Engineering Flash Graphene for Novel Low-Cost Plastic Recycling Technology

Overview

The production of non-fiber plastics between 1950-2017 has been estimated at 6789 million metric tons, and production is growing every year (Geyer et al., 2017). Much of the plastic is used for packaging, which becomes waste very quickly. Between 1950 and 2015, about 6300 million metric tons of primary and secondary (recycled) plastic waste was produced, of which only 9% was recycled, 12% was incinerated and 79% was deposited in waste dumps. Despite improvement in selective waste collection and less recyclable waste disposal to landfills, much of the plastic waste is still deposited in the environment.

Nearly all types of plastics are recyclable. However, the extent to which they are recycled depends upon technical, economic and logistic factors. Plastics are valuable resource, so the best outcome after their initial use is typically to be recycled into a new product. In recent years, many scientists have focused on developing effective and efficient methods to recycle plastic waste back into plastic polymers, solvent, oil or other chemical components. It was demonstrated recently that by flash Joule heating of inexpensive carbon sources such as rubber tyres and mixed plastic waste, plastic could be recycled to carbon allotropes (Luong, et al. 2020). This ground-breaking method can recycle plastics into graphene in a very fast process which takes less than a second. The product, named flash graphene (FG) after the process used to produce it, shows turbostratic arrangement (that is, little order) between the stacked graphene layers.

FG synthesis is a sustainable method for plastic recycling without the need for purification steps and uses no furnace and no solvents or reactive gases. The electric energy cost for FG synthesis is only about 7.2 kilojoules per gram, which could render FG suitable for use in bulk composites of plastic, and other carbon-based materials. So far, little is known about the underlying mechanism of formation of flash graphene. This PhD project aims to develop novel methodology to model formation of flash nanographene from plastic polymers and to develop the scientific understanding necessary to optimise the formation process and identify plastics that can be converted to nanographene efficiently.

Figure 1: (a)Schematic of the Flash Joule Heating process, and plot of the temperature rise versus time during flashing. (b) Schematic of the Flash Joule Heating process, and plot of the temperature rise versus time during flashing.(adopted from Loung et al., 2020).