Pulp fact: smart paper detects water leaks

Detecting the precise source from which a water leak springs in a city, large industrial plant or other complicated system can take a long time and sometimes never be reconciled. The costs to the public purse and industry are enormous. It is estimated the water utility companies in the USA alone lose some $2.8 billion each year to water leaks.

Now, a University of Washington team has developed a "smart" paper that can sense the presence of water. The paper, doped with conductive nanoparticles can be implemented as a switch to trigger an alarm or turn on LED lights to show where the water is. [Dichiara et al., J Mater Chem A (2017), 5, 20161-20169; DOI: 10.1039/C7TA04329E]

"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," explains Anthony Dichiara.

To make their smart paper, the team begins with pulp, manipulated lignocellulose wood micro fibers and adds a composite nanocoating of cationic polyacrylamide and aqueous dispersion of hydroxyl-functionalized carbon nanotubes (CNTs) with pre-adsorbed alkali lignin. In terms of cost and sustainability the team has already demonstrated that carbon sources as diverse as banana skins, tree bark and even animal feces could be used.

It was, however, a chance observation after a water spillage when attempting to fabricate smart paper for another application that they spotted the water-sensing capacity of their material. When water touches the paper, it causes the fibrous cells to swell by up to three times their original volume. The expansion displaces the conductive nanomaterials within the composite removing its conductivity. A simple circuit attached to the smart paper can spot this loss of conductivity and invert the response to switch on an LED or sound an alarm. The wetting process is reversible and as the paper dries the cells shrink and it becomes conductive once more.

The same smart paper could be used not only to detect water leaks but to sense the presence of water in mixtures of liquids, which could have utility in the petrochemical and biofuel industries, where water is an unwanted impurity. "I believe that for large-scale applications, this is definitely doable," Dichiara said. "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."

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase.