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In this study, multicomponent flame retardant systems, consisting of Ammonium polyphosphate (APP), aluminum trihydroxide (ATH), and polyaniline (PANI), were used in ethylene propylene diene monomer (EPDM) rubber. The multicomponent system was designed to improve flame retardancy and the mechanical properties of the rubber compounds, while simultaneously reducing the amount of filler. PANI was applied at low loadings (7 phr) and combined with the phosphorous APP (21 phr) and the mineral flame retardant ATH (50 phr). A comprehensive study of six EPDM rubbers was carried out by systematically varying the fillers to explain the impact of multicomponent flame retardant systems on mechanical properties. The six EPDM materials were investigated via the UL 94, limiting oxygen index (LOI), FMVSS 302, glow wire tests, and the cone calorimeter, showing that multicomponent flame retardant systems led to improved fire performance.
In cone calorimeter tests the EPDM/APP/ATH/PANI composite reduced the maximum average rate of heat emission (MARHE) to 142 kW·m-2, a value 50% lower than that for the unfilled EPDM rubber. Furthermore, the amount of phosphorus in the residues was quantified and the mode of action of the phosphorous flame retardant APP was explained. The data from the cone calorimeter were used to determine the protective layer effect of the multicomponent flame retardant systems in the EPDM compounds.
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.
Elastomers are used in a wide range of automotive and railway applications. However, a severe drawback of most rubbers are their high flammability. Therefore, flame retardants (FRs) are added to improve the performance in fire. Generally, rubber composites are filled with high amounts of mineral fillers such as aluminium trihydroxide (ATH) to fulfil fire safety regulations. These high loadings may cause deterioration of the physical properties of the material. This work shows the implementation of two new strategies to achieve the modern demands on non-toxic FRs and the reduction of fillers.
The first approach was the implementation of multilayer graphene (MLG), acting as a multifunctional filler, reinforcing agent and FR. The study presents filler combinations with a systematic variation of the fillers carbon black (CB), MLG and ATH. The nanocomposites were prepared via master batch by an ultrasonically assisted solution mixing. Afterwards the master batch was compounded into the rubber in a two-roll milling. MLG substituted high amounts of the conventional filler CB, leading to reduced filler loadings and a consistent improvement in curing, mechanical and FR properties.
The second strategy was the combination of phosphorous-containing FRs with a potential new polymeric char promoting agent polyaniline (PANI). Char promoting additives such as pentaerythritol (PER) improve the effectiveness of the FR system. The combination of ammonium polyphosphate (APP) with PER was successfully investigated for natural and styrene-butadiene rubber composites. This work investigates the flame retardancy of the combination of FRs with PANI and its capability to act as a char/barrier promoter in EPDM.
The morphology of the rubbers and homogenously dispersion of MLG was investigated via scanning/transmission electron microscope (SEM/TEM) micrographs. Rheological and mechanical measurements assessed the influence of the fillers on the physical properties of the rubber composites. Characterization via thermogravimetric analysis (TGA) led to a broader understanding of the decomposition. In order to determine the flame retardancy effect of these materials, a multi-methodical approach was selected. Limiting oxygen index (LOI) and UL-94 were used to quantify the flammability of the rubber composites. The cone calorimeter provided information about the fire behaviour in forced flaming conditions. Residues were investigated via elementary analysis and XPS to clarify the composition of the remaining material. Glow-Wire and FMVSS 302 tests revealed significant results in terms of flame retardancy. The flame retardancy investigation of rubber composites, combinations of ATH with MLG and ATH with phosphorous-containing FRs, broaden the horizons of rubber flame retardancy solutions. By examining alternate FR formulations and their effect on mechanical and physical properties of the rubber, new insight into the range of applicable additives for rubber composites may be won.
Three novel liquid ethyl (diethoxymethyl)phosphinate derivatives (EDPs) were synthesized and incorporated into flexible polyurethane foams (FPUFs). The flame retardancy of FPUFs were evaluated by limiting oxygen index (LOI), vertical burning and cone calorimetry tests, and the results indicated the structure-flame retardancy relationship of EDPs. Among these EDPs, P-(diethoxymethyl)-N-phenylphosphonamidate (EDPPA) exhibited the best flame retardant effect, methyl 3-((diethoxymethyl)(ethoxy)phosphoryl)propanoate (EDPMA) the second, and ethyl phenyl (di-ethoxymethyl)phosphonate (EDPPO) the worst. When the incorporation of EDPPA was 10 wt%, the FPUFs could self-extinguish and pass the vertical burning test. Meanwhile, the LOI value of FPUF-PA increased to 23.6% with 20 wt% loading of flame retardant. According to the investigation of volatiles during the thermal degradation of FPUFs and the morphologies of char residues after cone test, we inferred the pos- sible flame retardant mechanism. The results indicated that EDPs could release phosphorus-containing compounds in the gas phase, which would generate phosphorus-containing radicals and play the role of radical scavenger. In the condensed phase, EDPs can promote the formation of dense, intact and thermal stably char layer on the surface of FPUFs. Moreover, we found that the structure influence on flame retardancy was attributed to the atoms linked to the central phosphorus. Our results indicate that these EDPs are promising flame retardants in FPUFs that can be applied to improve the flame retardancy of FPUFs in various practical applications.
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.
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.
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
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.
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.
Advanced analysis of flame retarded epoxy resin/melamine poly(metal phosphate)/synergist systems
(2017)
Synergistic multicomponent systems containing melamine poly(metal phosphate) have been proposed as flame retardants. 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) (MMgP) and EP/melamine poly(zinc phosphate) (MZnP). A multi-methodical approach was used to investigate the pyrolysis, fire residues, flame retardant modes of action, and synergistic effects. The decomposition and the fuel released into the gas phase were investigated by thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR). A detailed analysis of the condensed phase was done by FTIR and comprehensive solid-state nuclear magnetic resonance spectroscopy (NMR). The fire behaviour was investigated by the cone calorimeter and the morphology of the fire residues with micro-computed tomography (µCT) and scanning electron microscopy (SEM). The best performance is observed for EP/MMgP/MPP and EP/MZnP/MPP based on a synergistic effect between the flame retardants. Particular the formation of a highly voluminous fire residue plays a major role and is stabilized by the interaction between the flame retardants. As a result highly effective protection layer was formed which led to the interesting results.