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- Flame retardancy (9)
- Solid-state NMR (5)
- Zinc borate (4)
- Aryl phosphate (3)
- Aluminium diethylphosphinate (2)
- Epoxy resin (2)
- Flame retardance (2)
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- Magnesium hydroxide (2)
- Polycarbonate (PC) blends (2)
The fire retardancy mechanisms of aluminium diethylphosphinate in combination with melamine polyphosphate and zinc borate was analysed in glass-fibre reinforced polyamide 6,6. The influence of phosphorus compounds on the polyamide decomposition pathways was characterized using thermal analysis (TG), evolved gas analysis (TGFTIR), and FTIRATR analysis of the residue. The Lewis acidbase interactions between the flame retardants, the amide unit, and the metal ions control the decomposition. The flammability (LOI, UL 94) and performance under forced-flaming conditions (cone calorimeter using different irradiations) were investigated. Fire residues were analysed with FTIRATR, SEMEDX, and NMR. Aluminium phosphinate in polyamide 6,6 acts mainly by flame inhibition. Melamine polyphosphate shows some fuel dilution and a significant barrier effect. Using a combination of aluminium phosphinate and melamine polyphosphate results in some charring and a dominant barrier effect. These effects are improved in the presence of zinc borate due to the formation of boronaluminium phosphates instead of aluminium phosphates.
Thermal, thermo-oxidative and fire residues of high impact polystyrene/magnesium hydroxide/red phosphorus (HIPS/Mg(OH)2/Pr) are investigated by solid-state NMR and compared with the results for the binary subsystem Mg(OH)2/Pr. The influences of oxygen, nitrogen and temperature are discussed. For a thermal decomposition and pyrolysis during combustion, the main pyrolysis of HIPS takes place while the remaining residue is a rather intact polymer, with a major share of the embedded Pr still present. Subsequently, mainly amorphous phosphates and a slight amount of crystalline Mg3(PO4)2 and Mg2P2O7 are formed at the highest temperatures. Only with increasing mass loss does the remaining polystyrene structure decompose and graphitic structures occur. The influence of oxygen on the decomposition mechanism is most obvious for the binary system Mg(OH)2/Pr. Pr vanishes more rapidly and crystalline, oxygen-rich magnesium phosphates are formed. In HIPS/Mg(OH)2/Pr systems the polymer acts as a barrier to reaction by the embedded particles, so that major characteristics of an anaerobic decomposition are found. Significant amounts of phosphorus are retained in the condensed phase through a reaction of Pr with Mg(OH)2 to mostly amorphous phosphates. This formation of amorphous inorganic magnesium phosphates can act as an additional physical barrier. This study outlines some advanced approaches for controlling the condensed-phase mechanisms of phosphorus and underlines that solid-state NMR is a most powerful tool for investigating the organic and inorganic residues.
Bisphenol A polycarbonate/acrylonitrile–butadiene–styrene (PC/ABS) with and without bisphenol A bis(diphenyl phosphate) (BDP) and 5 wt.% zinc borate (Znb) were investigated. The pyrolysis was studied by thermogravimetry (TG), TG-FTIR and NMR, the fire behaviour with a cone calorimeter applying different heat fluxes, LOI and UL 94. Fire residues were examined with NMR. BDP affects the decomposition of PC/ABS and acts as a flame retardant in the gas and condensed phases. The addition of Znb results in an additional hydrolysis of PC. The fire behaviour is similar to PC/ABS, aside from a slightly increased LOI and a reduced peak heat release rate, both caused by borates improving the barrier properties of the char. In PC/ABS + BDP + Znb, the addition of Znb yields a borate network and amorphous phosphates. Znb also reacts with BDP to form alpha-zinc phosphate and borophosphates that suppress the original flame retardancy mechanisms of BDP. The inorganic–organic residue formed provides more effective flame retardancy, in particular at low irradiation in the cone calorimeter, and a clear synergy in LOI, whereas for more developed fires BDP + Znb become less effective than BDP in PC/ABS with respect to the total heat evolved.
