Spectroscopic Studies on the Molecular Structural Changes of Plastics and Plasticizers at Model Environmental Interfaces.

Abstract

The mainstream introduction of plastics poly(vinyl chloride) (PVC) and poly(styrene) (PS) has been integral to the formation of modern urban infrastructures and the advancement of medical, electronic, and industrial technologies. Global annual production of phthalate-plasticized PVC and PS plastics exceeds tens of millions of tons. Thus, it is important to further understand how these plastics interact with surrounding matter at a molecular level in order to more accurately gauge their impacts on a wide variety of environments. This work develops new in situ and ex situ experimental platforms to study PVC, phthalate, and toxin molecules at air, water and silica interfaces with surface sensitive spectroscopic techniques sum frequency generation vibrational spectroscopy, x-ray photoelectron spectroscopy and secondary ion mass spectrometry. Studies on the molecular effects of heat and water contact on phthalate-plasticized PVC revealed that phthalates can exist on plastic surfaces even when small percentages of plasticizers are used, increased temperatures induce phthalate leaching in hours, and water contact induces permanent plastic surface restructuring and phthalate leaching. Leached phthalates transfer to new surfaces via water in minutes. The molecular mechanisms and effects of plasma and UV light treatments designed to reduce phthalate leaching and degrade phthalates, respectively, were determined. Air plasma treatment induces drastic surface-bound radical reactions with PVC including scission, chlorine removal, and minor crosslinking. UV light exposure, deemed a potentially efficient method of phthalate removal for disposed plastics, results in surface and bulk phthalate degradation and little PVC damage. Short wave UV/H2O2 treatments lead to competing radical reactions with PVC chains and increased molecular surface disorder. Long wave UV-based treatments induce very minor chemical reactions in and on phthalate-plasticized PVC. Lastly, studies on PS plastics interacting with gas-phase environmental toxins revealed that nonylphenols (NPs) deposit and order differently on PS plastics when the plastic is located above a calm water surface versus over land. NPs remain much more highly ordered on PS if originally deposited under humid conditions even after moving water and air exposure. Ultimately the information gained on the molecular behaviors of plastics aids in the future design and formulation of newer, more environmentally friendly plastics.