TRIBOLOGICAL BEHAVIOR OF BLENDS OF POLYETHER ETHER KETONE AND POLYETHER IMIDE

In this study polyether ether ketone (PEEK) and polyether imide (PEI) were blended to raise the glass transition temperature (T(g)) above that of PEEK while retaining the low-wear characteristics of PEEK. The friction and wear of injection-molded blends were measured in dry sliding by a stainless steel ball sliding on a polymer blend disk. The test variables were normal load, sliding speed and the percentage crystallinity of the PEEK component of the blend. The wear mechanism of the pure PEEK was plowing with no net loss of material. This mechanism persisted for blends up to 70% PEEK/30% PEI (70/30) for which the T(g) was raised to 15-degrees-C above that of PEEK. For 50/50 and pure PEI the wear mechanism changed to that of fatigue, as evidenced by the generation of small particles after a period of sliding with no wear. The wear rates were higher for the PEI-dominated blends: as much as 40 times larger at the highest load and sliding speed. As the percentage of PEEK in the blends was reduced, the crystallinity of the PEEK component was also reduced; for the 50/50 blend the crystallinity was zero. Annealing the injection-molded samples raised the crystallinity of the PEEK in the blends to that of the pure PEEK injection-molded sample. In general, the increase in crystallinity caused by annealing reduced the wear rate of the blends. The coefficient of friction for the blends with low wear was below 0.15, while it was 0.2 to 0.3 for the blends which had the higher wear rates. For these latter blends, the friction coefficient was low until the wear track formed, at which time it increased to the higher level.