Screening of vegetable drying oils as potential self-healing agents for smart anticorrosive coatings

Abstract

The microencapsulation of vegetable drying oils is an established strategy to develop smart coatings with self-healing properties. The literature has mostly focused on evaluating linseed oil (LO) and tung oil (TO) as self-healing agents. There is a lack of studies regarding the application of other drying oils in smart coatings and a comparison between different vegetable oils as self-healing agents has yet to be carried out. In this work, the self-healing potential of different seed oils was assessed in terms of their drying and anticorrosive properties. The investigation was focused on chia oil (CO), dehydrated castor oil (DCO), LO, and TO. Drying times were assessed under different cobalt (Co) drier contents. Drying kinetics was carried out by monitoring changes in viscosity with time and following the evolution of infrared spectra during drying. Barrier properties of the polymerized oil-based coatings were assessed by electrochemical impedance spectroscopy of carbon steel coated samples during immersion in 0.1 mol/L NaCl solution. It was found that the type of oil and concentration of drier play an important role on favoring the self-healing effect. The concentration of 0.2 wt% Co was found optimum for encapsulation to accelerate self-healing, as oils dry up to three times faster in comparison with the lowest drier content studied (0.025 wt% Co). TO obtained the best drying properties, with set-to-touch times around 1 h and rapidly forming a tack-free film, however, TO coatings ended up being extremely cracked, which compromised its barrier properties. LO obtained the slowest drying, while CO and DCO exhibited intermediate drying between TO and LO. DCO showed the best anticorrosive properties among investigated oils, as its coating was the only one that did not show any decrease in impedance with time, whereas TO and LO coatings presented a decrease in up to one order of magnitude in impedance. Overall, the good drying and barrier properties of DCO strongly stimulate its use as feedstock for self-healing coatings. Results are discussed in terms of fatty acid composition and oxidative polymerization mechanisms. Conclusions help with the selection of seed oils as self-healing agents that can further extend the lifetime of anticorrosive coatings.