All-Biobased Seaweed-Derived Composite Films with Improved Mechanical Properties and Active Functionality Enabled by Fiber Bridging and Interfacial Engineering

The environmental crisis caused by the persistence of petroleum-based plastics is intensifying, exacerbating the urgent need for alternative biodegradable materials. However, most biodegradable materials such as polysaccharides, which simultaneously possess mechanical robustness, functional performance, and biodegradability, remain challenging to synthesize. Herein, we report a high-strength, fully biobased seaweed-derived composite film constructed by bridging sodium alginate through high aspect ratio microcrystalline cellulose. Tannic acid (TA) is further introduced as a multifunctional component, strengthening cellulose-alginate interactions while imparting antibacterial activity and ultraviolet (UV) shielding capability. The resulting composite film exhibits a tensile strength of ∼15 MPa with improved mechanical properties and excellent thermal stability (>180 °C), demonstrating competitive mechanical performance and multifunctional properties compared with those of many reported seaweed-based materials. Moreover, the film offers nearly complete UV protection (∼2% transmittance) and intrinsic antibacterial activity, enabling effective inhibition of food spoilage. Furthermore, the film undergoes near-complete disintegration within four weeks under the tested soil conditions. Overall, this work presents a facile strategy for sustainable polymers and multifunctional films.