New method can provide odor-free nappies

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Published 26 September 2022 at 08.11

Domestic. Active carbon is used in the kitchen hood to remove food. A new thesis shows that activated charcoal could also remove urine odor in diapers.

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Modern diapers can absorb and encapsulate a lot of liquid and therefore do not need to be changed as often as before. But the smell is still a problem.

In a new thesis, Isabelle Simonsson at the University of Gothenburg has looked at a specific odor molecule and discovered that in the right environment it can choose to remain in the liquid and not cause a bad smell.< /p>

– The odor molecule is called para-cresol and is an organic, volatile hydrocarbon. It is the one that gives rise to the musty smell in pig breeding and in horse stables. Para-cresol is also found in human urine and is hydrophobic, meaning it avoids water. That is one of the reasons why it leaves the urine and goes out into the surrounding air, i.e. the smell spreads, says Isabelle Simonsson in a dispatch.

Manufacturers of diapers and other hygiene articles have long known that an electrically charged surface can have the ability to absorb odors. There is also an old patent on this, but a lot has been about doing tests on different materials and seeing what works. The tests have not reached a solution.

The main goal of the thesis is to investigate which material properties are important for absorbing odor molecules in urine. One of the materials used was activated carbon, which today is found in every second cooker hood to neutralize odors, it is also an economical and environmentally friendly material.

In tests with carbon materials that had been manipulated in various ways, it was found that the carbon with the least charge was most effective at attracting the para-cresol molecules from the liquid with less odor as a result. The material that was best at binding the odor molecule was the activated carbon, which mostly consisted of the carbon variant graphene.

– Our results demonstrate that there is a direct “ion-specific effect” on the material's properties and adsorption capacity in synthetic urine. The active carbon has a large surface area and it is advantageous when it needs to be able to adsorb the odor molecules.

In tests where the para-cresol was dissolved in water, the same effect was not achieved and it depends on the salts found in the urine. The salt's ions, including sodium, lower the water solubility of organic molecules, which then bind to the active carbon instead.

The thesis mainly concerns basic research, but its results can be of great use in many industrial processes, for example in the mining industry, water and sewage treatment, development of new hygiene items, pharmaceuticals, and building materials.

– These results are promising, but there are obstacles on the way to an odor-free diaper. Like the color for example, is it possible to sell a diaper that is black? says Isabelle Simonsson.