The objective of the project was the development and testing of methods for the collection, processing and analysis of carbon nanofibers (CNF) in samples of fine particulate matter from atmospheres containing soot particles to enable the drawing of conclusions on the detectability of CNF overlaid with soot particles. The result is an initial approach for a detection method consisting of one purification step and two correlated microscopic analysis steps. This allows the localisation and identification of CNF in samples that contain soot particles.
The soot particles are less resistant to oxidation than CNF. By selectively removing the soot particles on the basis of the non-thermal plasma oxidation the chemically inert (partially-) graphitic CNF retain. The characteristic Raman spectra for graphitic materials are used in a subsequent Raman spectroscopic examination to localise objects suspected to contain CNF. The analysis of these areas with a high-resolution SEM provides morphological information for the doubtless identification and quantification of CNF. In this way, the necessary basis for the development of a measurement method in a regulatory context was developed to reliably quantify CNF overlaid with soot particles.
For operations involving fibrous (nano) materials, the release of fibre dust during manufacturing or handling can pose a risk to employees. To verify applied protective measures and to be able to reliably determine the exposure of employees to fibrous materials such as CNF, validated measurement and evaluation methods are absolutely essential. At workplaces, however, the background exposure to ubiquitous sources of UFP, such as oil mist and soot from car exhaust, fumes or domestic fuels, is frequently high. Such contaminants can render a localisation and doubtless identification of CNF through an evaluation of filter samples which is based solely on SEM impossible. The results of this project helped to define key points regarding an implementation-friendly method of measurement for the unequivocal identification and quantification of CNF in an atmosphere containing soot particles. This constitutes a necessary prerequisite for the reliable determination of the exposure of employees to fibre dust from advanced fibrous materials.
Unit 4.5 "Particulate Hazardous Substances, Advanced Materials"