Placing the novel moisture-trapping film in a protective suit brings down the heat index by about 40%, lowering the likelihood of heat stroke. Credit: NUS

The good news about medical coveralls and personal protective suits is they perform their job function very well—not allowing bacteria, toxins and other harmful substances to penetrate the suit. That’s also the bad news since what can’t get in also can’t get out.

Under room temperature of about 35˚C, a worker who dons a protective suit for 1 hour typically experiences a heat index of about 64˚C. In addition to discomfort, this prolonged thermal strain can result in heat stroke and even death.

Scientists at the National University of Singapore (NUS) are solving this problem through the development of a novel super-hygroscopic material that enhances sweat evaporation within a personal protective suit to create a cooling effect. The new desiccant film, which is biocompatible and non-toxic, has a fast absorption rate, high absorption capacity and excellent mechanical properties. It is also affordable, light-weight, easy-to-fabricate and reusable.

More than anything, though, the research team says the innovation is practical. The solution involves placing the super-hygroscopic composite film in the protective suit, where it will absorb water vapor from sweat and drop the humidity level. This, in turn, speeds up sweat evaporation from the skin. As a result, more heat is dissipated from the human body through sweating, ultimately providing thermal comfort for users.

To examine the effectiveness of their solution, the NUS team conducted tests of the material using a Newton manikin within a climatic chamber. A Newton manikin is a type of thermal manikin regularly used for the scientific testing of thermal environments without the risk or inaccuracies inherent in human subject testing—essentially manikins are the lab mice of the thermal testing world.

As described in the journal Small, with the composite film, relative humidity under moderate sweating dropped from 91% to 48% after 1 hour of sweating. After 2 hours of sweating, relative humidity dropped to 53%. Additionally, within the first hour of sweating, the heat index dropped significantly from 65˚C to 40˚C at air temperature of 35˚C. While users will still feet hot at this temperature, the reduction in heat index remarkably lowers the risk of heat stroke, heat cramps and/or heat exhaustion. The research team showed that body temperature could be reduced by 1.5˚C through evaporative cooling.

“This proves that the composite film can potentially help relieve thermal stress, especially during strenuous activities,” said Tan Swee Ching, research team leader and assistant professor of materials science at NUS.

Additionally, regeneration of the NUS composite film is more energy-efficient than today’s alternatives. For example, most hygroscopic materials regenerate at a temperature of more than 100˚C over a duration of more than 1 hour. However, at 50˚C, the NUS film releases 80% of its water contents after 10 minutes, reaching 95% after 40 minutes.

The scientists say the positive manikin results are an important experimental milestone in assessing the feasibility of applying the composite film to the scale of full body clothing—which they feel can be successfully done. Now, Ching and his team are looking for opportunities to commercialize the novel material.

In the meantime, they are continuing to work toward improving the material, altering it to absorb more and faster. They are also planning to apply their cooling strategy to other types of protective apparel, such as those for firefighters.

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