Soil and enzyme-driven degradation mechanisms of alginate- and chitosan-based biocomposite films

We prepared biocomposite films based on alginate (A) and chitosan (Ch) reinforced with cellulose nanocrystals (CNC) or acetylated CNC (mCNC). Their behaviour in native forest soil was evaluated using two set-ups: film on top of soil (TOP) and film between two soil layers (MID). Under the tested conditions, all films reached complete disappearance, with the TOP set-up degrading notably slower (ca. 80–100 days) than the MID set-up (ca. 30 days). Ch-based films disappeared faster than A-based films in the TOP set-up. To obtain mechanistic insight, the films were exposed in vitro to four soil-associated enzymes: lipase (Lip), cellulase (Cel), laccase (Lac), and alcohol dehydrogenase (ADH). Lip and Cel produced the highest release of reducing sugars, whereas Lac and ADH showed only minor effects. ATR-FTIR analysis of residual chitosan-based films showed spectral changes consistent with chemical modification/depolymerization, but not direct proof of specific bond cleavage. Finally, the potential phytotoxicity of degradation products was assessed using barley seeds, but no major inhibitory effect on germination or growth was observed. Overall, the results support the environmental disappearance and enzymatic susceptibility of these biocomposite films, while also highlighting the qualitative nature of the soil assay and the need for future mineralization-focused studies.