteristics of ceramic or glass-ceramic foams after fire resistance testing, suggesting superior performance under challenging conditions. The thickness of the coatings influenced their foaming and intumescent behavior and thus the time for the coated steel plates to reach 500 °C. A number of additives were also studied with the best performance obtained from samples containing sodium tetraborate.Acoating of just 6mmwas able to delay the time it takes for a steel substrate to reach 500 °C to more than 30 minutes.
The impact of polyaniline in phosphorus flame retardant ethylene-propylene-diene-rubber (EPDM)
(2019)
Usually elastomers are loaded with high amounts of flame retardants to fulfill fire safety requirements. In this study the potential char precursor polyaniline (PANI) and the established fire retardant pentaerythritol (PER) were implemented in ethylene-propylene-diene monomer rubber (EPDM). PANI and PER were used in low loadings (7 phr) and combined with two phosphorous flame retardants, Ammonium polyphosphate (APP) and a piperazine-pyrophosphate/phosphoric acid compound (FP), to boost their performance. A comprehensive study is presented, explaining the impact of PANI on curing and mechanical properties, including compensation for the plasticizer-like effect of APP in EPDM, and improved flame retardancy. In the cone calorimeter test, the combination of EPDM/FP/PANI reduced the effective heat of combustion by 20%. All nine EPDM rubber compounds were investigated with the LOI and UL 94 tests, cone calorimeter, FMVSS 302 and glow wire testing to quantify fire performance. The PANI containing EPDM rubbers, EPDM/APP/PANI and EPDM/FP/PANI outperformed the corresponding PER containing, EPDM/APP/PER and EPDM/FP/PER rubbers in various tests. Moreover, the study investigated the impact of PANI and PER on the mode of action of the phosphorus species and showed that the addition of PANI increased the amount of phosphorus in the condensed phase. To receive a broader understanding of the flame retardant mode of action of PANI in combination with APP and FP, calculations were carried out to estimate the impact of PANI on the protective layer effect.
The impact of phosphorus-containing flame retardants (FR) on rigid polyisocyanurate (PIR) foams is studied by systematic variation of the chemical structure of the FR, including non-NCO-reactive and NCO-reactive dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO)- and 9,10 dihydro-9-oxa-10 phosphaphenanthrene-10-oxide (DOPO)-containing compounds, among them a number of compounds not reported so far. These PIR foams are compared with PIR foams without FR and with standard FRs with respect to foam properties, thermal decomposition, and fire behavior. Although BPPO and DOPO differ by just one oxygen atom, the impact on the FR properties is very significant: when the FR is a filler or a dangling (dead) end in the PIR polymer network, DOPO is more effective than BPPO. When the FR is a subunit of a diol and it is fully incorporated in the PIR network, BPPO delivers superior results.
As most of polymeric materials are inherently flammable, flame retardants (FR) are commonly used to reduce their fire risks. Nevertheless, these flame retardant materials are often detrimental to smoke parameters like specific optical density or smoke toxicity. The influence of several smoke suppressants (SP)-zinc stannate, zinc phosphate, titanium oxide and hydrotalcite-were investigated with respect to flame retardancy, smoke emission, particle emission and smoke toxicity in a diethyl aluminum phosphinate (AlPi) flame retardant polyamide 6.6 (PA6.6). It was shown that the interaction between SP, FR and polymer is crucial for smoke and fire properties and can change the mode of action of the FR as well the decomposition mechanism of the polymer. Small amounts of SP show less effect on forced flaming behavior and the optical density, but they can influence flammability and the particle size distribution of the soot particles. The flame retardancy was significantly enhanced by 5 wt.-% zinc stannate in PA6.6 under forced flaming conditions. The charring mechanism was improved, and the mode of action of AlPi switched from the gas to the condensed phase. This resulted of in a reduced PHRR and TSP and an increase in residue yield. The smoke toxicity and optical density were reduced in the smoke density chamber as well. The smoke particles shifted to smaller sizes as the time in the pyrolytic zone increased. The formation of a dense char is assumed to be the key factor to enhance smoke suppression and flame retardancy properties.
Main message: Sustainability, or in other words, exploiting environmental conservation for the economic welfare and prosperity for all, would revolutionise the plastics industry were it to become predominant practice as a linear, fossil-fuel–based economy is switched to a carbon circular economy. Food for though is given by dint of a critical overview of the current trends in sustainable flame-retardant polymeric materials.
