Cellulose is a renewable, biodegradable material whose functionality can be enhanced by chemical modification. Conventional cationization relies on organic solvents and yields low substitution, whereas deep eutectic solvents (DESs) offer a greener alternative.

In this thesis, an environmentally friendly DES-based approach was applied to produce cationized dialdehyde cellulose and to evaluate its performance as a wet-end additive and as a paper coating. The modified cellulose significantly improved hand-sheet strength without negatively affecting dewatering and retained its performance when synthesized using recycled DES, demonstrating solvent reusability. As a coating material, cationized dialdehyde cellulose formed dense films with improved mechanical and air barrier properties.

To further enhance additive performance, two pretreatment strategies, enzymatic treatment and cold alkaline dissolution–precipitation, were applied to increase the reactivity of the starting pulp and thereby improve the charge density of the cellulose derivatives.

 In addition, hornification, a phenomenon that negatively affects pulp reactivity, was investigated. Drying experiments on swollen cellulose showed that freeze-drying and glycerol-drying mitigate hornification, whereas air-drying intensifies it. For air-dring method, solvent exchange prior to drying reduced hornification. The results indicate that water-mediated hydrogen bonding dominates the hornification mechanism, which is strongly influenced by solvent polarity and molecular weight.

Overall, this work demonstrates that combining green solvents, targeted pretreatments, and controlled drying strategies can substantially enhance cellulose reactivity and functionalization. These findings broaden cellulose applications from papermaking additives to bio-based barrier coatings and support efforts to replace petroleum-based plastics with renewable materials.

Cellulose is a renewable, biodegradable material with functionality that can be expanded through chemical modification. Cationization enables applications in water treatment, antimicrobial, and energy fields, while improving papermaking performance. However, conventional cationization relies on organic solvents, whereas deep eutectic solvents (DES) provide a greener, more efficient alternative.

In this thesis, a sustainable DES-based route was applied to produce cationized cellulose derivatives (CDAC), which improved handsheet strength and formed coatings with enhanced mechanical and barrier properties.To further improve additive performance, enzymatic pretreatment and cold alkaline dissolution-precipitation were used to enhance pulp reactivity. The reduction in reactivity caused by drying-induced hornification was also investigated. Freeze-drying and glycerol-drying mitigated hornification, whereas air-drying intensified it. Further analysis showed that hornification strongly depends on solvent polarity and molecular weight prior to drying.

Overall, this work demonstrates that combining green solvents, targeted pretreatments, and controlled drying strategies significantly enhances cellulose reactivity and expands its application toward high-performance bio-based coatings.