Synthesis Of A Phosphorus-containing Flame Retardant And The Study On Surface Modification Of Carbon Fiber

Carbon fiber reinforced epoxy resin composites are widely used in civil industry,energy technology and aerospace,for the characteristics of light weight,high strength,low shrinkage,and excellent adhesion performance.However,the decomposition and combustion of epoxy resin at high temperature and the generation of harmful fumes pose severe challenges to its application.Thus,the certain method must be implemented to modify the flame retardancy of composites to meet the application requirements.At present,most flame-retardant modification methods are likely to damage the mechanical properties of composites,or complicated the preparation process.In this thesis,a class of silane-modified phosphorus-containing flame retardants were synthesized and applied as sizing agent to flame-retardant modification on the surface of carbon fiber,which are expected to achieve the improvement on fire resistance and interfacial performance simultaneously in composites.In this thesis,a phosphorus-containing active amine phosphoric triamide(TEDAP,)with a simple structure was used as the basis for the subsequent synthesis.Firstly,TEDAP(T)was synthesized by amidation reaction from Triethyl phosphate(TEP),and two products Ti and T3 with different degrees of polymerization were prepared.Afterwards,TEDAP was modified with epoxy silane coupling agent(KH560,K)and a class of silane-modified phosphorus flame retardants T-K were successfully synthesized by varying the polymerization degree of T and the molar ratio of T to K.Thermogravimetric analysis(TG)was used to characterize the heat resistance of the T-K film.The temperature corresponding to 10%weight loss of the T-K film with higher K ratio exceeded of those with lower K ratio by 18.9-21.8?,and the temperature corresponding to the maximum weight loss rate peak right shifted 15-21.3?.A series of T-K sizing agents were prepared and utilized on surface treatment of carbon fiber.The conductivity analysis method was used to determine the hydrolysis time which was 60 min and the methanol content was 15%vol.Combined with the sizing amount and interlaminar shear strength(ILSS)analysis,the suitable concentration range of sizing agent was set between 3-5%vol.The T-K modified fiber reinforced epoxy resin composites were prepared by hand-molding process,and explored the effects of concentration and molecular structure of T-K(which was determined by the degree of oligomerization of T and the ratio of T to K)on the surface/interfacial properties and flame retardancy of fibers and relevant composites.Scanning electron microscope(SEM),Energy dispersive spectroscopy(EDS-Mapping)and X-ray photoelectron spectroscopy(XPS)were used to analyze the surface morphology,element distribution and element content of T-K sized carbon fiber.The results showed that a uniform coating could be formed when the concentration of sizing agent is 5%vol,and the content of Si on the surface of fiber grew from 3.42%to 5.77%with the increase of K ratio.The electromechanical universal testing machine was used to test the monofilament tensile strength,multifilament tensile strength and modulus of the T-K sized carbon fibers,as well as the ILSS of the relevant composites.It turned out that the application of T-K with a higher degree of polymerization of T and a lower K ratio was beneficial to the interface performance of composites,the ILSS maintained at 61.1 MPa,the monofilament tensile strength was 4.53±1.16 GPa,and the tensile modulus was 380 GPa.The T-K sized fibers and the corresponding composites were characterized via TG and Limit oxygen index test(LOI),respectively.The results showed that the T-K with a higher degree of polymerization of T and a higher K ratio was conducive to the heat resistance and flame retardancy of fibers and composites.The temperature corresponding to 5%weight loss increased significantly from 450? to 780? after sizing,and the LOI of the relevant composite rose from 34%to 46%.In addition,the constructed molecular models intuitively illustrated the effect of molecular structure of T-K on the interfacial and flame retardancy of the composite.