Antifouling: Using Fouling Release films
As many biocides face regulatory pressure, biocide-free fouling release coatings are increasingly in the focus of R&D. A different approach are fouling release films. We spoke to Dr Ricarda Heckel of Renolit about their product and in how far it compares to a coating.
Please describe the “Dolphin S” film
Dr Ricarda Heckel: The “Renolit Dolphin S” is a biocide-free antifouling film which is IMO-certified according to DNVGL-CP-0110. Thus, it complies with the IMO AFS Convention International Convention on the Control of Harmful Anti-Fouling Systems on Ships (2001). Antifouling coatings are primarily based on toxic additives. A silicone-based coating that is characterised by its absence of biocides is known as a fouling release system. The product should therefore correctly be referred to as a fouling release film.
The special feature of the antifouling film is its amphiphilic (two-functional) property. Two functions because the molecules of the amphiphilic surface exhibit both hydrophilic and hydrophobic regions. Studies show that certain fouling organisms adhere to hydrophobic surfaces and others to hydrophilic surfaces. Previous silicone solutions are exclusively hydrophobic and therefore cannot prevent fouling from the hydrophilic area. For this reason, Renolit has developed “Renolit Dolphin S”, a silicone film which combines both properties, i. e. is “amphiphilic”.
Is the technology comparable to a fouling release coating?
Heckel: Yes, it is a fouling release coating. This means that the fouling itself is not prevented, but only its adhesion to the surface.
How long does the film last and can damages be repaired afterwards?
Heckel: The film lasts up to five years, somewhat depending on the application. After these five years – depending on the condition of the film – a new layer of silicone can be applied, thus extending the service life even further.
Damages in the film can be repaired in small parts. The affected area is cut out and then replaced by a section. The edges are coated with silicone and thus sealed.
The layers of the “Dolpin S” film. Source: Renolit
To what extent is the hull protected against corrosion damage by the film?
Heckel: In addition to its fouling release effect, the film also offers a certain degree of corrosion protection. However, depending on the substrate, we recommend using a corrosion protection coating – especially on steel.
Further advantages of the film are: The reduction of the flow resistance due to its smooth surface, easy application or mounting and a reduction in fuel costs. Furthermore, the film also reduces maintenance and running costs: as the film lasts for five years, a new antifouling coating does not have to be applied every year.
To what extent can an antifouling coating be dispensed by using the film?
Heckel: The film makes it possible to completely dispense with an antifouling coating. After a pre-treatment of the surface with a primer or a corrosion protection coating, the film is applied and thus offers protection against fouling. An antifouling paint coat is completely omitted.
Test results by Dr. Brill + Partner: Left: Untreated PVC plate: Untreated PVC sheet after 3 years / middle left: Renolit film after 3 years / middle right: Biocide-containing paint after 2 years / right: Silicone paint after 3 years