Distinct approaches are used to reduce the fire risks of polymers, a key issue for many industrial applications. Among the variety of approaches, the use of synergy in halogen-free multicomponent systems is one of the most auspicious. To optimize the composition of such flame-retardant systems it is essential to understand the mechanisms and the corresponding chemistry in the condensed phase. In this work different methods are used, including cone calorimeter, thermogravimetry (TG), and TG-FTIR, with the main focus on the solid-state NMR analysis of the solid residues. The structural changes in the condensed phase of two thermoplastic elastomer systems based on copolymer styrene-ethylene-butadiene-styrene (TPE-S) were investigated: TPE-S/aluminium diethylphosphinate (AlPi)/magnesium hydroxide (MH) and TPE-S/AlPi/zinc borate (ZB)/poly(phenylene oxide) (PPO). Strong flame inhibition is synergistically combined with protective layer formation. 13C-, 27Al-, 11B- and 31P MAS NMR (magic angle spinning nuclear magnetic resonance) experiments using direct excitation with a single pulse and 1H31P cross-polarization (CP) were carried out as well as double resonance techniques. Magnesium phosphates were formed during the pyrolysis of TPE-S/AlPi/MH, while for the system TPE-S/AlPi/ZB/PPO zinc phosphates and borophosphates were observed. Thus, the chemistry behind the chemical interaction was characterized unambiguously for the investigated systems.
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.
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.
Various inorganic additives belonging to four different groups: layered materials, metal hydroxides, metal oxides/carbonate and metal borates are investigated in bisphenol A polycarbonate/silicon rubber/bisphenol A bis(diphenyl phosphate) (PC/SiR/BDP) to improve flame retardancy. The pyrolysis, reaction to small flame and fire behaviour of the blends are characterised and structure–property relationships discussed. Among the added layered materials, talc functions as an inert filler with potential for commercialisation, whereas organically modified montmorillonite (LS) enhances decomposition. PC/SiR/BDP + talc and PC/SiR/BDP + LS reinforce the char and induce a flow limit. The different dispersion and location of boehmite (AlO(OH)) nano-particles and Mg(OH)2 micro-particles determine the impact on performance. PC/SiR/BDP + Mg(OH)2 shows additional hydrolysis and thus reduced flame retardancy. AlO(OH) is embedded in SiR and thus behaves as an inert filler. Both additives worked as smoke suppressants. Using selective filling with nano-particles is proposed as an interesting route for flame retardancy in PC/SiR blends. Adding metal oxides and carbonate (MgO, CaCO3 and SiO2) changes the decomposition pathways of PC/SiR/BDP, worsening the fire performance of PC/SiR/BDP. CaCO3 harbours the potential to intumescence, even though an early collapse of the char structure occurred. Adding hydrated metal borates, CaB, MgB and ZnB, changes the pyrolysis and flame retardancy action. Smoke suppression occurs; LOI is improved as well as UL 94 classification. ZnB performs better than MgB and CaB. The comprehensive study, also based on systematic material variation, delivers valuable guidelines for future development of flame-retarded multi-component PC blends.
The pyrolysis and flame retardancy of a bisphenol A polycarbonate/silicon rubber/bisphenol A bis(diphenyl phosphate) (PC/SiR/BDP) blend were investigated and compared to those of PC/BDP and PC/SiR. The impact modifier SiR consists mainly of poly(dimethylsiloxane) (PDMS > 80 wt %). The pyrolysis of PC/SiR/BDP was studied by thermogravimetry (TG), TG–FTIR to analyze the evolved gases, and a Linkam hot stage cell within FTIR as well as 29Si NMR and 31P NMR to analyze the solid residue. The fire performance was determined by PCFC, LOI, UL 94, and a cone calorimeter under different external irradiations. The fire residues were studied by using ATR-FTIR as well as the additional binary systems PC + PDMS, PC + BDP, and BDP + PDMS, focusing on the specific chemical interactions. The decomposition pathways are revealed, focusing on the competing interaction between the components. Fire retardancy in PC/SiR/BDP is caused by both flame inhibition in the gas phase and inorganic-carbonaceous residue formation in the condensed phase. The PC/SiR/BDP does not work as well superimposing the PC/SiR and PC/BDP performances. PDMS reacts with PC and BDP, decreasing BDP's mode of action. Nevertheless, the flammability (LOI > 37%, UL 94 V-0) of PC/SiR/BDP equals the high level of PC/BDP. Indeed, SiR in PC/SiR/BDP is underlined as a promising impact modifier in flame-retarded PC/impact modifier blends as an alternative to highly flammable impact modifiers such as acrylonitrile–butadiene–styrene (ABS), taking into account that the chosen SiR leads to PC blends with a similar mechanical performance.