Upcycling Sargassum biomass into biodegradable mulch films via sodium alginate and recycled polyvinyl alcohol

Abstract

Sargassum accumulations along tropical coastlines create major environmental and socioeconomic burdens due to odor, ecosystem disruption, and high cleanup costs. Here, we develop biodegradable mulch films that valorize Sargassum-derived sodium alginate (SA) blended with recycled polyvinyl alcohol (PVA), glycerol (plasticizer), and zein (functional additive), followed by beeswax surface coating to improve water resistance. The coated films achieved tunable hydrophobicity (water contact angle 73.6–116.5°) and tensile strength of ≥8 MPa (up to ∼13 MPa without coating), with strong UV shielding (<1% transmittance below 400 nm). Under outdoor rainfall and sunlight exposure, double-side coated films fully degraded within 35 days. Soil safety was supported by OECD Guideline 207 testing with Eisenia fetida, showing 0% mortality. These results demonstrate a low-toxicity pathway to convert Sargassum waste and recycled polymer into functional biodegradable mulch films for agricultural applications.