OCSiAl: Exploring the Safety of SWCNT Nanocomposites: Exposure Assessments in Epoxy Resins and Lithium-Ion Batteries

Carbon nanotubes (CNTs) have revolutionized material science, offering exceptional mechanical, electrical, and thermal properties. Among them, single-wall carbon nanotubes (SWCNTs) hold great promise for enhancing polymer nanocomposites, conductive inks, and lithium-ion batteries (LIBs). However, concerns persist about potential airborne exposure throughout their life cycle, especially during product use and recycling. To address this, Gunther van Kerckhove of BioNanoNet Association member OCSiAl Europe S.a.r.l. investigated SWCNT (brand name TUBALL™) release in two key applications: epoxy resin floor coatings and LIB materials, emphasizing the importance of Safe-and-Sustainable-by-Design (SSbD) approaches.

Understanding Potential Exposure

OCSiAl conducted two case studies to examine the potential release of airborne SWCNTs during different life cycle stages. The first focused on epoxy floor coatings enhanced with TUBALL™, SWCNT which exhibits improved durability. The second investigated LIB components, where TUBALL™ contributes to electrode performance and stability. In both cases, mechanical stress tests were performed to simulate real-world wear and recycling processes.

Methodology: Simulating Wear and Recycling

For the epoxy resin study, we employed a pin-on-disk tribometer to mimic surface abrasion during use. The LIB study involved the mechanical disassembly and milling of battery components to simulate industrial recycling. Airborne particle samples were collected using the STAT PEEL Identifier C2 system, which selectively captures and analyses CNT-containing particulate matter. Raman spectroscopy and scanning electron microscopy (SEM) were then used to quantify and characterize the released nanomaterials.

STAT PEEL Identifier C2 system

Key Findings

1. Epoxy Resin Abrasion

The tests revealed minimal release of free SWCNTs from the epoxy resin matrix. The detected concentrations were near the system’s limit of quantification (0.004 ng) and remained three orders of magnitude below the NIOSH-recommended exposure limit of 1 µg/m³ (figure 2). Raman spectra indicated some structural degradation of SWCNTs under mechanical stress but suggested a low risk of airborne exposure under typical usage conditions. Scientific paper: https://doi.org/10.3390/nano14010120

2. LIB Recycling Process

Grinding and milling of LIB components resulted in the release of airborne SWCNTs at levels of 0.097 µg/m³ (cutting mill) and 0.875 µg/m³ (centrifugal mill). While these values are below the NIOSH exposure threshold of 1µg/m³, the released particles primarily consisted of CNT agglomerates rather than individual nanotubes which was not detected during SEM/TEM investigations (figure 3). This finding underscores the need for further real-world exposure assessments in industrial settings.  Scientific paper: expected to be released soon.

figure 3: Overview and detailed secondary electron microscopy images taken from the collection membrane of a filtration slide, which was loaded during simulated mechanical recycling processes of lithium iron phosphate (LFP) batteries

Implications for Safety and Regulation

The results suggest that TUBALL™ SWCNTs, when incorporated into epoxy resins and LIBs, present a low risk of airborne exposure under simulated conditions. However, ongoing research of exposure assessments is crucial to fully assess the long-term implications across all life cycle stages of the used nanomaterials. With such data collections the SSbD principles should continue guiding material design to minimize potential health and environmental risks.

Conclusion

OCSiAl’s findings enable the broader industrial use of single-wall carbon nanotubes across a wider range of products while helping end-product manufacturers mitigate human exposure risks. However, to support the responsible development of nanocomposite technologies, OCSiAl emphasizes the need for further large-scale studies, particularly in industrial recycling environments. This includes integrating Safe and Sustainable by Design (SSbD) strategies and implementing continuous monitoring (Figure 1).

Contact:

Gunther Van Kerckhove
OCSiAl Europe S.a.r.l.
gunther.van.kerckhove@ocsial.com
www.tuball.com