University of São Paulo: USP laboratories study intelligent coatings with self-healing power
Corrosion is a phenomenon of deterioration of metallic materials that happens spontaneously, through chemical and electronic reactions with the environment. It is estimated that 30% of the world’s production of iron and steel is lost to corrosion. In Brazil, maintenance costs against this phenomenon were equivalent to 4% of the Gross Domestic Product (GDP) in 2019, which corresponds to BRL 290 billion. The data are from a study by the multinational mining company Nexa Resources that operates in the country.
Inspired by the medical field, a new intelligent coating technology with self-healing properties is being studied at USP to mitigate corrosion on metallic surfaces. The technology uses microcapsules with a repairing agent that acts on the damaged area locally, autonomously, preventing the advance of corrosion of the painted metallic substrate. These smart coatings are studiedby professor and researcher Idalina Vieira Aoki, from the Department of Chemical Engineering at the Polytechnic School (Poli) at USP. She is the researcher who claims that the encapsulation of corrosion inhibitors was inspired by the medical field, more precisely by “drugs that can cause unwanted reactions or side effects, which are encapsulated and functionalized to go directly to the diseased organ”.
In order for the self-repair process to be possible, the microcapsules are generally spheres with polymeric walls with an encapsulated repair agent present in the first layer of paint on the metallic substrate, the so-called primer. When the metal surface suffers mechanical damage, such as scratches or impacts, the microcapsules are ruptured and release the repair agent at the damaged site, covering the exposed metal with the formation of a polymeric film, reducing or ceasing the corrosive process.
The use of this type of coating with self-healing properties brings practical and economic advantages, reducing the frequency of maintenance of painted structures and saving efforts, time and resources. Idalina comments that “these additives are not expensive, which makes their use very attractive”.
Studies in oral health
Recently, in partnership with professor Taís Scaramucci Forlin and post-doctoral student Sávio José Cardoso Bezerra, both from the Faculty of Dentistry (FO) at USP, fluoride ions and tin salts, encapsulated in mesoporous silica and added to a type of based on polysilanes, have been studied to prevent caries, dental erosion and dentin hypersensitivity.
Dental erosion, explains Professor Taís, is a chronic illness defined as the loss of hard dental tissue resulting from a chemical process without the action of bacteria, caused by acids originating from the body itself or from external sources. “The consequences of this wear can be the loss of dental morphology, shorter and more yellow teeth, in addition to pain, resulting from dentin hypersensitivity.”
The intelligent coatings, according to the professor, enable specific treatments as they adhere to the dental structure forming a thin and transparent protective layer. There is also the possibility of adding these coatings with agents known to be beneficial to oral health. Taís says that these encapsulated agents allow “controlled release, on demand, at the moment the tooth is challenged”.
Protection of steel reinforcements in civil construction
The use of microcapsules with corrosion inhibitors and self-healing properties in civil construction is studied as a concrete additive to reduce the number of microcracks, which can allow the entry of aggressive agents that cause corrosion of steel reinforcement present in reinforced concrete.
Developed basically for metallic structures, these intelligent coatings do not have the power to repair cracks in masonry walls, because according to Idalina, there is not enough material in the microcapsules to fill such large voids.