Quantitative measurement of nanoparticle release from rubber composites during fabrication and testing

Carbon black has been a key ingredient in high-performance composites, such as tire rubber, for over a hundred years. This reinforcing filler increases rubber rigidity and reduces tire wear, among many other useful effects. New nanomaterials, such as graphene and carbon nanotubes, may bring new performance improvements. However, their usefulness cannot be evaluated unless worker safety is assured by demonstrating that the nanoparticles are not released at harmful concentrations during manufacture and testing. Here, we present a flexible, general method for the quantitative evaluation of nanoparticle release from rubber nanocomposites. We evaluate manufacturing steps such as powder handling, uncured rubber milling, and curing. We also evaluate particle emission during cured rubber abrasion as an aggressive example of the testing rubber goods are subjected to. We quantify released nanoparticle concentrations for clay nanoparticles, graphene-like materials, and carbon nanotubes. We also describe a mechanistic framework based on the balance of adhesive and kinetic energies, which helps understand when nanoparticles are or are not released. This method contributes to the assessment of workers' exposure to nanoparticles during the various stages of the industrial process, which is an essential step in managing the risk associated with the use of nanomaterials in manufacturing.