As the main load-bearing component in fiber-reinforced composite materials, reinforcing fibers must possess excellent mechanical properties, and PBO fibers have the highest tensile strength (up to 5.8 GPa) and modulus among polymer fibers, making them widely applicable in the field of high-performance composite materials. However, PBO fibers exhibit strong surface inertness and lack polar functional groups, which leads to the accumulation of defects at the interface when combined with the resin matrix, damaging the overall performance of the composite material.

Therefore, PBO fibers need to undergo a certain degree of pretreatment before preparing composite materials to improve their surface condition, enhance their adhesion with the resin matrix, and thus prepare high-performance composite materials. However, surface modification of PBO fibers is extremely difficult, as their unique rigid rod-shaped molecular structure provides strong corrosion resistance, while a smooth surface is not conducive to the adhesion of active substances on the fiber surface. And oxygen plasma cleaner can form rough structures and generate active oxygen and dangling bonds on the surface of PBO fibers by high-energy oxygen plasma bombardment. The active surface after oxygen plasma cleaner is more conducive to coating adhesion, increasing the designability of PBO fiber surface structure.

Plasma Cleaning

Plasma cleaning, as an important means of surface modification of PBO fibers, is based on the physical etching and chemical synergistic effect of high-energy active particles on the fiber surface. In a plasma field, excited particles (such as electrons, ions, and free radicals) bombard the surface of fibers through kinetic energy transfer. On the one hand, nanoscale groove structures are formed by physical sputtering to increase surface roughness, and on the other hand, oxygen-containing polar groups (such as hydroxyl and carboxyl groups) are introduced into the inert surface through chemical bond breaking and recombination, thereby improving the interfacial compatibility between fibers and matrix. The advantages of this technology are reflected in high process efficiency, environmental friendliness, and strong parameter controllability. By adjusting the discharge power, processing time, and working gas composition (such as N2, Ar/O ₂ mixing ratio), the surface topology and chemical activity can be directionally controlled.

Principle of oxygen plasma cleaner of PBO fibers

The working principle of oxygen plasma cleaner of PBO fibers is shown in Figure 1-1. When the sample is placed in the chamber, when the oxygen molecules in the vacuum chamber are subjected to sufficient external electric field, the electrons will gain enough energy to enter higher energy levels, and then undergo ionization to produce charged particles or metastable particles. This ionized atmosphere has an energy higher than the chemical bond energy of PBO, causing it to be partially oxidized and decomposed under the bombardment of charged particles, producing gaseous oxides such as CO2 and NO2. At the same time, this process can also form oxygen-containing functional groups and surface microstructures on the surface of PBO fibers, thereby improving the surface state of the fibers and enhancing surface activity, and improving the interfacial compatibility between PBO fibers and resin matrix.

Figure 1-1 Schematic diagram of oxygen plasma cleaner of PBO fibers