Preparation of Green and Degradable Seaweed-Based Straws by Directional Diffusion Assembly as a Plastic Substitute

The extensive and persistent utilization of disposable plastic straws by humans has engendered significant environmental issues. However, it is challenging to find suitable substitutes for plastic straws with comparable properties. Here, we propose a versatile design of all-natural, degradable straws as a plastic substitute, using a directional diffusion assembly (DDA) method, which controls the directional diffusion of a cross-linker for subsequent cross-linking, without the constraints of rolling-up, extrusion, and injection molding techniques. Employing the DDA method on alginate, the seaweed-based straws prepared exhibited excellent hygrostability, especially in hot water, better than commercial paper and PLA straws. Scanning electron microscopy (SEM) images and Fourier transform infrared spectroscopy (FT-IR) spectrum demonstrated the high cross-linking between alginate and Ca²⁺ after resoaking. Moreover, they displayed natural degradability (within 180 days, indicated by the significant changes in residual weight, molecular weight, and microstructure) and high mechanical properties, including bending resistance (∼14 MPa) and tensile strength (∼80 MPa). Considering these advantages, the seaweed-based straws developed in this work hold significant promise as substitutes for petroleum-based plastic products like straws.