Effect Of Carbon Fibers Surface Modification On Interface And Mechanical Properities Of Composites

Carbon fibers?CFs?/epoxy polymer?EP?composites are widely used in aerospace,automotive,construction,marine and other fields due to their light weight,excellent corrosion resistance and high strength.However,there are huge differences between CFs and EP in the modulus and other physical properties,which will introduce different stress to the interface and make stress uneven delivery.Therefore,in order to improve the performance of the interface and composites,it is necessary to optimize the design of carbon fibers which is of great significance.In this paper,three modification approaches,including a compound modification with amino-walled carbon nanotubes?CNTs?,octa-aminopropyl polyhedral oligomeric silsesquioxanes?OA-POSS?and two single-layer with CNTs,OA-POSS,are applied to decorate carbon fibers in the sizing-grafting and sizing-coating modifications.And there are preparations of carbon fibers and those reinforced composites modified by CNTs,OA-POSS,CNTs-POSS.A discussion about that the process parameters of CNTs,OA-POSS,CNTs and POSS compound modifications and the effects of the three improvements on carbon fibers surface,composites interface and mechanical properties shows in the followings.Results showed that:?1?CFs-CNTs fibers were sonicated at 40?for 10-40 min and sintered at 1000?for1-2 h.CFs-CNTs fibers modification process examined by X-ray photoelectron spectroscopy?XPS?shows the combination of amino groups of CNTs and carboxyl groups of CFs.Scanning electron microscopy showed that the CNTs were grafted on the surface of CFs.Atomic force microscopy demonstrated that the roughness of CFs before and after modification was 4.615?m and 28.651?m,respectively.During the CFs modification progress,the main influencing factors of surface energy are the intermolecular attraction energy terms called?^LW.The element near the interface is analyzed by line scan proves that the CNTs is penetrated into the resin.According to the test results of the mechanical properties and the cross-sectional scanning images,the fibers of the composite material are pulled out less,and the tensile,bending,shearing and impact properties of the composite material get some degree of improvements.?2?CFs-POSS fibers were sonicated at 60?for 20-60 min and on no sintering.XPS verified the acid-base bonding between-NH₂-?OA-POSS?and-COOH-CFs,and the hydroxylation reaction of-NH₂-?OA-POSS?with epoxy groups.There is a distribution of particles on carbon fibers surface.The roughness of the CFs before and after modification is4.394?m,17.394?m respectively.The influencing factors of CFs-POSS surface energy are?^LW.The electron acceptor term?⁺and electron donor?^—have a certain influence on the surface energy of the carbon fibers.The mechanical test and cross-sectional analysis show that OA-POSS enhances the toughness and bonding strength of composites,and the properties of composites are improved significantly.?3?XPS verification of CFs-CNTs-POSS shows that the chemical reactions of?1?and?2?above occurred during this modification.The CFs-CNTs-POSS fibers surface of is relatively flat under scanning electron microscope.During the modification process,the roughness of CFs,CFs-CNTs-POSS surface are 4.355?m,and 8.893?m respectively.The main factor influencing CFs surface energy is the intermolecular energy term?^LW and?^—.And the interface analysis confirms the cross existence of Si and O,which proved its existence of structural chimerism.From the mechanical properties test and the cross-sectional scan,CFs-1.0%CNTs-POSS/EP composites have excellent tensile and bending properties,that is to say,it has better plasticity and toughness.