Ask Joe Powder: Suitability of powder coatings for military applications

Abstract

Coal tar epoxy (CTE) coating system has been widely used for protection of steel structures under atmospheric, buried and immersion conditions because of their low water vapour permeability, high electrolyte resistance and good antibacterial properties. However, coal tar has been classified as carcinogen, mutagen and toxic for reproduction (CMR) as per International guideline (REACH, IARC and GS 11). It is now banned in the developed nations like US, Europe, Japan, etc. As the use of coal tar is being restricted, there is an urgent need to formulate a coal tar free epoxy product for corrosion protection of structures. In the present study, alternative approaches have been proposed to replace coal tar such as bitumen (BIT), hydrocarbon resin (HR), flexibilizer (FL) and curing agents like polyamide (PAD) or polyamine (PAM). Four different coal tar free formulations were formulated separately by using these approaches. The standard CTE and coal tar free epoxy compositions were evaluated for mechanical properties such as elongation at break, tensile strength, adhesion strength and resistance to abrasion, impact and flexibility. The resistance to corrosion of optimized composition (epoxy-HR-FL-PAD-PAM) and coal tar epoxy coating was evaluated by exposing to different environments. The corrosion resistance property was also evaluated by cathodic disbondment and electrochemical impedance spectroscopy (EIS) technique. Results indicate that epoxy-hydrocarbon resin-flexibilizer composition cured with blend of polyamide and polyamine has comparable mechanical and corrosion protection properties to that of standard CTE.