| Composite materials are widely used in aircraft structures due to their light weight,high strength,corrosion resistance and fatigue resistance.With the rapid development of high-tech and defense-oriented fields,polymer materials are also shifting toward high performance and multi-functionality,which further promotes the diversification of high-performance resin-based composite materials.Phthalonitrile polymers are a new type of high temperature resistant resin,which NASA has studied for nearly 30 years.However,it has only a short history in China,and there is almost no application case in the aerospace field.It is developing at a faster speed,at present it has achieved many results in the molecular structure design,modification of resin and polymerization mechanism.As a high temperature resistant organic material,the Tg of phthalonitrile composite material is above 400?.It is an ideal material for aero-engine such as cold end,nacelle and thrust reverser.However,the material is always faced with the problems of high melting temperature,complex curing mechanism,long curing temperature,narrow processing window,and brittle polymer.Based on the current research and technology,the feature of low melting point and autocatalytic of resin molecular structure is an efficient idea to solve the above problems.Taking this as a starting point,the main research contents and conclusions of this paper are as follows:Firstly,the autocatalytic reaction behavior of the phenolic hydroxyl-containing phthalonitrile resin was investigated.The results of the curing kinetics showed that the activation energy of the autocatalytic reaction was 58.349 KJ/mol,and the reaction order was 0.856.The resin system was determined by characterization of the dynamic curing reaction behavior and thermal weight loss behavior of the resin: 200?/1 h;260?/4 h;310?/5 h.With this system,the residual carbon ratios of the polymer at 800 ? in air and nitrogen were 59% and 73%,respectively.The bending strength residual rate of the resin poured body to the room temperature in a high temperature environment were 64%(150?)and 52%(300?),respectively.The melt viscosity of the resin was about 0.1 Pa·s,and the processing window was 180?.By controlling several important parameters of pressure,time and temperature in the hot press forming of carbon fiber reinforced phthalonitrile polymer composites,the optimal hot press forming process was determined: after 200 min incubation at 200 ?,a pressure of 1.2 MPa was applied,260?/4h/5MPa,and a post-treatment 310?/ 5h.The brittle modification of polymers was mainly the introduction of flexible novolacs.A major feature of the blending component is that it has a high proportion of phenolic hydroxyl groups.The curing behavior test results showed that as the blending ratio of the phenolic resin increases,the curing exothermic peak shift ede toward the low temperature.The rheological test results showd that the addition of 10% phenolic didn't bring about a significant change in the melt viscosity of the resin,but the gel time of the resin at 170?were significantly shortened: 4461s(0% pf added),2084s(5% pf added),1641s(10% pf added).It is indicated that the addition of phenolic resin has a significant acceleration effect on the polymerization of nitrile groups.The infrared spectrum of the polymer showed that when the blending ratio of the phenol resin was 10%,the peak of the peptide cyanine forming polymer was significantly stronger than the former two.Finally,composite samples of different phenolic ratio resin systems were tested for their mechanical properties.When the phenolic blending ratio was 5% and 10%,and the tensile elongation at break of the material increased by 78% and 122%.The toughening effect was very significant.As the post-cure temperature increased,the Tg of the composite increases.Within the range of 10% phenolic blending ratio,as the proportion of phenolic resin increased,the Tg of the material increases,and the stability at 300-400 °C was improved. |
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