Enhanced flame retardancy of flax bio-composites for the construction market

Abstract

Bio-composites made of natural fibres are an attractive alternative to conventional composites with synthetic fibres such as glass or carbon fibres not only because of their intrinsic properties but also because of their contribution to sustainability. However, natural fibres are flammable, and bio-composites need to be protected against fire for safety reasons but also to meet the strictest EU regulations for the transportation and construction sectors. Thermosetting composites need high loadings of flame retardant additives to achieve satisfactory results in terms of flammability which may lead to significant deterioration in their mechanical properties. This work explores the possibility of reducing the flammability of flax bio-polyester composites with potential use in the transportation and construction sectors through the combination of several novel fire retardant additives, which are halogen-free and considered environmentally friendly. Cone calorimeter tests indicate that proper combinations of fire retardant additives such as alumina trihydrate, ammo-nium polyphosphate and Exolite 740 reduced heat release rate and flammability up to a 60%; delaying the ignition time with respect to the unfilled material. These results were achieved at concentrations much lower than those with traditional solutions. However, the addition of dimethyl propyl phosphonate to the resin formulation with alumina trihydrate and ammonium polyphosphate failed to demonstrate any significant synergistic effect at reducing the heat release rate. Nomenclature ATH Aluminium trihydrate APP Ammonium polyphosphate DMPP Dimethyl phosphate DMA Dynamic mechanical analysis TGA thermogravimetric analysis DTG first derivative of the TGA curve pHRR Peak heat release rate THR Total heat release rate TTI Time to ignition MARHE Maximum average of heat emission