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Recent Developments on the Use of Polymers as Corrosion Inhibitors - A Review

The use of corrosion inhibitors is the one the most economical and practical means of controlling metallic corrosion in different corrosive media. Interest on the use of eco-friendly organic compounds as corrosion inhibitors has extended to the use of polymers to inhibit metallic corrosion. The use of polymers as corrosion inhibitors has attracted attention and has gained wide acceptance in recent times. This has been attributed to a number of factors namely: (i) they are low cost and stable to metallic materials in acid media, (ii) they possess multiple adsorption sites, (iii) through their functional groups, they form complexes with metal ions and on the metal surface these complexes occupy a large area, thereby blanketing the surface and protecting the metal from corrosive agents present in the solution. A number of synthetic and natural polymers as metallic corrosion inhibitors have been investigated and reported. As an update to previous review work on the use of polymers as corrosion inhibitors, the present review presents most of the contributions made to the literature on the use of polymers as corrosion inhibitors of diverse metals in different corrosive media in the last four (2010-2013) years. Metals have continued to be a choice raw material in areas such as structural, fabrication, electrical and electrochemical, hot-dip galvanizing, etc. This usage stem from the many interesting properties of metals which include: high melting and boiling points; characteristic lustre; malleability; ductility; hardness with great tensile strength; relatively high densities; and good conductivity. Unfortunately, these properties deteriorate when metals interact with certain elements that recur within their environments; a process which is technically called corrosion. The rate and extent to which metal corrode depend on two broad factors: the nature of the metal and the nature of the corroding environment. The nature of the metal encompasses the position of the metal in galvanic series (metals in the active zone of the galvanic series corrode faster than those in the noble zone), overvoltage (reduction in overvoltage of the corroding metal promotes corrosion process), relative areas of anodic and cathodic parts (when two dissimilar metals are in contact, the corrosion of the anodic part varies as the ratio of the area of cathodic part), purity of metal (impurities present in a metal give rise to heterogeneous state which form minute electrochemical cell and as a consequence, corrosion of the anodic part is accelerated), physical state of the metal (grain size, stress orientation of crystals, etc. affect corrosion rate), nature of surface film (the specific volume ratio which is the ratio of