Abstract
Long-term exposure to ultraviolet (UV) light can degrade and discolor bamboo; thus, coatings to protect it from UV exposure are required, especially for outdoor use. Benzotriazole (BTZ) and zinc oxide nanoparticles (NZnO) are organic and inorganic UV absorbers commonly used in UV shielding coatings. This study investigated the photostabilizing efficiency of acrylic-based bamboo exterior coatings using a combination of BTZ and NZnO. Different film formulations covering bamboo substrates were irradiated with artificial UV light for 500 h to accelerate aging. The UV-shielding effect on bamboo beneath various films was determined by CIELAB color space and Fourier transform infrared (FTIR) analysis. The film effectiveness was analyzed by scanning electron microscopy, wettability, UV-vis spectroscopy, and FTIR-attenuated total reflection (ATR) spectroscopy. Films containing BTZ provided higher resistance to photodegradation and more effectively inhibited photodiscoloration of the bamboo substrates than those prepared solely with NZnO. After 500 h of UV irradiation, the BTZ–NZnO film containing 2 wt % BTZ and 1 wt % NZnO showed the best coating performance. Strong synergistic effects were detected in the BTZ–NZnO coatings, particularly for the 2:1 ratio formulation. This study also demonstrated the potential of combining BTZ and NZnO as additives for developing stable, effective UV-shielding bamboo exterior coatings for outdoor applications.
Highlights
Bamboo is an ecologically sustainable lignocellulosic material with reliable processing performance and is widely used for building, decorating, and flooring
This study demonstrated the potential of combining BTZ and NZnO as additives for developing stable, effective UV-shielding bamboo exterior coatings for outdoor applications
The UV-shielding capability of coatings with different formulations was determined by changes in UV-induced surface discoloration and chemical composition of the bamboo substrate underneath the film
Summary
Bamboo is an ecologically sustainable lignocellulosic material with reliable processing performance and is widely used for building, decorating, and flooring. Bamboo and its products undergo environmental degradation without protective treatment, which results in surface photodiscoloration [1,2]. This degradation causes cracks in the cells’ walls [3], considerably affects lignin and hemicelluloses [4], and gradually decreases the mechanical properties of bamboo [5]. Light has a short wavelength, and its energy is high enough to cleave many critical functional groups and linkages in bamboo components (e.g., lignin, cellulose, and hemicellulose) [6]. Lignin itself promotes such photochemical reactions [7,8].
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