Marine antifouling coatings: environmental challenges and innovation opportunities

 

Summary

Biofouling of marine vessels (e.g. ship hulls) and structures (e.g. piers) by sea organisms such as barnacles and algae is a major issue for the marine sector.  In the PEM Techology Gateway and IT Sligo, we are pursuing research in bio-inspired polymers for biofouling prevention. 

Bioinspired materials are synthetic materials whose structure, properties or function mimic those of natural materials or living matter1 – for example we are studying the remarkable adhesion properties which mussels exhibit.  We are currently investigating if bio-inspired polymers can be turned into durable coatings.  Such work is of interest to a variety of industries (marine, food, medical).

For more information on this research and the potential benefits to Irish companies, please feel free to contact us.

 

 

 

                           Image source – Hull fouling & in-water cleaning: Risks and updates,

                               Ministry for Primary Industries, New Zealand (www.mpi.govt.nz)

Areas where biofouling can accumulate on a non-trading vessel

                                                                                                                                                                                                            Image source – Marine Pest Sectoral Committee 2018, National biofouling management guidelines for non-trading vessels,

                                                                                                                                                                                                                 Department of Agriculture and Water Resources, Canberra, Australian Government (http://www.marinepests.gov.au)

 

Further details of our work in this area

Biofouling of marine vessels (e.g. boat and ship hulls) and structures (e.g. piers, aquaculture infrastructure) by different sea organisms such as mussels, barnacles and algae is a major issue for the wider marine sector. For marine vessels in particular, a fouled hull results in high drag forces and thus increased fuel consumption and greenhouse gas emissions. Maintenance costs and downtime increase accordingly. As a result, the economic and environmental impact of biofouling on the shipping sector and sectors that rely on shipping is very significant. Biofouling occurs in seawater as well as in fresh water environments (though different fouling organisms are involved).

Coatings

In order to tackle and minimise biofouling, marine vessel manufacturers, owners and operators use antifouling coatings on their vessels. Antifouling coatings prohibit the attachment and growth of biofouling species on the surface they are applied on. This has been achieved historically with the use of metal-based biocides as part of the coating formulation. Copper (e.g. Cu2O) and tin (e.g. tributyltin) compounds have led the biocide and antifouling paint market for decades. However, organotin compounds were banned completely as biocides in antifouling paint in the early 2000’s, due to their detrimental effects on marine ecosystems and related aquaculture industries. As a result, copper biocides dominated the market and at the same time the organotin ban created a need for new biocide options. These are known as booster biocides, and were designed to tackle the so called soft biofouling (e.g. algae) whilst copper is particularly efficient against hard biofouling (e.g. shellfish). Booster biocides comprise a variety of nitrogen and sulfur heterocyclics and zinc organometallic compounds.

Regulatory pressures

However, the pressure on antifouling paint manufacturers with respect to the ecotoxicity impact of biocides has been continuously increasing. The European Biocidal Products Regulation (BPR, EU Regulation 528/2012) has led to further changes in the composition of antifouling coatings in the EU and further bans of specific biocidal compounds (e.g. cybutryne, a diamino-1,3,5-triazine). Inevitably, concerns around copper usage will increase even further, and the regulatory pressure on these long-established and highly performing products will intensify in the coming years.

Such regulatory hurdles can, on the other hand, incentivise and drive innovations on biocidal-free antifouling coatings.

Non biocidal compounds

Antifouling coatings that would not rely on a biocidal compound to stop biofouling may be categorised as follows:

  • Anti-adhesive (non-stick) coatings: based on hydrophobic, low surface energy polymers (e.g. silicones, fluoropolymers), which make attachment and anchoring of biofoulers challenging. However, the coating itself would need to adhere strongly on the substrate it is protecting.

Coatings based on poly(ethylene glycol)s, PEGs, are on the other hand exploiting the hydrophilic nature of these polymers to prevent protein adsorption and subsequent fouling (obviously a different mechanism compared to low surface energy polymers).

  • Non-biocidal self-polishing coatings: the top layer of the paint on which biofouling occurs is sacrificial and is continuously removed, along with the fouling species

  • Hard composite coatings: these are based on standard thermoset polymer resins (epoxies, vinylesters, polyesters) reinforced with different particulate fillers (e.g. glass). Their unique selling point is lower maintenance costs/longer service life combined with additional anticorrosion protection.

Several products in all above categories have been reported and some have been commercialised. However, matching the performance, durability and customer acceptance (including DIY option for leisure boats) of existing biocide-containing solutions and claiming a market share is not straightforward.

Innovations in coating technology

Further innovations in antifouling coating technology have been reported following a biomimetic approach, where inspiration from nature is sought. In fact, it is the actual biofouling species and/or the natural defences against these (e.g. surface chemistry, surface topography) which provide valuable information on how to minimise biofouling. Approaches include coatings with UV light emitting diodes (LEDs), anti-thrombogenic polymers, or coating textures mimicking those of natural antifouling surfaces such as shark skin.

Interestingly, such innovations could potentially address converging needs of other industry sectors (such as medical and food) for non-toxic and sustainable, yet cost-efficient and durable coatings to prevent biofouling of surfaces at different levels (e.g. protein adsorption, bacteria, other pathogens).

PEM research in bio-inspired polymers for durable coatings

In PEM and IT Sligo we are pursuing relevant research in bio-inspired polymers for biofouling prevention, where we synthesise polymers in-house that mimic the structure of mussel adhesive proteins (MAPs), and therefore the mechanism of the remarkable adhesion which mussels exhibit. We can therefore produce a polymer that would bear the structural features of MAPs that provide good universal adhesion, and yet the overall polymer backbone structure would prevent adsorption and anchoring of different biofouling species on the coating itself.

We are currently investigating the formulation of such polymers into durable coatings, which could be of interest to a variety of industrial sectors (marine, food, medical).

For more information on this research and the potential offerings to Irish companies please feel free to contact us.

 

Dr Ioannis Manolakis

PEM Principal Investigator

Assistant Lecturer in Chemistry

School of Science, Dept. of Life Sciences, IT Sligo

manolakis.ioannis@itsligo.ie

References

1. https://www.nature.com/subjects/bioinspired-materials

2. https://www.chemistryworld.com/news/antifouling-coatings-cling-to-copper/3010011.article

3. J.M. Wezenbeek, C.T.A. Moermond & C.E. Smit “Antifouling systems for pleasure boats: Overview of current systems and exploration of safer alternatives” RIVM Report 2018-0086, Rijksinstituut voor Volksgezondheid en Milieu (RIVM) https://rivm.openrepository.com/handle/10029/622160