High-value nanocellulose from laser-printed waste paper: From comparative synthesis to mechanistic insights on...

Laser-printed waste paper, as a high-quality cellulose resource, has garnered significant attention for its potential high-value utilization. This study represents the first instance of preparing waste cellulose nanofibers (WCNF) from de-inked waste paper using a combination of sulfuric acid hydrolysis and catalytic deep eutectic solvent (DES) method with FeCl₃. We comprehensively compared the impact of these two methods on the comprehensive properties of the resulting WCNF. The results revealed that the FeCl₃-DES method achieved a yield of 56.6% at a DES dosage of 0.3 mmol/g, producing WCNF with an average length of 831 nm and an average width of 25 nm. Additionally, this method exhibited exceptional thermal stability, with a maximum decomposition temperature of 349.6 °C, significantly outperforming the sulfuric acid method, which yielded only 46.6% WCNF and suffered a decrease in thermal stability due to the introduction of sulfate ester groups. Analytical results indicate that the DES method effectively avoids thermal degradation while maintaining the cellulose I crystalline structure through the competitive coordination of Fe³⁺ and hydrolysis with hydrogen bonding. This research provides a new strategy for the high-value utilization of laser-printed waste paper and offers theoretical support for the large-scale production of cellulose nanofibers using green solvent methods.