New thermal fiber textiles keep you as warm as polar bear fur

Polar bear fur is an inspiration for highly heat-insulating textiles: Chinese researchers have developed a fiber with a structure similar to arctic animal hair, with a porous core and covering. The porous interior traps plenty of air, reducing heat loss. Packaging provides stability to the structure.

The group led by Mingrui Wu of Zhejiang University in Hangzhou wore a sweater knitted from these fibres. The researchers wrote in the specialized journal that at -20 degrees Celsius, the fabric retained as much heat on the body as five times as thick a jacket. Sciences. Wu and his team used so-called airgels to air-core the fibers. Developed over 90 years ago, airgel forms a highly porous solid that is well suited as an insulating material.

Microfiber textiles keep you warm even at -20°C

“Unfortunately, their use in textiles is very limited due to their fragility and poor processability,” the researchers wrote about airgel. They overcome this obstacle by covering the airgel fibers with thermoplastic polyurethane, a stretchy plastic. To obtain a longitudinally aligned microstructure, Wu's team used a freeze-spinning technique: a liquid-air thread is passed through a cold copper ring to generate ice crystal growth. This creates rigid lamellar structures with air gaps. After freeze-drying the structure is stable.

The airgel fibers then pass through the polyurethane solution. Depending on the viscosity of the solution, the fibrous shell has different thicknesses. Tests showed that a 0.08 mm thick polyurethane layer around a 0.6 mm diameter core represented the best compromise between insulation and stability. The researchers then tested the properties of the new fiber. They stretched the fibers ten times their length, so they remained undamaged. Even 10,000 cycles of expansion to twice the length caused no change in thermal insulation. “We attribute this stable thermal insulation performance to the strong capsule layer, which ensures fiber integrity,” the study authors wrote.

At -20°C, the outside temperature of the cotton shirt was 10.8°, the wool shirt was 7.2°, the down jacket was 3.8°, and the new fiber shirt was 3.5°. The lower the temperature, the better the insulation of the clothing. This did not change after washing – another advantage of the fibre, as most airgels lose their function when they come into contact with water.

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Fiber spinning is still time consuming for industrial production

The researchers also showed that the fibers can be dyed. They mixed the dyes into an airgel solution. Because the shell is transparent, the colors of the airgel core can be seen. The coating protects both the paint and the airgel from corrosion. “In contrast to traditional strategies for grafting or coating textiles with airgels, we used a biomimetic approach where the thermal and mechanical properties of the airgel fibers were modeled separately,” the team summarizes.

And in a comment as well Sciences“This may lead to the development of advanced thermal textiles for personal use,” wrote Zhizhi Sheng and Xuetong Zhang of the Institute of Nanotechnology and Nanoelectronics in Suzhou, China. However, they note that fiber spinning is still too slow a process for industrial use. Wet spinning produces about ten times the amount of fiber in the same amount of time. But they note: “With simultaneous material development and manufacturing, airgel fibers could have many potential applications.”