Water-repellent textiles are found in everyday items like raincoats, sportswear, shoes, and furniture, which they help keep dry, clean, and stain-free. However, industries produce these fabrics using chemicals based on carbon-fluorine bonds, known as fluorinated compounds, which are durable yet toxic pollutants that persist in the environment for centuries. At the same time, polyester-based fabrics, which account for half of the world’s textile demand, continue to accumulate as waste. These fluorinated fibers drift across waterways, shed microplastics, and find their way into feeding turtles and other aquatic life, turning yesterday’s T-shirts into tomorrow’s pollution.
In a clever twist, researchers at Cornell University found a way to turn this textile waste into part of the solution. They developed a new way to upcycle discarded fabrics into coatings that provide durable water resistance, or hydrophobicity, without the need for harmful fluorinated compounds.
Commercial textiles contain additives, dyes, and blended fibers that make recycling difficult. Instead of removing these stubborn impurities, these scientists leveraged them as an opportunity. They used waste from a mixture of polyester and spandex fabrics to form a material made of tiny metal clusters connected by long carbon chains called organic linkers. These materials, known as metal-organic frameworks or MOFs, have a net-like microstructure that can be customized to trap or repel different substances, including water. They synthesized the MOFs under mild heat and pressure rather than the intense conditions commonly used, turning a complex reaction into a cleaner and more sustainable process.
To produce these new, sustainable MOFs, the team began by synthesizing the necessary ingredients. First, they prepared the organic linkers by submerging the waste fabrics in sodium hydroxide. This highly alkaline chemical unzips the long polyester fabrics into their building blocks and partially unravels the spandex fibers into water-resistant fragments.
Then, they prepared the MOF metal clusters using a compound that is often used to create coatings and ceramics, called zirconium (IV) oxide chloride octahydrate. They dissolved this compound in acetic acid and immersed a new piece of waste fabric in the solution for 15 hours at 70°C (158°F). This step allowed the zirconium metal clusters to anchor onto the fabric surface, creating active sites for the MOF to form.
Next, the researchers added the organic linkers dropwise to react with the metal sites on the fabric, forming molecular bridges that connected the metal clusters together into an MOF. They repeated this process using pure polyester fabrics to observe how the absence of spandex affected the coating’s structure and performance. The process of forming an MOF is similar to string art, where the metal clusters act as pins fixed to the surface and the organic linkers weave around them like yarn, creating an intricate, ordered network across the fabric.
Person making string art, photo by Monstera Production: https://www.pexels.com/photo/a-person-making-a-string-art-7411932/
Once the MOF was formed, the researchers tested its hydrophobicity by placing water droplets on the coated and uncoated fabrics and comparing how long the water drops remained unabsorbed on the fabrics’ surfaces. They observed that both untreated spandex-polyester and untreated polyester fabrics were naturally hydrophobic, which they attributed to polyester’s innate ability to repel water. However, the droplets got absorbed by these fabrics after only 5 seconds and 6.5 seconds, respectively.
In contrast, droplets on the MOF-coated spandex-polyester fabrics remained intact even after 5 minutes, which they considered superhydrophobic behavior. Meanwhile, MOF-coating made from polyester alone showed the opposite effect, immediately absorbing the droplet. The researchers explained that the MOFs derived solely from polyester tended to attract water because of their exposed metal clusters. However, the addition of hydrophobic spandex fragments modified the structure by occupying the reactive metal sites, thus imparting superhydrophobicity.
The researchers also noted that many superhydrophobic coatings are too fragile to withstand multiple washing cycles during practical textile applications. As such, they subjected their MOF-coated spandex-polyester fabrics to 10 cycles each of knife-scratching, finger-pressing, hand-twisting, and tape adhesion tests, followed by 20 cycles each of sandpaper abrasion and washing durability tests. They observed that the fabric’s superhydrophobicity remained practically unchanged throughout all of these tests.
The researchers concluded that durable superhydrophobic coatings can be synthesized from discarded spandex-polyester textiles through a clean and scalable process. They suggested that their work demonstrates a sustainable alternative to toxic fluorinated chemicals and opens new possibilities for researchers to upcycle textile waste into high-performance materials.
