Hydrogen peroxide-mediated oxidative modification of chitosan: Structural, physicochemical, and colloidal changes

Chitosan is a versatile biopolymer widely explored for biomedical, environmental, and functional material applications; however, its limited aqueous dispersibility and structural rigidity restrict broader utilization. In this study, aqueous hydrogen peroxide (H₂O₂) was employed as a green oxidizing agent to induce oxidative modification of chitosan under varying H₂O₂ concentrations (1-6%) and treatment durations (1-6 h). The resulting structural, physicochemical, thermal, and colloidal changes were systematically investigated using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG/DTG), UV-vis spectroscopy, dynamic light scattering (DLS), zeta potential analysis, and aqueous solubility measurements. The results indicated that oxidative treatment promoted chain fragmentation, disruption of crystalline domains, and incorporation of oxygen-containing functional groups, leading to progressive transitions from semi-crystalline to more amorphous structures. Increased oxidation severity reduced hydrodynamic size, altered colloidal stability, and significantly enhanced aqueous dispersibility and soluble chitosan yield under near-neutral conditions. FTIR and UV-vis analyses suggested the formation of carbonyl- and carboxyl-containing functionalities associated with hydroxyl radical-mediated oxidation pathways. Thermal analyses further demonstrated decreased thermal stability and modified degradation behavior with increasing oxidation intensity. Moderate oxidation conditions provided a balance between enhanced dispersibility and recoverable product yield, whereas severe oxidation promoted excessive fragmentation and reduced material recovery. Therefore, this work demonstrates that H₂O₂-mediated oxidative modification provides a simple, environmentally benign, and tunable strategy for tailoring the structural and colloidal properties of chitosan for potential applications in biomedical delivery systems, sustainable coatings, and environmental remediation materials.