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- Polyurethane (3)
- Fire behaviour (2)
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Both alkylphosphinates and inorganic phosphinates (based on sodium, calcium, magnesium or zinc) have been recently proposed as flame retardants for polyesters, polyamides and polyurethane foams as well. The main aim of this work was to compare the flame retardant effectiveness of inorganic (already proofed in PU foams) and organic phosphinates in PU foams which have never been used in polyurethane (PU) foams. The thermal stability in nitrogen and air as well as limiting oxygen index and cone calorimeter behaviour have been studied to assess the effectiveness of such flame retardants in PU foams.
The results obtained showed that both inorganic and organic phosphinates are effective in enhancing fire behaviour of PU foams since they improve thermal stability, LOI and fire performance. Cone calorimetry highlighted the flame inhibition action in the gas phase due to the release of phosphorus-containing molecules. The better results obtained for inorganic phosphinate are probably related to the better quality of the char layer developed during burning, but may also be related to the higher phosphorus content of such flame retardant with respect the other ones. It was also verified that both inorganic and organic phosphinate containing N-synergic compound showed a fuel dilution effect, deriving from water and/or ammonia release in the gas phase.
Nanocomposites of a charring polymer (like polyurethane foam) filled with aluminum phosphinate (AlPi) with or without melamine cyanurate (MelCy) have been prepared by microwave processing and their thermal stability and fire behavior have been studied. Results on the interaction between flame retardants and layered silicates were provided as well as detailed investigation of the char strength, which has been carried out using a suitably developed method based on dynamic-mechanic analysis.
Generally, the thermo-oxidative stability in presence of layered silicates was higher than the counterparts even if an additive rather than synergic effect took place; however, in some cases the interaction between clays and phosphinate led to a significant decrease of weight residue. In nitrogen the residue amounts were about the same but a higher amount of phosphorus was retained in the solid phase in presence of clays. Cone calorimeter results showed that the use of phosphinates led to a decrease of the PHRR; further addition of clays did not reduce the PHRR owing to the worse quality of char layer as demonstrated by the char strength test. However, it has been shown that the partial substitution of aluminum phosphinate with melamine cyanurate gave improved results: the AlPi–MelCy filled foams showed similar pHRR and THE but lower TSR and higher char strength than AlPi filled foams. It was also confirmed that phosphinate acted by flame inhibition but its action was depressed by the use of nanoclays owing to their interaction.
Rigid polyurethane foams (RPUFs) exhibit short times to ignition as well as rapid flame spread and are therefore considered to be hazardous materials. This paper focuses on the fire phenomena of RPUFs, which were investigated through a multimethodological approach. Water-blown polyurethane (PUR) foams without flame retardants (FRs) as well as waterblown PUR foams containing triethyl phosphate as a gas phase-active FR were examined. The aim of this study is to clarify the influence of the FR on the fire phenomena during combustion of the foams. Additionally, materials’ densitieswere varied to range from 30 to 100 kg/m3. Thermophysical properties were studied bymeans of thermogravimetry; fire behavior and flammability were investigated via cone calorimeter and limiting Oxygen index, respectively. During the cone calorimeter test, the temperature development inside the burning specimens was monitored with thermocouples, and cross sections of quenched specimens were examined visually, giving insight into the morphological changes during combustion.
The present paper delivers a comprehensive study, illuminating phenomena occurring during foam combustion and the influence of a FR active in the gas phase. The superior fire performance of flameretarded PUR foams was found to be based on flame inhibition, and on increased char yield leading to a more effective protective layer. It was proven that in-depth absorption of radiation is a significant factor for estimation of time to ignition. Cross sections investigated with the electron scanning microscope exhibited a pyrolysis front with an intact foam structure underneath. The measurement of temperature development inside burning specimens implied a shift of burning behavior towards that of non-cellular materials with rising foam density.
Rigid polyurethane foams (RPUFs) typically exhibit low thermal inertia, resulting in short ignition times and rapid flame spread. In this study, the fire phenomena of RPUFs were investigated using a multi-methodological approach to gain detailed insight into the fire behaviour of pentaneand water-blown polyurethane (PUR) as well as pentane-blown polyisocyanurate Polyurethane (PIR) foams with densities ranging from 30 to 100 kg/m3. Thermophysical properties were studied using thermogravimetry (TG); flammability and fire behaviour were investigated by means of the limiting oxygen index (LOI) and a cone calorimeter. Temperature development in burning cone calorimeter specimens was monitored with thermocouples inside the foam samples and visual investigation of quenched specimens’ cross sections gave insight into the morphological changes during burning. A comprehensive investigation is presented, illuminating the processes taking place during foam combustion. Cone calorimeter tests revealed that in-depth absorption of radiation is a significant factor in estimating the time to ignition. Cross sections examined with an electron scanning microscope (SEM) revealed a pyrolysis front with an intact foam structure underneath, and temperature measurement inside burning specimens indicated that, as foam density increased, their burning behaviour shifted towards that of solid materials. The superior fire performance of PIR foams was found to be based on the cellular structure, which is retained in the residue to some extent.