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More than half of the 7.5 million bales of cotton produced annually in the U.S. will be used in clothing manufacturing. The finishing techniques used to make cotton fabric smooth, water-repellent and resistant to wrinkling can be detrimental to the environment and the wearer.

Now, researchers propose a method for using cottonseed oil as a "greener" and safer alternative to formaldehyde and per- and polyfluoroalkyl substances (PFAS), often called forever chemicals, when finishing cotton fabrics.

Taylor Kanipe, a graduate student at North Carolina State University (NC State), presented her results at the fall meeting of the American Chemical Society () held Aug. 17–21.

The process for harvesting cotton and creating fabric for textiles includes collecting the wispy cellulose fibers of the cotton boll, removing the cotton seeds interspersed in the fibers, spinning the cotton into yarn, weaving the yarn into fabric and then finishing the fabric with a variety of chemicals that alter its physical properties—for example, making it softer or wrinkle resistant.

Formaldehyde-based resins have traditionally been used as a fabric finishing agent. The sticky resin easily binds to cotton's cellulose fibers, forming chemical bridges to make the long cellulose fibers resistant to wrinkling or stretching.

While formaldehyde is cheap, easy to use and highly reactive, at high concentrations it is . Formaldehyde can also cause skin and respiratory irritations.

Fluorine-containing water-repellent coatings create a hydrophobic surface to make cotton fabric water resistant. However, these coatings contain PFAS, such as perfluorooctane sulfonate and perfluorooctanoic acid, and are being phased out due to their persistent nature and potential link to health conditions.

To eliminate the need for formaldehyde-based resins and PFAS in cotton fabric finishing, a group led by Richard Venditti, a professor of forest biomaterials, paper science and engineering at NC State, set out to create a green alternative by chemically altering seed oil from the cotton plant itself.

Drawing on previous research at NC State, Kanipe, Venditti and colleagues took advantage of specific chemical properties in cottonseed oil to insert epoxy groups along the long carbon chains that make up the oil molecules.

The epoxide group allows epoxidized cottonseed oil (ECSO) molecules to create strong chemical bonds with the cellulose fibers in cotton fabric and with each other, forming a polymer and making the fabric hydrophobic. The epoxy groups also create oil molecule bridges between the cellulose fibers, making the fabric resistant to wrinkling.

In addition to fabric finishing, ECSO could provide a use for the cottonseed oil harvested along with the cotton fibers, making it as inexpensive, easy to use and effective as formaldehyde resins.

"Epoxidized vegetable oils have a range of applications," Kanipe explains. "While native cottonseed oil lacks the reactivity of formaldehyde-based resins, this simple epoxidation process produces a safer, more user-friendly alternative for applications like durable press finishes."

The researchers weighed and chemically analyzed the ECSO-treated fabric using a type of infrared spectroscopy to ensure the ECSO molecules had successfully bonded to the fabric's surface. To evaluate the finished fabric's water-repellent qualities, the researchers used a high-speed camera to measure the contact angle at which water droplets would interact with the cotton surface.

The larger the angle between the water droplet and the surface of the fabric, the greater the water resistance. Untreated fabric showed no contact angle (in other words, the water was fully absorbed into the fabric), while ECSO-treated fabric showed a contact angle of 125 degrees, indicating a significant increase in water-repelling ability.

Future studies will measure additional performance factors in ECSO-treated cotton fabric, including tear strength, durability and wrinkle resistance. The team's ultimate goal is to create a process of treating cotton with an ECSO water emulsion, a green process that does not require hazardous finishing substances.

"If we can achieve our goal of changing the properties of the cotton fabric—making it anti-wrinkle, anti-staining and water-resistant—using a water-based process, we'll have a green process for putting a bio-based material onto cotton as a replacement for formaldehyde- and PFAS-based finishes," says Venditti.