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Communication: Fire retardant coatings are deposited on polyamide-66 using plasma polymerisation. Chemical composition and thickness of deposits are adjusted varying the plasma treatment based on hexamethydisiloxane mixed with oxygen. The fire retardancy performances are evaluated using a cone calorimeter. The correlation between fire retardancy and thickness as well as chemical composition is discussed.
Low amounts (<7.5 wt%) of organically modified layered silicate (LS) as well as large amounts (>10 wt%) of spherical amorphous SiO2 (sSiO2) has been used successfully as adjuvants in commercial polymeric materials flame retarded with metal hydroxide. The combination of LS and SiO2 is investigated in different thermoplastics with respect to their fire behavior, particular to overcome the restrictions in maximum and minimum filler contents know for the single additives. The aim was to check the potential of combinations of the inert fillers in absence of a real fire retardant. The combination of LS and sSiO2 harbors the potential for flame retardancy effects close to superposition or even synergy, due to an improved structure of the fire residue. LS-sSiO2 combinations are proposed to work as adjuvants superior to LS and sSiO2 in flame retarded polymeric materials.
Basic paths towards fully green flame retarded kenaf fiber reinforced polylactic acid (K-PLA) biocomposites are compared. Multicomponent flame retardant Systems are investigated using an amount of 20 wt% such as Mg(OH)2 (MH), ammonium polyphosphate (APP) and expandable graphite (EG), and combinations with Silicon dioxide or layered silicate (LS) nanofillers. Adding Kenaf fibers and flame retardants increases the E modulus up to a factor 2, although no compatibilizer was used at all. Thus, in particular adding EG and MH decreases the strength at maximum elongation, and kenaf fibers, MH, and EG are crucial for reducing the elongation to break. The Oxygen index is improved by up to 33 vol% compared to 17 vol% for K-PLA. The HB classification of K-PLA in the UL 94 test is outperformed. All flame retarded biocomposites show somewhat lower thermal stability and increased amounts of residue. MH decreases the fire load significantly, and the greatest reduction in peak heat release rate is obtained for K-PLA/15MH/5LS. Synergistic effects are observed between EG and APP (ratio 2:1) in flammability and fire properties. Synergistic multicomponent systems containing EG and APP, or MH with adjuvants offer a promising route to green flame retarded natural fiber reinforced PLA biocomposites.