*Article* **Glycerin-Grafted Starch as Corrosion Inhibitor of C-Mn Steel in 1 M HCl Solution**

**Sihem Lahrour 1, Abderrahim Benmoussat 2,\*, Brahim Bouras 1, Asma Mansri 1, Lahcene Tannouga 1 and Stefania Marzorati 3**


Received: 29 September 2019; Accepted: 29 October 2019; Published: 3 November 2019

**Featured Application: In the last decade, many research works were focused on the use of "green" corrosion inhibitors, lacking in the adverse health issues connected to the organic compounds used in the past. The use of biomaterials as corrosion inhibitors takes considerable attention due to their inherent stability, availability, cost e**ff**ectiveness, and environmentally-friendly nature.**

**Abstract:** C-Mn steels, commonly employed in structural applications, are often exposed to near-neutral aerated environments and hence subjected to general corrosion. In broader contexts, for example during pickling, acidizing treatments, or acid-releasing processes, where steel comes in contact with more aggressive solutions, the use of corrosion inhibitors is a supplementary strategy to cathodic protection and/or coating. This work focuses on the C-Mn steel corrosion protection in the presence of HCl, either as process fluid or by product. In order to avoid the toxicological issues related to conventional synthetic products, a bio-copolymer containing glycerin-grafted starch, synthesized by modification of maize starch, was studied as a "green" corrosion inhibitor by the weight loss method and electrochemical techniques (open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy). Corrosion-related parameters, such as inhibitor concentration and temperature, were varied and optimized to characterize the corrosion process. Results showed that inhibition efficiency increases with increasing bio-copolymer concentration, reaching a maximum of 94%at the concentration of 300 mg L−1. The kinetic and thermodynamic parameters were determined and discussed. The obtained values of corrosion potential and corrosion current density, *Ecorr* and *icorr*, obtained by potentiodynamic polarization, are in agreemen<sup>t</sup> with the weight loss method. The corrosion current densities decrease when the concentration of the inhibitor increases.

**Keywords:** C-Mnsteel; corrosion inhibitors; bio-copolymer; starch; glycerin