Introduction:
Transforming the plastics industry into a carbon circular economy over the next 30 years requires an immediate revolution entailing the development of cutting-edge materials and the planning of future industrial production plants. Hence, the innovative field of flame-retardant polymeric materials should lend its strength to drive this challenge. Visionary solutions are proposed to inspire us, while the implementation of economically feasible concepts can take us forward into the future.
Experimental The synthesis, processing, polymer analysis, thermal analysis, and investigation of fire behaviour from our own research are performed according to the state of the art, mostly in accordance with the pertinent ISO standards. Indeed, some of our equipment is part of the accredited lab; for the other methods we fulfil equivalent quality standards in terms of maintenance, calibration, participation in round robins, etc. Work steps such as the synthesis or preparation of new materials are usually outsourced or done with partners that have the relevant core competence. The talk also presents examples from other groups whose experimental is described in the corresponding scientific papers.
Results and Discussion An overview of current trends towards producing sustainable, flame-retardant polymeric materials is presented, using examples from the literature and by sketching our own projects performed in recent years. The examples are structured along a common theme leading from the use of old and new natural materials with some intrinsic flame retardancy, via flame-retardant biopolymers and biocomposites, to using renewable sources for flame retardants with the objective of exploiting natural sources available as industrial waste streams. Natural flame retardants and adjuvants are highlighted, although the status of most may be assessed as merely motivating our vision. Nevertheless, there are natural material streams finding their way into polymer mass production as fillers, adjuvants, polymers, or renewable educt sources. Natural substances originating from industrial waste streams open the door to sustainable solutions, because they are often available at low cost and avoid competition for land with farming or virgin forests. Aside from this main topic, remarks will address the recycling of flame-retarded polymeric materials; vitrimers are mentioned as a potential material for recyclable thermosets. At the end of the day, only convincing property profiles will prevail both for exploiting renewable sources and circular design, including cost effectiveness, sufficient availability, consistent quality, processibility, mechanical properties, and flame retardancy. However, sustainability must not be merely tolerated as an additional demand, but should instead be recognized as a solution, because sustainability aspires to ensure our economic welfare now and in the future.
Acknowledgement:
The examples shown from own project were supported by funding grants: BMBF WTZ: 01DN16040, DFG Scha 730/19-1, VW-Stiftung: Experiment No: 97437, DFG Scha 730/20-1, BMBF KMU Innovativ 031B1289B.
Only the nano-scaled structure of the nanocomposite and the dispersion of nanoparticles within the polymer matrix harbor multifunctional potential including superior fire retardancy. Thus, this chapter focuses on the dispersion of nanoplates, based mainly on studies of layered silicates and graphene/graphene-related nanoplates. The nanostructure and properties of the nanocomposites are dependent mainly on thermodynamic and kinetic factors during preparation. Improving nano-dispersion often directly improves flame retardancy. Therefore, the modification of the nanoplates as well as the preparation of nanocomposites becomes very important to control this dispersion. The dispersion of nanoplates functions as a prerequisite for the formation of an efficient protective layer, changing the melt flow and dripping behavior, or the improvement of the char properties.
Polyamide 4.6 (PA46) is a high-heat-resistant polymer, but it has no dripping resistance under fire. Three commercial grades of PA46 are investigated under UL 94 vertical fire test conditions. Their performances are discussed based on the materials’ structural, thermal, and rheological properties. PA46 presents flaming drops, whereas dripping is prevented in the flame-retarded PA46.
Friction-modified PA46 has increased flaming dripping. Temperature profiles of the specimens under fire and the temperature of the drops are measured by thermocouples. A UL 94 vertical test configuration consisting of two flame applications is designed to assess the quantitative dripping behavior of the set of materials by the particle finite element method (PFEM). Polymer properties (activation energy and Arrhenius coefficient of decomposition, char yield, density, effective heat of combustion, heat of decomposition, specific heat capacity, and thermal conductivity) in addition to rheological responses in high temperatures are estimated and measured as input parameters for the simulations. The dripping behavior obtained by simulated materials corresponds with the experimental results in terms of time and drop size. A consistent picture of the interplay of the different phenomena controlling dripping under fire appears to deliver a better understanding of the role of different materials’ properties
Im Rahmen des Forschungsprojektes IGF 20470N wurden Untersuchungen zum Alterungsverhalten von reaktiven Brandschutzsystemen (RBS) auf Stahlbauteilen durchgeführt. Mithilfe der Ergebnisse einer umfangreichen Literaturrecherche sowie experimentellen und numerischen Untersuchungen sollte ein Vorschlag für ein Prüfkonzept zum Nachweis einer Nutzungsdauer von RBS von mehr als 10 Jahren auf Basis von Kurzzeitversuchen abgeleitet werden. Dabei setzt die Bewertung des Alterungsverhaltens von RBS voraus, dass die Mechanismen der Alterung hinreichend bekannt sind.
