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The correct use of scientific terms, performing experiments accurately, and discussing data using unequivocal scientific concepts constitute the basis for good scientific practice. The significance and thus the quality of scientific communication rely on the proper use of terms and methods. It is the aim of this two-part article to support the community with recommendations for discussing the flame retardancy of polymers by addressing some of the most relevant points. The first article (part one of two) clarifies some scientific terms and, in some cases, such as for ‘‘pyrolysis,’’ ‘‘thermal decomposition,’’ and ‘‘fire resistance,’’ critically discusses their definitions in the field of fire science. Several comments are made on proper fire testing and thermal analysis, including some thoughts on uncertainty in fire testing. The proper use of distinct concepts in flame retardancy is discussed briefly in the subsequent second article (part two). This article tries to Balance imparting background on the subject with recommendations. It encourages to check scientific practice with respect to communication and applying methods.
A systematic comparison of chemical interactions and fire behaviour is presented for the thermoplas-tic elastomer (block copolymer styrene-ethylene-butadiene-styrene) (TPE-S)/diethyl- and methylvinylsiloxane (Si)/poly(phenylene oxide) (PPO), flame-retarded with aluminium diethylphosphinate (AlPi)and with ammonium polyphosphate (APP), respectively. TPE-S/APP/Si/PPO performed better in the conecalorimeter test (reduction in peak heat release rate from 2042 to 475 kW m−2), but TPE-S/AlPi/Si/PPO inthe flammability tests (oxygen index (OI) and UL 94). This difference was caused by the different modes ofaction of APP (more in the condensed phase) and AlPi (mainly in the gas phase). Thermogravimetry cou-pled with Fourier transform infrared spectroscopy (TG-FTIR) was used to analyse the mass loss and theevolved gas products, while a Linkam hot-stage cell to investigate the decomposition in the condensedphase. Moreover, a detailed analysis of the fire residues was done using solid-state NMR.13C MAS NMRshowed that both flame-retarded compositions form graphite-like amorphous carbonaceous char, orig-inating from PPO.31P MAS NMR and29Si MAS NMR delivered important information about interactionbetween phosphorus and the siloxane. For TPE-S/AlPi/Si/PPO aluminium phosphate and silicon dioxideoccurred, while also silicophosphate was produced in TPE-S/APP/Si/PPO. The direct comparison of two ofthe most prominent halogen-free flame retardants containing phosphorus delivered meaningful insightsinto the modes of action and molecular mechanisms controlling flame retardancy.
In recent years, different nanoparticles have been proposed and successfully introduced as nanofillers in rubber nanocomposites. In this study, multilayer graphene (MLG) is proposed as a nanoparticle that functions efficiently at low concentrations. MLG consists of just 10 or so graphene sheets. Chlorine isobutyl isoprene rubber (CIIR)/MLG nanocomposites with different MLG loadings were prepared using an ultrasonically assisted solution mixing procedure followed by two-roll milling. The incorporation of MLG provides a clear improvement in the rheological, mechanical, curing, and gas barrier properties of the nanocomposites. Adding only 3 phr ofMLGto CIIR increased the Young’s modulus by more than two times and reduced the permeability ofO2 andCO2 by 30%. Higher nanofiller concentrations yielded further improvement in the properties of the nanocomposites. Moreover, CIIR/MLG nanocomposites showed reduced flammability.
