Polymer coated cotton can harvest water from desert air

Collaboration between researchers from the Eindhoven University of Technology (TU/e) and the researchers at the Hong Kong Polytechnic University (PolyU) resulted with the development of a special treatment for cotton fabric that allows it to absorb exceptional amounts of water from misty air. Since the coated cotton releases the collected water by itself when it gets warmer, the material could be used to provide water to the desert regions, for example for agricultural purposes.

The researchers were inspired by nature, since beetles in desert areas are able to capture water from air by collecting humidity onto their bodies, as well as the ability of some spiders to capture humidity on their silk network. Led by Professor John Xin at PolyU and Dr. Catarina Esteves at TU/e, the researchers applied a coating of PNIPAAm polymer to the cotton fabric. While ordinary cotton fibers absorb around 18% of their own weight of water from misty air, fibers coated with the PNIPAAm coating can absorb 340% of their own weight.

At lower temperatures, the coated cotton has a sponge-like structure at microscopic level. Up to a temperature of 34°C (93.2°F), the material is highly hydrophilic (strongly absorbing water). Once the temperature gets over 34°C, the material becomes hydrophobic (water-repellant). When these temperatures are reached, the cotton releases all the absorbed humidity in the form of pure water. According to researchers, the process could be repeated many times.

While fine-mesh ‘fog harvesting nets’ are already being used in some mountains and dry coastal areas, they do have a high dependence on strong winds which bring the humidity the area. Whilst cotton fabric can be locally produced at low costs, the researchers claim that their polymer coating increases the cost by only about 12%. Novel coated cotton has the advantage over previously mentioned approach since it can function without wind.

Another advantage of the polymer coated cotton fibers is that they can be laid directly onto desired parts of the cultivated soil. This property implies that the material may potentially be suitable for providing water in deserts or mountain regions, where the air is often misty at night. The researchers are also considering completely different applications such as camping tents that collect water at night, or sportswear that keeps athletes dry.

TU/e and PolyU researchers plan to optimize the quality of the new material by increasing the amount of water absorbed by the coated-cotton, as well as by adjusting the temperature at which the material changes from water-collecting to the water-releasing state, towards lower temperatures.