Dafür wurden zunächst systematisch Daten von Kurz- und Langzeitversuchen von nationalen Zulassungsprüfungen der letzten Jahrzehnte ausgewertet. Anschließend wurden umfangreiche experimentelle Untersuchungen an einer wasserbasierten sowie einer epoxidharzbasierten Richtrezeptur durchgeführt. Da aus der Literatur bekannt ist, dass die Einflüsse der Bewitterung zu einer Veränderung der Konzentration der Bestandteile innerhalb der Beschichtung führen können, wurden Untersuchungen mit Mangelrezepturen durchgeführt, wobei systematisch einzelne Bestandteile reduziert wurden. Neben optischen Untersuchungen wurden thermoanalytische Verfahren (DSC-TG-, ATR-FTIR-, Elementar-, Farbanalyse) angewandt sowie Brandversuche an beschichteten Stahlplatten durchgeführt. Des Weiteren wurden die Richtrezepturen den beschleunigten Kurzzeitversuchen gemäß EAD 350402-00-1106 (2017) unterzogen, welche die Zulassung von Produkten auf europäischer Ebene regelt. Für die wasserbasierte Richtrezeptur wurden die Bewitterung für den feuchten Innenraum (Typ Z1) mehrfach wiederholt (1x, 3x, 6x). Für die epoxidharzbasierte Richtrezeptur entsprach die Bewitterung dem Zyklus für die Außenanwendung (Typ X). In Brandversuchen sowie thermoanalytischen und optischen Untersuchungen wurde das Alterungsverhalten sowie die thermische Schutzwirkung analysiert.
Anschließend wurden numerische Simulationen von Stahlbauteilen mit gealterten RBS durchgeführt und anhand der experimentellen Untersuchungen validiert. Mithilfe der numerischen Modelle kann eine Bewertung der thermischen Schutzwirkung von Stahlbauteilen mit gealterten RBS vorgenommen werden.
Mithilfe der gesammelten Erkenntnisse wurde ein Vorschlag für ein Prüfkonzept für den Nachweis einer Nutzungsdauer von mehr als 10 Jahren abgeleitet. Das Prüfkonzept besteht dabei aus einem Katalog von Möglichkeiten, die aktuellen Zulassungsprüfungen auf europäischer Ebene für eine Nutzungsdauer von 10 Jahren auf einen längeren Zeitraum zu erweitern.
The addition of nanoparticles as reinforcing fillers in elastomers yields nanocomposites with unique property profiles, which opens the door for various new application fields. Major factors influencing the performance of nanocomposites are studied by varying the type and shape of nanoparticles and their dispersion in the natural rubber matrix. The industrial applicability of these nanocomposites is put into focus using two types of graphene and a nanoscale carbon black, all commercially available, and scalable processing techniques in the form of a highly filled masterbatch production via latex premixing by simple stirring or ultrasonically assisted dispersing with surfactant followed by conventional two-roll milling and hot pressing. Different processing and measurement methods reveal the potential for possible improvements: rheology, curing behavior, static and dynamic mechanical properties, swelling, and fire behavior. The aspect ratio of the nanoparticles and their interaction with the surrounding matrix prove to be crucial for the development of superior nanocomposites. An enhanced dispersing method enables the utilization of the improvement potential at low filler loadings (3 parts per hundred of rubber [phr]) and yields multifunctional rubber nanocomposites: two-dimensional layered particles (graphene) result in anisotropic material behavior with strong reinforcement in the in-plane direction (157% increase in the Young's modulus). The peak heat release rate in the cone calorimeter is reduced by 55% by incorporating 3 phr of few-layer graphene via an optimized dispersing process.
