Upcycling from Wasted Plastics to Carbon Nanotube Devices

In recent years, marine pollution has been increasingly severe. Eight million tons of plastics are disposed into the ocean every year. It is predicted that the amount of plastics in the ocean will exceed the amount of fish by 2050 on a mass basis. From the viewpoint of upcycling, we are trying to convert waste plastics into “value-added” carbon nanotubes (CNTs). Although there have been reports on the conversion of virgin plastic into multi-walled CNTs (MWNTs) by chemical vapor deposition (CVD), the conversion efficiency η was poor (4% at maximum), and the available plastic species were few. In addition, the correlation between the plastic species and the properties of MWNTs has not been well understood.<br/>In this study, we have newly developed a CVD system that can convert various types of plastics into MWNTs with high efficiency. This method consists of three regions: the pyrolysis region of the plastic, the sublimation region of the metal-organic catalyst, and the growth region of the MWNTs. The features of this method are that η is much higher than those reported previously (maximum η &gt; 50%) and that a variety of plastic species can be used. In addition, we have fabricated patterned CNT wirings on plastic films using upcycled MWNTs by laser-induced transfer method [1]. After that, the we also demonstrated upcycling the plastics films with CNT wirings into MWNTs again.<br/>In this presentation, I will introduce the detail of the conversion method. Specifically, the relationship between pyrolysis gas species, which were characterized by infrared and mass spectroscopy, and the properties of resultant MWNTs will be presented. Furthermore, I will show some demonstrations of conversion from “real” marine debris (fishing nets, etc.) collected at beaches and inland into MWNTs with a conversion efficiency of more than 30%.