Unzipped Multiwalled Carbon Nanotubes for Mechanical Reinforcement of Polymer Composites

Multiwalled carbon nanotubes (MWNTs) have been widely used as mechanical reinforcement agents in the past few years. However, the enhancement of mechanical properties of composites has been greatly hampered by its limited available interface area in composites. Toward solving this intrinsic limitation of MWNTs, in this paper, we report the use of unzipped MWNTs (uCNTs) as nanofillers for reinforcement of polymer composites for the first time. The uCNTs were produced by an oxidative unzipping process, involving the lengthwise cutting and opening the walls of MWNTs, and yielded separated ribbonlike graphene layers, thus increasing the surface area of MWNTs. With different amounts of oxidant (KMnO4), uCNTs with different unzipping degrees were obtained. For the surface functional groups that were generated during oxidation treatment, the morphologies and structures of uCNTs with different unzipping degrees were well characterized by several measurements. The mechanical testing of the resultant poly(vinyl alcohol)-based composites confirmed that the uCNTs were more effective than pristine MWNTs in terms of reinforcing polymers in strength and modulus, and the uCNTs oxidized by 400 wt % KMnO4 showed the highest reinforcement effect. The reinforcement effect is correlated with the structure changes of CNTs. This study may provide an important guideline and alternative way to design and fabricate low-cost and high-performance polymer-CNT composites.