Research On Polyphosphazene Thermal-protective Materials And Phosphazene-modified Phenolic Resin

Phosphazene compounds that have excellent flame-retardant properties and ablation properties due to their special phosphorus-nitrogen skeleton structure and various substituents,have important applications in the field of thermal insulation materials.Phenolic resin and rubber are two common types of internal insulation materials.Cyclophosphazene compounds can be added as flame retardants into resin matrices to improve their properties,and fibers are commonly used as reinforcing fillers for polyphosphazene rubbers.(1)The sodium salt formed by the reaction between NaH and p-hydroxybenzaldehyde is used as a nucleophile to react with hexachlorocyclotriphosphazene.A series of test methods such as mass spectrometry(MS),infrared FTIR,1H-NMR,31P-NMR and TGA confirmed the successful synthesis of six pairs of hydroxybenzaldehyde substituted cyclotriphosphazene(HPCTP).(2)PF-HPCTP modified resin was prepared by adding different ratios of HPCTP to pure phenolic resin(PF).The infrared spectrum shows that-CHO of HPCTP reacts with phenolic resin.However,the flexural strength of the HPCTP modified PF-HPCTP resin is lower than that of the pure phenolic resin,mainly because the HPCTP and the phenolic resin are heterogeneously mixed and cannot completely react.The HPCTP is unevenly dispersed in the resin causing uneven local stress.The flexural modulus of PF-HPCTP resin is lower than that of pure phenolic resin.The morphology analysis shows that the fracture mode of PF-HPCTP resin is ductile fracture,which shows that HPCTP can improve the toughness of phenolic resin.(3)DMA and TGA data of PF-HPCTP resin show that HPCTP has a certain plasticizing effect,which makes the glass transition temperature of phenolic resin decrease,while the carbon residue at 800℃ slightly increases.Oxygen index data indicate that the addition of the cyclophosphazene derivative can improve the flame retardancy of the phenolic resin.Among them,with the increase of HPCTP from 0 to 5,the LOI value of PF-HPCTP resin increased from 27%to 35%.The vertical combustion data show that the flame retardant effect of PF-HPCTP resin has reached V-0 level.(4)The TG results of seven different kinds of fibers showed that the carbon residue rate of carbon fiber(CF),pre-oxidized polyacrylonitrile fiber(PANOF),polyimide pulp(PI pulp)and polyimide short-cut fiber(PI)is pretty high at 800 ℃ and the thermal stability of them is better.The carbon residue rate of polyacrylonitrile fibers(PAN)and aryl sulfone fibers(PSA)is lower,and the carbon residue rate of aramid fibers(PA)is the lowest.According to the study of the mechanical properties of different fiber-reinforced polyphosphazene thermal insulation materials,it was found that due to the destruction of the surface structure of the carbon fiber during processing,the CF/PDAP thermal insulation material had the lowest tensile strength,which was 3.69 MPa;due to the hydrogen bonding between PA and polyphosphazene,the PA/PDAP insulation had the highest tensile strength,which was 11.78 MPa.(5)The flame retardancy of different fiber reinforced polyphosphazene insulation materials reached V-0 level,and the carbon layer was intact and hard after ablation,of which the ablation properties of CF/PDAP and PA/PDAP materials were better,and the rate of line ablation reached 0.056mm/s and 0.062mm/s respectively.On the one hand,it is related to their higher tensile strength,which makes it more resistant to scour under the high temperature flame.On the other hand,with respect to the type of fiber,the more complete the fiber covers the substrate,the more stable the carbon layer obtained.(6)Explore the effect of PA and PI pulp fiber content on the properties of the reinforced polyphosphazene insulation material.With the increase of fiber content,the tensile strength of polyacrylonitrile thermal insulation material increases gradually,but the ablative performance varies.With the increase of PA fiber content,the ablation rate of polyphosphazene insulative material first decreases and then increases.The ablation performances of 15-PA/PDAP and 25-PA/PDAP are the best,and the ablation rate of wire is 0.049mm/s.With the increase of PI pulp fiber content,the ablation rate of polyphosphazene thermal insulation material did not change obviously.The line ablation rate of 35-PI pulp/PDAP is the lowest,0.057mm.