Influence of Plant-Derived Modifiers on the Properties of Solvent Free Epoxy Coatings

In this study, the effect of five natural plant modifiers, i.e., clove, ginger, dandelion, stinging nettle, and quinoa, on the surface and optical properties of epoxy coatings based on the Epidian^® 5/IDA system was evaluated. The modifiers were introduced in a constant amount of 3.0 wt.% of the total sample mass. The samples were subjected to short-term UV-Vis (460 nm), UVB (320 nm), and UVC (254 nm) exposure, followed by measurements of Ra/Rz roughness, CIELAB colour, gloss, Raman spectra, reflectance, light transmittance, and moisture resistance under condensation conditions. The addition of modifiers increased the roughness compared with the reference coating, particularly in the case of the coating containing dandelion (R_a = 2.110 µm; R_z = 8.463 µm in the series without UV exposure), whereas UV exposure in many cases led to partial smoothing of the surface. The greatest colour change was observed after UVB irradiation for the coating containing quinoa (ΔE* = 7.10), with a simultaneous increase in the yellow component Δb*. The 60° gloss was strongly dependent on the type of additive; the lowest values were recorded for dandelion, and relatively higher values for clove and ginger. Raman spectra confirmed the presence of bands typical of plant components, while reflectance revealed the greatest sensitivity of changes in the UV range. The condensation test after 500 h showed that plant modifiers may deteriorate the barrier properties of the coatings, particularly in the case of nettle, dandelion, and clove. The results indicate that plant modifiers are promising additives for modifying the properties of epoxy coatings, but their application requires control of particle size, dispersion, and compatibility with the matrix.