Scientists at the Hohenstein Institute in Germany have developed a ceramic coating for continuous batch washers, which is based on copper and silver and has a lasting antibacterial effect. It prevents laundry that has already been disinfected from being re-contaminated by bacteria entering the rinsing zone.
Working on a joint research project with the Friedrich Baur Research Institute for Biomaterials, the researchers have shown that washing can be re-contaminated by bacteria during the rinsing process, immediately after it has been disinfected. Such re-contamination of washing that has already been disinfected reduces the microbiological quality of the whole treatment process, because there is no further disinfecting of the washing in subsequent stages.
The cause of this re-contamination is normally to be found in the batch drainage systems, presses and centrifuges. Here, if the rinsing water is contaminated, or bacteria have entered from some other source, biofilms may form because the hygrothermal moisture and temperature conditions in these places are ideal for colonisation by bacteria. These biofilms often present a major problem in maintaining hygiene standards.
The Hohenstein researchers’ objective was to develop an effective and lasting anti-biofilm coating to cover both the inside surfaces and the perforated outside surface of the drum in batch washing machines.
In the first stage of this project, they investigated what quantity of active substances was required to achieve the desired antibacterial effect in the coating. Various modifications to the coating were tested in extensive microbiological studies. In addition to the standard test procedures for examining antibacterial surfaces, some new tests, specially developed for the project, were used.
The findings revealed that a combination of the biocidal metal ions of silver and copper, when applied in 2–3 coats, had the strongest antibacterial effect. In some cases the bacterial growth was entirely suppressed.
Furthermore, the biofilm plaque was removed far more effectively when mechanical pressure was applied to the active coatings than from uncoated metal.
The researchers then worked out the material parameters for the best possible coating using a combination of silver and copper metal ions. They established that, in a variety of different media, the metal ions only washed off very slowly.
Extrapolating the release rates suggested that the coating would remain effective over a period of 10–15 years. The adhesion of the coating was also studied and this was shown to be highly resistant to mechanical pressure.
The results obtained in laboratory conditions were verified in conditions similar to the conditions in practice.
