Radical Degradation Processes Initiated by Catalytic Nanoparticles of CoFe2O4 Towards Polymer Waste Application

Polymer waste presents a modern environmental challenge due to the long-term stability of these materials. Elastomer-based polymers (e.g., tires, pipelines and shoes) are unique in comprising numerous double bonds, which are typically sensitive to radical-initiated oxidative degradation leading to the scission of polymer chains. In this paper, we propose a new approach for radical-initiated oxidative degradation of polymers using cobalt ferrite (CoFe2O4) nanoparticles (NPs). We show that magnetic CoFe2O4 NPs can effectively catalyze the oxidative degradation of polybutadiene (PB), offering easy magnetic recycling and reuse without affecting their catalytic efficiency. The CoFe2O4 NPs were synthesized via a facile surfactant-free method based on a sonochemical reaction. We used methyl ethyl ketone peroxide (MEKP), a model system, to study the rate of radical decomposition catalyzed by the NPs. The radical decomposition rates were determined by following the discoloration of methylene blue (MB) using ultraviolet-visible (UV/Vis) spectroscopy; electron paramagnetic resonance (EPR) measurements were used to study radical formation. The radical-initiated oxidative degradation of PB was studied by thermogravimetric analysis with mass spectrometry detection (TGA-MS). Our results show that cobalt ferrite NPs lead to formation of polymers with low molecular weight fragments and crosslinking, indicating that these NPs are very effective catalysts for the radical degradation of PB. CoFe2O4 NPs are potentially suitable for other polymers, hence this approach may provide a novel route for the chemical (tertiary) recycling of polymers.