| In the present work, the liquid oxygen compatibility of epoxy resins was enhanced through improving its flame retardancy. The flame retardants were added into the epoxy resin to verify whether the flame-retardant modification can make the epoxy resin compatible with liquid oxygen. The results showed that the bisphenol F epoxy resin including9.0wt.%hexab-romocyclododecane was compatible with liquid oxygen and no any sensitive reactions in20impact tests.The epoxy resins were modified by the polycondensation between tetrabromobisphenol A and epoxy resins. The4,4’-diaminodiphenyl methane (DDM) and4,4’-diaminodiphenyl sulfone (DDS) were used as the curing agents to cure epoxy resins. The liquid oxygen impact test results showed that the bisphenol A epoxy resin including10.0%bromine content and bisphenol F epoxy resin including21.20%bromine content cured by4,4’-diamino diphenylmethane (DDM) were compatible with liquid oxygen. The scanning electron microscope, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis, differential scanning calorimetry and limiting oxygen index were used to analyze the essential reasons of epoxy resins incompatible with liquid oxygen.The types of curing agent have a obvious influence on the liquid oxygen compatibility of epoxy resins. The curing agent T-31is better than593and the DDM better than DDS.DSC analysis showed that the glass transition temperatures of cured epoxy resins were almost higher than100℃. And there is no direct relation between the Tg and the liquid oxygen compatibility.During the impact process, the C-C/H group could be oxidized to the C-O-H/C and C=O groups. In addition, a large number of high activity radicals·O· could be released on the surface of epoxy resins and therefore caused the chain exothermic reaction and finally leaded to the epoxy resins incompatible with liquid oxygen. However, the Br· radical that was largely released due to the poorer stability of C-Br could inhibit the chain reactions through capturing the high activity radicals OH·,·O· and H· and finally enhanced the liquid oxygen compatibility of epoxy resins.With the increasing of bromine content, the limiting oxygen index did increase. For the cured epoxy resin including the same type of epoxy resin but different bromine content and the same kind of curing agent, the liquid oxygen impact sensitivity decreasing with the oxygen index did increase.The brominated epoxy resins showed a typical brittle material. For the same kind of modified epoxy resins, the tensile strength of modified epoxy resins cured by DDM was higher than that of cured by DDS. And the tensile property of modified epoxy resins including21.20%bromine content were better than that of including10.0%bromine. |
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