Wesentlich für das Sicherheitsniveau und damit die nachhaltige Wettbewerbsfähigkeit des Technologiestandortes Deutschland ist der Brandschutz in Industrieanlagen, in Gebäuden und im Transportwesen. Der vorbeugende bauliche Brandschutz hat u. a. das Ziel, die Brand- und Rauchausbreitung im Brandfall für eine gewisse Zeit zu behindern, damit die erforderlichen Lösch- und Rettungsarbeiten durchgeführt werden können. Dies geschieht u.a. durch Anforderungen an die Feuerwiderstandsfähigkeit brandbeanspruchter Bauteile. Der Feuerwiderstand eines Bauteils ist die Fähigkeit während eines angegebenen Zeitraums in einer genormten Feuerwiderstandsprüfung bezüglich mechanischer Stabilität und/oder thermischer Isolierung nicht zu versagen. Reaktive Brandschutzbeschichtungen erhöhen für viele Bauteile sehr effektiv den Feuerwiderstand. Die Beschichtungen und die Brandprüfungen müssen jedoch an die immer komplexeren Anwendungen und/oder extremeren Anforderungen angepasst und weiterentwickelt werden. Aktuelle Forschungsschwerpunkte liegen dabei in der Entwicklung neuer Materialien (z.B. Geopolymere, keramisierende Beschichtungen, silikonbasierte Beschichtungen) für extreme Brandszenarien (extreme Temperaturen, lange Beanspruchungszeiten) und in der Realisierung komplexer Funktionalitäten (komplexe Geometrien, bewegliche Komponenten) sowie in der Entwicklung neuer Testmethoden (Feuerwiderstand als bench-scale Tests, kostengünstiges Screening, Feuerwiderstand in extremen Brandszenarien). Die Entwicklung geht dabei weg von der präskriptiven Bewertung hin zur leistungsorientierten (performance-based) Bewertung in individuellen Brandszenarien oder von komplexen Bauteilen. Im Rahmen dieser Arbeit werden Lösungsansätze für die neuen Herausforderungen an die reaktiven Brandschutzsysteme unter Extrembedingungen und deren Testmöglichkeiten vorgestellt und diskutiert. Im Mittelpunkt stehen dabei neu entwickelte bench-scale Testmethoden zum Screening von neuen Beschichtungsmaterialien sowie zur Beurteilung spezieller bzw. materialspezifischer Aspekte des Feuerwiderstands unter Extrembedingungen.
Multilayer graphene/chlorine-isobutene-isoprene rubber nanocomposites: the effect of dispersion
(2016)
Multilayer graphene (MLG) is composed of approximately 10 sheets of graphene. It is a promising nanofiller just starting to become commercially available. The Dispersion of the nanofiller is essential to exploit the properties of the nanocomposites and is dependent on the preparation method. In this study, direct incorporation of 3 parts per hundred of rubber (phr) MLG into chlorine-isobutene- isoprene rubber (CIIR) on a two-roll mill did not result in substantial enhancement of the material properties. In contrast, by pre-mixing the MLG (3 phr) with CIIR using an ultrasonically assisted solution mixing procedure followed by two-roll milling, the properties (rheological, curing, and mechanical) were improved substantially compared with the MLG/CIIR nanocomposites mixed only on the mill. The Young’s moduli of the nanocomposites mixed in solution increased by 38%. The CIIR/MLG nanocomposites produced via solution showed superior durability against weathering exposure.
The functionalization of a natural sodium montmorillonite (MMT) with (3-glycidyloxypropyl)trimethoxysilane by a silylation procedure is presented, and its use as nanofiller in the melt compounding of low density polyethylene (LDPE) nanocomposites. In particular, the effects on the thermal stability and flame retardant properties of melt compounded LDPE nanocomposites are analyzed, with and without magnesium hydroxide (MH) as an additional conventional flame retardant. The purpose was to investigate possible synergistic effects between the two inorganic fillers on fire behavior. The obtained organosilylated clay showed higher interlayer spacing than the original MMT and good thermal stability, higher than that of many commercial organoclays modified with alkylammonium salts. Its addition to LDPE allowed the production of hybrids with nanoscale dispersion of the filler, as demonstrated by X-ray diffraction. The simultaneous presence of MH, which strongly interacts with the nanoclay, hindered intercalation of the polymer chains between the clay galleries and clay layer exfoliation within the LDPE resin.
