Strong, anti-swelling, and biodegradable seaweed-based straws with surface mineralized CaCO₃ armor

While the extensive utilization of disposable plastic straws has resulted in significant environmental issues such as microplastics and soil and ocean pollution, the quest for alternative straws for versatile use remains a formidable challenge. Here, drawing inspiration from naturally water-resistant materials such as bones and sea urchins, we have developed seaweed-based straws with significantly improved water resistance and mechanical strength via in-situ mineralization of CaCO₃ on their surfaces. Specifically, the COO^- groups on the G (α-L-guluronate) blocks of alginate were employed to establish a robust cross-linked network, while the COO^- groups on the M (β-D-mannuronate) blocks attracted free Ca²⁺ through electrostatic forces, thereby promoting CaCO₃ nucleation. This effectively prevents COOH groups from hydrating, reducing swelling, and results in the fabrication of nano- to micron-sized CaCO₃ particles that reinforce the structure without compromising the cross-linked network. Compared with the control group, the S5% sample (prepared with 5 % Na₂CO₃ solution) exhibited a 102 % increase in water contact angle, a 35 % decrease in swelling degree, and a 35.5 % and 37.5 % increase in ultimate flexural and tensile stress, respectively. Furthermore, the potential use of these straws as a waste for heavy metal adsorption was investigated, addressing environmental concerns while demonstrating economic feasibility.