Investigation of the Tendency of Carbon Fibers to Disintegrate into Respirable Fiber-Shaped Fragments

• Published in: Fibers Vol. 11; no. 6; p. 50
• Main Authors: Meyer-Plath, Asmus, Kehren, Dominic, Große, Anna, Naumann, Romy, Hofmann, Marcel, Schneck, Tanja, Ota, Antje, Hermanutz, Frank, Dziurowitz, Nico, Thim, Carmen, Plitzko, Sabine, Bäger, Daphne
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.06.2023
• Subjects: carbon fiber; Carbon fiber reinforced plastics; Carbon fibers; Disintegration; Fiber composites; fiber-shaped fragments; fracturing behavior; Fragments; Laboratory tests; Long fibers; Machining; Market shares; Material properties; Mechanical properties; Mesophase; microstructure; Morphology; Polyacrylonitrile; Polymer matrix composites; Polymers; Reinforced plastics; respirable dust; Respiration; Spallation; Tensile tests; Textile fibers; WHO-fibers; Germany
• ISSN: 2079-6439; 2079-6439
• DOI: 10.3390/fib11060050

Recent reports of the release of large numbers of respirable and critically long fiber-shaped fragments from mesophase pitch-based carbon fiber polymer composites during machining and tensile testing have raised inhalation toxicological concerns. As carbon fibers and their fragments are to be considered as inherently biodurable, the fiber pathogenicity paradigm motivated the development of a laboratory test method to assess the propensity of different types of carbon fibers to form such fragments. It uses spallation testing of carbon fibers by impact grinding in an oscillating ball mill. The resulting fragments were dispersed on track-etched membrane filters and morphologically analyzed by scanning electron microscopy. The method was applied to nine different carbon fiber types synthesized from polyacrylonitrile, mesophase or isotropic pitch, covering a broad range of material properties. Significant differences in the morphology of formed fragments were observed between the materials studied. These were statistically analyzed to relate disintegration characteristics to material properties and to rank the carbon fiber types according to their propensity to form respirable fiber fragments. This tendency was found to be lower for polyacrylonitrile-based and isotropic pitch-based carbon fibers than for mesophase pitch-based carbon fibers, but still significant. Although there are currently only few reports in the literature of increased respirable fiber dust concentrations during the machining of polyacrylonitrile-based carbon fiber composites, we conclude that such materials have the potential to form critical fiber morphologies of WHO dimensions. For safe-and-sustainable carbon fiber-reinforced composites, a better understanding of the material properties that control the carbon fiber fragmentation is imperative.