Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Development of new materials with improved fire resistance reduced smoke and toxicity

New alternative halogen free thermoset polymers that meet processing, thermal, flammability and environmental requirements have now become necessary for mass transport applications. Based on the synergistic effects of nitrogen and phosphorus compounds, new telechelic phosphorylated crosslinkable monomers (reactive phosphine oxide, phosphazenes) were chosen to be synthesized as alternatives to the hazardous fire retardant systems presently in service. Using these compounds in thermoset resins provided optimized formulations selected on the basis of simple thermomechanical characteristics, fire specifications and predictive toxicity assessment. Parallel fundamental investigations on the toxicity of the basic compounds, the degradation mechanisms, the flammability of the products released and the toxicity of the smoke formed on burning allowed optimization of these materials through an iterative process. The formulations selected were fully characterized and used for fibre impregnation of composite test pieces. Moulding was carried out to demonstrate application and indicate the level of improvement reached by this new type of fire retardant material. More than 20 novel phosphorylated flame retardant crosslinkable monomers have been prepared. 2 based upon phosphine oxide and phosphazene chemistries, were scaled up more than 10 kg. These dual function telechelic materials act both as flame retardants and as curatives. Around 50 preliminary formulation studies of (toughened and untoughened) epoxides, BMI cyanates all containing phosphorylated flame retardant crosslinking monomers resulted, after screening tests in the choice of 3 phosphorylated materials for scale up, in depth formulation and evaluation in 6 formulation classes. The 3 formulations selected were: toughened phosphine oxide based epoxy, untoughened phosphine oxide based BMI, toughened phosphazene based epoxy. These were fully characterized and assessed for fire retarding and toxicity parameters. The novel materials developed showed an improvement from 40 to 70% of fire properties without loss of thermal and mechanical behaviour. 3 real aerospace workpieces, have been manufactured, as demonstrators. These show a good quality. Exploitation plans include:
extension of the concept to a range of materials;
adding new crosslinkable molecules;
improving processability for resin transfer moulding;
validation of the concept by full scale testing.