A series of flexible polyurethane foams (FPUFs) were prepared with single and different combinations of flame retardants and additives. Expandable graphite (EG), phosphorous polyol (OP), copper (II) oxide (CuO), and/or castor oil (CAS) were added to FPUF during the foam preparation in a one-step process. The purpose of the study is to evaluate the synergistic effects of the flame retardants, additives, and the presence of bio-based content on the mechanical properties, flame retardancy, and smoke behavior of FPUFs. The combination of 10 wt % EG and 5 wt % OP in FPUF significantly improves the char yield. In the cone calorimeter experiment, the char yield is nearly three times higher than that with 10 wt % EG alone. The smoke behavior is additionally evaluated in a smoke density chamber (SDC). Comparing the samples with a single flame retardant, 10 wt % EG in FPUF considerably reduces the amount of smoke released and the emission of toxic gases. Replacing the amount of 10 wt % polyether polyol in FPUF with CAS maintains the physical and mechanical properties and fire behavior and enhances the bio-based content. The presence of 0.1 wt % CuO in FPUF effectively reduces the emission of hydrogen cyanide. As a result, this study proposes a multicomponent flame retardant strategy for FPUF to enhance the biomass content and address the weaknesses in flame retardancy, smoke, and toxic gas emissions. A starting point is disclosed for future product development.
A few layer/multilayer graphene (MLG) with a specific surface area of BET ≥ 250 m2/g is proposed as an efficient multifunctional nanofiller for rubbers. The preparation method, i.e., ultrasonically-assisted solution or latex premixing of master batches followed by conventional two-roll milling, strongly influences the dispersion in the elastomeric matrix and is fundamental for the final properties. When homogenously dispersed, single stacks of only approximately 10 graphene sheets, with an aspect ratio of ca. 35, work at low loadings, enabling the replacement of large amounts of carbon black (CB), an increase in efficiency, and a reduction in filler load. The appropriate preparation yielded nanocomposites in which just 3 phr are sufficient to significantly improve the rheological, curing, gas barrier properties, electrical and thermal conductivity, as well as mechanical properties of different rubbers, as shown for chlorine-Isobutylene-Isoprene rubber (CIIR), nitrile-butadiene rubber (NBR), natural rubber (NR), and styrene-butadiene rubber (SBR).[1-5] 3 phr of MLG tripled the Young’s modulus of CIIR, an effect equivalent to 20 phr of CB. The stronger interactions between MLG and NR or SBR also resulted in a reduction in the elongation at break by 20% and 50%, respectively, while the same parameter was hardly changed for CIIR/MLG and NBR/MLG. CIIR/MLG and NBR/MLG were stiffer but just as defomable than CIIR and NBR. The strong reinforcing effect of 3 phr MLG was confirmed by the increase of greater than 10 Shore A in hardness. MLG reduces gas permeability, increases thermal and electrical conductivities, and retards flammability. We investigated MLG also as a synergist for reducing the aluminium trihydrate loading in flame retardant hydrogenated acrylonitrile-butadiene (HNBR), polybutadiene chloroprene (BR/CR), and chlorosulfonated polyethylene rubber(CSM).[6-8] The higher the nanofiller concentration is, the greater the improvement in the properties. For instance, the permeability decreased by 30% at 3 phr of MLG, 50% at 5 phr and 60% at 10 phr, respectively. Moreover, the MLG nanocomposites improve stability of mechanical properties against the effects of weathering. In key experiments an increase in UV-absorption and a pronounced radical scavenging were proved as stabilizing mechanisms. In a nutshell, MLG is an efficient multifunctional nanofiller ready to be used for innovative rubber development.
The dripping behaviour of polymers is often observed experimentally through the UL94 flammability standard test. In this work, polymeric dripping under fire is investigated numerically using particle finite element method. A parametric analysis was carried out to observe the influence of a single property on overall dripping behaviour via a UL94 vertical test model. Surrogates and property ranges were defined for variation of the following parameters: glass transition temperature (Tg), melting temperature (Tm), decomposition temperature (Td), density (ρ), specific heat capacity (Cp), apparent effective heat of combustion of the volatiles, char yield (μ), thermal conductivity (k), and viscosity (η). Polyamide, poly(ether ether ketone), poly(methyl methacrylate), and polysulfone were used as benchmarks. Simulated results showed that specific heat capacity, thermal conductivity, and char yield allied with viscosity were the properties that most influenced dripping behaviour (starting time and occurrence).
