Study On The Interfacial Properties Of Aramid Fiber/epoxy Resin Reinforced By Dopamine And Secondary Modification

Aramid fiber,as a high-performance fiber,has excellent mechanical properties,heat resistance,insulation,and aging resistance,and is widely used in aerospace,transportation,sports,safety protection,environmental filtering,electrical insulation,and other aspects.When aramid fiber is used as a reinforcement for composite materials,its smooth surface and chemical inertness,as well as its low interfacial strength with the resin matrix,limit the application of aramid fiber and the development of its composite materials.In this paper,dopamine is used to enhance the interfacial properties of aramid fiber/epoxy resin.Dopamine(DA)is deposited on the fiber surface for self polymerization,forming polydopamine(PDA)to coat the fiber surface,enhancing the surface roughness and polarity of the fiber,thereby enhancing the interfacial properties of aramid fiber/epoxy resin.In addition,the polyamine coating was used as a modification platform to graft silane coupling agent(KH560)and polyethylene imide(PEI)to further improve the interfacial properties of aramid fiber/epoxy resin.Thermogravimetric analysis(TG),X-ray photoelectron spectroscopy(XPS),scanning electron microscopy(SEM),infrared spectroscopy,and contact angle characterization were performed on the fibers before and after modification with dopamine.The test results showed that polydopamine was successfully coated on the surface of aramid fiber,and the oxygen element content on the fiber surface was increased,and the wettability of the fiber was also enhanced.The aramid fiber/epoxy resin tow composite was prepared.The interfacial properties of aramid fibers with different dopamine modification times were characterized by measuring the tensile strength of the composite.After the modification time reached 4 hours,the tensile strength value was basically stable,and the tensile strength under this condition was 28.06%higher than that before the modification.After successfully depositing a polydopamine coating on the fiber surface,KH560 was further used for grafting modification.XPS and infrared spectroscopy were used to characterize the chemical composition of the fiber before and after modification.TG,SEM,and contact angle tests were used to characterize aramid fibers with different reaction temperatures,KH560 dosage,and modification time.It was concluded that KH560 was successfully grafted,and the oxygen content and wettability increased after modification.As the reaction temperature increases,the coating content on the fiber surface first increases and then decreases.When the reaction temperature is 50 ℃,the coating is more and uniform.At higher temperatures,loose agglomerates will appear on the surface,affecting the interfacial properties.During the process of increasing the mass ratio of KH560 to dopamine from 0.5:1 to 2.5:1,when the mass ratio is1:1,the coating is the most compact and uniform.When the modification time increases from1 h to 9 h,the coating content gradually increases,but too long a reaction time can lead to uneven coating and loose aggregates.The tow composites prepared from aramid fibers with different modification conditions were tested.When the mass ratio of dopamine to KH560 is1:1,the modification time is 5 hours,and the reaction temperature is 50 ℃,the interfacial properties are improved most,the tensile strength is increased by 51.15%,and the maximum peeling force is increased by 49.69%.On the basis of coating the surface of aramid fiber with dopamine coating,PEI was used for grafting modification.XPS and infrared spectroscopy were used to characterize the chemical composition of the surface of the fiber before and after modification.Thermogravimetric analysis,SEM,and contact angle testing were used to characterize the fibers modified with different PEI levels.The results showed that the grafting of PEI was successful,the surface nitrogen and oxygen content increased,and the surface wettability increased.As the mass ratio of PEI to dopamine increases from 0.5:1 to 2.5:1,the coating content on the fiber surface continues to increase,and the surface coating becomes more uniform and dense.When the mass ratio of PEI to dopamine is 2:1,the interfacial properties of aramid fiber/epoxy resin are the strongest,with a tensile strength increase of 64.71% and a maximum peeling force increase of 66.85%.