Mussels´ ability to attach themselves to various materials may offer the environment-friendly way of providing rust protection in the future. Corrosion of metals, such as rust, is expensive for society. In the USA alone, the estimated bill is USD 350 billion a year (approximately EUR 267bn).Hazardous
The corrosion process, which is natural, goes on all around us. It cannot be stopped, but it can be slowed down. Traditionally, ‘corrosion inhibitors´ are used to reduce the rate of corrosion and thereby reduce the damage. These are effective, but many are also hazardous to health and the environment. The chromate process is one example.
In cooperation with the company Biopolymer Products AB in Gothenburg, five researchers at the Royal Institute of Technology in Stockholm (KTH) — Jinshan Pan, Per Claesson, Andra Dėdinaitė, Fan Zhang and Olga Krivosheeva — have come up with an environment-friendly alternative to the chromate process, which is hazardous to health and the environment.
Composed of proteins
The alternative was found in the blue mussel. This animal has the ability to cling to virtually every material by making ‘byssal threads´ (the ‘byssus´), which it attaches to underwater substrates. The mussel´s unique means of adhesion, i.e. the thread, permits attachment even to surfaces with such low surface energy as wax and Teflon®. A bioadhesive material composed of proteins, the byssus also has an unusual capability to repel water from a surface while attaching itself to the surface and hardening under water.
Mussel adhesive protein (MAP) also has the ability to form film that protects materials against corrosion.
‘We have a patent-protected production method for MAP, which is one of the key components in the adhesive film,´ says Björn Strandwitz, CEO of Biopolymer Products AB.
Advanced technology
The KTH research team has used advanced surface-sensitive techniques to evaluate how rapidly the molecules attach to the surface (adsorption kinetics), how the protective film is formed and how far the corrosion rate is reduced (corrosion inhibition) by means of mussel protein.
The scientists have also looked at how these properties are affected by the mussels´ surroundings, such as the ambient water salinity and pH value. Their findings show that MAP adsorbs rapidly and forms stable films that markedly slow down corrosion within a large pH interval.
‘In-situ AFM microscopy and electrochemical measurements of carbon steel in saline water show that MAP adsorbs on carbon steel across a broad pH interval, and that it forms a carbon film that covers the whole substrate and thickens over time,´ says Professor Jinshan Pan at KTH.
This means that the MAP can effectively protect carbon steel from rusting.
Björn Strandwitz adds: ‘Carbon steel is one of the commonest materials in, for example, steel building structures. And there is reason to believe that MAP would work superbly in a coastal maritime environment — bridges, for example.´
Increasingly effective over time
The corrosion-protective effect also increases over time. This appears to be due to the formation of a composite film by MAP and corrosion products. At best, this spontaneously formed film has resulted in a reduction of as much as 99% in the corrosion rate.
The most effective forms of corrosion protection today are active ones that might be termed ‘self-repairing´ or ‘self-healing´. If damage to the protective film arises, it can repair itself. This is how the chromate process works, for example.
The MAP of the blue mussel has the same effect, and it can be used in both passive and active corrosion-protective films. Biopolymer Products has taken out patents on these discoveries.
