The effects of rubber modification on friction and wear of epoxy networks

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Virginia Polytechnic Institute and State University

An epoxy resin (Epon 828) was chemically modified with two different elastomers, poly(dimethyl-co-diphenyl) siloxane (PSX) and carboxyl-terminated butadiene-acrylonitrile (CTBN), to enhance its fracture toughness. The friction and wear of specimens modified with different amounts of elastomer were investigated in a pin-on-disk wear machine. An attempt was made to correlate the fracture toughness of the epoxy material to its fatigue wear rate for experiments in which a steel ball was sliding on a modified epoxy disk. A different type of experiment, modified epoxy pin sliding on an abrasive disk, was performed to detect whether abrasive wear of modified epoxies responds differently than fatigue wear to the fracture toughness. Other experiments were performed in which the wear debris produced during sliding was blown out of the interface to study its influence on friction and wear behavior. The effect of surface morphology on friction and wear was also studied.

The results indicated that a marked improvement in fracture toughness was achieved for samples with higher elastomer content. Regardless of the type of the experiment, epoxy pin-on-abrasive disk or steel ball-on-epoxy disk, wear rates correlated positively with inverse of fracture toughness. Both friction coefficient and wear rate were found to be influenced by the removal of the wear debris, especially for samples with higher elastomer content. The friction coefficient was reduced for samples with higher elastomer content and this was attributed to the low surface energy of the elastomer. CTBN-modified epoxies exhibited lower friction coefficients than epoxies modified with polysiloxane. It was found that sample morphology had a significant effect on both friction coefficient and wear rate; the sample with approximately the same domain size but the least number of elastomeric domains exhibited the highest friction coefficient and the highest wear rate.