Functionalization of carbon nanotube sheets for high-performance composites applications

Nanotube sheets or buckypapers, which are thin films or sheets of a nanotube networks, can serve as material platform for incorporating nanotubes into composites to transfer the nanotubes' exceptional mechanical and multifunctional properties into the composites. However, chemical functionalization of buckypaper is challenging since the structure integrity of sheets can be easily damaged or destroyed by intense chemical reactions. In this research, we demonstrated a unique process to effectively graft epoxide groups on nanotubes in the nanotube sheets using m-Chloroperoxylbenzonic acid (m-CPBA). This process can be performed at room temperature, requiring a relatively short reaction time and resulting in a mild reaction condition, such that the integrity of the sheets is not damaged. Raman spectrum analysis shows the success of grafting epoxide groups on nanotubes in the sheets. The resultant nanocomposites with 43.7 wt.% functionalized MWNT nanotube sheets resulted in an 80GPa modulus and 631MPa strength, which are comparable to aerospace-grade IM7 fabric composites for structural applications. This paper also discusses the improvement in interfacial bonding and failure mode changes of the nanocomposites, which were observed.