Coupled thermal and dielectric signatures of glycerol-induced structural organization in ulvan-based films

Gonzales K.N.; Torres F.G.; Carsí M.; Sanchis M.J. · Algal Research (2026) · DOI: 10.1016/j.algal.2026.104998

Resumen

This work examines how glycerol modulates the structure–dynamics coupling in ulvan-based films derived from the green macroalgae Ulva nematoidea and Ulva papenfussii. FTIR revealed glycerol-induced changes in the local interaction environment: the O-H stretching band (∼3360 cm−1) broadened and shifted to lower wavenumbers, while changes in the C-O and glycosidic region (∼1030–1070 cm−1) were consistent with modifications in intermolecular interactions and possible conformational rearrangements within the polysaccharide matrix. Consistently, thermal analysis shows an increase in the glass-transition temperature (Tg), most pronounced in U. papenfussii films, suggesting reduced segmental mobility rather than conventional plasticization. Dielectric spectroscopy revealed an apparent shift of both β- and α-relaxation regions towards higher temperatures upon glycerol incorporation in the pH 7 films. While the α-process could only be assessed qualitatively because of overlapping conductive and other contributions, quantitative analysis of the well-resolved β-relaxation revealed a higher activation energy and lower relaxation strength in U. papenfussii films, consistent with a more constrained molecular environment. In contrast, U. nematoidea films showed more moderate changes, which may be related, at least in part, to their higher sulfate content. Overall, glycerol acts as a structural modulator, inducing tighter chain interactions and restricting molecular mobility, resulting in an antiplasticization-like response at the thermal and molecular relaxation levels. The results demonstrate how compositional differences in ulvan extracted from distinct Ulva species can be exploited to tune the performance of algae-derived films. This understanding provides a mechanistic basis for tailoring ulvan-based films towards sustainable functional materials and supports the development of high-value biomaterials from marine macroalgal resources.

Instituciones: Pontificia Universidad Católica del Perú