Modification Of EP And CF Composite With Magnetic Field Induced MWCNTs-Fe₃O₄

In recent years, the carbon fiber（CF） based composites materials have been widely used in many areas because of its decline prices, low temperature setting matrix and innovative molding techniques, its excellent mechanical properties has caused great concern. A lot of research has been focused on the problem how to effectively improve the poor interlaminar properties of CF based composites. Polymer matrix modified by oriented reinforcement can obtain some special performance, and the multiwall carbon nanotubes（MWCNTs） has been regarded as the ideal reinforcement material. While there are relatively few researches about CF based composites reinforced by vertical aligned MWCNTs.In this work, the MWCNTs purified by concentrated nitric acid was coated by magnetic Fe₃O₄ nanoparticle, and the magnetic MWCNTs was aligned by external magnetic field. The interlaminar properties and enhancement mechanism of aligned MWCNTs filled epoxy resin（EP） and EP/CF composites were studied. The main work is described as follows:Firstly, Fe₃O₄ nanoparticle coated carbon nanotubes（MWCNTs-Fe₃O₄） was prepared by ethanol solvothermal method. MWCNTs-Fe₃O₄ particles were characterized by X-ray diffraction, scanning electron microscope, thermogravimetry analysis, physical property measurement system and optical microscopy. The pristine CNTs was purified by concentrated nitric acid to dissolve the impurities by which the hydroxyl, carboxyl and carbonyl are successfully grafted to the surface of CNTs. The MWCNTs-Fe₃O₄ prepared at 240℃ for 2h possesses optimal properties when the ratio of MWCNTs and acetyl acetone iron is 0.1g: 0.2g. under this condition, the Fe₃O₄ nanoparticles with high purity and uniform morphology and particle size are evenly distributed on the surface of MWCNTs, and the grain size of the nanoparticle is 22 nm. The coating density and grain size of Fe₃O₄ nanoparticles could be controlled by changing the mass ratio of iron acetyl acetone and MWCNTs. The saturation magnetization of MWCNTs-Fe₃O₄ is 29.87emu/g, leading to its good response to a weak magnetic field（≤0.12T）.Secondly, the effects of MWCNTs content and magnetic field induction on the performance of two types of EP/CNTs composites were investigated; the type of EP was E51 and RIMR-135, respectively. The results show that the fracture toughness of EP is improved after the introduction of CNTs without magnetic field induction, and it is further improved after magnetic field induction. In the EP-51 system, the fracture toughness of EP/MWCNTs composites with a MWCNTs content of 0.75wt% without magnetic field induction is the highest, and the KIC and GIC of the composite are increased by 15% and 32.7%, respectively. While when the MWCNTs content is 1wt% the fracture toughness of the composites with magnetic field induction is the highest, and the KIC and GIC of the composite are increased by 34.1% and 80%, respectively. The maximum KIC and GIC of EP/MWCNTs composites are respectively increased by 16.7% and 35.7% through magnetic field induction.In the EP RIMR-135 system, the fracture toughness of EP/MWCNTs composites without magnetic field induction and with a MWCNTs content of 0.75wt% is the highest, and the KIC and GIC of the composite are increased by 54.3% and 138%, respectively. The fracture toughness of the composites with a MWCNTs content of 1.5wt% is the highest after applying the magnetic field, and the KIC and GIC of the composite are increased by 94% and 276.8%, respectively. The maximum KIC and GIC of EP/MWCNTs composites are respectively increased by 25.8% and 58.2% through magnetic field induction. The enhancement mechanism of fracture toughness of EP by MWCNTs and magnetic field induction was analyzed by SEM. The addition of MWCNTs has little effect of on the conductive property, dielectric constant, dielectric loss and thermal stability.Thirdly, the effect of magnetic field induced CNTs on interlaminar properties of EP/CF composites was studied. The results show that the EP RIMR-135 with a viscosity of is 331.1mPa.s at room temperature can be applied to Vacuum Assisted Resin Transfer Molding（VARTM）. The pullout shear strength, double cantilever beam shear strength（DCB） and three-point short-beam shear strength（SBS） of CF in composites prepared by CNTs with or without magnetic field induction are improved by 29.9% and 13.4%, 28.8% and 7.1%, 23% and 14%, respectively.