Toward More Sustainable Dialdehyde Starch Synthesis via Organic-Acid-Assisted Hydrolysis: Application as a Covalent Crosslinker in Bioactive Chitosan/PVA/Artemisia herba-alba Films

Abstract

Hydrochloric acid is conventionally used to pre-hydrolyse starch before periodate oxidation into dialdehyde starch (DAS), which may generate chloride-containing waste. This study proposes a sustainable one-step hydrolysis–oxidation route using acetic acid, a biodegradable organic acid, evaluating reaction time (24–72 h) to maximise aldehyde content while minimising acid hazard. Acetic-acid-derived DAS (24 h) achieved a significantly higher aldehyde content than the HCl route (59.57 ± 0.55% vs. 49.91 ± 1.00%; p < 0.001). This DAS was applied as a covalent crosslinker in chitosan/poly(vinyl alcohol) films loaded with Artemisia herba-alba extract, benchmarked against a non-crosslinked film. Crosslinking increased tensile strength (67.1 vs. 51.5 MPa) and crystallinity (40.83% vs. 17.04%), reduced porosity, and slowed extract release in phosphate-buffered saline (27.5% vs. 41.9% at 168 h; Weibull model, Adj. R2 ≥ 0.97) while preserving predominantly Fickian diffusion. Despite releasing less extract, the crosslinked film retained significantly higher DPPH radical-scavenging activity, consistent with hemiacetal interactions between residual aldehydes and extract phenolics. Antibacterial testing against six clinical strains suggested that crosslinking modulates rather than suppresses activity. These findings support acetic-acid-mediated DAS synthesis as a low-hazard, waste-reducing route toward bioactive, controlled-release biopolymer films as promising candidates for future biomedical or active-packaging applications.