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Effect of well dispersed amorphous silicon dioxide in flame retarded styrene butadiene rubber
(2013)
Spherically shaped amorphous silicon dioxide with broad size particle distribution was used in combination with aluminium trihydroxide (ATH) in styrene butadiene rubber composites. The pyrolysis, flammability, fire properties, flame spread and gas diffusion were investigated. The kind and amount of ATH, but in particular the fine silicon dioxide chosen as an additive, influenced the thermal decomposition and fire behaviour of styrene butadiene rubber composites. Gravimetric gas sorption measurements showed that the gas diffusion was systematically lower with silicon dioxide. The initial pyrolysis gas release was hindered, increasing the temperature at which decomposition begins as well as the ignition time in fire tests. During combustion, ATH and silicon dioxide accumulate on the surface of the specimen, forming a residual protective layer. A reduced peak heat release rate and fire spread were observed. The addition of a special kind of silicon dioxide is proposed to play a key role in optimising fire retardancy.
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.
The known flame-retardant synergism between phosphorus-based additives and metal oxides, already used for petroleum-based plastics, has been extended to bio-based materials. The pyrolysis and the flame-retardancy properties of aluminium phosphinate (AlPi) in combination with nanometric iron oxide and antimony oxide on a poly(3-hydroxy-butyrate-co-3-hydroxyvalerate)/poly(butylene adipate-co-terephthalate) (PHBV/PBAT) blend were investigated. Better fire retardancy, ascribed to increases in intermediate char, favoured improvements in the UL 94 classification. Both the phosphorus and the nanofiller components participate simultaneously in the flame-retardancy mechanism: the first acting as flame inhibition in the gas phase, and the second promoting cross-linking in the solid phase. Redox reactions between iron oxide and the phosphinate additive were confirmed by XRD analysis and provided further evidence of the activity of metal compounds.