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Researchers Sniff Out Unpleasant Odors

Nov. 17, 2017
Studies focus on better understanding off-odors in chemical products and their physical impact

Smelly chemicals make money: Dublin-based Research and Markets estimates the value of the global market for flavors and fragrances exceeds €37 billion ($43 billion). However, odors of a less pleasant kind are a nuisance and often poorly understood.


For a number of years, these odors have been a main focus of research at the department of sensory analytics at the Fraunhofer Institute for Process Engineering and Packaging, Freising, Germany. Here, an interdisciplinary group studies how people interact with unpleasant odors found in everyday products such as textiles and cosmetics.

One such project involved identifying chemicals that cause off-odors in children’s products. Increasing physiological conditions in children, including allergies and multiple chemical sensitivity, triggered the work funded by the Bavarian Ministry for the Environment and Consumer Protection. Using techniques such as gas chromatography, mass spectrometry and olfactometry, the researchers evaluated more than 50 products to identify the chemicals responsible for the odors.

The studies found that plastic products contain a large number of compounds, with diverse chemical structures, that can lead to off-odors and even irritation. Some of these were identified for the first time in this project and some were found to be physiologically harmful. The plan is to use this work as a basis to determine the sources of contamination and identify reaction pathways leading to the formation of undesirable substances. Follow-up studies will evaluate the physiological and toxicological properties of these substances, with particular focus on the exposure of these substances to consumers, people involved in the manufacturing process, and those involved in sales and retail.

The team now has turned its attention to deodorants in acrylic adhesives routinely used in shoes, carpets, windshields, cell phone displays and a host of other applications requiring strong, optically clear bonds. It’s a market already worth €9 billion (over $10 billion) and growing, according to Markets and Markets, Pune, India.

While some adhesives contain solvents with unpleasant smells, those that are solvent-free or low-solvent can be noxious as well. Department head and Fraunhofer deputy director professor Andrea Büttner leads the research team trying to find out why; so far, they have tested four solvent-free acrylic adhesives to determine which components trigger the offensive odors.

The researchers have identified 27 odorants that cause unpleasant smells, including methyl methacrylate, acetophenone, 1-butanol, 4-methylphenol, phenylacetic acid methyl ester and acetic acid. It’s the first time that 20 substances, including the chemical compound borneol, have been identified as odor-active compounds in adhesives.

“If a product emits a particularly strong odor, this can indicate the presence of hazardous substances,” warns Büttner.

Some of the samples contained phenolic compounds suspected of being mutagenic. Büttner sees a clear need for action to optimize the product development of adhesives: “Our analysis shows that a series of substances we found ought to be eliminated, and not just in terms of odor emissions. Strong odors can most definitely cause headaches and dizziness. We should be asking why adhesives smell. The mindset of both the user and the manufacturer needs to change in this regard.”

She added: “We’ve set ourselves the task of supporting manufacturers in product development, as the methods they employ mean they are often not in a position to know which of the components are causing the odors. This requires special analysis as well as trained test subjects to detect triggers, possible impurities and byproducts arising during the manufacturing process.”

In other words, using advanced analytical techniques on their own is not enough. So, test subjects are trained to become odor experts with weekly “follow your nose” sensory training sessions. The test subjects receive samples in odorless glass containers. The sensor panel sets characteristic odor attributes for each sample; in a second sensory session, it evaluates them against reference compounds on a predetermined scale. The overall intensity and the personal preference or dislike of an odor impression is then evaluated, with the mean values of the evaluations used to summarize an odor profile.

Philipp Denk is the team member charged with turning this work into reliable testing regimes.

“A globalized market and an ever-growing e-commerce sector is a major challenge for the official testing authorities — regarding the wide range of products they must test for hazardous components. That’s why we’re developing new technologies to support quality control and official entities and allow decentralization of the testing of products for hazardous substances,” he says.

The October issue of the International Journal of Adhesion and Adhesives contains the team’s latest findings.

Seán Ottewell is Chemical Processing's Editor at Large. You can email him at [email protected].

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