CHARACTERIZING DEGRADATION OF NANO-ENABLED MATERIALS AND ENGINEERED NANOMATERIAL RELEASE FOLLOWING NATURAL AND ARTIFICIAL WEATHERING

engineered nanomaterial;degradation;Chemistry

Lankone, Ronald SkyeFairbrother, DavidH ;

Johns Hopkins University

关键词: engineered nanomaterial;    degradation;    Chemistry;   

Others  :  https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/61115/LANKONE-DISSERTATION-2018.pdf?sequence=1&isAllowed=n

瑞士|英语

来源: JOHNS HOPKINS DSpace Repository

【 摘 要 】

Engineered nanocomposite materials are increasingly utilized in consumer products. Nanocomposite degradation is inevitable and therefore must be studied as degradation is likely to cause nanomaterial release, resulting in nanomaterial exposure to humans and the environment. To address existing knowledge gaps, a two-tiered investigative strategy that characterized both nanocomposite degradation and resulting nanomaterial release following either accelerated or natural weathering is described herein. To that end, this body of work had two primary focuses: a) Determine how the initial nanoparticle content within a polymer nanocomposite impacted said nanocomposite’s photodegradation following accelerated weathering; b) Identify the impact of local climate in driving nanomaterial release from a nano-enabled consumer product following natural weathering. Overall, data from these studies described the interplay of nanoparticle, composite matrix, and weathering conditions in regulating nanocomposite degradation and subsequent nanomaterial release. This information is crucial in the development of adequate and accurate risk assessments of products and materials composed of nanocomposites.The first investigative strategy focused on the lab-based accelerated weathering and photodegradation of carbon nanotube polymer nanocomposites (CNT-PNCs) with a span of initial CNT concentrations (0 – 5% w/w). A point of emphasis in this study was the extensive characterization of the CNT-PNCs surface throughout the photodegradation process. Data obtained details the CNT-PNCs’ changing surface chemical composition, molecular structure, and morphology as a function of photodegradation. In addition to characterizing CNT-PNCs as they photodegraded, single particle inductively coupled plasma mass spectrometry was used to simultaneously quantify the concentration and characterize the form (individual CNTs vs. aggregates of CNTs embedded in polymer fragments) of released CNTs. Combined, characterization data of both the CNT-PNC and released material served as the foundation for developing mechanistic insight that described how increasing concentrations of CNTs within CNT-PNCs mitigated the rate and magnitude of polymer nanocomposite photodegradation.The second investigative strategy required the installation and coordination of outdoor weathering stations in five distinct locations across the continental United States with the explicit goal of measuring both nanomaterial release and local weather conditions at each location. Lab prepared carbon nanotube and silver nanoparticle polymer nanocomposites (CNT-PNCs & Ag-PNCs) were weathered during the first phase of this study and commercially available pressure treated lumber (containing copper nanoparticles) was weathered during the second phase. Throughout the study, all samples were secured in custom designed outdoor sample holders and set out to weather and release naturally. Nanomaterial release in the accumulated rain runoff was collected monthly and quantified with inductively coupled plasma mass spectrometry or inductively couple plasma optical emission spectrometry. The total nanomaterial release measured was analyzed in tandem with site specific weather data to determine which climate factors are most important in regulating nanomaterial release in the natural environment. Additionally, information from these studies was used to inform more accurate life cycle assessment models. At the conclusion of phase one of this study, it was found that after a year of weathering, polymer nanocomposites released less than 5% of their originally embedded nanoparticulate mass, irrespective of climate conditions. Following the conclusion of phase two, it was determined that the most important factor in regulating copper release from pressure treated lumber is rainfall. It was also found, however, that drier climates led to wood cracking, which in turn led to sustained and increased copper release into the second year of weathering