24-09-2013, 04:15 PM
Modern approaches to marine antifouling coatings
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Abstract
Marine structures such as platforms, jetties and ship hulls are subject to diverse and severe biofouling. Methods for inhibiting both organic and
inorganic growth on wetted substrates are varied but most antifouling systems take the form of protective coatings. Biofouling can negatively
affect the hydrodynamics of a hull by increasing the required propulsive power and the fuel consumption. This paper reviews the development of
antifouling coatings for the prevention of marine biological fouling. As a result of the 2001 International Maritime Organization (IMO) ban on
tributyltin (TBT), replacement antifouling coatings have to be environmentally acceptable as well as maintain a long life. Tin-free self-polishing
copolymer (SPC) and foul release technologies are current applications but many alternatives have been suggested. Modern approaches to
environmentally effective antifouling systems and their performance are highlighted.
Introduction
Engineered structures such as ships and marine platforms, as
well as offshore rigs and jetties, are under constant attack from
the marine environment. These structures need to be protected
from the influences of the key elements of the marine environ-
ment such as saltwater, biological attack and temperature fluc-
tuations. Besides injectable biocides in closed systems, methods
of protecting marine structures must be capable of expanding and
contracting with the underlying surface, resist the ingress of water
and control the diffusion of ions. Protective organic coatings can
offer these functions [1] and consequently are largely used in the
shipping industry to increase the working life of systems and
improve its reliability. Paint coatings on ships are used for a wide
range of functions such as corrosion resistance, ease of mainte-
nance, appearance, non-slip surfaces on decking as well as the
prevention of fouling on the hull by unwanted marine organisms.
The use of antifouling coatings for protection from the
marine environment has a long history.
Fouling effects
Antifouling systems are required wherever unwanted growth
of biological organisms occurs. This is often in most saline
aqueous phase environments; hence applications include medi-
cal, freshwater and marine systems. Marine engineered systems
have been categorised into seven key types of submerged
structures of which ship hulls account for 24% of the total
objects fouled [16]. A variety of materials can be used for ship
hulls including steel, aluminium and composites such as glass
reinforced polymer. The fouling of ship hulls is often prolific as
vessels move between a diverse range of environments and
remain constantly in the most productive region, the photic
zone, of the water column. Although coatings are used for hull
protection, they can fail due to the build up of inorganic salts
[17], exopolymeric secretions, and the calcium carbonate skele-
tal structures that form the fouling organisms.
Further antifouling coatings
A wealth of alternatives have been initially investigated for
various marine applications to replace the use of TBT (Table 5).
Further alternatives to the approaches of SPC, FRC, control
depletion polymer, natural products and surface micro-archi-
tectures can be seen in Table 5.
The process of surface flocking is where electrostatically
charged fibres are adhered to a coating perpendicular to the
surface and is currently undergoing trials as an antifoulant
mechanism. The fibres can be made of polyester, polyamide,
nylon or polyacryl [41]. Using nylon fibres on a polyvi-
nylchloride plastic sheet a decrease in green algae and barnacles
was recorded for a 6 month field trial [97]. Other non-toxic
coatings have been developed such as the two coat systems of
basecoat polybutadiene or urethane and a topcoat of silicone or
hydrocarbon [100]. All five two coat systems were fouled by
slime and algae but were resistant to fouling by barnacles and
bryozoans in field trials 6–12 months in length. Alternative
surfaces that resist bioadhesion such as short chain PEG have
been investigated [101] as well as alternative surface architec-
ture to resist protein adsorption [102].