Properties Of BMI Composites Ex-Situ Toughened With Phosphorus-Containing Poly (Arylene Ether Ketone)

Resin Transfer Molding(RTM), which is consider to be a typical representative of the Liquid Composite Molding(LCM) technology has been an efficient and economical technique to produce high-quality fiber-reinforced and complex shape composite parts. It has aroused widespread concern around the world and developing rapidly. Bismaleimide(BMI) resins as one of the RTM resin, have excellent processing characteristics, heat and radiation resistance, low viscosity and hot/wet properties. However, BMI resins in general are inherently brittle because of their highly cross-linked structure. Therefore, the application of BMI matrix composites reinforced with graphite fibers has been limited to some degree by their poor damage resistance and the reduction in compression strength after impact(CAI). A traditional approach to improve the toughness of the thermoset(TS) resin is introducing thermoplastic(TP) or rubber particles component into the matrix system. Unfortunately, many problems such as dramatically increased matrix viscosity and the changing original process of matrix resin are followed by this method which cannot appropriate to the RTM technology.An innovative concept, the so called ex-situ was proposed by Yi Xiaosu. The key advantage of ex-situ technique is to significantly increase the interlaminar properties of thermosetting resin matrix carbon composites by toughening selective and specifically in the interlaminar regions. The BMI resin still has the ability of flow and impregnation by separated the TS and TP component at the beginning of curing reaction. The microstructure of the interlaminar layers which can significantly improve the delamination resistance of composites is characterized by the phase separated and inverted morphology while the composite is cured. The inplane static mechanical properties of the composite toughened through ex-situ RTM technique were well kept because of the graphite plies themselves are still fully impregnated with the thermosetting matrix.The phosphorus-containing poly(arylene ether ketone)(P-PAEK) which has higher glass transition temperature was used as toughener to improved the toughness of BMI matrix composites. Meanwhile, the TP resin is insoluble at the inject temperature of BMI resin, causes little effect to the RTM technology. A series of P-PAEK with different molecular weight and endgroups are synthesized. The structure and thermal properties of P-PAEK were characterized by means of FTIR, DSC, TGA and NMR. The cure kinetics of TP/TS resin systems were investigated by DSC, and then the time-temperature-transition diagram which stands for the characteristics of curing process were built.The dissolution and phase separation occurred between TP and TS system observed by hot-stage microscope and the phase separation mechanism, thermal properties, rheological properties and mechanical properties of diphase systems were investigated to represent on the relationship between the microstructure and properties of the material.The optimal P-PAEK resins were chosen to improve the damage tolerance of composites through interlayer film or particles forms respectively. A remarkable increase in the Mode I interlaminar fracture toughness(GIC) was found by using tiny amount of rigid P-PAEK particles with high molecular weight toughened composite through ex-situ RTM technique. Meanwhile, the GIIC of toughened system increased from 960 J/m2 to 1360 J/m2 and the CAI raised to 200 MPa. Thermodynamic tests showed that rigid particles interlayer toughened composites did not reduce the Tg of the composite. The toughened composite still kept the original thermodynamic properties, which indicated the advance of ex-situ RTM technique. A flexible P-PAEK with low molecular weight was made into thin film to interlayer toughening composite materials. Mode II interlaminar fracture toughness(GIIC) increased by 74% dramatically. The CAI of composites increased from 155 to 280 MPa. Approximately 81% in CAI was improved. The inplane static mechanical properties of the composites were well kept.