Flame Retardant And Toughened Functional Glass Fiber Structural Mat And Its Application In Carbon Fiber Reinforced Composites

With the advantages of light weight and high strength,corrosion resistance and good designability,carbon fiber reinforced resin matrix composites（CFRP）have been widely used in aerospace,rail transportation,wind power blades and other fields.However,due to the flammability of the resin matrix itself,it is extremely sensitive to temperature,resulting in CFRP being prone to fire at high temperatures,accompanied by large amounts of smoke and causing structural damage,which seriously threatens the safety of life and property.Especially for passenger carriers such as passenger aircraft and high-speed trains,the composite structural parts must have excellent flame retardant properties and structural strength to ensure sufficient escape time for passengers in case of fire.However,although the current traditional additive flame retardant strategy can efficiently improve the flame retardant performance of CFRP,the damage of the flame retardant to the resin matrix structure and the fiber-resin interface can seriously affect the structural performance of the material.Therefore,how to achieve both good flame retardant performance and structural mechanics of CFRP through flame retardant structural design is the key to the application of composite materials in high precision air and space fields.In view of the excellent flame retardant and smoke suppression performance of organic-inorganic synergistic flame retardants in fire,this paper designs a"sandwich"structure with flame retardant and smoke suppressing glass fiber structural mat as the"skin"and CFRP as the"core".In this paper,we designed a sandwich flame retardant structure with CFRP as the"core"and glass fiber structural mat as the"skin",and constructed a flame retardant carbon fiber reinforced composite material by layering design and molding process.Among them,the flame retardant glass fiber structure mat is made of DOPO,APP and Ni（OH）₂flame retardant as the flame retardant functional unit and the ultra-fine glass fiber as the heat insulation and flame retardant structural skeleton.This project first explored the flame retardant formulation design and morphology control strategy of flame retardant fiber mat,and further studied the effect of flame retardant fiber mat on the flame retardant and mechanical properties of CFRP.On this basis,the organosilicon modified waterborne polyurethane（SWPU）was used as a toughening unit to toughen the glass fiber mat to prepare high performance flame retardant and toughened carbon fiber composites,and the microstructure and thermal stability of the fiber mat as well as the flame retardant performance,mechanical properties and flame retardant and toughening mechanism of the composites were systematically studied.The main research works are as follows:（1）Development of DOPO-Ni（OH）₂synergistic flame retardant and smoke suppression glass fiber mat and performance study of carbon fiber reinforced composites:The flame retardant and smoke suppression functional fiber mat was constructed with ultra-fine glass fiber as the heat insulation skeleton and Ni（OH）₂and DOPO as the synergistic flame retardant.Based on the design of sandwich structure,the flame retardant fiber mat was used as the surface flame retardant structure of carbon fiber reinforced epoxy resin matrix composites,and the flame retardant composites were prepared by molding process.When the flame retardant unit ratio（Ni（OH）₂:DOPO）in the flame retardant fiber mat（GF-5）was 1:1,the flame retardant and smoke suppression effect of the composite material（CGF-5）was the best,and compared with the control group,the total heat release（THR）decreased by 24.2%,the total smoke release decreased by 19.4%,and the ultimate oxygen index（LOI）reached 31.4%,which had good flame retardant and smoke suppression performance.Among them,DOPO can phosphorylate the matrix to induce the formation of carbon layer,while Ni（OH）₂can capture the carbon black particles in the smoke,which plays a synergistic flame retardant effect of cohesive phase and gas phase.However,the bending strength of CGF-5 composites decreased by 25.5%compared with that of CGF-5 composites,which was attributed to factors such as insufficient structural toughness of the flame retardant fiber mats themselves and poor interfacial compatibility between fibers and resins,and then the structural toughening optimization of flame retardant composites was carried out in the next stage.（2）Flame retardant glass fiber mat SWPU modification and structural toughening composite performance study:In order to prepare fiber-reinforced composites with both flame retardant and mechanical properties,based on the"ex-situ"toughening strategy of fiber-reinforced composites,we prepared flame retardant toughened composites by using silicone modified waterborne polyurethane（SWPU）as the toughening unit,grafting with glass fibers through Si-O-Si chemical bonding,and constructing flame retardant-toughened glass fiber structural mats with flame retardants.The results showed that the bending strength of the composite（CGF-8）increased by 62.2%,and the tensile strength and impact strength increased by 47.6%and 59.5%,respectively,compared with the control group when SWPU was added at 8 wt%.The introduction of SWPU significantly improved the interfacial compatibility between the structural mat and the resin matrix,and the fracture process was accompanied by a large number of fiber breakage and pull-out,resulting in additional fracture energy dissipation.However,the lack of flame retardant properties of SWPU itself led to a decrease in the flame retardant efficiency of the composite（CGF-8）,with a decrease in LOI value of 11.6%and an increase in peak heat release rate（PHRR）of 16.9%compared to the control group.Based on this,a more suitable flame retardant should be used to adapt to SWPU to further improve the flame retardant performance of the composite material and achieve both flame retardant and smoke suppression and structural mechanics.（3）Construction of fire retardant and toughened integrated functionalized glass fiber structural mats and performance study of high performance composites:Continuing the work in the previous chapter,we constructed high performance flame retardant and toughened glass fiber structural mat with microencapsulated ammonium polyphosphate（APP）and Ni（OH）₂as new flame retardant units and organosilicon modified waterborne polyurethane（SWPU）as toughened units,and prepared high performance flame retardant and toughened composites by compounding them with carbon fibers as flame retardant toughened structures,and systematically evaluated the structural morphology,flame retardant properties and mechanical properties of functionalized glass fiber structural mat and flame retardant and toughened composites,respectively.The results showed that the ultimate oxygen index LOI value of the composites could reach 32.2%when the ratio of flame retardant units（Ni（OH）₂:APP）was 1:1 and the addition of SWPU was 8 wt%.Compared with the control group,the THR decreased by 24.3%and the TSP decreased by 46.3%,and the stable and dense residual carbon structure on the surface of the material was observed,thus effectively reducing the heat transfer to the interior and preventing the smoke particles from penetrating to the outside,which confirmed its excellent flame retardant and smoke suppression performance.At the same time,the tensile strength,flexural strength and impact strength of the composites were improved by 34.5%,36.9%and 51.2%,respectively,based on the toughening effect of SWPU.The failure section of the sample showed a large roughness of the fracture surface,irregular crack extension and a large number of fiber breakage and pull-out,but the structural integrity of the material was good,which confirmed that the sandwich structure composite formed by flame retardant toughened glass fiber structural mat and carbon fiber can achieve both flame retardant and smoke suppression and structural toughness to meet the needs of high performance and high value applications.In summary,this paper proposes a functional glass fiber structural mat,which is doped with APP,DOPO,Ni（OH）₂,SWPU and other functional units to make it have the target performance of flame retardant,smoke suppression,toughening,etc.This is used as a"skin"for flame retardant protection and structural toughening of carbon fiber reinforced composites（core）,which not only avoids the destruction of the composite matrix structure by adding flame retardants,but also enhances the structural toughness of the composite,providing a new strategy for the multi-functionalization of flame retardant,smoke suppression and toughening of high performance composites.