Topic of the Month: January 2015

Scented polymers

What fragrant plastics tell us

Odours have a direct impact on our perception and our decision-making processes: it is a well-known fact that anything which smells good gets a good response. However, it is not always the case that something which smells good is good for us too, while something that stinks is not always bad for us. In actual fact, this article outlines a specific example of where the opposite is the case.

We don’t have a nose merely for visual effect. And it would be just as inaccurate, on the other hand, to describe the nose as an olfactory organ alone – in view partly of the extremely complicated smelling process (which has not been explained completely yet at the scientific level) and partly of the psychological element associated with our nose that is reflected in many idioms we use.

The nose and its significance

We cut off our nose to spite our face when we harm ourselves by acting spitefully or resentfully. When we annoy people, we get up their nose, while we keep our nose clean by behaving properly and keeping out of trouble. We put a person’s nose out of joint when we make someone jealous and thumb our nose at them when we act with blatant disregard for their feelings. We turn our nose up at someone when we are showing disdain or scorn. We are sticking our nose into something when we interfere or intrude where it is not of proper concern to us. And, finally, we are acting haughtily when we have our nose in the air.

Irrespective of its metaphorical meaning, our nose renders us great service in everyday life, for example when we are assessing something: what smells goods generally elicits a positive response from us. This is true not only of people but also of all the different things that we eat and wear, that care for or decorate our bodies or that are useful to us in some way or another: as soon as they reach our nose, odours can start a more powerful neuronal firework show in us than any of our other senses and can lead to reactions ranging from disgust to delight and even addictive sniffing.

Awareness of the importance of olfactory forces proves to be valuable in many different respects. Manufacturers of consumer goods are virtuosos in using this instrument to stimulate product careers and to avoid the fate of ending as an unwanted shelf warmer: a pleasant fragrance increases the consumer’s perception and acceptance of a product and therefore promotes sales – notwithstanding possible cultural differences in the assessment of what smells good or stinks; there is no accounting for taste, as the saying goes. This fact explains the use of aromas and fragrances in the manufacturing of consumer goods that have the same product name but taste different in Asia than in Central Europe or the United States.

The toy industry also gives in to the temptation to stimulate the life of its products by using substances with olfactory appeal – without making any attempt to hide the fact. On the contrary: the advertising for them frequently even stresses that this doll smells of cinnamon while another one has a vanilla scent (more about this later on). Some fragrances have allergenic potential, however, which should not be underestimated – particularly in view of the fact that some of the population (about five per cent in Germany) is sensitive to allergenic fragrances. And: something that is an approved ingredient of cosmetics is not by any means necessarily approved for use in a children’s toy.

Bestseller or shelf warmer – the “nose factor” is crucial

Regulation of allergenic fragrances in scented toys

In their article in the Journal “Analytical Methods” [1], Dr Ines Masuck, Dr Christoph Hutzler and Professor Dr Dr Andreas Luch from the German Risk Assessment Institute (BfR) in Berlin point out that allergenic fragrances are one of the main causes of contact dermatitis in children. The BfR scientists report that the revised European Directive on the safety of toys 2009/48/EC [2] therefore bans 55 fragrances, although it permits up to 100 µg of the fragrance per gram of material when this is technically unavoidable under good manufacturing practice.

The aromatic compounds that are banned or are only permitted in limited concentrations include, for example, d-limonene, linalool, benzyl alcohol, citronellol, methyl heptine carbonate, geraniol, citral, hydroxy-citronellal, cinnamal, anisyl alcohol, cinnamyl alcohol, eugenol, isomethyl ionone, isoeugenol, lilial, amyl cinnamal, farnesol, lyral, amylcinnamyl alcohol, hexyl cinnamaldehyde, benzyl benzoate, benzyl salicylate, benzyl cinnamate and coumarin. There should be no expectation that the packaging will indicate whether any of these substances have been used as a additive. It is not possible to conclude, on the other hand, they are not present because they are not permitted. Be very careful has to be the motto. Some manufacturers who have not committed themselves to compliance with a quality standard tend on occasions to try and improve their products by adding banned substances.

Quality control is important to monitor potential allergens

It is in the interests of individual consumers in particular to check and evaluate the potential risks of toys – not just whether small components can get detached and swallowed or whether there is any danger of poisoning by chemical additives but also whether there is any allergenic potential. Migration and emission studies, that are carried out in the context of emission chamber measurements in the case of fragrance allergies, play a decisive role here. Since fragrances are by their nature volatile or semi-volatile organic compounds (VOC/SVOC), gas chromatography combined with mass spectrometric detection (GC/MS) [LINK] is an additional analytical method of choice to obtain a quick insight into suspicious products, which – in the final analysis – can be subjected to chamber testing in accordance with the regulations if and when they are identified as being allergenic and harmful to health.

Masuck et al. ordered five different scented dolls from an Internet shop. Source: Masuck et al.

Beware of scented dolls

Quality control of children’s toys is essential – there is really no alternative to it – particularly in view of the fact that products from all over the world can be ordered nowadays via the Internet and some of them are manufactured to quality standards that are nowhere near as strict as those applied in Germany. This is confirmed by an experiment carried out by Masuck et al.

