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- Cone calorimeter (2)
- Asphalt (1)
- Degradation (1)
- Fire behaviour (1)
- Fire retardancy (1)
- Intumescence (1)
- Weathering resistance (1)
The influence of weathering on the fire retardancy of polymers is investigated by means of a cone calorimeter test, before and after artificial weathering. The surface degradation was monitored using different techniques (ATR–FTIR, microscopy, colour measurement). Different kinds of polymeric materials were chosen, all as they are used in practice: polycarbonate (PC) blends, polyamide (PA) and polypropylene (PP) flame-retarded with arylphosphate, melamine cyanurate (MC) and intumescent formulation based on ammonium polyphosphate (APP), respectively.
All samples show material degradation at the surface due to weathering. No significant weathering influence occurs on the flame retardancy when it is a bulk property, as was observed for aryl phosphates in PC blends and MC in PA. When the fire retardancy is dominated by a surface mechanism, dependence on the duration of weathering is detected: for intumescent formulations based on ammonium APP in PP, a worsening in the formation of the intumescent network was observed.
Eyewitnesses describe burning pavement surfaces in extreme fire scenarios. However, it was believed that the pavement plays a negligible role in comparison to other items feeding such an extreme fire at the same time. The asphalt mixtures used differ widely, thus raising the question as to whether this conclusion holds for all kinds of such materials. Three different kinds of asphalt mixtures were investigated with the aim of benchmarking the fire risks. Cone calorimeter tests are performed at an irradiance of 70kWm-2. All three investigated asphalts burn in extreme fire scenarios. The fire response (fire load, time to ignition, maximum heat release rate and smoke production) is quite different and varies by factors of up to 10 when compared to each other. The fire load per mass is always very low due to the high content of inert minerals, whereas the effective heat of combustion of the volatiles is quite typical of non-flame retarded organics. The heat release rate and fire growth indices are strongly dependent on the fire residue and thus the kind of mineral filler used. Comparing with polymeric materials, the investigated Mastic Asphalt and Stone Mastic Asphalt may be called intrinsically flame resistant, whereas the investigated Special Asphalt showed a pronouncedly greater fire risk with respect to causing fire growth and smoke. Thus the question is raised as to whether the use of certain kinds of asphalts in tunnels must be reconsidered. Apart from the binder used, the study also indicates varying the kind of aggregate as a possible route to eliminate the problem.
The fire retardancy mechanism of aluminium diethyl phosphinate (AlPi) and AlPi in combination with melamine polyphosphate (MPP) was investigated in glass-fibre reinforced polyamide 6 (PA6/GF) by analysing the pyrolysis, flammability and fire behaviour. AlPi in PA6/GF-AlPi partly vaporises as AlPi and partly decomposes to volatile diethylphosphinic acid (subsequently called phosphinic acid) and aluminium phosphate residue. In fire a predominant gas-phase action was observed, but the material did not reach a V-0 classification for the moderate additive content used. For the combination of both AlPi and MPP in PA6/GF-AlPi-MPP a synergistic effect occurred, because of the reaction of MPP with AlPi. Aluminium phosphate is formed in the residue and melamine and phosphinic acid are released in the gas phase. The aluminium phosphate acts as a barrier for fuel and heat transport, whereas the melamine release results in fuel dilution and the phosphinic acid formation in flame inhibition. The higher amount of aluminium phosphate in PA6/GF-AlPi-MPP stabilised the residue in flammability tests in comparison to PA6/GF-AlPi, so that this material achieved a V-0 classification in the UL 94 test.