Understanding the Influence of Molecular Weight on the Corrosion Inhibition Performance of Two Cellulosic Polymers

Corrosion inhibitory efficacy of two cellulosic polymers, hydroxyethyl cellulose (HEC) and hydroxypropyl methylcellulose (HPMC) on mild steel in 1 M HCl have been investigated with a view to assessing the influence of molecular weight on the inhibition performance. In the study, weight loss measurement technique, electrochemical impedance spectroscopy and potentio-dynamic polarization corrosion monitoring techniques were employed. Weight loss results reveal that on comparative analysis, HPMC gives better inhibition performance than HEC, though both polymeric molecules achieved inhibition efficiency up to 90%. Changes in impedance and polarization parameters suggest the adsorption of HEC and HPMC on the mild steel surface, leading to the formation of protective polymeric films. Furthermore, HPMC that has larger molecular weight than HEC also showed higher adsorptive capability following thermodynamic-kinetic isotherm model. The experimental results were corroborated by results from theoretical studies which involve quantum chemical calculation and molecular dynamics simulation, whereby the HPMC molecules demonstrated higher ability to donate electrons to the vacant d-orbital of the metal, than HEC molecules.