The effect of rue ( Ruta graveolens ) and ginger ( Zingiber officinale ) extracts as antifouling agents in silicone matrix coatings

The use of rue extract and ginger oleoresin as natural antifouling agents in a silicone matrix was verified in this work. 13 C nuclear magnetic resonance ( 13 C NMR) analysis identified a series of compounds with bactericidal properties in the two investigated natural products. Thermogravimetric analyses showed that the addition of rue extract and ginger oleoresin in the silicone matrix increased the thermal stability of the formed films. Electrochemical impedance spectroscopy analysis showed that the presence of both antifouling agents increases the velocity of water diffusion into the film, improving contact between marine water and the two products. Fourier transform infrared spectroscopy confirms that both antifouling agents were trapped inside the silicone matrix. Bacterial adhesion tests showed that rue extract reduced the adhesion of gram-negative bacteria, Escherichia coli , while ginger oleoresin did not show any significant effect. Optical microscopy images demonstrated that the presence of rue extract slightly increased the film’s porosity without impairing the silicone hydrophobicity, while ginger oleoresin significantly altered the film’s morphology (reducing the water contact angle). Finally, the sample containing rue extract showed excellent results against marine fouling after 6 months of immersion in a real marine environment. The polymer containing ginger oleoresin showed satisfactory results against marine fouling; however, the film showed adhesion failures after 6 months. Graphic abstract