Modulating the mechanical performance and characteristics of modified Canna edulis ker. starch bioplastic films through co-polyol plasticizer blends

This study investigates the structure–property relationships of sodium acetate–modified Canna edulis ker. starch (md-CEkS) films plasticized with sorbitol–glycerol co-plasticizer ratios of 1:0, 3:1, 1:1, 1:3, and 0:1 (w/w, relative to dry md-CEkS). Sodium acetate modification induces partial substitution and ionic association of starch hydroxyl groups, reducing excessive hydrophilicity and creating a tunable polymer matrix. Film properties were evaluated in terms of mechanical performance, optical transparency, moisture permeability, crystallinity, hydrogen bonding, and biodegradability. Increasing glycerol content decreased tensile strength (from 16.15 ± 0.64 to 12.49 ± 0.13 MPa) while increasing elongation at break (from 17.6 ± 1.9% to 44.1 ± 1.2%). The 1:1 sorbitol–glycerol formulation exhibited the most balanced performance, combining moderate strength (12.99 ± 0.69 MPa), high flexibility (42.0 ± 3.0%), and high optical transparency (T₆₆₀ ≈ 91%). Structural analyses showed that higher glycerol content reduced crystallinity (39.5% to 24.5%) and increased hydrogen-bonding index (6.83 to 8.38), which was associated with increased water vapor transmission and accelerated biodegradation under soil burial conditions (≈ 66% mass loss after 14 days). These results demonstrate that controlled sodium acetate modification combined with sorbitol–glycerol co-plasticization enables systematic tuning of mechanical flexibility, moisture sensitivity, and optical clarity in starch-based bioplastic films.