The Mechanics of Forming Ideal Polymer–Solvent Combinations for Open-Loop Chemical Recycling of Solvents and Plastics

The inherent value and use of hydrocarbons from waste plastics and solvents can be extended through open-loop chemical recycling, as this process converts plastic to a range of non-plastic materials. This process is enhanced by first creating plastic−solvent combinations from multiple sources, which then are streamlined through a single process stream. We report on the relevant mechanics for streamlining industrially relevant polymers such as polystyrene (PS), polypropylene (PP), high-density polyethylene (HDPE), and acrylonitrile butadiene styrene (ABS) into chemical slurries mixed with various organic solvents such as toluene, xylene, and cyclohexane. The miscibility of the polymer feedstock within the solvent was evaluated using the Relative Energy Difference method, and the dissolution process was evaluated using the “Molecular theories in a continuum framework” model. These models were used to design a batch process yielding 1 tonne/h slurry by setting appropriate assumptions including constant viscosity of solvents, disentanglement-controlled dissolution mechanism, and linear increase in the dissolved polymer’s mass fraction over time. Solvent selection was found to be the most critical parameter for the dissolution process. The characteristics of the ideal solvent are high affinity to the desired polymer and low viscosity. This work serves as a universal technical guideline for the open-loop chemical recycling of plastics, avoiding the growth of waste plastic by utilising them as a carbon feedstock towards a circular economy framework

On the Use of Carbon Cables from Plastic Solvent Combinations of Polystyrene and Toluene in Carbon Nanotube Synthesis

For every three people on the planet, there are approximately two Tonnes (Te) of plastic waste. We show that carbon recovery from polystyrene (PS) plastic is enhanced by the coaddition of solvents to grow carbon nanotubes (CNTs) by liquid injection chemical vapour deposition. Polystyrene was loaded up to 4 wt% in toluene and heated to 780 °C in the presence of a ferrocene catalyst and a hydrogen/argon carrier gas at a 1:19 ratio. High resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Raman spectroscopy were used to identify multiwalled carbon nanotubes (MWCNTs). The PS addition in the range from 0 to 4 wt% showed improved quality and CNT homogeneity; Raman “Graphitic/Defective” (G/D) values increased from 1.9 to 2.3; mean CNT diameters increased from 43.0 to 49.2 nm; and maximum CNT yield increased from 11.37% to 14.31%. Since both the CNT diameters and the percentage yield increased following the addition of polystyrene, we conclude that carbon from PS contributes to the carbon within the MWCNTs. The electrical contact resistance of acid-washed Bucky papers produced from each loading ranged from 2.2 to 4.4 Ohm, with no direct correlation to PS loading. Due to this narrow range, materials with different loadings were mixed to create the six wires of an Ethernet cable and tested using iPerf3; the cable achieved up- and down- link speeds of ~99.5 Mbps, i.e., comparable to Cu wire with the same dimensions (~99.5 Mbps). The lifecycle assessment (LCA) of CNT wire production was compared to copper wire production for a use case in a Boeing 747-400 over the lifespan of the aircraft. Due to their lightweight nature, the CNT wires decreased the CO2 footprint by 21 kTonnes (kTe) over the aircraft’s lifespan.We would like to thank Keysight Technologies for the use of a test model of the B2900A SMU. We would like to acknowledge the assistance provided by Swansea University College of Engineering AIM Facility. We would like to thank TRIMTABS Ltd. for purchasing equipment required for making ethernet cables. Thanks to Swansea Employability Academy (SEA) for the summer placements scheme. Thanks to the Swansea University Texas Strategic Partnership. R.E.P. acknowledges his work was associated with the IMPACT operation. We acknowledge pixabay for use of imagery in the graphical abstract (https://pixabay.com/vectors/airplane-boeing-747-transport-48 11157/ (accessed on 1 December 2021))

Upcycling potential of waste carbonaceous feedstock to carbon nanotubes

The overarching problem of plastic pollution perturbing our ecosystems along with the need for inexpensive feedstock material have turned scientists’ research focus to plastic waste. In this work, the feasibility of various plastic waste streams as carbon feedstock for carbon nanotubes (CNTs) was assessed both theoretically and experimentally. The three main plastic waste streams were comprised of medical plastic, fridge and car plastic. In the first project (Chapter 2), waste ostomy bags were dissolved in H2SO4 at 43 wt.% and 96 wt.%. The low H2SO4 concentration had minimal effect towards the materials of the ostomy bag whereas the high H2SO4 concentration effectively dissolved three of the bag’s components due to increased concentration of H+ ions. Based on the acid dissolution results, further dissolution tests were proposed towards achieving a higher percentage of dissolved ostomy bag material. Moreover, electrochemical cell set ups were proposed in order to succeed towards the growth of CNTs from the waste ostomy bags. In all proposed set ups, Nickel was chosen as the catalyst due to its face centered cubic nature, which is compatible with graphene and forms strong and stable bonds. Sodium sulphate as the best electrolyte and a constant current density of 7-8 mA∙cm-2 were theoretically determined to create a suitable environment towards the selective growth of CNTs over other carbon-based nanomaterials. A process map of each step was developed to aid further testing in this project. For the second project (Chapter 3), theoretical and experimental dissolution tests using various organic solvents were performed for fridge (WEEE) and car waste plastic, aiming to find the optimum solvent for each case. The fridge plastic waste was in a form of powder, whereas for the automotive waste, the waste came from different streams and was in various forms. The effects of different organic solvents and solvent blends were tested both theoretically and practically towards dissolving the waste fridge powder. M-cresol and cyclohexanone: ethanol: m-cresol (40:20:40) were determined as the best solvent and solvent blend, respectfully. Regarding the automotive waste plastics, dissolution tests were performed in toluene under reflux with two samples showing promising results. Finally, CNTs of o.d. 62.24 ± 12.73 (std. dev.) nm were grown from fridge plastic waste as a proof of concept, while the practicality of growing nanomaterials from the other plastic types was evaluated