Release of Carbon Nanotubes from Nano-polymer Composites during Environmental Aging

E. Sahle-Demessie, C. Han, A. Zhao, J. Wang, H. Grecsek
U.S. Environmental Protection Agency,
United States

Keywords: carbon nanotube, polymer-composite, nanorelease, life cycle, weathering


Over the past two decades there has been a significant increase in commercial products incorporating engineered nanomaterials (ENM) that are now are used in electronic, cosmetics, automotive and medical products and in environmental applications. Although many of these products have a long term use, thermoplastic polymer foil-laminated food package films, including low density polyethylene (LDPE) and LDPE-Clay by Meal-Ready-to-Eat are used in a short term, which may result in the generation of large amount of waste. As the volume of nano-enabled materials increase in the market, their potential release of nanoparticles can be very high during their use or at the end of their use life from their immobilized matrix due to weathering. Understanding the relationship between the inherent characteristics of nanocomposite based consumer products and the likelihood of the release and implication of ENM throughout the life-cycle of the product is critically important for risk assessment. Environmental aging may cause deterioration of the properties of nanocomposites and changes in their structure, and may affect their long-term performance encountered in service. If nanoparticles are released from their matrix, the high surface to volume ratio and reactivity of ENMs make them highly dynamic in environmental systems. The resulting transformations of the ENMs may affect their fate, transport, and toxic properties. This study aims to better understand the environmental risks of long term use of carbon composites and the influence of fillers on the extent of chemical photodegradation depending on the combination of polymers and fillers. The study will include information on the degradation of multi-walled carbon nanotube, carbon nanofiber-polyolefins, polyurethane and polyetherimid composites under artificial weathering conditions as pre-requisites for degradation and some changes in structure during long-term. It is of great importance to know the form of released nanomaterials if they are in matrix-bound form or individually dispersed particles. Various characterization techniques - spectroscopic, thermal and imaging methods – were used to determine changes in composite properties and forms of released ENM. The photooxidation of nanocomposites and the effects of different parameters, including irradiation dose, humidity, polymer properties, types of polymer and polymer compositions, and film thickness, on the amount and form of nanoparticles released from the polymer matrix were studied. The goal of this project is to develop a predictive model on the fate of nanocomposites in the environment.