Effect of morphology of carbon black fillers on the tribological properties of fibrillated PTFE

The tribological properties of fibrillated PTFE filled with 12 kinds of carbon black were studied using ring-on-disk tribometer. The effects of the average particle diameter, the nitrogen surface area and the DBP absorption of carbon black on the friction coefficient and the specific wear rate were studied. The carbon blacks used in this experiment were categorized into small carbon blacks (d ≤ 25 nm) and large carbon blacks (d ≥ 38 nm). The 10 mass% of carbon black was the best concentration for the highest wear resistance. The PTFE composites filled with the large carbon blacks showed lower friction coefficient than that of the pure PTFE. The friction coefficient decreased linearly with the decrease of the nitrogen surface area and with the decrease of the g-factor or the product of the nitrogen surface area and the average particle diameter. The specific wear rate of the PTFE composites decreased with the decrease of the average particle diameter and with the decrease of the product of the average particle diameter and friction coefficient. These results mean the wear reducing action of carbon black is to make it difficult to extract the PTFE fibre from the composite by getting caught in the carbon black and the large fillers promote the inter-winding between the fibre and the carbon black on a large degree, and result in high wear rate.