Fraunhofer IWM: Smell technology for checking the integrity of plastic

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Researchers at the Fraunhofer Institute for Mechanics of Materials (IWM) in Freiburg have developed a new process which causes plastic materials to issue a smell alert if they are cracked or damaged.

This involves encapsulating odoriferous oils within the plastic, which exude and start to smell if the plastic develops small cracks that could undermine its structural integrity.

The researchers suggest one application would be in the plastic used to manufacture cycling helmets.

“Cyclists often replace their helmets unnecessarily after dropping them on the ground, because they cannot tell whether they are damaged or not. The capsules eliminate this problem. If cracks form, smelly substances are released,” explains Christof Koplin, research scientist at the IWM.

The capsules are added to a polypropylene mass which is injection-molded to form the final component. In the case of the bicycle helmet, the microcapsules are inserted in a thick foil made of polypropylene, which is fastened to the head gear.

A layer of melamine formaldehyde resin encloses the capsules so that they are completely airtight and mechanically sealed. It also protects the tiny capsules, which are subjected to temperatures of 200 to 300 degrees and pressures of up to 100 bar, during injection molding.

Koplin said the smell detection method offers several advantages. “It not only indicates when safety-critical polymer components need to be replaced. The exuding smells also enable damage outside the safety range to be detected.”

The process is therefore suitable for all products which are difficult to test for defects, such as cycle, motorbike and construction helmets. It can also be used to check pressure hoses, for example, in washing machines, which are difficult to access.

Smell sensors could also monitor plastic water and gas supply pipes to detect any cracks, because the odoriferous substances emitted are noticeable over long distances. “Smell detection is already in use for coated metal components. We are applying the process for the first time to polymer materials. The cycle helmet is being used as a demonstrator. Work on the capsules has finished and we are now completing characterising tests on individual configurations,” says Koplin.