Abstract
Chemical upcycling of polyethylene terephthalate (PET) waste into functional corrosion-control materials offers a route to combine polymer-waste valorization with metal protection. In this study, secondary PET was used as the starting feedstock in a stepwise chemical-processing route to obtain p-phenylenediamine, which was subsequently employed with formalin and monochloroacetic acid to prepare the PPD-F-MK oligomeric corrosion inhibitor. The inhibitor was evaluated for St20 carbon steel in 1 M HCl by potentiodynamic polarization at 298±1 K after 2 h exposure. Increasing the PPD-F-MK concentration from 100 to 400 mg/L decreased the corrosion current density from 0.167±0.10 to 0.072±0.001 mA/cm² and increased the inhibition efficiency from 81.67 to 92.10%. Surface coverage increased from 0.8167 to 0.9210, while the inhibition coefficient rose from 5.46 to 12.65. The results demonstrate that a corrosion inhibitor prepared through a PET-waste-derived p-phenylenediamine platform can effectively suppress the electrochemical corrosion of St20 steel in hydrochloric acid.
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