Exploring the utilities of rice straw black liquor (part XI): Enhancing the UV resistance, color, antimicrobial, and mechanical characteristics of epoxy coatings using lignin-based hybrid nano-pigments

The key purpose of this work is to prepare multifunctional colored coatings with good UV resistance and antimicrobial activity by incorporating lignin complex nanoparticles as hybrid nano-pigments. Firstly, four complexes [e.g., zinc (lignin/silica/fatty acids), calcium (lignin/silica/fatty acids), aluminum (lignin/silica/fatty acids), and copper (lignin/silica/fatty acids)] were synthesized on a nanoscale utilizing rice straw pulping black liquor. Then, epoxy was reinforced with 1, 2, and 4% of each of the four complexes, and their visual inspection and their mechanical properties were investigated. The findings demonstrate that four paint films of 2% Zn (LSF)-epoxy, 2% Ca (LSF)-epoxy, 2% Al (LSF)-epoxy, and 2% Cu (LSF)-epoxy are the optimum films due to their surface being homogenous and uniform without agglomeration or voids. The coatings in group II were subjected to 100 h of continuous UV irradiation, and the changes caused were determined by FT-IR, SEM, and CIE Lab (color) techniques. The results reveal that there is no significant difference between the coatings before and after the UV irradiation. In the case of specimens containing only epoxy, a significant change was observed. These results confirm that the integration of the hybrid nano-pigments has improved the UV resistance of epoxy coatings. Besides, the results showed that Zn (LSF)-epoxy, Ca (LSF)-epoxy, and Cu (LSF)-epoxy coatings have good antimicrobial activity.