Preparation, Properties And Application Of Flame Retardant Polyamide6by In-situ Polymerization

With satisfying chemical stability, mechanical performance and electrical properties, polyamide6(Nylon6, PA6) is vastly applied in industrial fields; however, the low flame resistance of PA6is limiting its usage under certain circumstances.The object of this paper is to investigate on a novel method for the preparation of flame retarded PA6with melamine cyanurate (MCA), and the mechanism for the flame retardancy of MCA in PA6matrix was studied. Moreover, the industrialized amplification of the preparation of flame retarded PA6composites by in-situ polymerization was researched, and flame retarding PA6fiber was also prepared by melt spinning. The detailed content is described as follows:(1) Melamine cyanurate (MCA) was introduced into PA6matrix in the preparation of MCA/PA6composites by melt-blending method. According to the combustion characterization, the LOI value increased with the increasing of the content of MCA. To be more specifical, when the amount of MCA was20%, the LOI value reached36.8%though its grade was only V-2in the UL-94test. According to the TEM characterization, the dispersion of MCA in the nylon6matrix was not very good, which demonstrates the fact that MCA/PA6composites prepared by melt-blend method have low mechanical and flame-resistance properties.(2) In-situ polymerization method was adopted in the preparation of MCA/PA6composites, whose properties was further investigated. Firstly, through separate reactions of melamine with adipic acid, and cyanuric acid with hexane diamine at aqueous environment, melamine/adipic acid salt and cyanuric acid/hexane diamine salt were obtained. Then the two kinds of salts were introduced into the hydrolytic polymerization system of caprolactam to prepare MCA/PA6nanocomposites, and the preparation conditions were also optimized.The structures, mechanical and flame retarding properties of these composites were fully characterized and investigated. According to the TEM results, the MCA crystallites, which were self-assembled in the aqueous molten caprolactam, with diametric size of less than50nm, are nanoscaled, highly uniformly dispersed in the PA6matrix. From the FT-IR and XRD results, it can be seen that the self-assembly reaction is complete. With the in situ formed MCA nanoparticles increasing, the thermal stability of it shows a decreasing trend. More specifically, T10of P-7.34(the amount of MCA is7.34wt%) and P-9.52(the amount of MCA is9.52wt%) are45℃and64℃lower than that of pure PA6, respectively. With the amount of MCA increasing, Tm decreases from219℃(pure PA6) to201℃(P-9.52), but the change of percentage crystallinity is not so significant.In this research, increasing MCA content may relate to better flame retarding ability, but it would destroy the thermal stability and mechanical properties. Nanostructured MCA was well dispersed in the resin matrix of MCA/PA6composites prepared by in-situ polymerization method. Thus, these composites present good mechanical and flame retarding properties even at relative low MCA loading level. In a word, this novel nanomaterial may provide interesting practical application in industrial fields.(3) The mechanism of the flame retardancy of MCA in PA6matrix was studied. On the one hand, the introduction of MCA led to the change in the thermal degradation process of PA6, and the Tmax2and char yield rose with the increase of the content of MCA; meanwhile, MCA reduced the degradation activation energy△E, improving the heat resistance of PA6matrix. On the other hand, although it needed less time to lighten PA6as a result of introducing MCA, the entire combustion process has been significantly extended; at the same time, an obvious linear decrease occurred to the peak heat release rate with the addition of MCA, abating the burning intensity of PA6matrix resin.(4) The industrialized amplification of the preparation of flame retarded PA6composites by in-situ polymerization was researched in order to further verify the small-scale experiment and to provide raw materials for the spinning experiment. It is showed that the amplification test had favorable reproducibility, and the composites had a LOI value over36%with good mechanical and flame-resistance properties, laying a foundation for industrial production of these flame retarded PA6composites in the future.(5) Flame retarding PA6fiber was prepared by melt spinning. By TEM, mechanical property test and LOI experiment, fiber properties were evaluated. From TEM pictures, the MCA were uniformly dispersed in the flame retardant fiber. And from LOI test experiment, the LOI value was more than35%, which shows that it owns good flame retarding property. In the physical property test experiment, it shows the existence of MCA particle just influenced the physical property a little.