Molecular Structural Changes of Plasticized PVC after UV Light Exposure

Abstract

Plasticized poly(vinyl chloride) (PVC) materials for industrial, medical, and household use are often intentionally exposed to UV light, though its impact on the molecular integrity and toxicity of the surface and bulk of PVC materials is still not well understood. This paper investigates the surface and bulk molecular changes of plasticized PVC films with 25, 10, or 0 wt % bis-2-ethylhexyl phthalate (DEHP) plasticizer after exposure to short wave (254 nm) or long wave (365 nm) UV light. Surface analytical techniques including sum frequency generation vibrational spectroscopy (SFG) revealed short wave UV exposure induced major molecular changes on the plasticized PVC surfaces, resulting in increased surface hydrophilicity and decreased CH3 content with increasing exposure time. Additionally, it was deduced from multiple techniques that the surface and the bulk of the plastic exposed to short wave UV contained phthalic monoesters and phthalic acid formed from multistep radical reactions. In contrast, when exposed to long wave UV, molecular content and ordering on the surfaces of the plastic remained relatively unchanged and the introduction of DEHP in plastic helped protect PVC chains from degradation. Results from this study demonstrate short wave UV exposure will result in plastic surfaces containing phthalates and phthalate-related products accessible to contact by living organisms.