Photostable transparent wood composite functionalized with an UV-absorber

Abstract

Transparent wood composite (TWC) is an emerging material which combines good optical and mechanical properties with potential applications in smart windows, energy efficient building elements and solar energy concentrators etc. UV resistance of TWC is important for its suitability to be used in outdoor applications as a building material. In this study, functional TWC was prepared by lignin modification bleaching of poplar wood veneers followed by infiltration with epoxy resin doped with an UV absorber (2-(2H-Benzotriazol-2-yl)-4, 6-di-tert-pentylphenol) (conc. 1.0 and 1.75% w/v). Highly stable TWC (thickness 2 mm) with high optical transmittance was fabricated. The photostability of TWC was evaluated by exposing TWC sheets to a UVA340 fluorescent lamp in an accelerated weathering tester. For a comparison, wood, bleached wood, and epoxy samples were also subjected to UV light irradiation and the extent of degradation was evaluated by measuring colour change (yellowness index measured using spectrocolorimeter), chemical changes (monitored using FTIR spectroscopy) and optical transmittance. TWC was highly sensitive to UV light exposure and exhibited rapid photo-discolouration, chemical degradation and a decrease in optical transmittance. Incorporation of UV absorber in epoxy resin considerably reduced discolouration and photo-degradation of TWC. Moisture absorption behaviour (water uptake) of TWC was also evaluated by immersing it in water. The results indicated that TWC undergoes significant photo-degradation and needs application of UV stabilizer for its outdoor applications.