Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (218) (entfernen)
Schlagworte
- Flame retardancy (51)
- Flame retardant (26)
- Flammability (25)
- Flame retardance (22)
- Cone calorimeter (20)
- Epoxy resin (20)
- Nanocomposites (19)
- Fire retardancy (17)
- Pyrolysis (16)
- Nanocomposite (15)
Organisationseinheit der BAM
- 7.5 Technische Eigenschaften von Polymerwerkstoffen (73)
- 7 Bauwerkssicherheit (72)
- 7.3 Brandingenieurwesen (4)
- 6 Materialchemie (3)
- 7.1 Baustoffe (2)
- 5 Werkstofftechnik (1)
- 5.3 Polymere Verbundwerkstoffe (1)
- 6.0 Abteilungsleitung und andere (1)
- 6.3 Strukturanalytik (1)
- 6.6 Physik und chemische Analytik der Polymere (1)
Paper des Monats
- ja (2)
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.
Multicomponent flame retardant systems containing aluminum diethylphosphinate in thermoplastic styrene–ethylene–butylene–styrene elastomers are investigated (oxygen index, UL 94, cone calorimeter, and mechanical testing). Solid-state nuclear magnetic resonance, scanning electron microscopy, and elemental analysis illuminate the interactions in the condensed phase. Thermoplastic styrene–ethylene–butylene–styrene elastomers are a challenge for flame retardancy (peak heat release rate at 50 kW m-2 > 2000 kW m-2, oxygen index = 17.2 vol%, no UL-94 horizontal burn rating) since it burns without residue and with a very high effective heat of combustion. Adding aluminum diethylphosphinate results in efficient flame inhibition and improves the reaction to small flame, but it is less effective in the cone calorimeter. Its efficacy levels off for amounts >~25 wt%. As the most promising synergistic system, aluminum diethylphosphinate/melamine polyphosphate was identified, combining the main gas action of aluminum diethylphosphinate with condensed phase mechanisms. The protection layer was further improved with several adjuvants. Keeping the overall flame retardant content at 30 wt%, aluminum diethylphosphinate/melamine polyphosphate/titanium dioxide and aluminum diethylphosphinate/melamine polyphosphate/boehmite were the best approaches. An oxygen index of up to 27 vol% was achieved and a horizontal burn rating in UL 94 with immediate self-extinction; peak heat release rate decreased by up to 85% compared to thermoplastic styrene–ethylene–butylene–styrene elastomers, to <300 kW m-2.
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.
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.
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.
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 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.
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.
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.
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.
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.
The valorization of macroalgae digestate as a secondary resource for high value chemicals and nutrients will promote the sustainability and circularity of anaerobic digestion based biorefinery. In this study, three digestates from A. nodosum C.linum and L. digitata were separated into liquid and solid fractions to investigate the production of high value added chemicals through pyrolysis using Pyrolysis Gas Chromatography Mass Spectroscopy (Py-GC/MS) while the filtered liquid fractions were tested as an alternative culture media to grow C. sorokiniana under mixotrophic conditions. The digestates showed different thermal degradation and an improvement of bio-oil profiles compared to the starter material. Pyrolyzates from raw macroalgae were characterized by a high anhydrosugar content in contrast to high aromatics observed in the case of their digestates. Toluene, benzofuran and vinylphenol, base chemicals for many industries, represented together 30–37% of the total chemicals produced during pyrolysis of the three macroalgae digestate. On the other hand, C. sorokiniana cultured on digestate-based media showed a higher lipid content with an increase in monounsaturated fatty acids and a lower poly-unsaturated fatty acid content in comparison to microalgae grown in standard tris-acetate-phosphate media. Thus, the acyl composition was shifted in a direction more suitable for biodiesel production by this process. In addition, the increase of Chemical Oxygen Demand and Volatile Fatty Acids concentration in the digestate was found to reduce ammonium toxicity. Finally, 94% of Chemical Oxygen Demand and 83% of ammonium were removed by microalgae from the digestate-based media which will reduce the pollution risk of the biorefinery. Overall, the results indicate that using macroalgae solid digestates can generate improvements in the quality of
products obtained by pyrolysis and the liquid digestate can positively influence microalgae growth and its products.
Simulation of the burning and dripping cables in fire using the particle finite element method
(2022)
The behavior of the cable jacket in fire characterized by the tendency to melt and drip constitutes a major source of fire hazard. The reason is that the melted material may convey the flame from one point to another, expanding fire and contributing to the fire load. In this article, the capability of a new computational strategy based on the particle finite element method for simulating a bench-scale cables burning test is analyzed. The use bench-scale test has been previously used to simulate the full-scale test described in EN 50399. As the air effect is neglected, a simple combustion model is included. The samples selected are two cables consisting of a copper core and differently flame retarded thermoplastic polyurethane sheets. The key modeling parameters were determined from different literature sources as well as experimentally. During the experiment, the specimen was burned under the test set-up condition recording the process and measuring the temperature evolution by means of three thermocouples. Next, the test was reproduced numerically and compared with a real fire test. The numerical results show that the particle finite element method can accurately predict the evolution of the temperature and the melting of the jacket.
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.
