Surface modification of high performance PBO fibers using radio frequency argon plasma

The radio frequency argon plasma was applied to improve surface properties of the PBO fiber. The fiber tensile strength was measured, and the surface chemical components, topography and wettability were analyzed by X-ray photoelectron spectroscopy (XPS), atomic force microscopy and dynamic contact angle analysis (DCAA), respectively. Results suggested that over 90% of the fiber tensile strength was reserved after treatment at lower power levels. The surface oxygen atoms increased with a very small extent and the O/C ratio increased from 0.25 to 0.29. The plasma sputtering caused scission of chemical bonds and damage to the surface crystallizing layers, and thus created many active functional groups and roughened surface. However, at high power conditions the more effective ablation and sputtering effects dramatically reduced the tensile strength, surface oxygen contents and roughness. The fiber surface wettability was markedly increased as a result of the functionalization and roughening effects, but the calculated polar and dispersive free energy did not agree well with the measured surface chemical components due to the different effective depths of the surface layers analyzed by DCAA and XPS. The increased roughness was considered to be another reason. The treated fiber exhibited better adhesion with bismaleimide resin, but the maximum interlaminar shear strength of the PBO/bismaleimide composite could not be reproduced by increasing the treatment time at lower power level conditions.

► The fiber tensile strength was well preserved at lower power levels.
► Surface O content increased slightly, but many active groups generated through ring and chain scissions.
► High power levels markedly reduced the fiber tensile strength, surface active groups and roughness.
► Incompatibility existed in the results of XPS and DCAA.
► The optimal ILSS cannot be reproduced by increasing treatment time at low power levels.