Research On Thermal Oxidation Stability And Rare Earth Modification Of Carbon Fiber Reinforced Polyimide Resin Matrix Composites

Thermoset polyimide resin matrix composites has been applied in aerospace field and played an increasingly important role due to their excellent performances.The trend of performance and failure mechanism at high temperature environment,even modification method should be discussed to improve the safety and longevity of polyimide composites in long service.The influence of ageing temperature or ageing time on the properties of polyimide composites was analyzed by studying thermoset polyimide resin matrix composites,whose trademark was HT-350RTM.The weight loss and performance and the micromorphology of the composites were analyzed to explain the failure mechanism of the thermal oxidative ageing.It was shown,in the range of 330? to 370?,the mass loss of composite materials was accelerated in the longer aging time,which will be more obvious at higher temperature.The glass transition temperture(Tg)of composite materials was raised,and flexual strength and interlaminar shear properties at room temperture was decresed,but the mechanical properties at high temperture was increased first and then decreased.The further crosslinking reaction was the main reason for increasing of Tg.However the degradation of the polyimide resin leads to increased porosity and failure of the interface,which was the main reasons of larger mass loss and lower mechanical properties.Therefore the combination of the two effects made the mechanical properties at high temperature increased first and then decreased.The effects of such rare earth oxidesas Cerium oxide(CeO2),Lanthanum oxide(La2O3)and Neodymium oxide(Nd2O3)on the thermal stability of polyimide resin were studied,which was aimed to obtain the influence law of the species or content of rare earth oxides on the thermal stability,mechanical properties and process performance of polyimide resin.It was shown Cerium oxide was poorly dispersed,and easily precipitated in the curing process,whose modification effect was weakest.The initial particle size of Lanthanum oxide was the largest and the specific surface area was the smallest,so its modification effect was weaker than Neodymium oxide.The tensile strength of modified resin was improved by 41%and the aging time of the 5%weight loss was prolonged by 2.2 times as compared with the unmodified composites,when the content of Neodymium oxide was 1wt%.With increasing the content of Neodymium oxide,the elastic modulus was also improved,but thethermal oxidation stability,tensile strength and elongation at break were gradually reduced.On the basis of the modification effect of the matrix resin.The polyimide composites modified with Neodymium oxide was processed to investigate the effects of Neodymium oxide on the mass loss,glass transition temperature and mechanical properties of polyimide composites.It is shown that the thermal oxidation stability of modified polyimide composites could be improved because of addition of Neodymium oxide.However,when the content of Neodymium oxide was increased,glass transition temperature will be reduced,and thermal stability and mechanical properties became lower.Compared to the unmodified composites,The modification effect was best,which mass loss was reduced by 25%,flexual strength was increased by 46%,and glass transition temperature was improved to 425.3?when the content of Neodymium oxide was 1 wt%.In this paper,the thermal aging properties of the thermoset polyimide resin matrix composites aged at high temperature were studied.The polyimide resin and its composite was successfully modified with rare earth oxides.The thermal oxidation stability of polyimide composites was effectively improved,which is of great significance for thermoset polyimide composites to improve its application value.