E. Sahle-Demessie, C. Han, E. Varughese, H. Shi
U.S. Environmental Protection Agency,
United States
Keywords: nanocomposite, accelerated aging, nanorelease, toxicity study, Single particle ICP-MS
Summary:
In this study, epoxy and polypropylene filled with MWCNT were aged in an accelerated weathering chamber that simulates cycles of solar irradiation and rainfall. Aged plates were taken out at selected times to evaluate the effects of weathering. The changes in physicochemical properties modulated by sample thicknesses and the added MWCNTs during the weathering process were investigated. The results revealed that (1) surface oxidation increased in crystallinity causing the surface to become brittle during the weathering process. This loose of elasticity resulted in a craze and cracks formation and further degradation of the thinner samples. Oxidation penetrated selectively into the polymer structure. Cracks were reduced by the presence of CNT at high content; (2) composites containing CNT showed less loss of surface hardness, fewer cracks, and better hydrophobicity on weathered surface than other groups, confirming its functions of stabilization and antioxidation; (3) The 1775 cm−1/2879 cm−1 absorbance ratio of the FTIR plat surfaces increased steadily during ultraviolet degradation and was due to the increase in helical ordering which resulted from backbone scission during irradiation. (4) When the aged PP, and PP-MWCNT were placed in sonication water-bath fragments of polymer, CNT and metals were released. The release of nanomaterials from the composites was investigated with high-resolution transmission microscopy (HR-TEM), dynamic light scattering (DLS), and single particle-inductively coupled plasma (SP-ICP) analysis. The metal ions in released MWCNTs were quantified with a single particle-ICP analysis. (5) Lastly, the toxicity of released particles was investigated. The released polymer fragments and CNT did not show significant toxicity. Our combined results demonstrated the little toxicity of the released MWCNT-embedded polymer to A594 adenocarcinomic human alveolar basal epithelial cells. Epoxy composite show a significant amount of nickel in the wash water that has some toxicity. This study which will help with future risk based-formulations of exposure to engineered nanoparticles and it could provide very useful information to researchers and decision-makers in the field of environmental engineering for understanding weathering of polymers, nano released from polymer-nanomaterial composites, and their toxicity. This kind of model of photooxidation would be advantageously applied to other nanopolymer composites for which the absorbance behavior and other parameters are identified and their photochemical characteristics measurable with accuracy