Eco-friendly carboxymethylcellulose-based copolymers as effective corrosion inhibitors for mild steel in acidic media

Corrosion of carbon steel in acidic media remains a major challenge in petroleum production and industrial acidizing operations, creating a need for efficient and environmentally friendly corrosion inhibitors. In this work, two carboxymethylcellulose-based graft copolymers, carboxymethylcellulose-graft-polyacrylamide (CMC-AM) and carboxymethylcellulose-graft-poly(acrylamide-co-4-vinylpyridine) (CMC-AM-4VP), were evaluated as corrosion inhibitors for X60 mild steel in 1 M HCl and 0.5 M H₂SO₄ solutions. Their inhibition performance was investigated using weight-loss measurements, potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and adsorption studies. The inhibition efficiency increased with inhibitor concentration and decreased with increasing temperature. CMC-AM-4VP exhibited the highest performance in both acidic media. Potentiodynamic polarization measurements showed that CMC-AM-4VP reduced the corrosion current density from 452 to 46 μA cm⁻² in 1 M HCl and from 510 to 64 μA cm⁻² in 0.5 M H₂SO₄, corresponding to inhibition efficiencies of 89.8% and 87.4%, respectively. Weight-loss measurements confirmed its high inhibition performance, reaching 80.62% in HCl and 79.36% in H₂SO₄. Electrochemical results indicated that the copolymer acts as a mixed-type inhibitor by suppressing both anodic metal dissolution and cathodic hydrogen evolution. The enhanced inhibition performance is attributed to the synergistic contribution of carboxyl, amide, and pyridine groups, which strengthen inhibitor–metal interactions. These findings highlight CMC-based graft copolymers as promising environmentally friendly inhibitors for steel protection in acidic environments.