Role of α/γ Fe2O3 and ZnO nano-particles in reducing photodegradation of wood components

Nano-particles have attractive properties that may extend the protection periods for traditional coating systems against ultra-violet light degradation, but the direct role of nano-particles in UV performance remains poorly defined. The effects of UV light on relationships between nano-particles and radiata pine (Pinus radiata) sapwood samples were investigated using Fourier Transform Infrared spectroscopy to detect surface chemistry changes before and after 8 weeks of outdoor exposure. Color changes were characterized by measuring CIE L*a*b* parameters on specimens treated with water dispersions of α/γ-iron oxide (Fe2O3) or zinc oxide (ZnO) and exposed to sub-tropical conditions out of soil contact. Alpha Fe2O3 provided the most effective protection of wood from photo-discoloration especially at higher concentrations. Nano-particles exhibited limited interactions with the wood surface before exposure. All types of nano-particles examined were associated with reductions in the vibration of carbohydrate functional groups, while γ Fe2O3 and ZnO nano-particles increased the aromatic skeletal vibration in lignin. Although none of the selected nano-particles completely protected wood from UV damage, α Fe2O3 nano-particles provided some lignin protection with the primary lignin peak at 1509 cm−1 remaining after weathering. Both types of iron oxide provided similar UV protection to cellulose and hemicellulose. While ZnO nano-particles failed to prevent lignin degradation during UV exposure, they provided some cellulose protection as evidenced by the significant increases in cellulose-associated peaks. The results suggest that combinations of zinc and iron oxide nano-particles might be useful for UV protection. Further trials are underway studying mechanisms by which these systems function on wood surfaces.