Tribological behavior of unsaturated polyester hybrid composites containing wood flour and carbon nanotubes

The dry-wear behavior of hybrid composites comprising of multi-walled carbon nanotubes (MWCNTs) and wood flour (oil palm kernel shell powder) within an unsaturated polyester matrix was investigated in this paper. The results revealed that the incorporation of wood flour -even at little as 10 wt% filler content- significantly improved the tribological behavior of the composite. This improvement in tribological behavior was attributed to the transfer of a soft layer of wood flour on the worn area during the wear process, which acted as a self-lubricating material. Investigation of the effect of filler size revealed that composites containing smaller filler sizes exhibited higher values of friction coefficient (µ) and specific wear rate (Ws). This reduction attributed to the creation of a surface with a lower surface roughness (Ra) at the worn area which resulted in a larger number of contacts between counterpart surfaces. In addition, increasing in the normal load resulted in a considerable increment in the values of µ and Ws. Filler treatment with hot alkali solution (1 to 9 wt% concentration) showed that both µ and Ws reached their minimum values at 5 wt% alkali concentration due to improved interfacial bonding between the filler and matrix. Finally, a relatively small amount (0.2 wt%) of well-dispersed MWCNTs within the wood flour polyester composite was found to be capable of improving the tribological behavior of such hybrid composites.