New composite film reduces heat index or “felt air temperature” by approximately 40%

A team of researchers from the National University of Singapore (NUS) has developed a new super-hygroscopic material that improves the evaporation of sweat in a personal protective suit, to create a cooling effect for better thermal comfort for users such as healthcare workers and other frontline workers. . This invention has been validated by laboratory tests conducted in collaboration with researchers from HTX (Home Team Science & Technology Agency) in Singapore.

The new desiccant film, which is biocompatible and non-toxic, has a fast absorption rate, high absorption capacity and excellent mechanical properties. This means that the material is very robust and durable for practical applications such as protective suits worn by healthcare workers. It is also affordable, lightweight, easy to manufacture and reusable.

“At an ambient temperature of around 35 degrees C, a healthcare worker donning a protective suit for an hour typically experiences a heat index of around 64 degrees C. This causes discomfort and prolongs the heat stress that can lead to heatstroke and even death. Our new composite moisture-trapping film produces a cooling effect in the protective suit through evaporative cooling – by increasing the evaporation of sweat from the skin,” explained the Assistant Professor Tan Swee Ching, Research Team Leader, Department of Materials Science and Engineering, NUS College. of design and engineering.

Attaching a piece of new composite film in a protective suit – for example to the back of the suit – could reduce the heat index by around 40%, significantly reducing the risk of heat stroke.

This invention was published in the scientific journal Small on February 20, 2022.

This research breakthrough demonstrates the positive outcome of harnessing the complementary strengths of NUS and HTX to create tangible benefits for the local team and the wider community. By combining the NUS team’s scientific knowledge of advanced hydrogel materials and HTX’s deep understanding of the local team’s engineering needs and capabilities, the joint research team was able to customize and optimize the new hydrogel material. moisture trapping for practical applications to improve the performance and productivity of front line officers.

Cooling by increasing sweat evaporation

Medical protective suits have excellent antibacterial and waterproof properties. However, this high level of protection stops the escape of water vapor produced by the evaporation of sweat and prevents the loss of heat from the body. This is why users such as healthcare workers who must wear protective suits for long hours, especially in tropical environments, often report occupational thermal stress.

Thermal management solutions such as air-cooled clothing with electric fans or ingesting ice slurry are impractical due to limitations such as bulk, high weight, and limited efficiency. Although advanced textiles and coatings are promising solutions, they are difficult to manufacture and production costs are high.

The NUS team has proposed a practical strategy to overcome current challenges by exploiting the principle of evaporative cooling. Their solution is to use a super-hygroscopic composite film to control the level of humidity in the micro-environment of the protective suit. As the moisture-trapping composite film absorbs water vapor inside the protective suit, the moisture level drops. This in turn accelerates the evaporation of sweat from the skin. As a result, more heat is dissipated from the human body through perspiration, providing thermal comfort for users such as healthcare workers.

To examine the effectiveness of their solution, the NUS team conducted tests in collaboration with HTX researchers, using a 20-zone “Newton” dummy in a climate chamber. This is an important experimental step in evaluating the feasibility of applying the composite film to full garment scale.

With the composite film, the relative humidity (RH) under moderate sweating conditions dropped by approximately 40% – from 91% to 48.2% after one hour of sweating and to 53.2% after two hours of sweating . The team also found that during the first hour of sweating, the heat index or “felt air temperature” dropped significantly from 64.6 deg C to 40 deg C at a temperature of 35 deg C air. At this level, while users are still warm, the likelihood of heat stroke, heat cramps and heat exhaustion is remarkably reduced.

“These experiments show that our moisture-trapping film effectively reduces the relative humidity inside the protective suit, thereby significantly reducing the heat index and improving thermal comfort for users,” explained Professor Asst Tan .

In another lab experiment, the research team also showed that body temperature (or skin temperature) could be significantly reduced by 1.5°C through evaporative cooling. This further proves that the composite film can potentially help users – such as healthcare workers, soldiers or firefighters – relieve heat stress, especially during strenuous activities.

The NUS team’s composite film regeneration is also more energy efficient, as it requires a lower temperature to release trapped moisture. At 50°C, the composite film releases 80% of its water content after 10 minutes and this reaches 95% after 40 minutes. Most hygroscopic materials regenerate at a temperature above 100°C, over a period of more than one hour.

“Based on the results of various studies from this project, we hope that moisture-trapping film can be incorporated into the personal protective equipment (PPE) and/or personal protective clothing (PPE) of law enforcement officers. ‘local team, to improve thermal comfort and improve the performance of frontline workers,’ said Ying Meng Fai, Director, Human Factors and Simulation Center of Expertise, HTX.

Refinements and commercialization

Encouraged by the results of their latest study, the NUS team is now working to improve their hygroscopic material so that it can absorb more and faster. The team also plans to apply its cooling strategy to other types of protective clothing such as those for firefighters.

Additionally, Asst Prof Tan and his team are looking for opportunities to commercialize this technology.

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