Session: Undergraduate Research Posters: Analytical Chemistry:

As of 2017, 8.3 billion metric tons of plastic exist worldwide, and are therefore abundant in our natural environment. In order to understand the long-term impacts of plastic exposure in water and soil, this project aims to simulate the photooxidation of plastic in natural environments using UV-C light and flow systems of oxygen, water vapor, and ozone to generate gas-phase hydroxyl radicals. Analysis was performed using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Multiple spectra were collected in real time as hydrocarbon films were exposed to gas-phase hydroxyl radicals, and the reaction progress was monitored. To begin, plastic photooxidation was modeled with a thin film of squalene (0.7 μm thick), a branched C30 alkene selected as a benchmark system. The appearance of carbonyl signals between 1650 cm⁻¹ and 1850 cm⁻¹ validated our experimental set up as a proper modeling system for plastic photooxidation. When working with shorter chain alkanes, however, the hydrocarbon films required anchoring to the ATR crystal to prevent evaporation. Self-assembled monolayers (SAMs), a highly organized film of hydrocarbon molecules, is an ideal model for plastic photooxidation, assuming environmental degradation occurs on the outermost layer of a plastic object. Currently, efforts are underway to optimize the grafting and removal process of a C18 film on a germanium ATR crystal using chloro(dimethyl)octadecylsilane (CH₃(CH₂)₁₇Si(CH₃)₂Cl). Photooxidative degradation kinetics will be modeled to formulate mechanisms and dominant products for plastic degradation in the environment. Successful SAM assembly and photooxidation validates ATR-FTIR flow cell spectroscopy as a valuable tool in modeling polymer degradation. This project will inform the environmental community of the long term impact plastic degradation is having and will have on the natural world.

Jennifer Faust

Appearances