Sustainable Rewritable Paper Enabled by Colored Aqueous Inks for Writing, Painting, and Printing Applications

ABSTRACT The increasing environmental impact of single‐use paper highlights the urgent need for sustainable and reusable alternatives. Herein, we report a versatile rewritable paper platform enabled by biodegradable, water‐based colored inks composed of food‐grade dyes and sodium alginate. The aqueous inks are compatible with freehand writing, brush‐based painting, and inkjet printing, and can be completely erased using mild alkaline solutions such as sodium hydroxide or sodium bicarbonate. Rewritability is achieved by pre‐treating the paper substrates with naturally abundant organic acids, including citric, oxalic, tartaric, malic, and succinic acids, which promote fibrous hydrogel formation through intermolecular interactions with alginate. The resulting paper substrates demonstrate good reusability, retaining structural integrity and optical clarity over multiple write–erase–rewrite cycles. Ink patterns remain stable for more than 6 months under ambient conditions while allowing rapid and on‐demand removal. Additionally, a rewritable security ink system incorporating aromatic molecules within the alginate matrix enables hidden markings that become visible under ultraviolet light, offering potential for anti‐counterfeiting and secure documentation. This work provides a practical and scalable approach to sustainable documentation technologies, consistent with green chemistry and circular design principles, with broad applicability in education, packaging, creative media, and information security. image