Study On Surface Modification And Interface Modification

Polysulfonamide (PSA) fibers possess numerous desirable properties, such as electrical insulating properties and resistance to high temperature, flame, and chemical corrosion. PSA fibers can be applied in several fields, including metallurgical, fire control, aerospace, and military industry. However, PSA fiber presents difficulty in spinning owing to its high initial modulus and specific resistance, low friction coefficient, and poor crimp stability. Furthermore, owing to its smooth surface and few polar groups, PSA fiber binds poorly between fiber and resin matrices. Hence, surface modification of PSA fibers is necessary to improve their spinnability and the interface bonding strength of composite.First, to meet the requirement of PSA fiber spinning process and to enhance fiber spinnability, this research used electric resistance tester, crimp meter, friction coefficient tester, and laser particle size analyzer to filter the antistatic agent, friction coefficient adjustment agent, and emulsifier. Afterwards, a compound of the PSA fiber special oil was created. Surface tension meter, four-ball friction tester, contact angle meter, and centrifuge were utilized to evaluate various oil performance indicators. Field emission scanning electron microscopy (FE-SEM), scanning tunneling microscope (STM), carding machine, dynamic voltage meter, and cohesive force machine were employed to determine the effect of oil on the PSA fiber surface and spinning performance. Results showed that as oil content increased, the surface morphology of PSA fiber was changed; the wettability, antistatic property, and cohesion of fiber were enhanced; and the fiber-gliding properties increased then decreased. However, high oil content and ambient humidity may cause PSA fibers to become sticky, easy to wind into cylinder and roller, and unable to form continuous cotton net. Thus, the ideal PSA fiber oil content was suggested as 0.6%.Second, PSA fiber surface modification technology was systematically investigated in this study to improve its interfacial adhesion strength. Surface modification of PSA fibers was treated by plasma, sizing agent, sizing agent+plasma, and ultrasonic. The surface morphology, roughness, and chemical composition of PSA fiber were evaluated by FE-SEM, atomic force microscopy (AFM), and X-ray photoelectron spectrometry (XPS). Fiber electronic tensile strength tester, friction coefficient tester, contact angle meter, and universal testing machine were used to analyze the breaking strength, friction coefficient, wettability, interfacial shear strength (IFSS), and interlaminar shear strength (ILSS) before and after different PSA fiber treatments. Results showed that after the plasma treatment, fiber wettability greatly improved. With increasing air plasma treatment time, the surface roughness of the PSA fiber and the degree of plasma etching increased, whereas the polar groups on the surface of the PSA fiber first increased and then decreased. Results also indicated that extending treatment time decreased the incorporated polar groups and damaged the fiber surface, which produced a weak boundary and led to the degradation of interfacial adhesion of PSA fiber/epoxy composite. Under air plasma treatment conditions of 40 Pa,100 W, and 3 min, the IFSS value increased by 56.94%, the ILSS value increased from 16.51 MPa to 24.79 MPa, which was 50.15% higher than that of the untreated specimen. Furthermore, the single-fiber tensile strength test showed that the breaking strength of the PSA fiber only decreased by 2.59%.To further improve the ability of PSA fiber interface bonding strength and to easily realize industrialization, this thesis studied the influence of sizing agent and sizing agent+plasma on the surface and interface properties of PSA fibers. Results showed that sizing agent not only protected the fibers, reduced the damage in the post-processing stage, it also improved the interfacial adhesion of composite material causing the ILSS value increased by 28.16% compared with the untreated specimen. Air plasma was employed to modify the surface of sized PSA fiber. The interface properties of fibers were further improved. Moreover, the interface adhesion strength of PS A fiber/epoxy composite was greatly enhanced, and the ILSS value increased to 26.65MPa, which rose by 61.42% compared with untreated sample.This thesis studied the surface-modified PSA fiber through ultrasonic at room temperature. Results showed that after the improvement via the ultrasonic treatment, the friction performance and wettability of the PSA fiber, and the polar groups on the PSA fiber surface also increased. Under ultrasonic treatment conditions of 25 KHz, 250 W, and 80 min, the ILSS value increased to 23.59 MPa, which was 38.60% higher than the value of the untreated sample.