Commercial fishing operations with extreme antifouling needs may want to coat something besides their hulls, scientists say.
A 500-day study by researchers at National Taiwan Ocean University found that applying a conductive polyurethane coating to fishing nets and cages drastically reduced marine biofouling.
The coating acts as an anode that, when submerged in the sea, generates free chlorine that inhibits biofouling, the researchers report in “Marine biofouling inhibition by polyurethane conductive coatings used for fishing net,” recently published in the Journal of Coatings Technology and Research.
The 16-month field test found that the coatings reduced the quantity of marine biofouling attached to the nets by about 79%. Furthermore, researchers said, the chlorine generated was “within safe levels, and judged not to pollute the sea.”
Woods Hole Research Center
Could conductive coatings hold
a solution for biofouling?
The technique, which holds potential for other biofouling applications as well as aquaculture, offers a new spin on two traditional antifouling methods: chlorine and coatings. Chlorine additives are effective but can corrode equipment and poison marine life. Similarly, antifouling coatings can do the job, but they often contain toxic copper or organic metal compounds.
Electrolysis and Seawater
The new research builds on earlier studies that show antifouling potential by conductive silicate coatings and chlorine-based electrolysis technologies.
“Electrolysis within seawater using a platinum or graphite electrode leads to complex chemical reactions” that generate concentrations of hypochlorite ions and hypochlorous acid—so-called free chlorine that acts as a fungicide and inhibits marine biofouling attachment, the scientists report.
The research was conducted in two stages: laboratory development of the coating and long-term field testing in Nanao harbor in Taiwan. Black polyethylene nets (20mm mesh, 2.4mm diameter) were sprayed with two coats (250-300 µm film thickness) of a polyurethane resin with carbon black, then sprayed again with graphite. Field testing began 72 hours after application of the second coat.
Although the optimal formulation will require more research, scientists say, initial results were promising.
The coatings generated enough free chlorine to inhibit marine fouling by 79% after 500 days. Moreover, researchers found, the free and total chlorine concentrations were less than the maximum 0.5 ppm regulated by Taiwan’s Environmental Protection Administration.