Non - biocide control strategies Flashcards
What’s the ration of biocide and fouling release coatings on the market?
Fouling release – 10 % of the market – more expensive and does not contain biocide
Improved AF and slime release performance needed
Biocidal AF
- The mainstay for foreseeable future
- Improved environmental profile
- Eventual replacements?
What are the types of biocide coatings?
Soluble matrix – cheap coating which uses a resin called rosin which is obtained from pine trees. You put your biocide into this matrix and as it dissolves it releases the biocide. There is no real control and it has short effectiveness, only being active for just over a year or so.
Insoluble matrix paints are made from acrylic, or vinyl resins or chlorinated rubber polymers. These last a bit longer 2-3 years and are able to control the release but have a ‘leach layer’ which reduces the effectiveness over time. Widely used but do not achieve the 5-year target.
Self-polishing paints containing tin (TBT-SPC). Made from an acrylic polymer with TBT groups bonded to the main chain. The more expensive and more effective. Always biocide at the surface of the coating – give the life expectancy of 5 years plus.
Non-biocide control strategies
Fouling release approach – doesn’t stop fouling necessarily but does make it easier to release under hydrodynamic shear.
Other methods are being explored at the moment. Most of those that work bind water more tightly to the surface than is natural.
How does TBT work?
As it is a copolymer there are two polymers methyl methacrylate and tin methacrylate bonded together with the carboxyl function.
Under normal circumstances this polymer is hydrophobic. The coatings have a pigment that water can dissolve allowing water to enter. When the water gets in this bond is readily hydrolysable breaking a carboxyl bond and releasing tin.
When the copolymer is broken it switches to being hydrophobic, allowing it to dissolve more quickly giving the self-polishing effect.
The same principle applies to self-polishing copolymer coatings which are out there today.
Characteristics of SPCs
- Smooth paint surface during sailing - great in terms of ship hydrodynamics.
- Thin and stable leached layers, resulting in continuous and constant biocide release rates over time
- A polishing rate which allows AF activity during stationary periods and increases linearly with the sailing period
- When ships come into port it should have biocide at the surface which will last for a limited amount of time, specific to the paint - say 21 days.
What problems has replacing tin with copper caused?
Some organisms are resistant - Ulva and certain species of barnacle
Examples of booster biocides
As there are organisms resistant to copper you have to add co or booster biocides. Most of these work by targetting soft fouling, bacteria, algae or by interfering with photosynthesis.
- Irgarol 1051 - interferes with the photosynthesis of algae (not supposed to have much activity against animals)
- Diuron – urea-based herbicide – inhibits photosynthesis
- Sea-Nine 211 – isothiazolone active against soft fouling. Very short half-life - maybe good as they don’t biomagnify.
- Zinc and copper pyrithiones – bactericides/fungicides; active against soft fouling - widely used.
- EU Biocides Regulation (formerly EU Biocidal Products Directive) – limits biocide products available for use in antifouling The EU Biocides Regulation
Booster biocide for hard fouling
Until recently there were no good booster biocides reported for hard fouling species, including barnacles and tubeworm. ECONEA targets hard fouling allowing paints to reduce the levels of copper.
What recent co-biocide is non - toxic?
Selektope
Screened pharmacological agents - found Medetomidine - which interfered with barnacle settlement.
Very active at very low nanomolar concentrations and doesn’t kill larvae.
Subsequently been showed to activate octopamine receptors of cyprid and results in hyperactivity. Also works against tubeworms.
Now 8 products on the market containing this active ingredients.
Unique navy maintenance cycle
Naval vessels –
US Navy want their ships ready to go out all the time and be able to reach maximum speed. Ideally aiming for a 12 year dry dock interval.
Commercial tanker – 85% of time on the water., avarage 15 days in port in two day intervals.
Naval vessels 45% of time away, 200 days in port in 3 month avarage intervals.
However naval vessels can hit high speeds – fouling release – but only for 3 % of the time.
Challenges of the navy’s unique maintenance cycle.
- Need broad-spectrum solution
- Nontoxic or environmentally benign
- does not want to be restricted from certain waters
- 12-year docking cycle
- Limited or no hull cleaning
- Durable enough for Navy ships
- carbon nanotube to make them tougher - be able to pull onto a beach.
Testing ‘cycle’
- Lab-scale bioassays for down selection and mechanism of action studies rely on comparatively few species
Different groups interact - transdisciplinary challenge
- Biology Materials Science Nanotechnology Polymer science Spectroscopy
- Antifouling
- Private sector International/government agencies NGOs Policy makers ……….
Two approaches for antifouling
Two main approch FR and Biocide
FR – after it has settled but ideally as the organsms is exploring the sufrace
Niocide – but ideally repel through non-toxic means
How does nature repel fouling?
Only chemical defence has been well studied but there is also evidence of mechanical, surface physical-chemical properties, surface renewal (crabs that groom surface to clear eyes) and surface topography.
Nature uses a combination of strategies.
Sharkskin, dolphin, red alga and grooming have been used as inspiration for antifoulants.
Longfin pilot whale
Dolphins - inspiration
- Swim fast
- rubbing against each other and sand
- Other strategies but don’t always work
- Stalked barnacle that settles on dolphin, pseudo stalked barnacle
- Stick to caudal fin
- get entrained in water vortices around the caudal fin
- Skin replenished very frequently - (2 hours?)
- Improved hydrodynamics
