Untreated cotton fabric absorbs water droplets (top) and cotton fabric treated with a form of cottonseed oil repels water (bottom). Credit: Richard Venditti
Grab a garment from the wardrobe at random and there’s a good chance it’s made of cotton.
The breathable, moisture-absorbing textile is prised for its comfort and versatility in apparel and home textiles alike. But cotton fabric is often treated with finishing agents such as formaldehyde-based resins to make it more durable, wrinkle resistant and waterproof.
Fabrics treated with durable press or anti-wrinkle finishes, according to Advances in Functional and Protective Textiles (2020), “maintain good appearance as a result of crosslinking between cellulose chains with finishing agents, inhibiting the movement of the cellulose chains.
“Despite the good crosslinking performance of formaldehyde-based compounds, the concern about potential harm of free formaldehyde potentially releasing from the fabrics to the environment or human beings inspires people to develop formaldehyde-free agents.”
Chemists in the US have chemically altered a byproduct of cotton production – cottonseed oil – to produce a “greener” alternative for finishing cotton and other cellulose-based materials like paper.
The approach inserts epoxide groups along the long carbon chains of cottonseed oil molecules to create ‘epoxidised cottonseed oil’ (ECSO). In 2022, the world produced 4.03 million tonnes of cottonseed oil for use mostly as a cooking oil.
“Epoxidised vegetable oils have a range of applications,” says Taylor Kanipe, a PhD student at North Carolina State University (NC State) in the US, who presented the results today at the fall meeting of the American Chemical Society (ACS).
“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 epoxide groups bond with each other and the cellulose fibres on the surface of the cotton fabric to form a ‘hydrophobic’ polymer which enhances the fabric’s water repelling properties.
Kanipe and collaborators used a highspeed camera to measure the ‘water contact angle’ – the angle between a droplet and a surface – on untreated and ECSO-treated cotton fabric.
Contact angles above 90° mean water droplets sit higher and rounder above the surface. This is indicative of a hydrophobic surface – think drops of water on a lotus leaf (contact angle of 150°).
A contact angle below 90° means the water droplet can spread out more easily, which happens on a wettable surface.
The researchers found that untreated cotton had a contact angle of zero – the water was fully absorbed – while the highly hydrophobic ECSO-treated cotton had a contact angle of 125°.
Treating cotton with ECSO also creates oil molecule bridges between the fabric’s cellulose fibres, which makes it more resistant to wrinkling. The researchers aim to do further studies to determine whether ECSO-treated cotton fabric has favourable wrinkle-resistance, durability, smoothness and tear strength properties.
“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 Richard Venditti, a professor of forest biomaterials, paper science and engineering at NC State.