‘Smart’ paper senses presence of water

Technology News | November 7, 2017

By Rich Pell

The material was developed with the goal of simplifying the process for discovering water line breaks in complex pipe networks, of which nearly a quarter-million occur each year in the U.S. costing public water utilities about $2.8 billion annually.

“Water sensing is very challenging to do due to the polar nature of water, and what is used now is very expensive and not practical to implement,” says Anthony Dichiara, a UW assistant professor of bioresource science and engineering in the School of Environment and Forest Sciences and lead author of a related study. “That led to the reason to pursue this work.”

To address this, the researchers developed a paper embedded with electrically conductive carbon nanomaterials, which can then be used as a switch to turn on or off an LED light or alarm system indicating the absence or presence of water. Created from scratch by carefully mixing in nanomaterials with wood pulp using a standard papermaking process, the resulting sensing paper is stiff and smooth in texture, and exhibits a rich black color from the nanomaterials (see image).

When exposed to water, the paper’s fibrous cells expand up to three times their original size, which displaces the conductive nanomaterials in the paper disrupting the electrical conductivity and causing the LED indicator to turn off. When the paper dries, the conductive network re-forms, so the paper can be used multiple times.

When used in a practical application such as in a manufacturing plant, the researchers envision that a sheet of conductive paper with a battery could be placed around a pipe, or under a network of intersecting pipes. In the event of a leak, the paper could wirelessly send a signal to a central control center so a technician could be sent to quickly locate and repair the leak.

According to the researchers, the paper is also sensitive enough to detect trace amounts of water in mixtures of various liquids. This ability, they say, could be particularly valuable for the petroleum and biofuel industries, where the presence of water is seen as an impurity.

“I believe that for large-scale applications, this is definitely doable,” Dichiara says. “The price for nanomaterials is going to drop, and we’re already using an established papermaking process. You just add what we developed in the right place and time in the process.”

Currently, the smart paper prototypes are 8-inch disks made in the lab. The researchers next hope to test their process on an industrial-sized papermaking machine.

For more, see “Smart papers comprising carbon nanotubes and cellulose microfibers for multifunctional sensing applications.”