Preparations And Interface Modifications For Carbon Fiber Fabrics Reinforced Polyetheretherketone (CFF/PEEK) Aeronautical Composites

In recent years,carbon fiber fabric(CFF)reinforced thermoplastic composites has developed rapidly,due to the advantages of high forming speed,recyclability and high damage tolerance.Because of excellent mechanical perfomances,chemical resistance,fatigue resistance and thermal stability,polyether ether ketone(PEEK)becomes a potential candidate among thermoplastic matrices for advanced composites.However,the viscosity of the melted PEEK is quite high,so that it is difficult for it to infiltrate into CFF.Meanwhile,the interaction between the fiber and matrix is rather weak.These are huge problems faced by processing of CFF reinforced PEEK(CFF/PEEK)thermoplastic composites.In this paper,CFF composites were prepared by hot pressing.The properties of PEEK matrix were characterized by differential scanning calorimetry(DSC),thermal gravity analysis(TGA).The effects of temperature,pressure and other parameters on the mechanical properties of PEEK composites were studied.The optimum conditions were at a temperature of 395 °C and under a pressure 2.5 MPa.The composites processed under these conditions showed a tensile strength,a flexural strength,an interlaminar shear strength and an impact strength of 714.29 MPa,955.84 MPa,51.91 MP and 44.60 k J/m2,respectively.The cross-section of the composites was observed by SEM and metallographic microscope.The PEEK matrix penetrated completely into the monofilaments of CFF,the distribution of resin and fiber were homogeneous and the porosity was only 1.25%.Interfacial modifications of CFF/PEEK composites were studied based on surface modifications for carbon fiber(CF).Reflux in acetone and high temperature treatments were used to remove the original sizing agents on the surface of commercial CF.The optimum procedure was refluxing in acetone at 70 °C for 10 hours,although the strength of CF monofilament reduced by 5.75%.In order to enhance the interfacial bonding strength between PEEK and CF,the surface of CF was activated by concentrated HNO3 and high temperature treatments.Subsequently,the activated CF was coated with KH560 and KH570 silane coupling agent,soluble polyetherimide(PEI)solution,soluble polyimide(PI)paste and sulfonated polyetheretherketone(SPEEK)solution.The results showed that when CF was coated with dimethylformamide(DMF)solution containing 5 g/L SPEEK,the interlaminar shear strength and the storage modulus of CFF/PEEK composites are the highest,indicating the interface between matrix and reinforcement is markedly improved.Heat treatments were used to solve the problems in the products of CFF/PEEK composites such as warping,inhomogeneity of crystallization regions and residual stress in the matrix.The effects of treating temperature and time on the mechanical properties of CFF/PEEK composites were studied.The results showed that heat treatments lead to relaxations of PEEK molecular chains,higher crystallinity,uniform grain size and distribution of crystalls.This may bring a reduction or elimination of residual stress in matrix caused during processing.When treated at 290 °C for 4h,the flexural strength and interlaminar shear strength of the composites were improved by 22.43% and 25.65%,respectively.