The investigation of the thermal and burning behavior of the LDPE nanocomposites indicated that the organosilylated clay alone shows only a limited residual protection layer effect. In combination with MH the nanocomposites have a small adverse effect on the reaction to small flame as measured by the Oxygen index and UL 94 testing, and, surprisingly, no effect on the peak heat release rate in the cone calorimeter. The quality of the fire residue was lacking on the microscopic scale. The ternary LDPE/MH/ organoclay systems investigated did not open the door to reducing MH content in halogen-free flame retardant LDPE yet, but demand further research.
Multilayer Graphene (MLG), a nanoparticle with a specific surface of BET = 250 m²/g and thus made of only approximately 10 graphene sheets, is proposed as a nanofiller for rubbers. When homogenously dispersed, it works at low loadings enabling the replacement of carbon black (CB), increase in efficiency, or reduction in filler concentration. Actually the appropriate preparation yielded nanocomposites in which just 3 phr are sufficient to significantly improve the rheological, curing and 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). A mere 3 phr of MLG tripled the Young’s modulus of CIIR, an effect equivalent to 20 phr of carbon black. Similar equivalents are observed for MLG/CB mixtures. MLG reduces gas permeability, increases thermal and electrical conductivities, and retards fire behavior. The later shown by the reduction in heat release rate in the cone calorimeter. The higher the nanofiller concentration is (3 phr, 5 phr, and 10 phr was investigated), the greater the improvement in the properties of the nanocomposites. Moreover, the MLG nanocomposites improve stability of mechanical properties against weathering. An increase in UV-absorption as well as a pronounced radical scavenging are proposed and were proved experimentally. To sum up, MLG is interesting as a multifunctional nanofiller and seems to be quite ready for rubber development.
Synergistic multicomponent systems containing melamine poly(metal phosphate)s have been recently proposed as flame retardants. This work focuses on the decomposition pathways, molecular mechanisms and morphology of the fire residues of epoxy resin (EP) flame retarded with melamine poly(zinc phosphate) (MPZnP) to explain the modes of action and synergistic effects with selected synergists (melamine polyphosphate (MPP) and AlO(OH), respectively). The total load of flame retardants was always 20 wt.%. The decomposition pathways were investigated in detail via thermogravimetric Analysis coupled with Fourier transform infrared spectroscopy. The fire residues were investigated via elemental analysis und solid-state nuclear magnetic resonance spectroscopy. The morphology of intumescent fire residues was investigated via micro-computed tomography and scanning electron microscopy.
EP + (MPZnP + MPP) formed a highly voluminous residue that showed structural features of both EP + MPZnP and EP + MPP, resulting in a highly effective protection layer. EP + (MPZnP + AlO(OH)) preserved the entire quantity of phosphorus content during combustion due to the Formation of Zn₂P₂O₇ and AlPO₄.
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.
Melamine poly(metal phosphates) (MPMeP) are halogen-free flame retardants commercialized under the brand Name Safire. Melamine poly(aluminum phosphate) (MPAlP), melamine poly(zinc phosphate) (MPZnP), and melamine poly(Magnesium phosphate) (MPMgP) were compared in an epoxy resin (EP). The thermal decomposition, flammability, burning behavior, and glass transition temperature were investigated using thermogravimetric analysis, pyrolysis combustion flow calorimeter, UL 94 testing, cone calorimeter, and differential scanning calorimetry. While the materials exhibited similarities in their pyrolysis, EP+MPZnP and EP+MPMgP showed better fire behavior than EP+MPAlP due to superior protective properties of the fire residues. Maintaining the 20 wt % loading, MPZnP was combined with various other flame retardants. A synergistic effect was evident for melamine polyphosphate
(MPP), boehmite, and a derivative of 6H-Dibenzo[c,e][1,2]oxaphosphinine-6-oxide. The best overall performance was observed for EP+(MPZnP+MPP) because of the best protection effectiveness of the fire residue. EP +(MPZnP+MPP) achieved V1/V0 in UL 94, and an 80% reduction in the peak heat release rate. This study evaluates the efficiency of MPMeP in EP, alone and in combination with other flame retardants. MPMeP is a suitable flame retardant for epoxy resin, depending on its kind and synergists.