New research has shown that seawater can be integrated into cotton fabric dyeing without severely compromising quality. The team tested eleven water formulations, from pure freshwater to pure seawater, identifying optimal performance when seawater formed half to 70% of the dye bath. The study addressed colour retention, mechanical integrity, and washing fastness, using reactive blue dye on plain weave cotton under controlled industrial conditions.
- Cotton samples dyed with mixed water solutions achieved strong colour results when seawater comprised half the dyeing liquid.
- Ocean water from Brazilian coastal regions contains extremely high mineral content that typically disrupts conventional textile manufacturing processes.
- The sequestering agent Plexene RTN eliminated staining in the 50% seawater sample while ensuring fabric mechanical properties were not negatively affected during high-temperature dyeing cycles.
- Quality assessments included resistance testing for washing, saltwater exposure, perspiration contact and physical rubbing to verify performance.
- The findings have been published in the paper ‘The effect of seawater hardness on cotton fabric dyeing using reactive blue dye’ by Iêda Letícia de Souza Ferreira and others in Coloration Technology
THE STUDY: The research, conducted by Iêda Letícia de Souza Ferreira and colleagues, investigated the effect of seawater hardness on reactive dyeing of cotton fabrics. Using untreated seawater from the Areia Preta beach and freshwater from the local supply network, the team prepared mixtures from 0% to 100% seawater in 10% increments. The study measured colour strength (K/S value), colour difference (ΔE), washing fastness, and tensile strength, applying industry-standard dyeing protocols and auxiliary chemicals.
WHAT'S AT STAKE: Textile manufacturing relies heavily on freshwater for dyeing and finishing, with low hardness water preferred to avoid operational and quality issues. Seawater contains high levels of dissolved salts, including calcium and magnesium, which can precipitate with dyes or soaps, causing uneven colouration and reduced dye uptake. These effects can challenge sustainable water use in water-scarce industrial regions.
- High mineral content in process water can cause dyes or soaps to precipitate, leading to uneven colouration and reduced dyeing efficacy.
- Industrial equipment suffers scale buildup in heating systems, pipelines and processing machinery when hard water circulates through manufacturing facilities.
- Dyes and soaps may precipitate as calcium and magnesium salts, resulting in uneven dyeing and reduced efficacy.
- Removing minerals from process water requires treatment steps that add operational complexity in water-scarce regions.
WHAT THE DATA SHOWS: Performance analysis revealed non-linear relationships between seawater hardness and dye uptake. Freshwater produced the highest K/S value (6.5), while 50%, 60%, and 70% seawater samples each achieved 6.1. Lower concentration mixes from 10% to 30% yielded weaker results. Optimisation using a sequestering agent at 50% seawater raised K/S to 6.4, reducing the colour intensity gap with freshwater from 6.6% to just 1.6%.
- Mixed solutions containing 50%, 60% and 70% ocean water achieved nearly identical colour strength results in comparative testing.
- Lower ocean water percentages from 10% to 30% produced weaker colour outcomes than higher concentration mixtures.
- Pure ocean water dyeing generated considerably reduced colour intensity compared to optimal mixture ranges identified through systematic evaluation.
- Water mineral content varied dramatically from minimal levels in fresh water supplies to extremely elevated concentrations in ocean samples.
READING BETWEEN THE LINES: The study used untreated seawater from Areia Preta beach in Natal, mixed with freshwater in varying proportions. The 50% seawater sample was optimised by adding a sequestering agent to capture calcium and magnesium ions, reducing precipitation issues. This adjustment improved colour strength from 6.1 to 6.4 K/S, narrowed the gap with freshwater, and eliminated staining observed in unoptimised seawater mixtures.
THE BIGGER PICTURE: Freshwater scarcity is a growing challenge for industries, including textiles, which consume large volumes in wet processing. Seawater offers a widely available alternative, particularly in coastal regions, but its high mineral content has been a barrier to adoption.
- This study demonstrates that, with optimised treatments, seawater can be incorporated without damaging fabric structure, achieving acceptable dyeing performance even at hardness levels up to 5827 mg/L (70% seawater).
- Traditional textile training emphasises soft water requirements, but this research challenges established industry practices by demonstrating acceptable results under extreme mineral conditions.
- Coastal manufacturing regions could exploit ocean water availability while inland facilities continue to rely heavily on limited freshwater sources.
