Study On Modification And Properties Of Liquid Oxygen Compatible Epoxy Resin

With the development of the aerospace industry,carbon fiber reinforced epoxy resin?CF/EP?composites with high specific strength,high specific modulus,fatigue resistance,corrosion resistance and designability are in liquid hydrogen,liquid oxygen,etc.The use in ultra-low temperature environments has received extensive attention and has become a hot topic in current research.When used in a liquid oxygen low temperature environment,the CF/EP composite material is required to have liquid oxygen compatibility and excellent low temperature toughness.The liquid oxygen incompatible nature of the material is a thermo-oxidative aging process,which improves its flame retardancy and thermal stability to improve liquid oxygen compatibility.At present,the research mainly improves the liquid oxygen compatibility of the composite by modifying the epoxy resin matrix by adding an antioxidant or introducing a flame retardant group.However,most of the introduced antioxidants and flame-retardant groups contain a rigid structure which does not significantly improve the toughness of the resin matrix.In order to balance the low temperature toughness of epoxy resin,the paper introduces a flame retardant group to modify the epoxy resin,and introduces a tough group into the curing agent to improve the toughness,and obtain an epoxy resin system with both liquid oxygen compatibility and low temperature toughness.The structure of the resin system was characterized and the liquid oxygen compatibility and toughness properties of the resin cured product were studied.The research contents and research conclusions are as follows:First,the epoxy containing a phosphorus-containing flame retardant group was prepared by ring-opening reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide?DOPO?and bisphenol F epoxy resin.Through DSC,TGA,LOI,SEM,and liquid oxygen impact sensitivity test,the flame retardancy and liquid oxygen compatibility of the modified epoxy resin/alicyclic amine diaminodicyclohexylmethane?PCAM?cured product and toughness have been studied.The results showed that the infrared spectrum of the modified epoxy resin showed P-O bond,and the characteristic peak of P-H bond disappeared,indicating that the P-H bond of the DOPO and the epoxy group were ring-opened successfully to obtain the phosphorus-containing epoxy resin.From 0 to 2%,the residual carbon ratio increased from 4.0% to 10.3%,and the LOI increased from 22.4% to 27.4%.The thermal stability and flame retardancy of the resin increased.The liquid oxygen shock sensitivity test results showed the IRS decreased from 6.5%to 0,indicating that the liquid oxygen compatibility is improved,which is consistent with the thermo-oxidative aging mechanism.With the increase of phosphorus content,the fracture toughness K_ICC increases first and then decreases.K_ICC and elongation at break of pure epoxy were 1.58 Mpa·m^1/2 and 1.20%,respectively.When the phosphorus content was 1%,the fracture toughness K_IC and elongation at break were 2.12 Mpa·m^1/2 and 1.94%,respectively.,each increased by 34%and61%?When the phosphorus content increases,the tensile strength and elongation at break of the modified resin decrease at 77 K,and the elongation at break of the unmodified epoxy resin F/PACM system was 1.42%;the elongation at break of2P/PACM system with phosphorus content was 0.76%.The elongation at break is reduced by 46%,indicating a decrease in toughness at low temperatures.Secondly,in order to further improve the low temperature toughness of the epoxy resin,an alicyclic amine-containing alicyclic amine was synthesized by an addition reaction of acrylonitrile with a cycloamine diaminodicyclohexylmethane?PACM?.The results show that the infrared spectrum of the modified amine showed the stretching vibration peak of C?N,and the characteristic peak of C=C bond disappears,indicating that C=C and amino group in acrylonitrile react successfully;With the increase of the number of cyano groups in the modified amine,the strength and modulus of bending and stretching are increased.The K_IC and elongation at break of the unmodified amine were respectively 2.12 MPa·m^1/2 and 1.94%,when1.5 cyano groups were introduced,the fracture toughness K_ICC and the elongation at break were 3.72 MPa·m¹/2/2 and 5.47%,respectively,reaching a maximum value.Each increased by 182%and 60%,that was,the resin system toughness can be greatly improved;the cyano group in the PACM molecule increases,the?peak shifts to the left.Compared to 1P/PACM system,the elongation of the 1P/PACM1.5 resin system at 77K was 1.75%,the elongation at break increased by 38%,indicating an improvement in low temperature toughness.With the increase of the number of cyano groups in the modified amine,the residue decreased from 7.6 to 2.6,and the LOI decreased from 24.1%to 20.4%,indicating that its thermal stability and flame retardancy were reduced.The liquid oxygen shock sensitivity test showed that the IRS increased from 0 to 5%.It indicates that the compatibility of liquid oxygen is decreased.Comparing the resin system with no modification of resin and curing agent,1P/PACM1.5 system had a smaller sensitivity coefficient IRS than the F/PACM system,improved liquid oxygen compatibility.Compared with the K_IC and elongation at room temperature of the F/PACM system,each increased by 135%and355%of 1P/PACM1.5 system;the elongation got an increase of 23%;which indicated an increase in cryogenic toughness.It is proved that the DOPO modified epoxy resin and acrylonitrile modified alicyclic amine PACM can successfully obtain an epoxy system with both liquid oxygen compatibility and cryogenic toughness.