Chitosan-bridged amide networks in waterborne PVGA films: Structure-surface-barrier coupling and a moisture-retention...

Waterborne PVGA/chitosan films were prepared by blending chitosan with glyoxylic-acid-functionalized poly(vinyl alcohol) (PVGA) and vacuum-assisted curing at 100 °C without external crosslinkers. Blend mapping (3 wt% solids, pH 4.5-5.5) showed that GA feed >5.0 mol% (relative to repeat-unit -OH) triggered turbidity/phase separation, whereas ≤5.0 mol% enabled uniform casting. Bonding-related changes upon curing were evidenced by FT-IR (amide-region growth with reduced carboxyl CO) and XPS surface chemical-state trends (increased N 1s amide-like fraction with reduced free-amine contribution), complemented by bulk free-amine quantification (TNBS, Supporting Information). Substitution and curing reduced chain mobility and crystallinity (higher T_g; lower T_m and ΔH_m; reduced XRD crystallinity). Wettability varied non-monotonically, peaking near PVGA3/CS-CL and correlating with moisture transport. For uncured blends, increasing substitution lowered both OTR and WVTR. After curing, WVTR reached a minimum at PVGA3/CS-CL (138.1 g m^-2 day^-1, 38 °C/90% RH) whereas OTR showed a non-monotonic trend (23 °C/0% RH). A room-temperature cherry-tomato moisture-retention demonstration showed 9-10% weight loss after 15 days with PVGA3/CS-CL. Overall, the work provides a single-variable, water-processed framework linking blendability, bonding-related signatures, surface response, and barrier metrics.