Carbon nanotube yarns derived from gamma irradiated carbon nanotube forests

Gamma irradiation has been recognised as an effective microengineering tool for improving interfacial adhesion of carbon nanotubes (CNTs) in their macroscopic structures. In this study, we applied gamma-irradiation directly to vertically aligned CNT forests (grown on iron coated silicon wafers) in the presence of air, and the irradiated CNT forests were then spun into CNT yarns under various applied tensions. The effect of gamma-irradiation on the CNT forest morphology, spinning performance and mechanical and electrical properties of the resultant CNT yarns were evaluated and compared with the unirradiated controls. The results revealed that CNT yarns spun from the gamma irradiated CNT forests had higher tensile strength and lower breaking elongation than the yarns spun from the unirradiated CNT control forests under the same spinning conditions. Increasing spinning tension improved the strength of CNT yarns spun from both the irradiated and unirradiated forests, but the tension-induced improvements from the irradiated forests were much more profound. The relative improvements in the yarn tenacity due to the gamma-irradiation were in the range from 14% to 26% under various spinning tension applied. This study also showed that the gamma irradiated CNT forests retained good spinnability under relatively low spinning tension, but exhibited significantly inferior spinnability at high spinning tension, compared to the unirradiated controls. Possible mechanisms for the spinnability of CNT forests and the mechanical properties of CNT yarns were discussed. Further improvement in the CNT forest spinnability may be needed through the optimisation of gamma-irradiation doses applied to the CNT forests.