Surface characterization and biodegradability of sodium hydroxide-treated Moso bamboo substrates

Alkali solution immersion is widely used in pretreatment during bamboo and wood product manufacturing. In this study, we performed a surface analysis on the bamboo chips pretreated by sodium hydroxide with different concentrations at room temperature (25 ℃) and evaluated the surface performance and biodurability. Bamboo surface rapidly changed to darker color at sodium hydroxide concentration (NaOH) of 5% and become rough at 20% NaOH. The K-M curve showed absorption peak near 390-410 nm after alkali treatment, which was due to the presence of chromophore groups derived from lignin, especially from methylene quinone. X-ray diffraction (XRD) showed the area of the crystallization zone was enlarged rapidly at 5% NaOH and then declined. Fourier transform infrared spectroscopy illustrated the conjugate structure of lignin-phenols changed after proton transfer in hydroxyl radical solution and this was the main reason for the surface color changes. During alkali treatment, lignin and hemicellulose in bamboo degraded to some extent, but cellulose was less affected. X-ray photoelectron spectroscopy demonstrated the oxygen-carbon ratio (O/C) and the oxygenated to unoxygenated carbon ratio (Cox/Cunox) all increased, indicating the decrease of extractives and lignin and surface carbon atoms were oxidized in alkali solution and carbon bonds were i more stable. XRD showed sodium hydroxide immersion can not only degrade and dissolve low-polymerization substances in the amorphous zone, increased the crystalline region, but also reached crystalline region, swell the cell wall, which increased the accessibility of fungi and made bamboo more susceptible to fungi infection. Bamboo weight loss of decay after alkali treatment was all larger than the control and maximized at 10% NaOH.