| Micron-and nano-structured flame retardants have become hotspots in the research of flame retardant materials due to their low addition and high efficiency.Among them,organic-inorganic hybrid micro/nano materials may become a breakthrough point for further improving the performance of nano flame retardants due to the combination of the advantages of organic and inorganic flame retardants.One-dimensional organic-inorganic hybrid materials,due to their advantages in performance and morphology,are expected to achieve high-efficiency flame retardant effects at low addition levels while improving mechanical and other properties.Based on the above considerations,in this paper,the combination of transition metallic Cu and thiophenol monomers with good heat resistance and good carbon formation is aimed at synthesizing one-dimensional organic-inorganic nanowires.The synthesized nanowires are further hybridized and applied in epoxy resin（EP）to explore the flame retardant mechanism.The research contents are as follows:In the first part,a metal-organic nanowire（Cl-Cu）was prepared by one-step synthesis using 2,4-dichlorothiophenol and copper sulfate pentahydrate（CuSO4·5H2O）as reaction raw materials.At the same time,another nanowire F-Cu was prepared using 2,4-difluorothiophenol as a raw material by the same method.The chemical structure,micromorphology,surface structure and thermal stability of synthetic materials were characterized,the results show that F-Cu and Cl-Cu nanowires are uniform linear solid structures with an average diameter of 200-300 nm and their lengths range from several micrometers to more than ten micrometers.The specific surface areas of F-Cu and Cl-Cu nanowires are 46.708 m2·g-1 and 40.426 m2·g-1,respectively.The chemical structures of the two nanowires are similar.Both materials have good thermal stability but exhibit different degradation processes.F-Cu nanowires show a one-step degradation process.Compared with F-Cu nanowires,Cl-Cu nanowires have a slower degradation process,which is a third-order degradation process.The initial decomposition temperature of F-Cu nanowires is slightly higher than that of Cl-Cu nanowires,and the char formation is better.In the second part,the synthesized F-Cu nanowires and Cl-Cu nanowires were used in EP flame retardant research..The results are as follows:trace amounts（0.5 wt%）of two flame retardants could promote the early degradation of EP after the addition into EP separately.At800oC,the char residue rate of the composites is increaseds and the maximum heat release rate is decreased significantly.When 0.5 wt%F-Cu and Cl-Cu nanowires were added into EP,the LOI value is improved to 27.2%and 27.0%from 25.9%,respectively.Cone and XPS results show that the maximum heat release peaks（PHRR）of F-Cu/EP and Cl-Cu/EP composites are reduced by 27.0%,23.9%.The total heat release（THR）,total smoke release（TSP）and the release of toxic gases are also reduced to some extent.The inreasing of strength and density of the residual char is mainly due to the formation of CuO and Cu2O by the Cu element in the condensed phase,which acts as a barrier.And other elements in the nanowires are released during the combustion process.The mechanical properties including tensile strength and impact strength of F-Cu/EP and Cl-Cu/EP composites have been greatly improved.Compared with pure EP,the tensile strength of F-Cu/EP and Cl-Cu/EP composites increased by 41.7%,39.5%,the elongation at break increased by 51.3%,43.4%,and the impact strength are improved by 18.7%,19.4%,respectively.In the third part,Cl-Cu nanowires were coated with cyclo-crosslinked polyphosphazene（PZS）to obtain PZS@Cl-Cu nanorods.Two doping ratio hybrid materials,named 0.5PZS@Cl-Cu and 2PZS@Cl-Cu,were selected and applied into EP to investigate their flame retardancy.The results are as follows:the analysis of the structure and morphology of the hybrid material shows that PZS is uniformly coated on the surface of Cl-Cu nanowires and form a hybrid material with good dispersibility and uniformity.The amount of doping increases and there is an maximum with the increasing of the PZS amounts.The different doping of PZS lead to a different degradation process produces to the hybrid nanowires.The TG results of pure EP,Cl-Cu/EP,0.5PZS@Cl-Cu/EP and 2PZS@Cl-Cu/EP composites show that the doping of PZS promoted the Char formation of the EP composites,which is higher than the theoretical calculation.It shows that PZS and Cl-Cu nanowires play a synergistic role in the flame retardancy performance of EP composites.Cone data shows that the flame retardancy properties including heat release rate（HRR）,THR,TSP of the three composite materials have been significantly reduced.Moreover,the doping of PZS will promotes the earlier degradation of EP more significant than the pure Cl-Cu nanowires.The residue char quality is also significantly improved.All these data indicate the existence of synergy effects between PZS and the hybrid nanowires.With the addition of PZS@Cl-Cu nanorods,the structure of the residual char is more compact with a higher graphitization degree,and which is benifitial to a better anti-oxidation performance.The enhancement of the flame retardancy is mainly due to that the formation of the phosphoric acid or metaphosphoric acid derivatives generated from PZS during the thermal degradation process,which promotes the dehydration and crosslinking of EP into char and enhances the role of flame retardants in the condensed phase.Compared with pure Cl-Cu nanowires,PZS@Cl-Cu nanorods have a slightly lower enhancement of the mechanical properties of pure EP.However,the mechanical properties of PZS@Cl-Cu/EP composites are still significantly improved compared to pure EP,which is superior to general flame retardants.In summary,in this paper a one-dimensional organic-inorganic nanowire composed of transition metal copper and thiophenol units was synthesized,and modified the Cl-Cu nanowire with PZS to obtain PZS@Cl-Cu hybrid nanorods.With the slight addition of the obtained flame retardants（0.5 wt%）,the flame retardancy and mechanical properties of EP was significantly improved.The research work in this paper is beneficial to the future research on the molecular design,morphology control and structure-property relationship for micron-and nano-structured flame retardants. |