The BfR scientists ordered five different scented dolls from an Internet shop. Masuck et al. explain that one of the dolls had a sweet vanilla smell, while the others were supposed to smell of popcorn, strawberry and violet – according to the promises made on the packaging. What was at any rate the case was that “the smell of all the dolls investigated differed from the typical plastic smell with its synthetic associations”. In this context, it seems to be reasonable and only sensible to ask the question here: what does plastic smell like?

Making sure that quality control is comparable

In their analysis, the scientists detected such banned substances as coumarin, cinnamyl alcohol and amyl cinnamic aldehyde. Allergenic fragrances like benzyl benzoate were in addition detected in quantities that would have made declaration on the packaging necessary. d-limonene and linalool were also found, but only when the scientists used a different extraction process, which allows the conclusion to be drawn that quality control results and the analytical procedure used need to be subjected to a critical review and should be compared with acknowledged and guaranteed (i.e. validated) processes.

The following rule of thumb can, in a nutshell, be applied by all parents, grandparents, aunts and uncles who want to give young children a treat: hands off scented toys! They need to be treated with caution and should in dubious cases be kept away from children and disposed of – at the latest when playing with the toys leads to headaches, nausea or unaccountable skin reactions. The same is true of bicycle helmets that suddenly start to give off an unpleasant smell. Although there is a very different reason for this ...

Photo: Felizitas Gemetz, ©: Fraunhofer IWM

Fragrance to increase safety

The point of bicycle helmets is to protect the heads of the people wearing them. Only undamaged helmets do what they are supposed to do in an emergency, however. It is therefore advisable to replace such helmets at regular intervals. But who willingly throws out expensive equipment on the off chance that it may be damaged?

A new process that scientists from the Fraunhofer Material Mechanics Institute (IWM) in Freiburg have developed in co-operation with the Fraunhofer Institute for Environmental, Safety and Energy Technology (UMSICHT) in Oberhausen is supposed to provide clarity:

If small cracks form in polymer materials, they start to smell. Larger cracks virtually stink. What are responsible for the odours are fragrant oils that are enclosed in microcapsules and are integrated in the polymer. Christof Koplin, a scientist who works at IWM, explains that damage to the helmet material, e.g. due to a crash, leads to the formation of cracks in the polymer, so that the microcapsules integrated in the polymer break open and the fragrant oil they contain escapes – with the relevant olfactory impact. This is a good time to dispose of the helmet.

Bicycle helmets are available in all shapes and sizes: there are models that can be folded up and ones with a flashing back light or an iPhone display. In future, cyclists will be able to buy helmets that start to smell as soon as they are damaged. A new process makes sure that fragrant oils escape when cracks form in plastics. The damaged helmet releases fragrances. Bottom right: the microcapsule after it has broken open.

Additives have to survive the production process undamaged

The tiny fragrant oil capsules consist of a silicon core that is impregnated with oil and is enclosed by a layer of melamine formaldehyde resin, which acts as an odour-tight jacket for the capsules and protects them from the mechanical stresses that occur during further processing. These concentrated fragrances are added to a polypropylene material that is given the final shape of the component by the injection moulding process at high pressure (up to 100 bar) and at temperatures of 200 to 300°C. In the case of bicycle helmets, what is involved here is a film that is attached to them. The development of such an olfactory safety indicator is of much greater significance than it might sound.

In order to determine what stresses are needed to break open the tiny capsules (which are 1 to 50 micrometres in size), the scientists at the Fraunhofer IWM subject the material to numerous stress tests, to measure pressure, bending and flexing resistance levels. The experts only classify the tests as successful if the capsules open shortly before the product breaks and the fragrances can escape. Koplin explains: “Our odour detection method has several advantages. It not only enables polymer components that are critical for safety reasons to be replaced in good time. The fragrances that escape also make it possible to detect damage that is not visible.”

Unsuspected potential for further applications discovered

The process developed by the Fraunhofer research scientists is suitable, incidentally, not only for all safety products like bicycle, motorcycle or construction helmets that are difficult to test for defects. The viability of pressure hoses of the kind used, among other things, as washing machine supply lines that are not visible and are difficult to access could, for example, be monitored with them as well. Odour sensors could monitor plastic water and gas supply pipes for critical cracks too, since they detect fragrances that escape from long distances away. The scientists from the Fraunhofer institutes are convinced that it will be possible to find a market for their innovation – and they are justified in thinking this, since odour detection is, after all, already being used with coated metal components, as Koplin points out. A very early stage has only been reached with the plastics and polymer materials that are used in numerous different shapes and forms as well as in many different areas.
Talking about practical applications: the 17th “Odour and Emissions of Plastic Materials” workshop is being held by the Institute of Material Technology / Plastic Technology at Kassel University on 16. and 17. March 2015 (venue: Kassel University, Kurt-Wolters-Strasse 3, 34109 Kassel). Further details about the workshop, the programme and the registration arrangements can be found at and in the “Apropos K” section of our website

Sources and publications providing further information

[1] I. Masuck, C. Hutzler, A. Luch, Screening of fragrances in scented toys: a comparative study of different headspace techniques coupled to GC-MS, Anal. Methods, 2013, 5, 508
[2] Revised European Directive on the safety of toys 2009/48/EC []
[3] Fraunhofer Institute Umsicht, press release
Guido Deußing

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