Preparation And Characterization Of Novel Nylon 6 Flame Retardant Composites Containing Sulfonates

Polyamide is one of the five most important engineering plastics, which has been widely used in electronics, automobile traffic and aerospace field due to its excellent comprehensive properties. Unfortunately, its application has been limited in many fields because of its poor flame resistance. When polyamide burning, it can lead to large numbers of molten drops thus causing more dangers. Therefore, more and more researchers devoted themselves to flame retardant polyamide. Halogen-free, efficient and environment friendly flame retardants have attracted more and more attention in polyamide composites. Sulfonate based flame retardants have the characteristics of low smoke, low toxicity, high efficiency, which is a kind of ideal flame retardant applied to polyamide.In this research, novel flame retardant PA6 composites were prepared by melt blending. The effect of sulfonate based flame retardants on the flammability, thermal stability and mechanical property were studied. Therefore, this paper includes three parts:Part one, preparation and characterization of PA6/GAS composites.Guanidine sulfamate （GAS） was used as flame retardant in PA6. The results showed that GAS could effectively improve the flame retardancy of PA6. The limiting oxygen index （LOI） value reached 31.9 and UL-94 achieved VO rating at the presence of 9% GAS. Volatile products obtained from the decomposition were characterized by TGA-FTIR. The results showed that GAS could improve the flame retardant in gas phase. During combustion, GAS can dilute oxygen concentration by releasing NH3 and SO₂, reducing the inflammability of PA6. Meanwhile, it will promote degradation of PA6, generating amounts of char residue to protect the substrate.Part two, preparation and characterization of PA6/MoS₂/GAS composites.Firstly, MoS₂ was added into PA6. The results showed that the LOI increased slightly with the increasing of MoS₂. Cone calorimeter （CONE） data indicated that peak heat release rate （PHRR） was reduced from 978.9 KW/m² of PA6 to 707.9 KW/m² of the sample containing 15% MoS₂. As a grapheme-like layered nanomaterial, the thermal stability of MoS₂ is relative high, which will play a role in condensed phase. Secondly, MoS₂ in association with GAS were introduced into PA6. The results demonstrated that the LOI reached 31.4 and UL-94 achieved VO rating at the presence of 10% MoS₂ and 5% GAS. The analysis showed that GAS took effect in the gas phase and MoS₂ took effect in the condensed phase. MoS₂ was served as physical barrier. Above 800℃, oxidation will be ocured and produced molybdenum trioxide （MoO3） and sulfur dioxide （SO₂）. MoO3 was flame retardant and smoke suppressor, and SO₂ belonged to nonflammable gas. Both of them improved the flame retardancy of PA6.Part three, preparation and characterization of PA6/GO-GAS.In this part, GAS was grafted on the surface of graphite to obtain GO-GAS. The results showed GO-GAS could not only improve the flame retardancy of PA6 composites, but also improve the compatibility between graphite and PA6 matrix. The preparation process was traced by FTIR, TGA and XPS. The LOI of PA6 was only 22.0, after addition of 3% graphite, LOI was increased to 24.1; and LOI was further increased to 25.5 at the presence of 3% GO-GAS. The TGA indicated that the thermal stability of GAS modified graphite was higher than that of unmodified graphite. In CONE test, the PHRR of PA6 was 978.9 KW/m²,3% graphite recuded PHRR to 460.4 KW/m² sharply, and 3% GO-GAS reduced the PHRR to 435.6KW/m². Based on the analysis of TGA-FTIR, it was concluded that GO-GAS could take effect in both condensed phase and gas phase. In condensed phase, lamellar structure graphite could form carbon residue, covering on the surface of substrate and effectively separating heat and oxygen. In gas phase, the decomposition of GAS could release NH₃ and then promote the degradation of PA6. The noncombustible volatiles from GAS and PA6, such as NH3, SO₂ and H₂O, were in favor of the fire resistance of PA6.