Plasticizer modulation of dynamic mechanical properties and dielectric performance in sodium alginate-based biopolymer films

Abstract This work focuses on the effects of various plasticizers, such as glycerol (GLY), polyethylene glycol (PEG), and dioctyl phthalate (DOP) at 0%, 25%, and 50% concentrations, on the structure, dynamic mechanical behavior, and relaxation dynamics of charge carriers of sodium alginate (SA) film. The investigation of the structure was conducted using attenuated total reflectance fourier transform infrared (ATR-FTIR) and X-ray diffraction (XRD). The AT-FTIR analysis indicated changes in the OH and C–O bands of plasticized SA films, suggesting potential intermolecular interactions between the SA matrix and the plasticizers. Moreover, XRD revealed that GLY and PEG enhanced the amorphous phase of SA, promoting flexibility, while DOP increased crystallinity. Dynamic mechanical testing revealed that the pristine SA biofilm displayed a high storage modulus ( $$\:E^{\prime}$$ ) of 11 GPa at − 50 °C, indicating a stiff structure. The plasticization process with GLY, PEG, and DOP resulted in a decrease in the values to 0.09, 0.1, and 7.11 GPa, respectively, as well as a decrease in the glass transition temperature, which was attributed to weakened polymer chain interactions. The drastic reduction in storage modulus upon plasticization indicates enhanced flexibility. Dielectric measurements revealed significantly higher dielectric constants ranging from 1.65 × 10 6 to 0.12 × 10 6 at 0.1 Hz and direct current conductivity at lower frequencies, also decreasing in relaxation time for films plasticized with GLY and PEG linked to increased hydroxyl groups and higher amorphous content. These findings highlight the potential of SA films plasticized with GLY and PEG as advanced materials for electrochemical and conductive polymer electrode applications.