UV-Curable Coatings as Inhibitors to Biofouling and Biocorrosion

Bethesda, (PresseBox) - Biofouling and biocorrosion are very significant problems for many products and/or processes and are predominately caused by the formation of biofilms (i.e., a complex aggregation of microorganisms growing on a solid substrate). Heart stents are well-known for biofilm growth on the surface, thereby causing arterial blockage, infections or death.

In applications pertaining to cooling towers, biofilm formation can cause decreased system performance by clogging or deteriorating the water lines. Naval vessels (from the private fishing boat to aircraft carriers) often have biofilms adhere to the hulls, causing reduced slip through the water. Wastewater and drinking water treatment facilities also suffer from biofouling and/or biocorrosion from biofilms, causing costly cleaning and repairs of the facilities themselves.

Unfortunately, very few coatings can prevent biofilm growth and that can result in expensive remediation processes, including chlorine shock treatment; use of biocides; mechanical scrubbing; and/or heat treatment.1 Thus, we asked, "Can a coating be developed, specifically a UV-curable coating, that inhibits biofilm growth?"

In our laboratory, we synthesized six halogenated, acrylic monomers (Figure 1) that we incorporated into an existing UV-curable formulation2 at varying weight percents (5, 10, 15 and 20) and did a wet, manual drawdown (four mil thickness) onto plastic slides where one-half of the slide was coated leaving the other half uncoated as an internal control.

Each slide was cured with a medium-pressure mercury lamp in a custom-built apparatus under nitrogen and, thereafter, hot glued to a poly(methyl methacrylate) (PMMA) sheet obtained from a local home improvement store. The sheet was placed into another custom-built apparatus that resembled a metal cage, termed the biofilm resistance apparatus (BRApp), in order to protect the samples from mechanical processes that could remove either the coating or the grown biofilm.

Then, the BRApp was taken to the Abilene Wastewater Reclamation Plant and submerged into the secondary clarifier which allows the aerated raw sewage to grow existing microbes, some of which consume a portion of the raw sewage materials. It is important to note that the bulk of the solid sewage was removed via sedimentation in the primary clarifiers prior to aeration. Each secondary clarifier is capable of handling 1.75 million gallons of raw sewage each day.

The BRApp was left in the secondary clarifier for two days (3.5 million gallons of exposure) at approximately six feet deep, just above the paddle arm that mixes the contents at a rate of six revolutions per hour.

The BRApp was removed and transported back to the lab in a plastic bag, whereupon the PMMA sheet was removed; rinsed with deionized water; and treated with an ethanol spray to kill the microbes attached to the sheet and samples. The microbes were then fixated with a poly(ethylene glycol) spray and allowed to dry. Then the slides were immersed in a methylene blue solution (a nucleic stain) to make the biofims visible. Each stained slide was qualitatively evaluated by comparing each coating relative to the uncoated portion of the slide both with the naked eye and through a microscope (40X) in three different locations on the coating. If the coated portion of the slide had increased biofilm growth relative to the uncoated portion, the coating was determined to be a failure at biofilm inhibition. Figure 2 illustrates the sewage exposure and a positive result for biofilm resistance.

Of 24 formulations (four concentration variances of the six monomers formulated into the commercial formulation), we found that two-thirds of the monomers were indeed effective at inhibiting biofilm growth at one or more concentrations of the monomer. Furthermore, of the effective monomers 44% of the concentration variances demonstrated efficacy. Only one coating (6%) of the effective monomer concentrations failed the qualitative evaluation. While our evaluation was focused on biofilm inhibition, algae growth (a major problem for wastewater treatment facilities) was inhibited on all formulations and was only observed on the BRApp itself. Reasons for biofilm resistance are complex and are based on a biostatic mechanism which is not biocidal. Evidence suggests that biofilm resistance is combinatorial based on surface smoothness approximating surgical grade steel via a manual drawdown and unfavorable surface chemistry for initial colonization due to the active monomers.

Therefore, revisiting the original question (can a coating be developed, specifically a UV-curable coating, that inhibits biofilm growth?), the answer is indeed "yes" under very extreme conditions-submersion in raw sewage!

For more information, attend the presentation "Mitigating Biofouling and Biocorrosion via UV-Curable Coatings" on April 30, 2012 at RadTech UV/EB Technoogy Expo & Conference 2012 in Chicago. We will also present biofilm resistance efficacy to individual bacteria (e.g., Escherichia coli, Salmonella typhimurium, Streptococcus pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus), as well as effects of monomer incorporation on coating adhesion, hardness, flexibility and solvent resistance.

References

1. Dreeszen, Paula H. "Biofilm" Edstrom Industries Inc., The Key to Understanding and Controlling Bacterial Growth in Automated Drinking Water Systems, 2nd Ed. June 2003.
2. UV-curable metal coating formulation supplied by Allied Photochemical (KZ-7025-CL).

-Dr. Cavitt has worked at Abilene Christian University as an associate professor of chemistry for 10 years and owns two pending patents on the research described herein.
He is also an at-large member of the RadTech NA board and serves on the RadTech Report editorial board. Charles J. Holt and Jacob A.
Lowry are undergraduate research assistants at the university.

Press releases you might also be interested in

Subscribe for news

The subscribtion service of the PresseBox informs you about press information of a certain topic by your choice at a choosen time. Please enter your email address to receive the email with the press releases.

An error occurred!

Thank you! You will receive a confirmation email within a few minutes.


I want to subscribe to the gratis press mail and have read and accepted the conditions.