Exploring the Effects of Extraction Procedures on the Molecular Relaxation Processes of Ulvan Obtained from Ulva Papenfussii

Ulvan, a biodegradable sulfated polysaccharide from Ulva papenfussii, was obtained using hot water (neutral pH) and alkaline (pH 13) methods to evaluate how extraction conditions modulate its molecular dynamics and dielectric behavior. While compositional changes due to extraction pH are well documented, their impact on the relaxation processes and segmental mobility of ulvan remains largely unexplored. Here, we provide a comprehensive characterization of dielectric permittivity and dielectric loss over a wide frequency (10⁻²-10⁶ Hz) and temperature range (-150 °C to 150 °C), supported by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The alkaline-extracted ulvan showed a lower glass transition temperature (31.6 °C vs. 47.9 °C), higher molecular mobility, and enhanced dielectric response. In contrast, the hot water-extracted sample exhibited greater thermal stability and a more defined dipolar relaxation processes, including a β-relaxation characterized using the Havriliak–Negami model. These findings suggest that hot water-extracted ulvan is more suitable for applications like biodegradable packaging or biomedical films, while alkaline-extracted ulvan is better suited for electroactive materials such as polymer electrolytes. This study highlights the role of extraction strategy in designing ulvan-based sustainable materials. The results underscore the relevance of broadband dielectric spectroscopy as a powerful tool for guiding the design of polysaccharide-based functional materials.