Continuous Air DBD Plasma Treatment And Isocyanate Grafting Surface Modification Of Aramid Fiber

The aramid fiber（AF）has high mechanical performance,excellent thermal resistance,and good electrical insulation performance,so it is widely used in fiber reinforced polymer matrix composites.The surface of AF is smooth with few functional groups,and its bonding strength with the resin matrix is insufficient.The weak interface significantly reduces the properties of the AF reinforced polymers.Therefore,it is necessary to modify the surface of AF.Although the existing surface modification studies are effective,many techniques require complicated treatment conditions or long processing times,making them unsuitable for the continuous processing needed in some industrial application scenarios.Dielectric barrier discharge（DBD）plasma technology can generate stable plasma at room temperature and pressure for surface treatment of the AF,reduce treatment cost and process complexity,produce better modification effects,and achieve a continuous treatment process.This research combined the air DBD plasma technology with the toluene-2,4-diisocyanate（TDI）grafting method.Firstly,the air was used as the plasma atmosphere.The surface modification of the AF by DBD plasma technology at normal temperature and pressure removed the sizing agent from the AF,improved the surface roughness,and increased the content of polar groups on the surface.Then the plasma-treated AF was grafted with TDI to introduce-NH₂ onto the AF surface.The plasma discharge power,treatment time,and TDI concentration were investigated as major parameters.The surface morphology,chemical composition,polarity,and mechanical properties of the modified AF were characterized by scanning electron microscope（SEM）,Fourier transform infrared spectrometer（FTIR）,X-ray photoelectron spectroscopy（XPS）,Washburn contact angle,monofilament tensile test,and filament yarn tensile test.The micro-bond test and NOL-rings interlaminar shear test characterized interfacial properties of the AF/epoxy composite.The influence of different modification conditions on the dispersibility of the AF was characterized by NOL-rings resin content and tensile failure force.The defects inside the AF/epoxy composite were investigated by the dye penetration test.The insulation property of the AF/epoxy composite was investigated by the water diffusion test.Experimental results showed that the surface modification processing of aramid fiber via plasma treatment followed by TDI grafting caused a change in the roughness of the fiber surface and an increase in the content of polar groups.With the increase in plasma discharge power,the interfacial strength of the modified AF/epoxy interface increased first and then decreased.For the AF treated by 73W plasma for 30s and then reacted with 1wt%TDI solution,the IFSS and ILSS of AF/epoxy composites were increased by 32.8%and 20.2%at most,respectively.Plasma treatment weakened the strand integrity of the AF,while TDI grafting enhanced the strand integrity of the AF.Both plasma treatment and TDI grafting contribute to the insulation property of AF/epoxy composites.This modification method improved the interfacial properties without causing damage to mechanical properties of the AF.Overall,the surface modification method for TDI grafting after air DBD plasma treatment is simple,effective,and allows continuous treatment,which is suitable for industrial applications.