Experts from the German Plastics Center (SKZ) in Würzburg and the Chair of Measurement Technology (LMT) at Saarland University demonstrate promising gas sensor technology. This can help compounders and recyclers protect the health of their employees while monitoring process stability.

Illustration of a sensor-monitored plastics production (Photo: SKZ)

Continuous emission measurement improves occupational safety in plastics processing

Current occupational health and safety regulations require a sample measurement for volatile organic compounds (VOCs) once a year, based on which the impact on employee health is assessed. However, this approach is more than inadequate, especially in the case of constantly changing material mixtures, as is common among compounders and recyclers. For this reason, the SKZ and gas sensor experts led by Professor Andreas Schütze from LMT have been working on a joint cooperation project to continuously monitor emissions in plastics processing.

With the aim of showing companies an economical way to improve occupational safety, cost-effective sensor systems based on metal oxide semiconductor gas sensors (MOS sensors) were developed. "These can keep a reliable, non-stop eye on air quality during the manufacturing process and immediately sound the alarm as soon as VOC concentrations exceed critical limits," explains Dr. Christian Bur, project manager at LMT. "In the process, a wide variety of substances can be reliably detected even in small concentrations in the ppm range." Within the project framework, the emissions of styrene during the processing of polystyrene, chlorobenzene in polycarbonate and caprolactam in polyamide were investigated as examples. Measurements using gas chromatography with mass spectrometry coupling and photoionization detectors served as a reference for the quantitative evaluation models of the gas sensors.

"The use of MOS gas sensors not only improves occupational safety," explains Dr. Norbert Halmen, Scientist at SKZ. "Since VOCs allow inference of process and material variations, companies can adjust their process parameters to protect materials and machinery from damage." In the future, quantification models will be expanded to include additional emissions and focus on recycling applications. Interested companies are encouraged to contact SKZ to have the new measurement method evaluated for their own use cases.

In the compounding of plastics, complex mixtures of polymers, fillers and additives are processed in extruders at high temperatures and high shear. Various vapors or gases can be produced in the process. Although not all of these volatile organic compounds (VOCs) are fundamentally harmful to humans and the environment, substances can be released that are hazardous to health, carcinogenic, and irritating to the respiratory tract, skin and eyes. It becomes even more problematic when recycled materials are processed. Particularly in the post-consumer sector, despite sorting and washing of the waste, contamination with foreign substances (other types of plastics, printing inks, residues of detergents or cleaners, and adhesives and dyes from labels) can occur, which can lead to unknown and potentially hazardous VOC mixtures during processing.

The results are based, among other things, on project 20982 N of the research association "Fördergemeinschaft für das Süddeutsche Kunststoff-Zentrum e. V.". It was funded by the German Federal Ministry of Economics and Climate Protection through the German Federation of Industrial Research Associations (AiF) as part of the program for the promotion of joint industrial research (IGF) on the basis of a resolution of the German Bundestag. We are grateful for the financial support. The detailed research report of the project is available on request at SKZ.

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