With the rapid development of industry, carbon steel has been widely used in many engineering applications due to its advantages of high strength, high toughness, and low cost. However, mild steel is susceptible to corrosion in harsh environments, causing huge economic losses in many industries. There are many ways to protect steel from corrosion, of which the use of corrosion inhibitors is the most cost-effective.
Corrosion inhibitors are anticorrosive chemicals that reduce the rate of corrosion of metals in a medium. For example, the addition of corrosion inhibitors can overcome the problem of "over-picking" in the surface treatment of steel. Electronegative organic compounds, including small molecules and polymers, have proven useful in corrosion inhibition of mild steels because of their effective adsorption on metal surfaces in different corrosive media, in addition to the corrosion inhibition efficiency is closely related to their structure and electronic properties. At present, small molecule organic compounds are among the best among metal corrosion inhibitors because of their stable structure, good water solubility, and the properties that can be studied in theoretical chemistry. These organic inhibitors are generally composed of N, O, and S heteroatoms conjugated with an electronic backbone, and their corrosion inhibition efficiency depends on their adsorption capacity on the metal surface. It has been proven that the stronger the adsorption of the corrosion inhibitor on the metal surface, the higher the corrosion inhibition efficiency.
However, most inhibitors** based on small organic molecular structures are expensive and toxic to humans. With the enhancement of environmental awareness, the research and development of non-toxic and environmentally friendly corrosion inhibitors has received more and more attention. Water-soluble polymers have the advantages of environmental protection and high cost performance, can form polycentric adsorption, and have a high affinity for metal surfaces, making them the most suitable alternatives. To date, various natural and synthetic polymers have been developed as potential corrosion inhibitors for weak steels in acidic solutions. However, these polymeric corrosion inhibitors often require high concentrations to achieve effective corrosion inhibition, which largely limits their practical application. Therefore, it is of great significance to develop new, green, economical and efficient polymer corrosion inhibitors.
Hyperbranched polymers have a wide range of applications in many fields due to their branching structure and unique properties. In particular, a large number of electronegative functional groups can be grafted on the periphery of hyperbranched polymers, which helps to improve their adsorption capacity on the metal surface, so as to achieve effective corrosion inhibition. Terminal hydroxyl hyperbranched poly(amide) (HPAE) is a water-soluble hyperbranched polymer rich in electronegative hydroxyl and amino functional groups. In addition, the synthesis of HPAE is fairly straightforward. Here, Chunyan Bao's team from the School of Chemistry and Molecular Engineering of East China University of Science and Technology reports a terminal hydroxyl poly(amine) hyperbranched polymer (HPAE-OHS) as a green, effective and economical corrosion inhibitor for mild steel (Q235) in 1M HCl solution. HPAE-OHS is a third-generation hyperbranched polymer that can be synthesized by a simple, one-pot solvent-free esterification reaction.
The weight loss test showed that the presence of HPAE-OHS had an inhibitory effect on the corrosion of Q23S, and the corrosion inhibition rate (N(%) could reach 94 at 24 h at the dosage of 100 mg L-19%。The adsorption thermodynamic study showed that the adsorption of HPAE-OHS on the surface of Q235 steel followed the Langmuir adsorption isothermal model. Polarization measurements and electrochemical impedance spectroscopy (ES) showed that HPAE-OHS was a hybrid corrosion inhibitor, and Hape-OHS formed a protective film on the metal surface through the interaction of N heteroatoms and Fe atoms to prevent metal corrosion. Theoretical studies have further shown that the branched molecules diffuse in parallel and adsorb on the metal surface, resulting in maximum surface coverage, thus effectively isolating the corrosive medium from the metal surface. Based on the above results, this study is expected to provide new ideas for the design of green, economical and effective corrosion inhibitors.
Literature**: Shengjie Du, Shengyi Chen, Zekai Zhang, Zhicheng Ye, Huanv Mao, Huiting Yang, Cheng Lian, Chunyan Bao* materials chemistry and physics, 2022, 292, 126831.