A novel eco-friendly and economical approach of bamboo colorization through biomimetic polymerization of dopamine melanin inspired by photonic microstructure of bird plumage

Abstract

Bamboo is a low-carbon, sustainable, and versatile substitute for many synthetic materials, but limited variety of color restricts bamboo's decoration performance and added value. Traditional chemical colorization suffers poor generality, massive resource consumption, low colorfastness, high pollution, and remarkable damage to bamboo. This research pioneered an eco-friendly, economical approach to tailor bamboo color while keeping natural texture. Through a facile, mild modification by dopamine (a tyrosine derivative), its biomimetic polymerization endowed bamboo surface with a double-layered polydopamine melanin system mimicking morphology and composition of (keratin layer)/(melanin granules) microstructure of colorful bird plumage. Chromatic-optical and microstructural characterizations showed that polydopamine system's upper layer was nanoscale ∼ submicronscale (thickness 55∼215 nm) film bestowing on bamboo structural colors through thin-film interference. All colors at visible wavelength could be formed through controlling film thickness by adjusting dopamine concentration. Thicker film was more continuous and smoother, while thinner film was stabler. Polydopamine system's lower layer was micronscale (thickness 1.2∼4.4 μm) aggregate of particles enhancing color saturation through suppressing light scattering. Amorphous arrangement of polydopamine system made structural colors on bamboo display weak angle dependence. Physicochemical characterizations proved that bamboo featured non-covalent interaction with deposited polydopamine, which never destroyed bamboo's crystalline structure. Structural colors on bamboo exhibited satisfactory stability in long-term exposure and mechanical washing tests. Overall, proposed colorization was confirmed eco-friendly, convenient, and effective, thus contributing novel ideas to cleaner production in bamboo utilization.