Nanoparticles-Mediated UV Shielding of Isothiazolinone in Waterborne Acrylic/Alkyd Resins Coatings for Long-Term Protection of Bamboo

The rapid photodegradation of organic fungicides severely limits the durability of waterborne coatings for outdoor bamboo applications. In this study, inorganic nanoparticles were used as a protective barrier to stabilize a ternary isothiazolinone-based fungicide blend composed of 4,5-Dichloro-2- n -octyl-4-isothiazolin-3-one (DCOIT), 2- n -octyl-4-isothiazolin-3-one (OIT) and N -butyl-1,2-benzisothiazolin-3-one (BBIT), designated as DOB, for applications in waterborne acrylic/alkyd coatings. Nano-ZnO, TiO 2, and SiO 2 were compared under accelerated UV aging. Results showed that nano-ZnO provided the best protection for fungicide activity. After 7 days of UV exposure, the coating containing nano-ZnO maintained the highest antifungal grade (grade 1), whereas the coatings with nano-TiO 2 and nano-SiO 2 remained at grade 3 and grade 4, respectively, and the control coating degraded to grade 3. The 12 week outdoor natural weathering test further verified that the coating containing nano-ZnO exhibited negligible mold growth and only slight color variation, whereas the control coating suffered severe yellowing, obvious mold colonization, and serious surface deterioration. The modified coating also exhibited better color stability, gloss retention, and mechanical properties after aging, confirming that nano-ZnO effectively inhibited the photodegradation of DOB. The dual mechanisms of nano-ZnO include strong UV shielding ability and relatively low photocatalytic activity, which together reduce DOB photolysis. This work provides a simple and effective strategy for preparing durable antifungal coatings, which helps extend the service life of bamboo in outdoor applications.