Fusion of Incompatible Thermoplastics by Adapting Vitrimer Concept

Approximately 6,300 Mt of plastic waste had been generated as of 2015. However, only ~9 % of these polymers had been recycled as of 2015 in US, and ~79% of them ended up in landfills and natural environment. Almost all different types of plastics are thermodynamically immiscible, and their simple blends have poor mechanical performance. Complete sorting of these polymers present in plastic waste stream has been the main technological challenge, causing the complexity and huge additional financial costs of recycling. In this work, a method for efficient fusion of mainstream thermoplastic blends (polyethylene, polypropylene, and polystyrene) will be developed by incorporating dynamic, exchangeable covalent crosslinks through reactive processing. These crosslinks can break and reform at the interface under heat to enable covalent bonding between different immiscible polymer chains, thus increasing the kinetic barrier and minimizing micro- and macroscopic phase separation. Upcycling of plastic blends to vitrimers (malleable thermosets) can be achieved, which have high mechanical properties, creep resistance, melt strength, and dimensional, chemical, and thermal stability. The material can be reprocessed multiple times and degraded into thermoplastics, if desired, by cleaving the crosslinks, which eventually can be subjected to chemical cycling. In phase I, we will (1) Develop an efficient chemical approach to incorporate reactive groups into C-C polymer chains. (2) Demonstrate one-step reactive processing approach (extrusion, or compression molding) to transform recycled thermoplastics into vitrimers via reversible crosslink formation at a temperature < 190 °C, total residence time < 25 min. (3) Investigate the mechanical properties, thermal properties, reprocessibility of such vitrimers. (4) Develop a computational modeling tool to predict the fusion behavior and the mechanical properties of fused thermoplastic mixtures to guide their further development. The proposed upcycling of waste plastics to vitrimers (by-design recyclable thermosets) will give these polymers a new life by transforming them into value-added products and realize their circular lifecycle, while reducing the accumulation of plastic waste. Our approach does not require any expensive transition metal catalysts or energy/labor intensive purification process, and it is readily scalable through a continuous extrusion process, thus offering the possibility of on-demand high throughput processing similar to the existing industrially relevant setting. In Phase II and Phase III, we will seek large scale production of such thermoplastic vitrimers from recycled post-consumer plastic resins. We will partner with established companies in automotive industry and wind turbine manufacturing to carry out our commercialization plan.