Water-induced failure in polymer coatings: Mechanisms, impacts and mitigation strategies—A comprehensive review

Among the various strategies implemented to improve the integrity of metallic structures, polymer coatings have emerged as a compelling choice due to their capacity to offer cost-effective and enduring protection. However, humidity is a critical environmental factor that poses a risk to the integrity of polymer coatings, manifesting in dimensional alterations, induced internal stresses, diminished adhesion strength between coating and substrate, microstructural changes, and hydrolytic degradation. Many of these detrimental changes remain concealed until the advanced stages of coating failure. Comprehending the water-induced degradation mechanisms in polymer coatings is crucial for improving their protective effectiveness, ensuring safety and dependability, minimizing economic and environmental impacts, and promoting innovation and regulatory compliance. This study rigorously explores the water-induced failure mechanisms in polymeric coatings, highlighting both visible signs of degradation, such as corrosion, cathodic delamination, and blistering, and less apparent phenomena like hydrolysis, swelling, and plasticization. From the initial stages of water diffusion to the eventual delamination of the coating, diffusion mechanisms and the interaction between water molecules and coating constituents are scrutinized. Moreover, this review explores the distinctive and interrelated impacts of each phenomenon on the integrity of the coating, along with potential mitigation strategies. The review culminates with practical recommendations aimed at bolstering the integrity of coated structures.