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.
A phosphaphenanthrene and triazinetrione group containing flame retardant (TAD) is combined with organically modified montmorillonite (OMMT) in epoxy resin thermosets (EP) to improve the performance of the flame-retardant system. When only 1 wt% OMMT/4 wt% TAD is introduced into the EP, the limited oxygen index (LOI) rises from 26% to 36.9% and a V-0 rating is achieved in a UL 94 test. The decomposition and pyrolysis products in the gas phase and condensed phase were characterized using thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR). The influence on the decomposition of EP, such as the increase in char yield, is limited with the incorporation of OMMT; a large amount of the phosphorus is released into the gas phase. The flame-retardant effect evaluation based on cone calorimeter data testified that OMMT improves the protective-barrier effect of the fire residue of OMMT/TAD/EP on the macroscopic scale, while TAD mainly causes flame inhibition. The fire residues showed a corresponding macroscopic appearance (digital photo) and microstructure (scanning electron microscope [SEM] results). The protective barrier effect of OMMT and the flame-inhibition effect of TAD combined to exert a superior flame-retardant effect, resulting in sufficient flame-retardant performance of OMMT/TAD/EP
Flame retardancy for thermoplastics is a challenging task where chemists and engineers work together to find solutions to improve the burning behavior without strongly influencing other key properties of the material. In this work, the halogen-free additives aluminum diethylphosphinate (AlPi-Et) and a mixture of aluminum phosphinate (AlPi) and resorcinol-bis(di-2,6-xylyl phosphate) (AlPi-H + RXP) are employed in neat and reinforced poly(butylene terephthalate) (PBT), and the morphology, mechanical performance, rheological behavior, and flammability of these materials are compared. Both additives show submicron dimensions but differ in terms of particle and agglomerate sizes und shapes. The overall mechanical performance of the PBT flame-retarded with AlPi-Et is lower than that with AlPi-H-RXP, due to the presence of larger agglomerates. Moreover, the flow behavior of the AlPi-Et/PBT materials is dramatically changed as the larger rod-like primary particles build a percolation threshold. In terms of flammability, both additives perform similar in the UL 94 test and under forced-flaming combustion. Nevertheless, AlPi-Et performs better than AlPi-H + RXP in the LOI test. The concentration required to achieve acceptable flame retardancy ranges above 15 wt %.
A comparative evaluation of systematically tailored chemical structures of various phosphorus-containing aminic hardeners for epoxy resins was carried out. In particular, the effect of the oxidation state of the phosphorus in the hardener molecule on the curing behavior, the mechanical, thermomechanical, and hot-wet properties of a cured bifunctional bisphenol-A based thermoset is discussed. Particular attention is paid to the comparative pyrolysis of neat cured epoxy resins containing phosphine oxide, phosphinate, phosphonate, and phosphate (with a phosphorus content of about 2.6 wt %) and of the fire behavior of their corresponding carbon fiber-reinforced composites. Comparatively faster curing thermosetting system with an enhanced flame retardancy and adequate processing behavior can be formulated by taking advantage of the higher reactivity of the phosphorus-modified hardeners. For example, a combination of the high reactivity and of induced secondary crosslinking reactions leads to a comparatively high Tg when curing the epoxy using a substoichiometric amount of the phosphinate-based hardener. The overall mechanical performance of the materials cured with the phosphorus-containing hardeners is comparable to that of a 4,4-DDS-cured reference system. While the various phosphorus-containing hardeners in general provide the epoxy-based matrix with enhanced flame retardancy properties, it is the flame inhibition in the gas phase especially that determines the improvement in fire retardancy of carbon fiber-reinforced composites. In summary, the present study provides an important contribution towards developing a better understanding of the potential use of such phosphorus-containing compounds to provide the composite matrix with sufficient flame retardancy while simultaneously maintaining its overall mechanical performance on a suitable level.
A systematic and comparative evaluation of the pyrolysis of halogen-free flame-retarded epoxy resins containing phosphine oxide, phosphinate, phosphonate, and phosphate (phosphorus contents around 2.6 wt.%) and the fire behaviour of their carbon fibre composites is presented. Decomposition pathways are proposed based on the thermal analysis (TG), TG coupled with evolved gas analysis (TG-FTIR), kinetics and analysis of the residue with FTIR and XPS. All organophosphorus-modified hardeners containing phenoxy groups lead to a reduced decomposition temperature and mass loss step for the main decomposition of the cured epoxy resin. With increasing oxidation state of the phosphorus the thermally stable residue increases, whereas the release of phosphorus-containing volatiles decreases. The flammability of the composites was investigated with LOI and UL 94 and the fire behaviour for forced-flaming conditions with cone calorimeter tests performed using different irradiations. The flame retardancy mechanisms are discussed. With increasing oxidation state of the phosphorus additional charring is observed, whereas the flame inhibition, which plays the more important role for the performance of the composites, decreases. The processing and the mechanical performance (delamination resistance, flexural properties and interlaminar bonding strength) of the fibre-reinforced composites containing phosphorus were maintained at a high level and, in some cases, even improved. The potential for optimising flame retardancy while maintaining mechanical properties is highlighted in this study.