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- Flame retardance (7) (entfernen)
Combinations of different common flame retardants in wood–plastic composites (WPCs) are tested to identify synergistic or antagonistic effects with the goal of improving the fire performance of WPCs. Flame retardants investigated are expandable graphite (EG), ammonium polyphosphate (APP), and red phosphorus (RP) and combinations of two of them are used. The fire behavior is studied by cone calorimetric measurements. Additional thermogravimetry is used for further investigations. The fire tests show that EG has the highest potential for flame retardancy, but due to its expansion it cracks the formed residue layer. Combinations of EG with RP or with high amounts of APP are able to suppress this cracking.
Summary: The decomposition of novel phosphorus-containing poly(oxyphenylene-sulfonyl-phenylene-oxy-diphenyl phenylene phosphine oxide) (PSU_I), 2,5-dihydroxy-1-biphenylene-phosphine oxide based polysulfone (PSU_II), poly(sulfonyl-diphenylphenylene phosphonate) (PSU_P) and bisphenol A-based polysulfone (PSU) is studied. The influence of the chemical structure, charring and phosphorus release is discussed based on the mass loss, kinetics and products. The pyrolysis and fire behaviour of blends with epoxy resin (EP) are studied. For EP-PSU_II, phosphorus initiates water elimination and changes the decomposition pathway of EP. The fire behaviour of EP-PSU shows some improvements, whereas the heat release rate is crucially reduced for EP-PSU_II due to simultaneous char formation and flame inhibition.
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.
The pyrolysis and fire behavior of glass-fiber reinforced poly(butylene terephthalate) (PBT/GF) with two different metal phosphinates as flame retardants in combination with and without melamine cyanurate (MC) were analyzed by means of thermogravimetry, thermogravimetry coupled with infrared spectroscopy, flammability, and cone calorimeter tests as well as scanning electron microscopy/energy dispersive X-ray spectroscopy and X-ray fluorescence spectroscopy. In PBT/GF, dosages of 13-20% of the halogen-free flame retardant aluminum phosphinate or aluminum phosphinate in combination with MC fulfill the requirements for electrical engineering and electronics applications (UL 94 = V-0; LOI > 42%), whereas the use of the same amount of zinc phosphinate or zinc phosphinate in combination with MC does not improve the fire behavior satisfactorily (UL 94 = HB; LOI = 27-28%). The performance under forced flaming conditions (cone calorimeter) is quite similar for both of the metal phosphinates. The use of aluminum and zinc salts results in similar flame inhibition predominantly due to the release of the phosphinate compounds in the gas phase. Both metal phosphinates and MC interact with the polymer changing the decomposition characteristics. However, part of the zinc phosphinate vaporizes as a complete molecule. Because of the different decomposition behavior of the metal salts, only the aluminum phosphinate results in a small amount of thermally stable carbonaceous char. In particular, the aluminum phosphinate-terephthalate formed is more stable than the zinc phosphinate-terephthalate. The small amount of char has a crucial effect on the thermal properties and mechanical stability of the residue and thus the flammability.
The pyrolysis of an epoxy resin and the fire behavior of corresponding carbon fiber-reinforced composites, both flame-retarded with either 10-ethyl-9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide or 1,3,5-tris[2-(9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide-10-)ethyl]1, 3,5-triazine-2,4,6(1H,3H,5H)-trione, are investigated. The different fire retardancy mechanisms are discussed, and their influence on the fire properties assessed, in particular for flammability (limiting oxygen index, UL 94) and developing fires (cone calorimeter with different external heat fluxes of 35, 50, and 70 kW m-2). Adding the flame retardants containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide affects the fire behavior by both condensed phase and gas phase mechanisms. Interactions between the additives and the epoxy resin result in a change in the decomposition pathways and an increased char formation. The release of phosphorous products results in significant flame inhibition. The fire properties achieved are thus interesting with respect to industrial exploration.
The flame retardancy mechanisms of aluminium diethylphosphinate (AlPi) and its combination with melamine cyanurate (MC) in glass-fibre-reinforced poly(butylene terephthalate) (PBT/GF) were analysed using TGA including evolved gas analysis (TGA-FTIR), cone calorimeter measurements using various irradiations, flammability tests (limited oxygen index, LOI, UL 94) and chemical analyses of residues (FTIR, SEM/EDX). AlPi decomposed mainly through the formation of diethylphosphinic acid and aluminium phosphate and influenced the decomposition of the PBT only slightly. AlPi acted mainly through flame inhibition. A halogen-free V-0 PBT/GF material was achieved with a LOI of 44%. Additional charring influenced the flammability. MC decomposed independently of the polymer and showed some fuel dilution effects.
A new flame retardant based on an ammonium phosphonate is studied with respect to its thermal decomposition and its mode of action in wood-plastic composites (WPCs). The measurements are carried out by means of fire tests (cone calorimeter) and pyrolysis investigations (thermogravimetry, infrared spectroscopy). The flame retardant acts mainly in the condensed phase by increasing the amount of residue formed by the wood part in the WPC. Additional flame dilution is achieved by the release of water, ammonia and carbon dioxide during the decomposition of the flame retardant.