Study On The Properties Of The Modified Epoxy Resin For Composite Liquid Oxygen Tank

With the increasing attention on space resources in recent years,the development of spacecrafts such as rockets has become an important strategy of every country.One of the most urgent problems to be solved is how to improve the carrying capacity and reduce the launch costs of new generation spacecrafts effectively.Fuel tank is a vital part of spacecraft and determines spacecraft's carrying capacity.It also accounts for 30%~50% net weight of spacecraft.Liquid oxygen(LOX)tank is a kind of fuel tanks,which is generally made of alloy materials.CFRP composite is a kind of high performance material and can reduce 20%~50% weight when it replaces alloy materials applied on LOX tank.However,because of the oxidizability and the cryogenic temperature(90K)of LOX,it is necessary for CFRP composite matrix resin to own high cryogenic performance and excellent LOX compatibility.Therefore,the purpose of this paper is to improve the cryogenic performance and LOX compatibility of epoxy resin modified by efficient flame retardants.Bisphenol A epoxy resin E51 was modified by flame retardant EX-48 first and then cured by DDS.Results show that EX-48 played a positive role on the fracture toughness,the flexural strength at room temperature(RT)and 90 K.Epoxy resin containing 40 phr EX-48 owned the best flexural strength at both RT and 90 K with 27% and 15.8% enhancement while 20 phr EX-48 contributed 34% enhancement in the fracture toughness at RT.However,EX-48 had a negative effect on the heat resistance of epoxy resin,causing continuous declination of initial weight loss temperatures and glass transition temperatures.The incorporation of EX-48 improved the flame retardancy of modified epoxy resin.With 30 phr EX-48,the LOI of modified epoxy resin stabilized at 26%.Mechanical properties,thermal stability and flame retardancy of DOPO modified E51/DDS were investigated.Epoxy resin containing 0.5wt% phosphorus owned best tensile strength at RT and tensile elongation yield,with 10% and 20% increment respectively.When the content of phosphorus reached 1wt%,there was 20% improvement in the flexural strength at RT and 25% improvement in the fracture toughness.When the phosphorus content was up to 1.5wt%,the modified epoxy resin had the most improvement of 40% in the flexural strength of 90 K.DOPO had a negative effect on the heat resistance of epoxy resin,nevertheless,it caused better flame retardancy.Both EX-48 and DOPO were incorporated into epoxy resin.Results showed that the simultaneous addition of EX-48 and DOPO had a synergistic effect on the flame retardancy and mechanical properties of epoxy resin.Modified epoxy resin retained its tensile properties at RT and 90 K,without any side effects.Flexural strength at RT and 90 K of modified epoxy resin were improved a lot while the fracture toughness appeared the same tendency.Two flame retardants weakened the thermal stability but enhanced the flame retardancy of modified epoxy resin.Limit oxygen index of modified epoxy resin reached a peak of 33.5%.LOX compatibility of epoxy resin was investigated by LOX impact test.It showed that the LOX compatibility had a relationship with the LOI.It appeared that higher LOI represented better LOX compatibility in the modified epoxy resin system.