| Nowadays,advanced resin matrix composites are favored in aerospace and other fields due to their excellent properties such as light weight,high strength and high temperature resistance.With the rapid development of material technology and the continuous expansion of the cutting-edge field of national defense,the research of polymer materials is developing towards high performance and multi-function,which further promotes the diversification of advanced resin matrix composites.Phthalonitrile resin is a new type of high temperature resistant resin system.In this area,the National Aeronautics and Space Administration?NASA?has nearly 40 years of systematic study.In recent years,domestic research on molecular structure design and modification,polymerization mechanism and other aspects of phthalonitrile resin have made a lot of achievements but the practical application in the aerospace field is still very few.As a kind of high temperature resistant organic material,the glass transition temperature of phthalocyanine resin matrix composite can reach above 400?,which can be used as an ideal raw material for high temperature resistant structural parts.However,in the face of extreme high temperature service conditions and harsh reliability evaluation,we still need a variety of modified methods to further enhance the thermal stability of the phthalonitrile resin.At the same time,the research methods of phthalonitrile resin are still mainly based on theoretical analysis and experimental test,and there are few reports on molecular simulation,which will be of great value to the development of composite material design technology based on multi-scale modeling and characterization.In this paper,autocatalytic bisphthalonitrile-etherified novolac resin?BPN?was used as the research object,and its thermal stability was improved by blending it with gas phase SiO2 with a certain mass fraction.When the amount of SiO2 added was 0%,1%,2% and 3%,the lowest average viscosity of the resin was 0.1Pa·s,0.3Pa·s,0.6Pa ·s and 1.1Pa·s,and the processing window was reduced.The DSC curing peak exothermic enthalpy of resin was 118.1J /g,102.9J /g,99.1J /g and 78.8J /g.The rheological test and DSC test showed that the addition of SiO2 could catalyze the curing reaction of the resin to a certain extent,making it more mild,but the excessive SiO2?such as 3% content?would seriously sacrifice the melting processing performance of the resin.When the amount of SiO2 added is 0%,1% and 2%,SiO2 particles can be more evenly dispersed in the resin matrix.Moreover,under the same curing condition?270?/4h?,the bending strength of the cured resin was 55.3MPa,63.5MPa and 64.6MPa respectively,and the toughness was also improved.The bending property test shows that appropriate amount of SiO2 can enhance and toughen the resin.Also,after curing the phthalonitrile resin with content of 0% or 2%SiO2 at 320?/5h,thermophilic weight loss test?nitrogen atmosphere?showed that SiO2 could enhance the thermal decomposition temperature of the resin and improve the thermal stability.Meanwhile,in this paper,crosslinking model of pure phthalonitrile resin?pure BPN?and crosslinking model of phthalonitrile resin?SiO2/BPN?containing 2wt%SiO2 were constructed by means of molecular simulation to approximately represent the cured products in the experiment.Then,the thermodynamic parameters such as elastic modulus and glass transition temperature of the two models are simulated and predicted,and the difference of thermal stability of the two models is explained in micro.In the end,this paper draw the conclusion: when the gas-phase SiO2 and BPN are at the chemical binding interface,the motion behavior of SiO2 particles in the cross-linking model is similar to that of triazine ring.At high temperature,SiO2 particles have low mean square displacement,and their poor motion ability can inhibit the motion of molecular chain segments in the cross-linking model,thus improving the thermal stability of the cross-linking model. |
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