Preparation And Investigation Of Modified Cyanate Ester Resin Systems Used In Liquid Oxygen

CFRPs are gradually used to manufacture the Cryogenic fuel(Liquid Oxygen,LOX)tank in the next generation reusable launch vehicles(RLV)for meeting the weight needs instead of metallic materials.CFRPs must have the good mechanical properties in cryogenic,good thermal ability,and excellent liquid oxygen compatibility.The traditional epoxy resins cannot be used in manufacturing CFRP LOX tank,due to the deficiency of chemical structure.Recently,c yanate ester resins(CE)namely triazine resins are used as the potential matrices for CFRP LOX tank,because of their high-temperature resistance,outstanding mechanical properties,good anti-oxidative capacity and process-ability.However,the CE resins need to be suitability modified,showing the excellent performance before se rving structural functions.The research works are focused on the failure mechanism of CE matrix/composite in the LOX environment.Hence,as concerned as above,two different modified CE resin systems and their CFRP composites were designed and prepared,and the relevant relations of chemical compositions and structures with properties of two resin systems were discussed.Low viscosity epoxy resin(EP)and thermoplastic(PES-C)was applied to modify CE resin,designing a novel modified CE resin system(CYEP)with a good ductility at-196?.The results show that the ductile and adhesion property of CYEP resins are improved by the introduction of EP and PES-C into CE resins in cryogenic temperature.Exllecnt properties are obtained by co-adding 18 wt% EP and 6 wt% PES-C into the CE.Impact strength of CYEP matrix at-196? is increased by 200% than that of neat CE,and the modulus is only decreased by 6%,and there are no micro-crack on the surface of CYEP matrix sample by the 15 cryogenic-hot cycles(-196 ? ~50 ?).The process-ability of neat CE can be optimized by the adding the EP/PES-C blends,and the conversion is near to perfection after cured at 177?/4h+200?/2h.The viscosity of CYEP matrix is 734 cp at 80? and maintain a constant after 4h at the same temperature.However,the flammability test value of CYEP matrix is only UL94 V1 grade and is not satisfied.A novel bismaleimide resin contained phenyl ether structure(BMPB)and novel active diluents(DABDGE)were added into the CYEP matrix,and a new CEBM resin systems were also prepared.The results show that the viscosity of BMPB resin is obviously decreased with adding 5wt% of DABDGE diluents into them and the temperature of IDT is decreased by 10%.The better flammability and ductile of CEBM resin namely CEBM matrix is obtained by the addition 7wt% of BMPB into the CYEP matrix,but the excessive contents of BMPB might result in the negative impact strength and process-ability.The impact strength of CEBM matrix is increased by 20% more than that of CYEP matrix at-196?,and its retention rate of impact strength is lager than 80% through the 30 times cycle.The test value of flammability of CEBM matrix is V0 grade and it is of self-extinguish.The process-ability and storage stability of CEBM matrix is as well as that of CEYP matrix.In this thesis,the LOX compatibility and failure mechanism in LOX of prepared resin systems(CEBM and CYEP)were studied.The results show that the contents of BMPB and epoxy are the key factors for the LOX compatibility of resins,especially the structure of nitrogen bis-heterocyclic rings originated from the reaction of BMPB and CE can strongly improve the compatibility of matrix in LOX.When the content of BMPB is more than 5wt%,the temperature of oxidation weight gain is increased by 40?,the value of IRS go down to 4%.On the contrary,when the content of epoxy group is more than 15wt%,the value of IRS is sharply increase.The morphologies and oxidation weight gain of spherical PES-C domainsare influenced by the course of hot oxygen age,interface between the PES-C phase and continuous resin phase usually show the incompatibility in LOX impact.As well as CEBM matrix,the retention of mechanical strength is more 90% than thatof initial value is almost no change by the relevant durability experiments with LOX environment for 30 days.Using dynamic contact angle test and micro-debond test,the micro properties of two phase interfaces between the composite materials and matrix were estimated.The results show that low viscosity of matrix and polar molecules are all positive to improve the wetting performance.the interfacial shear strength(IFSS)and interfacial fracture toughness(Gdc)can be enhanced by the three effective methods.As follows: first,improving the self-strength of matrix,secondly,increasing the surface roughness of carbon fiber,last,raising the bonding force between the matrix and fiber.The processing temperature of matrix with fiber is raising every 10?,correspondingly,the IFSS value is increase by 3% in the range of Tg±50?.The addition of DADBGE is advantageous for forming the interfacial transition layer between matrix and fiber,with utilizing AFM defection,where the width of transition layer is about 200 nm.The transition layer may disperse the stress concentration and inhibit the micro-cracks propagation,The mechanical properties and cryogenic-hot cycle resistance of different resin based CFRP are studied.The results show that the CEBM matrix /T700 composite isof the excellent mechanical strength both at room temperatur e and at-196?.Specially,it is worth noting that the inter-laminar shear strength(ILSS)of CEBM matrix is 102.5MPa and the axial tensile strength is about 2602 MPa at-196?.There are no any micro-cracks in the surface of CEBM matrix/T700 laminate by the 40 times cycles.The existence of default in the surface of CFRP CEBM matrix/T700 is fatal to the compatibility in LOX,accordingly the IRS value of it is more than 5 times that of no default samples increased.