Improving fungal decay resistance of solvent and waterborne polyurethane-coated wood by free and microencapsulated thyme essential oil

Free and microencapsulated thyme essential oils (Zataria multiflora Boiss) were incorporated into solvent and waterborne polyurethane coatings separately to enhance decay resistance of the biocide free coatings. The essential oil was extracted by hydro-distillation in a Clevenger-type apparatus for 4?h. Poly (methyl methacrylate) (PMMA) microcapsules containing thyme oil as an active ingredient were prepared through solvent evaporation method with oil in water emulsion system. Fungal resistance of the coated hornbeam wood (Carpinus?betulus) against white rot fungus Coriolus versicolor CTB 863 A and brown rot fungus Coniophora?puteana BAM Ebw. 15 was tested according to European EN?113 standard before and after six-cycle accelerated aging test (ASTM D1037). The results revealed that the core-shell capsules were formed properly, and their sizes were in the range of 5–50?μ. The encapsulation efficiency determined by UV–visible spectrophotometer at λ?=?275 nm was 67%. The free essential oil was not efficient enough to improve the fungal resistance, while the microencapsulated oil enhanced the resistance even after the accelerated aging via a controlled-release mechanism as well as protected the susceptible ingredients through the shielding effect of the polymeric shell.