Solid lubricant additives for bismaleimide resin

Bismaleimides are the addition type of polyimide resin. They are synthesized by reaction of diamino compounds with maleic anhydride. By varying the structure of the diamino compound it is possible to make various bismaleimides. This paper discusses improvement of the friction and wear properties of bismaleimide resin, by the addition of solid lubricant additives such as MoS2, graphite and PTFE. The bismaleimide tested has the following structure: On heating, bismaleimide cross links through its unsaturated bonds, thus producing a highly cross linked polyimide. The friction and wear measurements were done on a Plint friction and wear machine (pin on disc type), wherein polymer pins slid against a steel disc at different loads and speeds. The polymer itself had a high coefficient of friction, ranging from 0.3 to 0.6 and a higher wear rate. Solid lubricant additives helped in improving its friction and wear characteristics. The addition of graphite brought the coefficient of friction to 0.3 but wear remained high at high loads. Best results were obtained with additions to the resin of MoS2-Sb2O3 and PTFE. Composites with MoS2-Sb203 and PTFE had low coefficient of friction and low rate of wear, at low as well as at high loads. It appears that these solid lubricant additives transfer to the counterface, thereby reducing effective counterface roughness, hence reducing both friction and wear.