Reduced Copper Antifouling Coatings Through Microencapsulation

WP-200306

Background

Biofouling on ships causes deleterious effects such as increased drag leading to reduced speed and increased fuel consumption. Controlling biofouling on ships is generally accomplished with biocide-based antifouling (AF) coating systems. As more restrictive environmental regulations are introduced (reduce or eliminate need for cuprous oxide) and as more rigorous service life demands emerge (extend drydocking intervals), the need for a next-generation long-life environmentally friendly coating system increases. Sustained and long-term biocide release is critical to effective AF coating performance. Microencapsulation of biocides results in increased biocide loading capacity in coatings as well as reduced and controlled biocide release rates.

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Objectives of the Demonstration

WP-200306 Project Graphic

Typical microcapsules. Diameters from 5-45 microns. (L) Capsule in solvent slurry. (R) Optimized dried powder of microcapsules. No drying agent required; few agglomerates.

The objective of this project was to develop a better understanding of how microencapsulation of biocides could be used in AF coatings. Specific objectives were to:

1) Identify and redefine key performance parameters of microencapsulated 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) and coatings containing those capsules to ensure focus on capsule/coating combinations suitable for effective performance as well as commercial viability.

2) Understand biocide loss over time under field exposure conditions and use these data to validate effective field performance.

3) Understand how modifications to capsule properties affect biocide release rate from capsules, and then from capsule-containing coatings.

4) Demonstrate sustained, low, and constant controlled release over longer periods of time with laboratory release rate analysis of capsules in AF coatings.

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Demonstration Results

This project demonstrated that microcapsules with DCOIT cores, that meet all of the identified key performance parameters, can be produced with at least two wall chemistries. Coatings containing microencapsulated biocide retain more DCOIT over long periods of time than coatings that are formulated with free DCOIT. This is true in both the laboratory and in the field. Microencapsulated DCOIT, when incorporated into commercially relevant AF coating systems, enhances overall coating performance. DCOIT release rates into seawater and xylene can be controlled through microencapsulation. Both laboratory release rate studies and field biocide loss studies produce predictable results based on capsule properties and coating formulation. Microencapsulation allows high levels of DCOIT to be loaded into coatings without negatively impacting liquid or cured coating properties.

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Implementation Issues

Controlled release technology in the form of microencapsulation has the potential to fill the performance gap that currently exists between the current and next generation of AF coating systems for the Department of Defense. Benefits of microencapsulation of biocides include (1) control of the rate of biocide release, resulting in highly predictable, steady-state rates of release; (2) assurance that more biocide remains in the coating over a longer period of time, resulting in extended utility and more effective performance; and (3) reduction in the rate of release of cuprous oxide. This project improved understanding of how capsule formulation modifications impact diffusion and the mechanics of diffusion/release of biocide from capsules and from capsules in coatings.

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Project Documents

Points of Contact

Principal Investigator

Mrs. Elizabeth Haslbeck

Naval Sea Systems Command (NAVSEA)

Phone: 301-227-4784

Fax: 301-227-4814

Program Manager

Weapons Systems and Platforms

SERDP and ESTCP

Project Documents

Document Types

  • Fact Sheet - Brief project summary with links to related documents and points of contact.
  • Final Report - Comprehensive report for every completed SERDP and ESTCP project that contains all technical results.
  • Cost & Performance Report - Overview of ESTCP demonstration activities, results, and conclusions, standardized to facilitate implementation decisions.
  • Technical Report - Additional interim reports, laboratory reports, demonstration reports, and technology survey reports.
  • Guidance - Instructional information on technical topics such as protocols and user’s guides.
  • Workshop Report - Summary of workshop discussion and findings.
  • Multimedia - On demand videos, animations, and webcasts highlighting featured initiatives or technologies.
  • Model/Software - Computer programs and applications available for download.
  • Database - Digitally organized collection of data available to search and access.