An advanced fabric can warm or cool the wearer

Oct. 11 () –

Japanese engineers have produced a fabric that can respond to changes in temperature to heat or cool its user as appropriate.

advanced weaving it’s made with nanometer-scale threads containing a phase change material in their core which can store and release large amounts of heat when the material changes phase from liquid to solid.

Combining the yarns with electrothermal and photothermal coatings that enhance the effect, in essence they have developed a fabric that can quickly cool the wearer down and warm them up as conditions change.

An article describing the manufacturing technique was published in ACS Nano.

Many occupations, from firefighters to farm workers, involve harsh hot or cold environments. Cold storage rooms, ice skating rinks, steel forges, bakeries and many other workplaces require workers to frequently transition between different and sometimes extreme temperatures.

Such regular changes in temperature are not only uncomfortable, they can also cause illness or even injury, and require a cumbersome constant change of clothing. A sweater will keep a worker warm in a cold meat locker, but could overheat the same worker when leaving that space.

One option to alleviate heat or cold stress for those workers, or anyone else from athletes to travelers, who experience such discomfort, is the emerging technology of personal thermal management textiles. These tissues can directly control the temperature of localized areas around the body..

Such fabrics often use phase change materials (PCM) that can store and then release large amounts of heat when the material changes phase (or state of matter, for example, from solid to liquid).

One of these materials is paraffin, which can in principle be incorporated into a textile material in different ways. When the temperature of the environment surrounding the paraffin reaches its melting point, its physical state changes from solid to liquid, which implies an absorption of heat. Heat is then released when the temperature reaches the freezing point of paraffin.

Unfortunately, the inherently strong rigidity of PCMs in their solid form and leakage when liquid has so far prevented their application in the field of portable thermal regulation. Several different strategies have been tried, including microencapsulation (in which PCM, like paraffin, is coated into extremely small capsules), to improve “packaging efficiency” to overcome stiffness and leakage problems.

“The problem here has been that the manufacturing methods for phase-change microcapsules are complex and very expensive,” said Hideaki Morikawa, corresponding author of the paper and an advanced textile engineer at Shinshu University’s Fiber Engineering Institute. “Worse, this option offers insufficient flexibility for any realistic portable application.”

So the researchers turned to an option called coaxial electrospinning. Electrospinning is a method of manufacturing extremely fine fibers with diameters in the order of nanometers. When a polymer solution contained in a bulk reservoir, typically a syringe with a needle at the tip, is connected to a high-voltage power supply, electrical charge accumulates on the surface of the liquid.

A point is soon reached where the electrostatic repulsion of the accumulated charge is greater than the surface tension and this results in an extremely fine jet of liquid. As the liquid jet dries in flight, it is further elongated by the same electrostatic repulsion that gave rise to the jet, and the resulting ultrafine fiber is collected on a drum.

Coaxial electrospinning is very similar, but involves two or more polymer solutions fed from neighboring spinnerets, allowing the production of coated or hollow nanofibers. These core and sheath fibers are similar in structure to coaxial cable that might be used in stereo, but they are much, much smaller.

In this case, the researchers encapsulated the PCM in the center of the electrospun nanofiber to solve the problem of PCM leakage. In addition to this, the ultrafine fibers allow extremely favorable flexibility appropriate for human clothing.

To further expand the range of work environments in which the textile would work and the precision of thermal regulation, the researchers combined the PCM material with two other personal thermal regulation technologies.

The combination of photosensitive materials (those that react to the presence of solar energy) with PCM potentially offers the possibility of further increasing the energy storage capacity of the textile. Furthermore, coating the composite material with polymers that convert electricity to heat (an electrothermal conductive coating) can compensate for a similar expansion of energy storage. in case the worker is in cloudy, rainy or indoor conditions.