Advances in Antifouling Coatings Technology
October 2016 www.coatingsworld.com Coatings World | 63
speed reduction, increased fuel consumption, loss in time and money and a higher
frequency of dry-dockings.
The process of biological fouling is
often grouped into key growth stages as
shown in Figure 1 which illustrates the
accumulation of adsorbed organics, settlement and growth of bacteria creating a
biofilm matrix and subsequent succession
of micro- and macrofoulers.
Biofouling consists of two main components: microfouling and macrofouling.
Microfouling refers to the formation of
biofilm and adhesion to the surface, and
macrofouling refers to the attachment of
organisms such as barnacles, diatoms and
sea weed to produce a fouling community. The growing bacteria and the chemicals they secrete make up microfouling,
also referred to as ‘slime’, which develops
within hours of an object’s immersion in
water. Within a few days, macrofouling
develops as unicellular eukaryotes, such
as protozoa and diatoms, that colonize
the surface. Multicellular eukaryotes begin colonizing the surface within several
weeks and include settlement of meroplankton larvae and algal spores.
New Technology Growth
Marine environment is a harsh environment in terms of corrosion and biofouling. Biofouling generates huge operational
losses for the shipping Industry. A high
degree of fouling on the ship’s hull significantly increases drag, reducing the overall
hydrodynamic performance of the vessel
and increasing the fuel consumption. Due
to these reasons, it is in the best interest of
the ship owners to use high-performance
coatings that prevent corrosion and anti-fouling growth on the ship’s hull.
Reduced fuel consumption and increasingly stringent environmental regulations have prompted the development
of new antifouling technologies. Marine
coatings manufacturers are generally
cautious in adopting new technologies.
However, increasingly stringent environmental legislation, paralleled by customer
preference for more eco-friendly products, is pushing innovation in the market.
The need to lower fuel consumption
and to reduce CO2 emission has become
a strong driving force for paint companies
to develop new technologically-advanced
antifouling coatings for ship’s hulls which
reduces the fuel consumption.
Foul-release technology, which also
results in substantial fuel savings, is
particularly useful for large cargo ships,
which consume a lot of fuel. Many companies are investing time and money in
developing eco-friendly products such as
low friction coatings, metal-free antifouling coatings, etc. Most recent participants
now offer silicone- or fluororesin-based
foul-release products.
Regulations Force New
Developments
The present working principle for most
of the marine paint systems is based on
a slow release of toxins (self-polishing
coatings). Although the antifouling per-
formance of such systems is excellent, the
amount of toxin released per ship may be
quite substantial. The impact of such tox-
ins on nature can be detrimental. Because
of this impact, the use of organotins, such
as tributyltin (TBT), on ship hulls was
completely banned in 2001. In addition,
the use of other toxins in antifouling
coatings is restricted by law. Although
the use of copper-based paints is not yet
prohibited it may be banned in the near
future. Recently, the use of copper-based
coatings for recreational boats has been
banned in the ports of San Diego and
Washington. This drives both science and
industry to evaluate new types of anti-
fouling mechanisms.
Alternatives to Self-
Polishing Coatings
The following systems are commonly suggested and are also applied as alternatives
to self-polishing coatings. Hydrophilic
antifouling coatings prevent or slow
down adherence of marine organisms to
ship hulls. (The latest solutions that are
provided by a marine coating manufacturer formulates anti-fouling paint based
on hydrogel technology which is comprised of a network of advanced polymer chains that absorb high amounts of
water to create a water-like boundary
layer. This water-like layer misguides the
fouling organisms into believing that the
hull is a liquid and solid surface and this
minimizes protein and bacterial adhesion
to the hull.)
• Low energy, hydrophobic foul-release
coatings facilitate an easy release of
marine organisms.
Traditional fouling release coatings consist of a silicone elastomer (PDMS) which
relies on low surface tension (
hydrophobic) and low modulus of elasticity, usually
with a good initial foul-free performance.
Over time, the coatings ability to self-clean is lowered, which results in a higher
hull skin friction. The technology behind
the third generation fouling release coatings is a unique blend of silicone polymers
which maintains a more hydrophobic
surface, with fouling release performance
that lasts. The foul-free period is longer,
and required speed for self-cleaning is
lower. This results in a lower hull skin
friction over time with potentially lower
fuel consumption.
• Enzyme-based coating systems.
Current antifouling technologies for
ship hulls are based on metals such as
cuprous oxide and co-biocides like zinc
pyrithione. Due to the adverse effect of Figure 1: Diagram of biofouling stages.
