Utilizing natural fibers for production of a fully bio-based textile is an appropriate approach to align with sustainability objectives. In case of dyed products, the used dye and further finishing agents also have to be bio-based. Algae-based materials are naturally colored and can be used as a natural dye product. The present study aims to investigate the use of algae materials as a color pigment for coating on cotton as a natural fiber material using a bio-based binder. Three different algae representing blue-green algae (BGA), unicellular microalgae (UNI), and filamentous algae (FIL) are investigated as colored additives for textile coatings. The algae are applied as powder to the coating recipe together with sodium alginate as binder component. Modification of the application is conducted by addition of calcium dichloride (CaCl₂) acting as a crosslinker for the natural binder system. Using these applications, strong coloration of cotton fabrics can be achieved. Scanning electron microscopy (SEM), infrared spectroscopy (FT-IR), color measurements, light fastness tests, and tests on the rubbing fastness are performed. Good values in rubbing and light fastness are reached (4–5 and 5, respectively) depending on the used algae material and the addition of calcium dichloride. Applications using the algae BGA and UNI perform better due to light fastness. In contrast, applications with the filamentous algae FIL lead to better rubbing fastness. The present study confirms that the proposed technique and formulations are appropriate for achieving fully bio-based, naturally colored textile products, offering a promising foundation for further research into and development of the use of algae for the modification and functionalization of textile materials.

A major obstacle to textile recycling is the presence of dyes, which limits the reuse of fibers in high-value applications. Despite previous studies on, cotton decolorization, the systematic development of an optimal formulation that preserves fabric integrity remains lacking. This study addresses this gap by investigating a decolorization method for mixed-dyed cotton textiles that enables successful redyeing while preserving fabric quality. Reactive and vat-dyed cotton fabrics were treated with sequential reductive and oxidative processes, in a full factorial design. The impact of input parameters on tensile strength was evaluated through statistical analysis using analysis of variance at a significance level of α = 0.05. The developed recipe was subsequently validated on post-consumer cotton textiles. Stripping efficiency was assessed using K/S values, and fabric quality was evaluated through tensile strength, pilling, and fuzzing appearance. Temperature showed the strongest influence on dye removal. Fabric strength was significantly affected by temperature and oxidizing agent, and by interactions of temperature with reducing agent and oxidation time. The optimized process achieved 98–99.5% color removal and retained 95% of the fabric’s tenacity. A stripping efficiency of >90% for post-consumer cotton validates the method’s applicability in real-world circular systems.