<p>Biopolymer-based solid polymer electrolytes (SPEs) are promising for safer, flexible energy-storage devices but typically show low room-temperature ionic conductivity. Here, we demonstrate glycerol-driven ion-transport enhancement in NaI-doped MC–dextran–sorbitol hosts reinforced with TiO₂ nanofiller. Films (MC/Dextran/Sorbitol = 50/30/20 wt.%) containing NaI (38 wt.%) and TiO₂ (3 wt.%) were solution-cast with graded glycerol plasticizer from 8 to 40 wt.%. FTIR verified polymer–salt complexation (ether-band downshifts) and stronger hydrogen-bond networks with increasing glycerol, while XRD showed a dominant amorphous halo without NaI crystalline reflections and retained anatase TiO₂ peaks. Glycerol systematically reduced crystallinity from 39.5% at 8 wt.% to 26.9% at 40 wt.% (near-linear trend, R2 ≈ 0.98), in tandem with marked electrochemical gains. Consequently, room-temperature DC ionic conductivity (σ_DC) increased from 1.67 × 10⁻1⁰ S·cm⁻1 at 8 wt.% to 1.49 × 10⁻⁶ S·cm⁻1 at 40 wt.%, an ~ 8.9 × 103-fold enhancement. Dielectric analyses showed low-frequency ε′ rising from ~ 10 (8 wt.%) to ~ 1750 (40 wt.%), and the tan δ loss peak shifting toward higher frequencies (e.g., ~ 53.8 kHz at 40 wt.%), evidencing faster polarization dynamics. Modulus spectroscopy (M″ peaks) corroborated relaxation-time shortening from ~ 1591.5 µs (8 wt.%) to ~ 6.52 µs (40 wt.%), accompanied by increases in ionic mobility and diffusion coefficient. These findings highlight the synergistic roles of glycerol plasticization and TiO₂ reinforcement in promoting amorphization, salt dissociation, and efficient hopping-type conduction. The 40 wt.% glycerol composition delivers one of the highest σ_DC values reported for this MC-based family, offering a viable route to high-performance Na-ion polymer electrolytes.</p> Graphical Abstract <p></p>