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

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.