Molecular structural changes of plasticized PVC after UV light exposure

Area of Science:

• Polymer Science
• Materials Chemistry
• Photochemistry

Background:

• Plasticized poly(vinyl chloride) (PVC) is widely used but its UV degradation is poorly understood.
• UV exposure impacts molecular integrity and toxicity of PVC surfaces and bulk materials.
• The role of plasticizers like bis-2-ethylhexyl phthalate (DEHP) in UV stability requires investigation.

Purpose of the Study:

• To investigate the surface and bulk molecular changes in plasticized PVC films under UV light.
• To compare the effects of short wave (254 nm) versus long wave (365 nm) UV exposure.
• To determine the influence of DEHP concentration on PVC degradation.

Main Methods:

• Exposure of plasticized PVC films (0, 10, 25 wt% DEHP) to short and long wave UV light.
• Surface analysis using sum frequency generation vibrational spectroscopy (SFG).
• Multiple techniques to analyze surface and bulk chemical composition.

Main Results:

• Short wave UV induced significant surface changes: increased hydrophilicity and decreased CH3 content.
• Phthalic monoesters and phthalic acid were detected on surfaces and in the bulk after short wave UV exposure.
• Long wave UV caused minimal surface changes; DEHP protected PVC chains from degradation.

Conclusions:

• Short wave UV light initiates radical reactions leading to phthalate degradation products on PVC surfaces.
• These degradation products are accessible to living organisms upon contact.
• DEHP acts as a protective agent against PVC degradation under long wave UV light.