DU bushings are oil impregnated bronze. Tough stuff. Still I can wear out DU bushings in 6 months. Perhaps the plastic bushings deform but spring back to the original shape. Polymer, Igus Its all in the plastic family. They never really wear out?. That would be something new.
So is carbon, what's your point? Plastic composites are the future. they last longer because they have a fraction of the friction that a D.U bushing has. I've ran a set on an M9 all season, they still look brand new. Usually i go through 1-2 lower D.U bushings in a season on an M9.