Elastic CNT-polyurethane nanocomposite: synthesis, performance and assessment of fragments released during use.

Intended for use in high performance applications where electrical conductivity is required, we developed a CNT-TPU composite. Such a composite can be prepared by melt processing (extrusion) on an industrial scale. Due to the known hazard upon inhalation of CNTs, we assessed three degradation scenarios that may lead to the release of CNTs from the composite: normal use, machining and outdoor weathering. Unexpectedly, we find that the relative softness of the material actually enhances the embedding of CNTs also in its degradation fragments. A release of free CNTs was not detected under any condition using several detection methods. However, since machining may induce a high acute dose of human exposure, we assessed the cytotoxicity potential of released fragments in the in vitro model of precision-cut lung slices, and found no additional toxicity due to the presence of CNTs. At very low rates over years, weathering degrades the polymer matrix as expected for polyurethanes, thus exposing a network of entangled CNTs. In a preliminary risk assessment, we conclude that this material is safe for humans in professional and consumer use.

On the lifecycle of nanocomposites: comparing released fragments and their in-vivo hazards from three release mechanisms and four nanocomposites.

Nanocomposites are the dominating class of nanomaterials to come into consumer contact, and were in general assumed to pose low risk. The first data is now emerging on the exposure from nanocomposites, but little is yet known about their hypothetical nanospecific physiological effects, giving ample room for speculation. For the first time, this comprehensive study addresses these aspects in a systematic series of thermoplastic and cementitious nanocomposite materials. Earlier reports that 'chalking', the release of pigments from weathered paints, also occurs for nanocomposites, are confirmed. In contrast, mechanical forces by normal consumer use or do-it-yourself sanding do not disrupt nanofillers (nanoparticles or nanofibers) from the matrix. Detailed evidence is provided for the nature of the degradation products: no free nanofillers are detected up to the detection threshold of 100 ppm. Sanding powders measuring 1 to 80 µm in diameter are identified with the original material, still containing the nanofillers. The potential hazard from aerosols generated by sanding nanocomposites up to the nuisance dust limit is also investigated. In-vivo instillation in rats is used to quantify physiological effects on degradation products from abraded nanocomposites, in comparison to the abraded matrix without nanofiller and to the pure nanofiller. In this pioneering and preliminary evaluation, the hazards cannot be distinguished with or without nanofiller.