High-Strength Pure Alginate Filaments via Controlled Stretching in Wet Spinning

As a globally pervasive issue, microplastic pollution poses a serious threat to human health and the environment. Therefore, it is urgent to develop high-performance, biodegradable, natural filament materials as sustainable alternatives to synthetic filaments. Alginate is an abundant and biodegradable material; however, alginate-derived filaments typically suffer from low mechanical strength, which has severely limited their practical applications. Herein, we developed a series of high-strength pure alginate filaments via wet spinning without the use of any additives, in contrast to most existing approaches. By deliberately enhancing the crystallinity and molecular orientation of alginate filaments, a straightforward two-step stretching strategy was applied during both spinning and post-treatment processes with precise control over the stretch ratio. The imposed axial shear forces promoted parallel alignment and ordered stacking of molecular chains, leading to a crystallinity of 25.4% and an orientation index of 0.79. The resultant filaments possessed a remarkable tensile strength of 557.5 MPa, a high Young’s modulus of 17.4 GPa, and a toughness of 36.4 MJ/m3, surpassing the performance of most previously reported alginate filaments, including those reinforced with additives. Owing to its simplicity and effectiveness, this additive-free strategy establishes a promising paradigm for the scalable production of high-strength alginate filaments.