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Preparation and Soil Degradation Behavior of Additive-Free Chitosan Films for Biodegradable Food Packaging
Summary
Scientists made food wrap out of chitosan (a natural material from shrimp/crab shells) using just water and vinegar-like acid — no synthetic chemicals or plasticizers needed, which matters because those additives can raise safety questions and complicate disposal. The film fully broke down in soil within 60 days, kept apples fresher longer by reducing browning and moisture loss, and offers a promising alternative to plastic wrap that won't leave behind the microplastic pollution linked to conventional packaging.
Chitosan is a renewable, biodegradable, and intrinsically antimicrobial alternative to petroleumbased packaging, but most chitosan films contain plasticizers or cross-linkers that complicate foodcontact safety and end-of-life disposal. Here, additive-free films were prepared from chitosan, water, and near-stoichiometric acetic acid. A 128 cP grade at 2.0% (w/v) provided the best castability. Single-step drying (55 ℃/6 h) and two-step drying (55 ℃/6 h followed by 120 ℃/0.5 h) were compared. The second step reduced residual chitosan–acetate-associated mass loss and produced a stiffer film (elongation at break, 11.9 ± 1.4%; elastic modulus, 351.7 ± 56.4 MPa) than the more extensible single-step film (43.2 ± 2.8%; 251.1 ± 19.1 MPa). Both films were water-insoluble, enzymatically degradable, and lost 17.7–21.9% of their dry mass after 28 days in lysozymecontaining buffer. A non-destructive transparent-pot soil assay allowed one specimen to span airexposed, enclosed-air, and soil-contact zones. Both films disintegrated completely within 60 days only in direct soil contact, whereas the air-exposed and enclosed-air regions remained intact for 180 days. This within-specimen design directly visualized soil-contact-driven degradation without specimen retrieval. In a preliminary apple-wrapping trial, the film reduced browning and dehydration relative to unwrapped controls. Drying protocol therefore provides an additive-free route to mechanically distinct chitosan films for flexible or semi-rigid packaging applications. Keywords: Chitosan film; biodegradable packaging; drying protocol; soil biodegradation 1. Introduction Petroleum-derived plastic packaging is one of the most persistent forms of environmental pollution, with several hundred million tons of plastic produced annually and only a small fraction recovered through recycling or composting [1,2]. Food packaging accounts for a large share of this waste stream, and its short service life relative to the multi-decade persistence of conventional polyolefins in the environment has intensified the search for biodegradable alternatives derived from renewable resources [3,32]. Among the biopolymers considered for this purpose, chitosan is one of the most extensively studied because it is abundant, non-toxic, film-forming, and intrinsically antimicrobial [4,5,7,25]. Cast chitosan films are transparent, provide a useful oxygen barrier, and have been explored as edible coatings and stand-alone packaging materials for fruit, meat, and bakery products [6,8,9,10].