| Epoxy resin（EP）is a comprehensive thermosetting polymer with excellent mechanical,electrical insulation,heat resistance,chemical stability and adhesive properties,which is widely used in various fields of national economy such as civil construction,electronics and electrical appliances,aerospace and automobile industry.However,the disadvantage that EP is highly flammable leads to serious fire hazards and generates a large amount of toxic and harmful fumes during combustion,which causes a great threat to human life,health and property safety that significantly limits the wide application of related products in areas with high flame-retardant requirements.To enhance the flame retardant of EP,researchers at domestic and abroad have conducted a lot of systematic and detailed research,especially the addition of inorganic flame retardant has the advantage of high-efficiency flame retardant and does not deteriorate the mechanical properties,the relevant research is highly preferred and has become one of the current research hotspots.In this work,nickel phyllosilicate（NiPS）with regular and ordered lamellar structure,large specific area and high designability of interlayer inorganic/organic functional groups was used as the investigation target,and nanoflame flame retardants with various functions such as nano-lamellar barrier,silica/phosphorus elemental flame retardant and nickel-catalyzed carbonization were designed and synthesized based on molecular design and microstructure modulation,then introduced into the EP matrix to construct composites with excellent flame retardant properties,and the conformational relationship between microstructure and macroscopic properties of the flame retardant functionalized EP composites was mainly explored.This research provides new design ideas for the construction of new high-efficiency flame retardant materials1)A series of NiPS were prepared based on different synthesis strategies,and products with different morphological structures were obtained by optimizing the process parameters such as silicon source,nickel source and reaction conditions.The effect of the introduction of NiPS on the structure and performances of the EP composites was investigated based on the confirmation of their composition and structure by various analytic tests.The results showed that the introduction of NiPS with hollow nanotubes,flower-like and whisker-like could promote the curing process of EP and improve the mechanical properties of the composites,resulting in an increase in tensile strength from77.3 MPa of EP to 78.0～89.4 MPa.The amount of residual char increased from 14.8 wt%of pure EP to 19.1～24.3 wt%of the composites.The flame-retardant performance tests confirmed that NiPS could give EP certain self-extinguishing properties and effectively inhibit the melt-drop phenomenon during combustion;compared with the EP,the duration of combustion of EP composites decreased from 214 s to 92～160 s,while the limite oxygen index（LOI）increased from 23.8 to 25.8～27.1.2)Based on the organic modification strategy,a series of organically modified NiPS were prepared by sol-gel method using organosilane coupling agent as the silicon source and introduced into EP.It is shown that the use of organosilane source can introduce specific organic functional groups into the lamellar structure of NiPS as group modifiers,thus enhancing the dispersion ability and interfacial compatibility of NiPS in the EP matrix to achieve the promotion of EP curing,so that the activation energy of curing reaction decreases from 54.4 k J/mol of EP to 44.9～47.4 k J/mol,and can be maintained mechanical properties of the composite.The introduction of organically modified NiPS lowered the thermal decomposition temperature and suppressed the thermal decomposition rate of the composites while increasing the residual char to 16.8～17.2 wt%,which has a certain promotion effect on improving the high-temperature thermal stability of the materials.By introducing the appropriate amount of organically modified NiPS,the EP composites showed better self-extinguishing ability and could significantly inhibit the occurrence of melt dripping during combustion;compared with pure EP,the duration of combustion of EP composites was reduced to 43～122 s and the LOI was increased to27.1～27.5;this was significantly better than the same content of unmodified NiPS.This is significantly better than the system with the same content of unmodified NiPS.3)From the perspective of molecular design,organophosphorus groups were introduced into the silane coupling agent by chemical grafting,and organophosphorus-modified NiPS was prepared using it as a silicone source,and the effect of its addition on the curing properties,mechanical properties,thermal stability and flame-retardant properties of EP composites was mainly explored.The results showed that the organophosphorus-modified NiPS could reduce the activation energy of EP curing reaction and promote the curing of the epoxy-ammonia system,and did not significantly reduce the mechanical properties of the composite system.Although the introduction of organophosphorus-modified NiPS decreased the thermal decomposition temperature of EP composites by about 17℃,it increased the residual char to 21.6 wt%,which was significantly higher than that of the organo-modified NiPS system.It was found that the addition of 5 wt%of organophosphorus-modified NiPS significantly increased the LOI of the EP composites to 29.2,and the vertical combustion time was also significantly reduced to 7 s,achieving the UL-94 V-0 rating.Compared with the EP,the heat release rate,total heat release,smoke production rate and total smoke release of EP composites were reduced by 62.4%,23.6%,28.5%and 27.8%,respectively;obviously,the organophosphorus-modified NiPS can give EP very excellent flame retardant properties.4)Based on the concept of microstructure regulation,organophosphorus-modified NiPS whiskers were synthesized by hydrothermal method with the organometallic framework as the nickel source.Based on the detailed examination of the composition and morphological structure of the resulting products,the effect of the addition of organophosphorus-modified NiPS whiskers on the curing reaction,and mechanical and flame-retardant properties of EP composites was systematically investigated.The organophosphorus-modified NiPS whiskers formed many lamellar structures on the surface,which gave a huge specific surface area and enhanced the interfacial bonding and homogeneous dispersion with the matrix resin,which was beneficial to promote the curing reaction of the epoxy-ammonia system.With the increase of the addition of FP-NiPS whiskers,the tensile strength of EP composites showed an increasing trend,and its maximum value reached 83.6 MPa at the content of 5 wt%,while the elastic modulus and elongation at break exhibited a decrease.Thermal performance tests showed that the thermal decomposition temperature of EP composites showed a gradual decrease,while the residual char increased significantly with the increase of organophosphorus-modified NiPS whiskers content,reaching a maximum value of 32.5 wt%at a content of 5 wt%,which was 14.6 wt%higher than that of pure EP;the organophosphorus-modified NiPS whiskers significantly improved the flame retardant properties of the material,increasing the LOI of the composite system and reducing the vertical burning time.and the vertical burning time,with maximum（minimum）values of 28.4 and 5 s at 5 wt%,respectively,passing the UL-94 V-0 rating.5)The flame retardant mechanism of EP/NiPS composites was studied in terms of thermal decomposition kinetics,condensed phase and gas phase,respectively.In terms of thermal decomposition kinetics,the activation energy of thermal decomposition of EP and the three composites was calculated by the Kissinger method,the FWO method and the Friedman method,respectively,and it was found that the results of the above methods proved that the introduction of organic modified NiPS reduced the activation energy of thermal decomposition of EP,indicating that the introduction of organic modified NiPS could promote the thermal decomposition of EP.In terms of the condensed phase,firstly,the NiPS barrier effectively hinders the escape of volatile pyrolysis products;secondly,the SiO2 and NiO formed by the thermal decomposition of NiPS have the functions of reinforcing the residual carbon layer and catalyzing the carbonization;thirdly,For EP/P-NiPS5,the phosphoric acid generated by pyrolysis can be esterified and dehydrated with the EP matrix to promote the formation of a phosphorus-rich carbon layer with a thick cyclic aromatic structure on the composite surface.In the gas phase,P-NiPS can release PO2·and PO·radicals when heated,which can trap the highly reactive H·and HO·and block the combustion chain reaction,thus achieving the flame retardant effect.Figure.[127]Table[29]Reference[194]... |
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