Transparent cellulose-based films with enhanced hydrophobicity, fluorescence, and mechanical performance via sequential post-functionalization

Transparent polymer films are widely used in optical devices, packaging, and information display, but most of them are derived from non-renewable petrochemical resources and show limited environmental sustainability. Cellulose represents an attractive natural polymer alternative owing to its high abundance and biodegradability. However, its pronounced hydrophilicity and limited functional integration restrict the development of advanced transparent cellulose-based films. In this work, highly transparent, water-resistant, and fluorescent cellulose-based films were fabricated from bleached forestry pulp through sequential carboxymethylation, periodate oxidation, silane coupling, diamine-assisted crosslinking, and post-functional fluorophore grafting. Carboxymethylation enabled the formation of transparent films, while silane modification and network construction significantly improved the surface hydrophobicity and water durability of the cellulose matrix. Subsequent immobilization of N-(1-pyrene)maleimide endowed the films with distinct fluorescence. The resulting films maintained high optical transparency after multistep functionalization, with a transmittance of about 90% in the visible region, exhibited a water contact angle of 101.6°, and a tensile strength of about 70 MPa. In addition, the fluorescent films showed clear optical responses under UV irradiation. This work provides an effective strategy for constructing a transparent cellulose-based platform that simultaneously integrates hydrophobicity, fluorescence functionality, and mechanical reinforcement through sequential covalent modification, and highlights their potential in optical labeling, smart packaging, flexible substrates, and security marking.