Fraunhofer LBF
Optimum plastic surfaces for UV disinfection

However, it can also destroy the organic macromolecules in plastics, causing damage to the material. Fraunhofer Institute for Structural Durability and System Reliability LBF has now launched a project to develop processes with the aim of better understanding the ageing of plastics due to UV radiation, preventing decay and enabling UV-C disinfection to be used routinely and on a large scale in future.

UV-C radiation destroys the DNA of micro-organisms such as viruses, bacteria, yeasts and fungi. So today it is used, for example, to disinfect surfaces in operating theatres or laboratories, to disinfect the air in rooms or to treat water. Contaminated surfaces are sterilised in a few seconds and without the use of harmful chemicals. The applied UV-C dose – i.e. irradiation intensity x time – must be sufficient to reliably kill the existing germs.

Already a reality: UV-C disinfection on escalators

Since the beginning of the corona pandemic, disinfection with UV-C radiation has attracted increased interest because protective masks or textiles, but also contaminated surfaces in department shops, shopping centres, railway stations, airports and hospitals or test laboratories, can be disinfected quickly, easily and automatically. UV-C disinfection is already in practical use on escalators, with a disinfection module installed in the shielded return of the handrail. The handrail is continuously irradiated and kept germ-free. In addition to containing the pandemic, this also serves safety, as many people shy away from holding on to the handrail if there is a risk of infection.

In the current situation, it may make sense to retrofit existing systems. At the same time, additional options are being developed for new installations in hospitals, shopping buildings or for public transport. Mobile systems or handheld devices are also being developed. Systematic investigations to reduce the germ load are still in their infancy. "During a pandemic, quick solutions are initially required. However, operators must also protect themselves against damage to plant, buildings or laboratory equipment caused by high-energy UV-C radiation so that their value is maintained over the planned life cycle," says Dr Robert Brüll, group manager for material analysis at the Fraunhofer LBF.

How does high-energy UV-C radiation affect plastics?

Up to now there have been hardly any studies on the ageing of plastics due to high-energy UV-C radiation. "Neither the exact mechanisms of polymer damage are known, nor is the effect of additional factors such as humidity and temperature researched. The same applies to the mode of action of stabilisers against UV-C photo-oxidation. But all this is a prerequisite for the targeted selection of polymer materials, the development of formulations with the longest possible service life in UV-C applications, and the gentle use of radiation," stresses Dr Brüll. Various customised solutions would have to be developed for the different types of plastics – elastomers (e.g. gloves, treadmills, handrails or cable sheathing), thermoplastics (food packaging, housings, cable ducts etc.) and coatings (e.g. shelves in supermarkets).

In response to numerous requests from industry, the Plastics Division at Fraunhofer LBF has launched an internal project to investigate the influence of UV-C on plastic ageing and develop UV-C-stable polymer materials. "We invite interested companies, for example from the fields of irradiation technology, trade and transport or plastic materials, to participate," says Dr Brüll.

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