Water-resistance of iota-carrageenan fibers enhanced by aluminum-ion coordination crosslinking

Abstract

Amid growing concerns over petroleum resource depletion and environmental pollution, the development of eco-friendly and sustainable fiber materials has become imperative. Iota-carrageenan, a natural polysaccharide extracted from red algae, is regarded as one of the most promising bio-based alternatives to synthetic fibers due to its good spinnability and biocompatibility. However, the large number of hydrophilic groups in ι-carrageenan molecules leads to poor water resistance of its fibers, which limits its practical application. In this study, we propose a novel approach to enhance the water resistance of ι-carrageenan fibers by using AlCl₃ solution as coagulation bath. The modified fibers retained structural stability after 180 days of immersion in water at room temperature or 2 h of treatment in 90 °C hot water, demonstrating significantly superior water resistance compared to existing ι-carrageenan fibers. Structural analysis revealed that Al³⁺ coordinates with the hydroxyl group, which originally exists as a free hydroxyl group or weak hydrogen bond in the ι-carrageenan molecule, forming a stable, six-coordinated symmetric octahedral structure centered on aluminum, while also increasing local crystallinity—thereby improving hydrophobicity. This study elucidates the structure-property relationship, providing a theoretical foundation for the design and application of waterproof ι-carrageenan fibers.