Plastic waste is a significant environmental challenge due to its rapidly increasing production and resistance to natural degradation. One potential solution is to break down plastics through autoxidation chemistry, which most commonly uses a Co/Mn/initiator catalyst, acetic acid solvent, and air as the oxygen source to convert polymers into aldehydes and carboxylic acids. However, understanding the catalyst-substrate interface in the autoxidation mixture is limited due to the complex morphology of polymers and unknown interaction with solvents.

In this contribution, we discuss our study on the behavior of polyethylene (PE) and polystyrene (PS) when exposed to acetic acid and autoxidation catalyst solutions at varying temperatures. We have used in situ simultaneous Small-Angle X-ray Scattering (SAXS) and Wide-Angle X-ray Scattering (WAXS) to investigate the physical properties of these polymers. Our findings show that acetic acid and catalytic species diffuse into the amorphous matrix of PE and PS at room temperature and elevated temperatures. This result has important consequences when designing the catalyst-substrate interface for chemical polymer deconstruction processes, as it shows that the autoxidation reaction is not limited to the polymer surface and likely occurs within the bulk of the polymer as well. Moreover, we find that increasing the temperature enhances the mobility of polymer chains and induces polymer chain clustering in PS and depression in melting point of PE, both of which may alter the accessibility of reaction sites to the catalyst and ultimately affect the deconstruction rate. These findings demonstrate the complexity of the polymer-catalyst interface, an important factor to consider when developing more effective chemical plastic recycling processes to reduce plastic waste.

Schematic of the multiscale structure of a semicrystalline PE plastic substrate and the diffusion of acetic acid and catalyst into the amorphous matrix

Ritimukta Sarangi

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