Hard water causes polyester to shed far more microplastics, and only some fabrics benefit strongly from protective coatings, revealing why water chemistry and unseen textile finishes significantly influence real-world pollution risks.
Study: Reducing microplastic fiber shedding from hand-washed polyester. Image Credit: Katarzyna Ledwon / Shutterstock
In a recent study published in the journal Scientific Reports, researchers investigated whether anti-microplastic fiber (MPF) coatings can effectively reduce the release of microplastics from polyester fabrics during hand washing.
They found that the coating reduced MPF release, but its effectiveness depended on fabric type and water quality. The coating reduced MPF release by up to 92 for green polyester and approximately 30% for black polyester.
MPFs, typically defined in the broader literature as microplastic fibers less than 5 mm, are a major contributor to marine microplastic pollution, with synthetic textile laundering responsible for approximately 35% of the microplastics found in the ocean.
The growth of fast fashion has intensified this issue, posing ecological threats to marine life, including coral reefs and fish, which can experience growth inhibition and genetic damage. Human exposure to MPFs is also associated with respiratory problems and other health issues.
Existing Coating Technologies for Fiber Control
One promising mitigation strategy is the use of special textile coatings that reduce fiber shedding during laundering. Studies have shown that coatings made from biodegradable materials or low-friction polymers can reduce MPF release by up to 90% during machine washing.
Need to Address Hand-Washing and Water Chemistry
However, all prior research has been limited to machine laundering in deionized water with or without detergent, despite the fact that two-thirds of the global population wash clothes by hand, often using natural or mineral-rich water.
The influence of water hardness, as measured by total dissolved solids (TDS), on MPF release is therefore a key focus of investigation.
Study Aims and Experimental Setup
Researchers tested the performance of an existing MPF-reducing coating during hand washing to assess how different water sources affect the amount and size of fibers released from polyester fabrics.
Fabric Preparation and Coating Procedure
Two 100% polyester fabrics (green and black) were tested. Each fabric was prepared as 15 × 15 cm swatches, either uncoated or coated using a two-layer process.
The first layer involved applying a primer solution of 3-aminopropyltriethoxysilane (APTES) in toluene, followed by hydrolysis, cleaning, and plasma treatment.
The second layer, polydimethylsiloxane (PDMS), was applied through vapor deposition to create a low-friction surface, aiming to reduce MPF shedding.
Hand-Washing Protocol and Water Selection
Each fabric swatch was washed manually on a bamboo washboard for 5 minutes using 1 L of water at approximately 25°C, containing standard detergent. Three water types were used: deionized (DI), tap, and Lake Ontario water, each differing in TDS content.
The wash effluent was filtered through 12 µm nylon filters, dried, and analyzed under a microscope to count and measure MPFs.
Surface and Fiber Characterization Methods
The surface properties of fabrics were assessed using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray Photoelectron Spectroscopy (XPS), as well as contact angle measurements to evaluate wettability and coating integrity.
Fiber fracture types were also visually classified as fatigue or tension failures, providing insight into how water properties influence fiber breakage.
Effects of TDS on MPF Release
TDS in washing water strongly increased MPF release: uncoated green and black polyester released over twice as many microplastics in high-TDS Lake Ontario water as in low-TDS deionized water.
Coating Performance Across Fabric Types
Two-layer coatings substantially reduce MPF release from green polyester by 77 to 92% across various water types, but only decrease black polyester fiber emissions by 26 to 37%. The reduction for black polyester in DI water was modest and not statistically significant (p equals 0.052), whereas reductions in tap and lake water were substantial.
For green polyester, the coating’s efficacy clearly decreased as TDS increased, but for black polyester, there was no consistent relationship between water hardness and performance.
Black polyester without coating still sheds about 60% fewer microplastics than green polyester.
Influence of Water Chemistry on Fiber Length
Increasing TDS led to a significant reduction in MPF length: length measurements were performed for the black polyester only, and fibres released in DI water averaged 1.19 mm, while those from Lake Ontario water averaged only 0.53 mm. The coating did not significantly alter MPF length or surface fibre breakage. Water contact angle tests revealed that the coated fabrics were initially hydrophobic, although the coating’s durability varied, particularly on green polyester.
Surface Contamination and Coating Adhesion
FTIR analyses revealed pre-existing silicone contamination, while XPS identified fluorine contamination on the green polyester, which may have affected coating adhesion. The authors note that the black polyester’s technical back already contained a silicone-based finish, which lowered its baseline shedding and made the added PDMS coating appear less effective relative to this altered starting point.
Air permeability and fibre failure mechanisms remained unaffected by the composition of the coating or washing water, confirming that differences in MPF release were primarily linked to water chemistry rather than fabric damage.
Impact of Water Hardness on MPF Fragmentation
This study demonstrated that higher TDS in hand-washing water increases MPF release and shortens fibre length, likely because dissolved minerals fragment already-detached fibres rather than causing extra fabric damage.
Coating Limitations and Practical Implications
The PDMS coating effectively reduced MPF emissions, particularly from green polyester, but its performance was hindered by surface contamination and water hardness. These findings highlight that water composition plays a key role in MPF pollution, even during manual washing.
Strengths and Constraints of the Evidence
Strengths include a comprehensive comparison of water types and advanced surface analyses. However, the small MPF mass limited verification of the proposed fibre-cutting mechanism.
The authors emphasised that future standards should also quantify MPF mass loss as the primary metric, not only fibre counts, especially for hand-washing scenarios.
Future Directions for MPF Mitigation Research
Future research should quantify MPF mass loss across different water chemistries and explore more robust coatings suitable for real-world textiles.
The results have practical implications for manufacturers, policymakers, and consumers regarding MPF mitigation, wastewater filtration standards, and the design of textile materials.
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