Effect of crosslinking on tribological behavior of tung oil-based polymers

In this study, the tribological properties of tung oil-based polymers synthesized by the cationic copolymerization of tung oil with divinylbenzene and styrene are evaluated as a function of crosslinking density. Tribological measurements were performed using a ball-on-flat reciprocating microtribometer on samples with three crosslinking densities of 20%, 30% and 40% by weight of the crosslinking agent. Friction and wear characteristics during dry sliding were evaluated using a spherical (1.2 mm radius) silicon nitride probe as well as a conical (100 μm radius, 90° cone angle) diamond probe. Microscale friction behavior was evaluated from single strokes at ramped normal loads, whereas wear experiments were evaluated from 100 to 500 reciprocating cycles at fixed normal loads. Elastic modulus and hardness information were evaluated using nanoindentation tests. Scanning electron microscopy of wear tracks was used to elucidate deformation mechanisms in the various samples. All samples showed friction coefficients ranging from 0.06 to 0.49. It was found that a higher crosslinking density resulted in lower abrasive wear due to increased hardness. These results provide some insight into the friction and wear behavior of tung oil-based polymers.