Development of corrosion resistant conducting polymer coatings for aircraft application

Epoxy based conducting polymer coatings were prepared by using polyaniline (Pani), modified with lignosulfonate (LGS) dopant for the aircraft AA2024-T3 alloy. High-strength, light-weight alloys such as AA2024-T3 is widely used for the skin construction of an aircraft. This type of coating resulted in enhancement of conductivity upto 4.88 S/cm compared to 10-8 S/cm for epoxy alone. However such a combination Pani-LGS loses its conductivity with time because of the loss of the dopant. Therefore, the Pani-LGS was further modified by grafting with another polymer i.e. poly(acrylamide co acrylic acid) which maintained the conductivity for longer duration by preventing the loss of dopant. The modification of Pani-LGS with poly (acrylamide co acrylic acid) exhibited conductivity of 3.9 S/cm but maintains it for longer time and showed 1200h salt spray test. The aim of the present work was to achieve conductivity of 5-10 S/cm and corrosion resistance equivalent to 2000h salt spray pass for the coating and hence, further improvements were made with the addition of montomorillonite clay (MMT), aluminium oxide nanoparticles (Al2O3) and graphene (G) to the coating. Other properties of these developed conducting coating, such as corrosion resistance, weathering resistance and mechanical properties were also studied. It was found that the modified coating system had better conductivity (8.76 S/cm in case of graphene), corrosion resistance (2400 h salt spray passes) and enhanced mechanical properties. Detailed stepwise mechanism of various modifications has been proposed which helps in overcoming the defects created by aggressive environment, by both barrier protection and anodic protection of conducting polymer coatings. Thesis submitted in partial fulfillment of the requirements of the degree of Doctor of Philosophy from the Indian Institute of Technology Bombay, India and Monash University, Australia.