Interfacial Modification Design And Performance Research Of CF/PEEK Composite Based On The Interfacial Wettability Theory

Carbon fiber reinforced poly(ether ether ketone)(CF/PEEK)composites are widely used in aerospace,automotive industry,oil/gas transportation industry and medical areas due to their high specific strength,stiffness and performance stability.At present,CF/PEEK composites are usually prepared by molding prepregs brought from abroad.The price of prepreg is expensive and it is in solid state at room temperature resulting to the difficulty of paving on mould with complex structur.It is easily to destory the continuity and decrease the mechanical properties in the manufactural process.While,the preparation of CF/PEEK composites from CF/PEEK fiber flexible woven fabric as flexible premix can not only solve the problem of difficult to infiltrate CF caused by high melt viscosity of PEEK,but also has broad prospects instead of prepregs in the application field of preparing complex structures.However,interface bonding between CF and thermoplastic resin is poor as a result of smooth and inert surface of CF.Therefore,the interface problem has become the primary problem restricting the application of CF/PEEK composites.We studied the importance of interfacial property on composite tensile strength using stimulation by ABAQUS and found that it was significant for the improvement of mechanical properties.In addition,the surface morphology,surface chemical groups,surface energy of CF and PEEK fibers and the wetting parameters were discussed.Dynamic contact angle methods and acid-base theory were introduced to caculate the the surface energy of CF and PEEK.As a results,the polar component of surface energy of them were both low,leading to a poor interface of CF/PEEK.The concept of parachor were proposed to caculate the surface energy of PEEK based on its chemical structure.The results obtained by these two methods were consistence with each other.The stress singularity theory at interface end of axisymmetric cylinder were studied and singularity index ?s corresponding to different angles in microdroplet test were caculated and discussed.It was concluded that when the wedge angles at about 30 o,?s is 0.0364 and the tested interfacial shear strength(IFSS)was 42.87 ± 3.62 MPa.Also,adhesive work Wa was found to be an indicator for increasing IFSS between CF and PEEK fiber by studying the relationship of Wa and IFSS in different matrix-fiber system.Then,the improved methods were promoted based on the surface chemical states and wetting parameters between CF and PEEK and wetting parameters were caculated and combined with Young's equation to predict the wedge angle(or static contact angle between CF and PEEK fiber)in microdroplet tests and the value was consistence with results of test.To enhance the wettability and interfacial properties of CF and PEEK,CFs and PEEK fibers were simultaneously put into the oven of plasma of air or Ar or Ar followed by airproduced by a radio frequency(RF)instrument.The surface roughness of CF and PEEK fiber observed by SEM and AFM were both increased after suitable plasma treatment time.While,the increased roughness of CF was beneficial to the mechanical meshing in composites.The effects of plasma treatment on chemical structure and properties of both fibers were studied and it was found that in the plasma treatment time described in our study,the it had no effects on these properties.XPS and acid/base titration were introduced to detect the changes of surface elements and groups and the results showed that elemental contents of nitrogen and oxygen were increased and the polar groups and acid groups were successfully grafted,leading to the increasing of polar components of surface energy and interaction.Wetting parameters and microdroplet test were performed after plasma treatment and it can be seen that Wa and IFSS were improved.Compared to the effect of plasma treatment by one gas,the effect of plasma treatment by Ar followed by air was better and anong them,the IFSS of system treated by Ar-1 min-air-1 min was enhanced 39.32 %,meaning that plasma treatment can increase the wettability and interfacial combination of CF and PEEK without altering the mechanical property of CF and thermal property of PEEK fibers.Mold technique was studied and the meting temperature,molding pressure and crystallization temperature were discussed and were set at 370 oC,0.5 MPa and 300 oC,respectively.The resin content,chemical structure and crystallinity of composites prepared by prepreg and woven fabric before and after plasma treatment were discussed and it was found that the chemical structure and crystallinity of composites were nearly the same but the resin contents of composites prepared by woven fabric was higher,leading to a poor mechanical property.Compared the grain size of composied made from woven fabric before and after plasma treatment,it can be seen that plasma treatment had an effect of decreasing the grain size as a result of increasing nucleation sites on carbon fiber,resulting in a higher mechanical property.Tensile strength were predicted by numerical caculation based on the IFSS results and the caculated results showed that the tensile strength increases with the increase of IFSS,which is consistent with the experimental data.Tesnile strength,bending strength and interlaminar shear properties(ILSS)of composites were studied and they were enhanced by 46.95 %,53.77 % and 52.67 %,respectively after plasma treatment.In addition,strength of curved beams prepared from prepreg and flexible woven fabric were studied to discuss the difference of prepreg and flexible woven fabric in fabricating complex structures by four-point bending test.It was found that the woven fabric possessed excellent flexibility and conformability,and was suitable for preparing components with complex shapes.The curved beam prepared after plasma modification had better performance than the curved beam prepared by prepreg.