Preparation and Properties of Multi-Walled Carbon Nanotubes/Polyether Ether Ketone (MWCNT/PEEK) Composites

The speed and weight of power machinery are growing as the manufacturing industry develops. The bearing capacity and tribological performances of a single polymer material are insufficient to suit various usage requirements. Material compositing is the most effective way for optimizing its overall performances. Polyether ether ketone is a semi-crystalline full aromatic thermoplastic engineering plastic, which possess excellent comprehensive properties such as good self-lubrication, high temperature resistance, and hydrolysis resistance. It is widely used in aerospace, electronic devices, automotive parts, medical devices, and other technical fields. MWCNTs (multi-walled carbon nanotubes) are hollow and seamless carbon nanotubes composed of graphite carbon atoms, which have good mechanical qualities and strong thermal conductivity. PEEK-based composite materials have attracted extensive attention of scholars at home and abroad. Filling modification, polymer blending modification, and surface modification are the most common methods of modification. However, there are limited studies focusing on the systematic research about the effects of filler content on the structure, thermal conductivity, thermal stability, as well as the effect of load and velocity, various filler contents on tribological performances of PEEK composite materials. In this paper, PEEK and MWCNT/PEEK composites were prepared using the hot pressing sintering method, and the molding process was optimized. The thermal conductivity and thermal stability of materials increased as MWCNT content increased, according to structural, mechanical, and thermal characterization. In the progress, the crystallization state of PEEK and MWCNT/PEEK composites did not change, where PEEK did not decomposition or cracking reaction, and MWCNT did not have other chemical reactions. Comparing to pure PEEK, prepared MWCNT/PEEK composites had a higher hardness. The effects of normal load, velocity, and different MWCNT contents on tribological performances and wear mechanisms were characterized systematically. The results revealed that MWCNT added to PEEK reduced the friction coefficient and wear rate in dry friction conditions at room temperature. At fixed speed of 200 r/min, when the load was 40 and 80 N, the friction coefficient and wear rate were the lowest with MWCNT mass fraction of 1%, which was 0.241 and 0.235 respectively. Meanwhile, the wear rate was reduced by 60% and 56% respectively, comparing to pure PEEK. When the load increased to 100 N, the friction coefficient and the wear rate reached to the lowest with the MWCNT mass fraction of 2%, which was reduced by 89% comparing to pure PEEK. The variation trend of wear rate and friction coefficient was similar at rotation speeds of 200 r/min and 400 r/min with fixed load of 40 N. The wear rate reached to the lowest when the MWCNT mass fraction was 1%, with 6.0×10⁻⁶ and 3.8×10⁻⁶ mm³/(N·m) respectively, which was reduced by 60% and 89% comparing to pure PEEK. When the rotation speeds increased to 600 r/min, the wear rate reached to the lowest with the MWCNT mass fraction of 2%, which was reduced by 85% comparing to pure PEEK. When the content of MWCNT was lower (<2%), adhesive wear happened at fixed speed of 200 r/min and load of 40 N. However, when the mass fraction of MWCNT was higher (≥2%), adhesive wear and plastic deformation occurred. Adhesive and abrasive wear coexist in composites with lower MWCNT concentration when the load was increased to 80 N. Adhesive wear, abrasive wear, and plastic deformation coexist in composites with higher MWCNT concentration when the load growed to 100 N. Adhesive and abrasive wear occur in composites with lower MWCNT content at fixed load of 40 N and rotation speed of 400 r/min. Adhesive wear, abrasive wear, and plastic deformation coexisted in composites with higher MWCNT concentration when the rotation speeds increasing to 600 r/min.