To ensure fire safety, polymers are filled with flame retardants and smoke suppressants. To meet the highest requirements, it is essential to understand the decomposition of those polymeric materials. This study reveals interactions between polymer, smoke suppressants, and flame retardants, and discusses their impact on the materials’ flame retardancy, smoke emission, smoke toxicity, and particle emission in conventional loadings to provide deeper general understanding. Low melting oxide glass, melem, spherical silica, sepiolite, melamine polyphosphate, and boehmite in an aluminum diethylphosphinate flame-retarded polyamide 6.6 were investigated. All smoke suppressants improve the protective layer and act as an adjuvant. Silica and melem performed best under forced flaming conditions. Spherical silica reduces the peak of heat release rate by 39% and the total heat evolved by 14%, whereas 10 wt% melem lowers the total smoke production by 41%. Melem alters the mode of action of aluminum diethylphosphinate from gas to more condensed phase activity. This change reduces flame inhibition and hence smoke toxicity, but further improves the protective layer due to charring reactions in the decomposition mechanism. In addition, the sizes of the smoke particles decrease because of the prolonged time in the pyrolytic zone. This study highlights that interactions between polymer, flame retardants, and smoke suppressants can significantly determine the smoking and burning behavior.
We report the selective ring opening copolymerisation (ROCOP) of
oxetane and phthalic thioanhydride by a heterobimetallic Cr(III)K
catalyst precisely yielding semi-crystalline alternating poly(esteralt-
thioesters) which show improved degradability due to the
thioester links in the polymer backbone.
Pressure-sensitive adhesive tapes are used in several industrial applications such as con-struction, railway vehicles and the automotive sector,where the burning behavior is ofcrucial importance. Flame retarded adhesivetapes are developed and provided, however,often without considering the interaction of adhesive tapes and the bonded materialsduring burning nor the contribution of the tapes to fire protection goal of the bondedcomponents in distinct fire tests. This publication delivers an empirical comprehensiveknowledge how adhesive tapes and their flame retardancy effect the burning behaviorof bonded materials. With a special focus on the interaction between the single compo-nents, one flame retarded tape and one tapewithout flame retardant are examined inscenarios of emerging and developing fires, along with their bonds with the commonmaterials wood, zinc-plated steel, mineral wool, polycarbonate, and polymethylmethacry-late. The flame retardant significantly improved the flame retardancy of the tape as afree-standing object and yielded a V-2 rating in UL 94 vertical test and raised the OxygenIndex by 5 vol.%. In bonds, or rather laminates, the investigations prove that the choiceof carrier and substrates are the factors with the greatest impact on the fire propertiesand can change the peak of heat release rate and the maximum average rate of heatemission up to 25%. This research yielded a good empirical overall understanding of thefire behavior of adhesive tapes and bonded materials. Thus, it serves as a guide for tapemanufacturers and applicants to develop tapes and bonds more substrate specific.
Short overview is given of BAM's research within the topic "Flame Retardancy of Polymeric Materials". Fire science is identified as a crucial compentenc of BAM following our mission "Safety in Technology and Chemistry". In the area of polymers we work interdisciplinary, in the dimensions from nm to 2m, and we love to combine experiment and simulation. Multimethodical examples are given to describe the burning phenomena and flame-retardant modes of action. Further some examples are presented for tailored bench-scale fire testing and assessing concepts. Our goal is to provide the fundaments for a evidenced-based development of future materials.
The residual post-fire mechanical properties of fiber-reinforced epoxy composites are influenced by their fire residues after burning. This study uses intumescent/low-melting glass flame retardants to tailor fire residues in epoxy resin. Processibility of prepregs and their quality are analysed for transfer of the flame-retardant epoxy resins to layered glass-fiber reinforced composites. Minimal effects were found on the pre-fire flexural strengths of the composites due to low loading of the flame retardants. However, when transferred to glass-fiber reinforced composites, the fire residues diminish significantly. Further studies are required to improve theoretical and experimental estimations of the post-fire mechanics of the composites.
Combining buffing leather fibers from industrial waste streams with ammonium polyphosphate and bentonite clay is proposed as a flame-retardant additive for polypropylene. The paper addresses how they can be processed into attractive composites with the desired mechanical properties. Buffing leather fibers function as a multifunctional bio-filler and as a synergist for the flame retardant, resulting in fire retardancy successful enough to increase the oxygen index (LOI) by up to 7 vol.-% and to achieve a V0 UL 94 classification. Impressively reduced heat release rates are obtained in the cone calorimeter at 50 kW/m2 irradiation; for instance, the maximum average rate heat evolved (MARHE) drops from 765 to below 200 kW m 2. The synergistic effects are quantified and shown to be very strong for LOI and MARHE. This work opens the door to use waste buffing leather fibers as a promising multifunctional and synergistic bio-filler.