Construction and characterization of layered double hydroxides on eucalyptus wood surface to imitate violet sandalwood color

Objective To address the issue of light color and uniform surface tone in fast-growing eucalyptus wood, layered double hydroxides (LDHs) were utilized to control the wood’s color and replicate the dark brown color of the valuable wood species, purple sandalwood (Dalbergia melanoxylon).

Method Co-based metal organic framework (Co-MOF) was employed as templates and precursors due to their strong affinity for wood. By catalyzing the hydrolysis reaction of MnCl₂ on the wood surface, CoMn-layered double hydroxide (CoMn-LDH) was synthesized on eucalyptus veneers. We investigated the color variations of eucalyptus veneers subjected to three concentrations of MnCl₂ solution (0.016, 0.032, 0.064 mol/L) and temperature of 20, 40, 60 and 80 ℃. The interaction mechanism of LDHs with eucalyptus veneer surface was analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR). Assessments of water resistance and light aging resistance of the color-modified wood were conducted through contact angle and light aging tests.

Result (1) At 40℃, CoMn-LDH-wood produced using 0.032 mol/L MnCl₂ solution successfully replicated the color effect of Dalbergia melanoxylon, exhibiting similar chromaticity values and UV spectra. (2) The hydrolysis of MnCl₂ induced an exchange process between Co-MOF and OH⁻, leading to the formation of metal hydroxides and the creation of CoMn-LDH. Characteristic techniques such as SEM, XRD, XPS, and FT-IR confirmed the composite structure of CoMn-LDH, with cobalt and manganese existing in Co²⁺ and Mn²⁺ forms, representing characteristic features of CoMn double hydroxides. The color-modified wood showed an increase in static water contact angle from 36.2° to 49.5°, and after 120 h of light exposure, the color difference fell within the range of 3 to 6, indicating a perceptible color shift at a moderate resolution. These results suggested that the prepared CoMn-LDH-wood displayed enhanced surface hydrophobicity and light aging resistance.

Conclusion The mild color adjustment treatment conditions applied in this study effectively enhance the color of eucalyptus wood, augmenting its aesthetic appeal and commercial value, thereby fostering the sustainable utilization of wood resources from artificial forests.