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Cathodic disbondment resistance with reactive ethylene terpolymer blends and composite coatings

Abstract

The cathodic disbondment (CD) of organic coatings is a continual problem in applications of cathodically protected steel in civil infrastructure and petrochemical production and transportation. Multiple researchers have proposed that the degree of disbondment is a function of factors such as service temperature, coating thickness and applied cathodic potential. While the mechanism by which disbondment occurs has received a fair amount of attention, efforts to develop new material coating systems to resist the disbondment of organic coatings on cathodically protected metal substrates has been lacking. The objective of this dissertation is to develop a new coating system to protect metal substrates under cathodic protection, such as buried pipelines. Pipeline coatings must be tough, durable, resistant to chemical and moisture diffusion, and maintain adhesion in wet environments. A reactive ethylene terpolymer (RET) was compound blended with standard high- density polyethylene (HDPE) as a potential coating material for steel. The HDPE component provides toughness and high chemical and moisture resistance, while the RET component provides high polarity and reactivity, which enhance adhesion to steel substrates. Micro- and nanocomposite approaches were taken to incorporate multi- walled carbon nanotubes (MWCNTs) to provide increased cohesive strength while inorganic particles (clay, talc, and zinc) micro-scale fillers and organically-modified nanoclays were explored to reduce diffusion pathways through the polymer coatings. The cathodic disbondment performance of the various blend and composite coatings are presented and analytical models developed to predict long-term durability of the coatings in corrosive environments

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