Uniform Lignin‐Epoxy Hybrid Colloidal Spheres With Unprecedented pH 14 Alkaline Resistance: Facile Synthesis for Sustainable Photonic Materials

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Lignin, the most abundant aromatic biopolymer in nature, holds great promise for carbon-neutral materials development yet is limited by its inherent dark color and poor solvent stability. Transforming it into uniform lignin colloidal spheres (LCSs) with ordered arrays enables specific visible light reflection and thus presents tunable colors. However, industrial lignin-derived LCSs via self-assembly typically exhibit broad size distribution and poor solvent resistance. To address these challenges, we proposed a novel strategy combining solvent fractionation and surface covalent polymerization. Acetone/water fractionation effectively reduced lignin heterogeneity, narrowing LCSs size distribution. Bisphenol A diglycidyl ether (BADGE) was used as cross-linker to covalently polymerize hydroxyl groups, inhibiting LCSs dissolution. Two hybrid LCSs were fabricated: hy-LCSs via co-self-assembly of lignin and BADGE and hy@LCSs through subsequent surface cross-linking. Hy-LCSs20 (20 wt% BADGE) shows stability in pH 12 alkali and acetone/water, while hy@LCSs70 exhibited unprecedented alkaline resistance up to pH 14, far exceeding the highest reported value of pH 12 for lignin colloidal spheres to date. Critically, BADGE incorporation preserved monodispersity of both hy-LCSs20 and hy@LCSs70, enabling precise size control without compromising uniformity. After centrifugation to form ordered structures, both hy-LCSs20 and hy@LCSs70 reflect specific wavelengths with tunable colors, overcoming key barriers in lignin valorization.

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