Direct extraction of functional whitened lignocellulose from wood via isocyanate modification in water–ethanol mixture

Lignocellulose was directly extracted from wood by introducing a bulky substituent to lignin in a polarity‐tuned solvent mixture of water and ethanol. This extraction process is based on the whitening method for lignin derivatives, which involves lignin modification with a bulky substituent in a water–ethanol mixture. The bulky substituent encapsulates the aromatic main chain of lignin, preventing light absorption and enabling lignin whitening. This encapsulation also changes the solvent affinity of lignin derivatives. By exploiting the change in solvent affinity during lignin whitening, whitened lignin‐containing lignocellulose was isolated from wood. This process only requires sawdust or a saccharification residue, an organic isocyanate as a bulky substituent, water and ethanol, representing a sustainable method compared with conventional lignocellulose extraction processes. The resulting lignocellulose exhibits whiteness despite the presence of brown lignin in wood. Notably, the whitened lignocellulose functions as a heat‐resistant filler for poly(ε‐caprolactone) and as a luminescent material. This method for extracting whitened lignocellulose under sustainable conditions advances the valorization of plant biomass for the fabrication of highly designable functional materials with industrial applications.