TW Special Report

When a consumer buys a clothing or textile product, the choices they make are more affected than ever before by concerns over health, safety and sustainability. They want products that reflect their values, and they are actively looking for evidence that a product is better for society, human health and the environment.

Textile dyeing is now an area of increasing concern. Traditional methods have been wasteful, requiring harmful chemicals and the use of large amounts of water and energy. These harmful chemicals are often lost into the process effluent and dumped into the environment.

Brands and consumers want commercial alternatives that provide improved sustainability, without a loss in quality. Forward-thinking manufacturers are turning to alternative dyeing techniques, such as dope dyeing and vegetable dyeing, to meet these requirements.

Dope Dye

Alternatively known as spun dyeing or coloration, mass coloration or dyeing, or solution dyeing, this technique involves the coloring matter being incorporated into a polymer solution, or polymer melt, before the fiber filament formation. It is an increasingly popular technique for coloring textiles, compared to piece dyeing.

Since the color is incorporated directly into the fiber, it provides exemplary colorfastness and superior coloring matter dispersal. This method also negates dye loss into effluents and ends the need for after-treatments and additional rinsing. However, it is only applicable to manufactured fibers, therefore slow to change and making it difficult to adapt quickly to changes in fashion.

Vegetable Dye

Many brands are also turning to natural dyes to improve sustainability. These dyes are biodegradable, renewable, and have a reduced negative impact on human health and the environment.

As the name suggests, vegetable dyes originate from plants — their seeds, flowers, roots, leaves, fruits, etc. While they are better for the planet, they do also have limitations for the manufacturer — poorer colorfastness and reproducibility of shades and a low affinity for synthetic fibers.

Challenge

These two dyeing techniques offer the textile industry multiple advantages in terms of reducing their environmental footprint while meeting the changing demands of consumers. However, without independent laboratory analysis, it can be difficult to differentiate between textiles that are dyed using traditional methods and those that have been dope or vegetable dyed.

This creates a challenge for garment makers and brands: how do they build trust in their products and demonstrate to consumers and buyers that they have used these alternative methodologies when dyeing fibers?

The solution is independent screening by a third-party service provider and the application of a recognized product mark that both consumers and retailers can understand and trust.

SGS Solution

SGS has developed two dedicated screening services to help manufacturers and brands confirm the dyeing method used in their products:

• SGS dope dyeing verification service; and
• SGS vegetable dyed material verification service.

Using an analytical laboratory testing approach that covers colorant type and/or index ingredients, SGS is able to differentiate between vegetable dyes, normal dyes, pigment dyes and dope dyes.

Once the dyeing method has been corroborated, the product can carry the SGS Independently Checked (IC) Mark. This is a clear indication to the buyer that a fabric or product has been independently verified as conforming to agreed test parameters, including dyeing criteria.

To display the mark, a product must undergo:

• Laboratory analysis to verify dyeing method;
• Compliance testing against mandatory regulations;
• Document review and on-site/remote assessment of manufacturing processes; and
• Restricted substances testing.

The mark also contains a QR code that gives stakeholders access to details of the used test criteria, thereby improving transparency and consumer trust. After all, in the end, it’s only trusted because it’s tested.

November 22, 2022

TW Special Report

Embroidering power-generating yarns onto fabric allowed researchers to embed a self-powered, numerical touch-pad and movement sensors into clothing. The technique offers a low-cost, scalable potential method for making wearable devices.

“Our technique uses embroidery, which is pretty simple — you can stitch our yarns directly on the fabric,” said the study’s lead author Rong Yin, assistant professor of textile engineering, chemistry and science at North Carolina State University. “During fabric production, you don’t need to consider anything about the wearable devices. You can integrate the power-generating yarns after the clothing item has been made.”

In the study published in Nano Energy, researchers tested multiple designs for power-generating yarns. To make them durable enough to withstand the tension and bending of the embroidery stitching process, they ultimately used five commercially available copper wires, which had a thin polyurethane coating, together. Then, they stitched them onto cotton fabric with another material called PTFE.

“This is a low-cost method for making wearable electronics using commercially available products,” Yin said. “The electrical properties of our prototypes were comparable to other designs that relied on the same power generation mechanism.”

The researchers relied on a method of generating electricity called the “triboelectric effect,” which involves harnessing electrons exchanged by two different materials, like static electricity. They found the PTFE fabric had the best performance in terms of voltage and current when in contact with the polyurethane-coated copper wires, as compared to other types of fabric that they tested, including cotton and silk. They also tested coating the embroidery samples in plasma to increase the effect.

“In our design, you have two layers – one is your conductive, polyurethane-coated copper wires, and the other is PTFE, and they have a gap between them,” Yin said. “When the two non-conductive materials come into contact with each other, one material will lose some electrons, and some will get some electrons. When you link them together, there will be a current.”

Researchers tested their yarns as motion sensors by embroidering them with the PTFE fabric on denim. They placed the embroidery patches on the palm, under the arm, at the elbow and at the knee to track electrical signals generated as a person moves. They also attached fabric with their embroidery on the insole of a shoe to test its use as a pedometer, finding their electrical signals varied depending on whether the person was walking, running or jumping.

Lastly, they tested their yarns in a textile-based numeric keypad on the arm, which they made by embroidering numbers on a piece of cotton fabric, and attaching them to a piece of PTFE fabric. Depending on the number that the person pushed on the keypad, they saw different electrical signals generated for each number.

“You can embroider our yarns onto clothes, and when you move, it generates an electrical signal, and those signals can be used as a sensor,” Yin said. “When we put the embroidery in a shoe, if you are running, it generates a higher voltage than if you were just walking. When we stitched numbers onto fabric, and press them, it generates a different voltage for each number. It could be used as an interface.”

Since textile products will inevitably be washed, they tested the durability of their embroidery design in a series of washing and rubbing tests. After hand washing and rinsing the embroidery with detergent, and drying it in an oven, they found no difference or a slight increase in voltage. For the prototype coated in plasma, they found weakened but still superior performance compared with the original sample. After an abrasion test, they found that there was no significant change in electrical output performance of their designs after 10,000 rubbing cycles.

In future work, they plan to integrate their sensors with other devices to add more functions.

“The next step is to integrate these sensors into a wearable system,” Yin said.

The study, “Flexible, durable and washable triboelectric yarn and embroidery for self-powered sensing and human-machine interaction,” was published online in Nano Energy. Co-authors included Yu Chen, Erdong Chen, Zihao Wang, Yali Ling, Rosie Fisher, Mengjiao Li, Jacob Hart, Weilei Mu, Wei Gao, Xiaoming Tao and Bao Yang. Funding was provided by North Carolina State University through the NC State Faculty Research & Professional Development Fund and the NC State Summer REU program.

November 22, 2022