The food industry uses heat exchangers for numerous steps in milk and juice processing. To eliminate risk to the consumers, the heat exchangers must be free from microbes. To do this, heat exchangers are cleaned at regular intervals with aggressive chemicals, which increases the potential for corrosion, especially if the heat exchanger is constructed of mild steel.
To reduce the effort required for cleaning heat exchangers and, in turn, decrease the possibility of corrosion, research scientists with INM–Leibniz Institute for New Materials (Saarbrücken, Germany) have developed nanocoatings that combine antiadhesive, anticorrosion and, on demand, antimicrobial properties.
The scientists achieved the antiadhesive characteristics by introducing hydrophobic compounds similar to polytetrafluoroethylene (PTFE). These inhibit biofilm formation and allow residues to be easily transported out of the heat exchanger before they clog the system’s channels. At the same time, the researchers use structures that act as diffusion barriers in the coatings. These protect against attack from corrosive substances or aggressive cleaning agents. To prevent microbes, bacteria, and fungus from adhering to surfaces, the scientists also use colloidal copper in the coating. Due to the oxygen or water that is present in many processes, copper ions are released from the copper colloids. These migrate to the surface and prevent microbial proliferation and growth due to their antimicrobial effect.
“In addition, we can keep the paint chemically stable. Otherwise it would not withstand the aggressive chemicals that are required for cleaning,” explains Carsten Becker-Willinger, head of Nanomers† at INM. By selectively adapting individual constituents, the developers can formulate a coating for the users’ special requirements, he adds. The coating can also be formulated to tolerate special mechanical loads, which is important for coatings used in heat exchangers. Due to mechanical vibrations, the individual plates of the heat exchangers could be subjected to a certain amount of abrasion at contact points.
The coating can be applied to stainless steel, steel, titanium, or aluminum using standard methods such as spraying or immersion and subsequent hardening. Other potential end-use applications include the large sector of air conditioning with heat exchangers, as well as equipment in water purification plants. To learn more, visit leibniz-inm.de/en.
†Trade name.