PTFE fibers are widely used in important fields such as aerospace, industry, medical, military, etc. due to their excellent comprehensive properties such as high thermal stability, chemical inertness, corrosion resistance, low surface tension, and low friction coefficient. Due to the non-polar nature of PTFE molecular segments, strong group inertness, low surface activity, and strong surface hydrophobicity, the adhesive strength when attached to other substances is weak. Not only does it affect the bonding effect of the material, but it can also lead to premature detachment of the PTFE transfer film, resulting in high material wear rate and serious safety hazards in application, posing certain risks to production and daily life. Especially when applied to joint bearings, it is necessary to fully demonstrate the lubrication characteristics of PTFE fabric to ensure that the bearing maintains a low friction coefficient and low wear during operation. Therefore, surface modification of PTFE fibers is usually considered to improve the adhesion performance of the finished product.

Plasma is a conductive gas with equal density of positively and negatively charged particles, known as the four forms of matter along with solid, liquid, and gaseous substances. Plasma surface modification is a convenient, efficient, green, and economical material surface treatment technology, characterized by effectively improving the surface properties of materials while maintaining their intrinsic properties.

Principle of plasma surface modification of PTFE fibers

The method of plasma surface modification is to place the material in a plasma of non polymeric gases such as Ar, H2, O2, N2, and air, and then bombard the material surface with high-energy plasma to transfer energy to the molecules on the surface of the sample, thereby changing the surface chemical structure and surface properties of the material.

Analysis of Plasma Surface Modification Mechanism of PTFE Fiber

In order to analyze and study the changes in surface functional groups during the modification process of PTFE fibers, infrared spectroscopy analysis and X-ray photoelectron spectroscopy characterization tests were conducted on the PTFE fibers before and after modification. The results are shown in Figure 1. After plasma modification, new characteristic peaks appeared in the infrared spectra of PTFE fibers at 3387 and 1589 cm-1, corresponding to functional groups such as - OH, - C=O, and - CH2, indicating that plasma modification increases the hydrophilic groups on PTFE fibers and enhances their hydrophilicity. It can be concluded that surface modification of PTFE fibers is beneficial for improving the bonding strength between PTFE fibers and resins.

Figure 1 Infrared spectra before and after PTFE plasma modification

In depth quantitative study of the effect of plasma modification on the surface functional groups of PTFE fibers using X-ray photoelectron spectroscopy technology. As shown in Figure 2, the XPS spectra of PTFE fibers before and after plasma modification are highly similar, with 292eV corresponding to the C-element diffraction peak (C-F chemical bond), and 685eV and 877eV corresponding to the F1s and FKLL diffraction peaks of the F element, respectively. After plasma modification, the relative intensity of the F-element diffraction peak of M-PTFE fibers decreased, indicating a decrease in the C-F chemical bond strength and fiber hydrophobicity after plasma modification.

Figure 2 XPS spectra of PTFE fibers before and after plasma modification

As shown in Table 2, the elemental composition of PTFE fibers changed before and after plasma modification, with a decrease in the content of C and F elements and an increase in the content of O element. According to literature reports, plasma modification can effectively introduce functional groups such as C-O and C=O, which help to enhance the bonding strength between fibers and resins.

After plasma modification treatment of PTFE fibers, the internal energy and kinetic energy of the surface molecules of the material will increase. The increase in internal energy will exacerbate the unstable state of the molecular chain segments, causing thermal corrosion, cross-linking, degradation, and oxidation reactions of the material. The C-F and C-C bonds on the surface of the sample will break, generating a large number of free radicals or introducing certain polar groups, greatly optimizing the surface properties of the material.