Effect of stepped microwave irradiation to develop carbon nanotubes on carbon fiber for enhanced performance

In the present research, carbon nanotubes were grown on carbon fiber (CF) by continuous and stepped micro-wave irradiation techniques. Ferrocene was used as a catalyst, and toluene was used as a microwave absorber to grow the CNTs on CF. Continuous microwave irradiation (CMI) was carried out at 720 W microwave power for 25 s. The stepped microwave irradiation (SMI) was performed at 720 W for 25 s, followed no irradiation for 15 s and further irradiation of 5 s. It was observed that SMI resulted in a dense forest of CNT without any agglomeration and damage to the CF surface compared to CMI. The ID/IG ratio of the CNTs grown with CMI and SMI was observed to be 1.03 and 0.99, respectively. This confirms the presence of denser CNT forest after SMI. The SMI showed improved wettability of the CF with respect to epoxy resin compared to CMI due to an 18% decline in contact angle. The ultimate tensile strength (UTS) of the resulting CFRP composite increased by 28% with SMI grown CNTs compared to CMI grown CNTs. The enhanced UTS is due to improved interfacial bonding between the CF layers due to denser CNTs obtained after SMI.