Stoichiometric Optimisation of Vat Dyeing for Sustainable Colour Fastness in Cotton Fabrics

Edward Apau; Benjamin Addo; Morrison Appiagyei Boadi; Charles Frimpong

doi:10.35738/ftr.v7.2025.72

Authors

Edward Apau Sunyani Technical University Author https://orcid.org/0000-0002-8390-5010
Benjamin Addo Kwame Nkrumah University of Science and Technology Author https://orcid.org/0009-0001-3552-5726
Morrison Appiagyei Boadi Sunyani Technical University Author
Charles Frimpong Kwame Nkrumah University of Science and Technology Author https://orcid.org/0000-0001-6842-0683

DOI:

https://doi.org/10.35738/ftr.v7.2025.72

Keywords:

Stoichiometry, vat dyes, colourfastness, sodium hydrosulphite, caustic soda, Ghana/artisanal dyeing

Abstract

Purpose: Vat dyes are widely recognised for their superior colour fastness on cotton substrates; however, the efficiency of their reduction–oxidation cycle is highly dependent on the stoichiometric balance among the dye, sodium hydroxide (NaOH), and sodium hydrosulphite (Na₂S₂O₄). This study investigates how controlled variations in reagent ratios influence colour fastness, to develop a stoichiometrically grounded optimisation framework applicable to artisanal and semi-industrial dyeing systems in Ghana.

Methodology/Design: An experimental factorial design was employed using mercerised cotton fabric as the substrate. All reagent ratios were expressed in a fixed order (dye: NaOH: Na₂S₂O₄), while the mixing sequence was treated as a separate variable. The commonly used 1:2:2 ratio was adopted as a comparative baseline rather than a universal standard. A total of 27 dyeing conditions were tested across three vat dye systems (golden yellow, red, and violet). Colour fastness to rubbing (dry and wet) and washing was evaluated using ISO-based grey scale assessments. Each experiment was replicated three times, and results are reported as mean ± standard deviation.

Findings: The results demonstrate that stoichiometric balance between NaOH and Na₂S₂O₄ governs the efficiency of dye reduction, fibre penetration, and subsequent fixation. Ratios approximating equilibrium, particularly 5:1:1 and 2:1:1 (dye: NaOH: Na₂S₂O₄), consistently produced superior fastness grades. In contrast, reagent excess or deficiency disrupted the redox balance, resulting in reduced dye stability and increased colour loss. While no clear sequence-dependent trend was observed, this outcome is interpreted cautiously due to confounding between dye type and mixing sequence.

Practical and Social Implications: The study provides an empirically validated, ratio-based guideline that can improve process consistency, reduce chemical excess, and enhance product durability in resource-constrained dyeing environments. The framework supports a transition from intuition-based practice to controlled, evidence-informed dyeing processes.

Originality: This research advances the application of stoichiometric theory within textile dyeing by linking quantitative reagent balance to measurable performance outcomes under practical conditions. It contributes a context-sensitive optimisation model that integrates chemical precision with artisanal production systems, extending beyond conventional laboratory-based studies.

Author Biographies

Edward Apau, Sunyani Technical University

Edward Apau is a Lecturer in the Department of Visual and Industrial Art at Sunyani Technical University in Sunyani, Ghana. Concurrently, he is a PhD Candidate in Textile Design Technology at Kwame Nkrumah University of Science and Technology (KNUST). He holds both a B.A. in Industrial Art (Textiles) and a Master of Fine Arts (MFA) in Textile Design, both from KNUST. His research interests are centred on weaving technology, sustainable dyeing, design thinking and innovation, textile surface designs, and printing technology.
Benjamin Addo, Kwame Nkrumah University of Science and Technology

Benjamin Addo is a final-year B.Sc. student in Textile Design and Technology, affiliated with the Department of Industrial Art (Textile and Fashion Section) at Kwame Nkrumah University of Science and Technology (KNUST). As a dedicated, disciplined, and committed scholar, he harbours a passion for research and academic activities. His primary research interests include printing technology, dyes & dyeing processes, textile testing, and surface textile designs.
Morrison Appiagyei Boadi, Sunyani Technical University

Morrison Appiagyei Boadi is an Assistant Lecturer in the Department of Visual and Industrial Art at Sunyani Technical University, Sunyani, Ghana. He holds a Bachelor of Arts (B.A.) in Industrial Art (Textiles) and a Master of Fine Art (MFA) in Textile Design, both earned from Kwame Nkrumah University of Science and Technology (KNUST), Kumasi. His research interests focus on indigenous textile production methods, textile design innovation, and textile art.
Charles Frimpong, Kwame Nkrumah University of Science and Technology

Charles Frimpong is a Full Professor in the Department of Industrial Art at Kwame Nkrumah University of Science and Technology (KNUST). His distinguished educational background includes a B.A. in Industrial Art (Textiles) from KNUST, a Master of Science in Textile Technology from the University of Ghent, Belgium, and a PhD in Art Education, also from KNUST. His primary research interests encompass smart textiles, dyes & dyeing technology, textile testing, and indigenous textiles.

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