Emission tests

Emissions – causes and effects

Plastics can release undesirable, irritating or even toxic chemical compounds. Some emissions in high concentrations can cause discomfort or damage health. Other emissions, on the other hand, are 'only' an odour nuisance. Therefore, car manufacturers have started to regulate the type and amount of emissions. Depending on the OEM, the regulations for automotive suppliers stipulate odour tests, fogging tests and emission measurements, which must be carried out under precisely defined conditions.

Odour test

In an odour test, the odour of a material is determined by a trained test panel and evaluated with grades. According to VDA 270, the scale for odour testing ranges from grade 1 "imperceptible" to grade 6 "unbearable" (e.g. VW/Audi, Saab Volvo). Depending on the OEM's regulations, however, there may also be different rating scales for the odour test (e.g. from 0 to 5 or -3 to +3).

Fogging test

Fogging is the term used to describe outgassing of individual material components, which then precipitates in the component environment. In a car, for example, fogging can lead to a greasy coating on the windscreen. The condensable components of the component can be measured by a gravimetric or reflectometric fogging test (DIN 75201). For this purpose, the sample is heated. The volatile components escape from the component and precipitate in the (colder) component environment. In the gravimetric fogging test, the increase in weight due to condensation is measured. The determined value is given in mg and is typically in the range of less than 5 or 2 mg. In the reflectometric fogging test, the reflection of the surface with coating is determined and given as a percentage and should therefore be as high as possible. A good reflectometer value is in the range >80%.

Emission test

An emission test is used to determine the concentration of undesirable or even harmful substances in a component. The mass-related formaldehyde value of a material can be measured, for example, using the bottle method (VDA 275). Formaldehyde is a pungent smelling gas that not only irritates the eyes and respiratory tract, but is also classified as "possibly carcinogenic". Due to its widespread use as a starting product of e.g. dyes or synthetic resins, a formaldehyde determination is one of the emission measurements often requested.

It is also possible to determine the total carbon emission of a sample within the scope of emission testing (VDA 277). The method of static headspace GC/FID is suitable for the simultaneous determination of low- and medium-volatile compounds, but not for the detection of higher-volatile components. The total carbon emission is given in µg C/g (micrograms of carbon per gram).

While VDA 277 measures the total amount of carbon emission alone, it is possible to identify highly volatile (VOC) and condensable (FOG) emissions more precisely by combining thermal desorption and GC/MS (VDA 278). A detailed table with qualitative and quantitative individual results is obtained, including an evaluation of individual critical substances. 

Ann-Kathrin Schönbein
Head of NMR spectroscopy
Dr. Florian Kerner
Head of Chromatography
Geruchsprüfung im Rahmen einer Automotive Freigabeprüfung

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