Molecular surface structural changes of plasticized PVC materials after plasma treatment

Area of Science:

• Polymer Science
• Materials Science
• Surface Chemistry

Background:

• Poly(vinyl chloride) (PVC) is widely used but often plasticized to improve flexibility.
• Phthalate esters are common plasticizers, but their migration and long-term stability are concerns.
• Understanding plasticizer behavior at the molecular level is crucial for material performance and safety.

Purpose of the Study:

• To investigate the molecular-level surface and bulk behavior of PVC plasticized with diethyl phthalate (DEP) and dibutyl phthalate (DBP).
• To evaluate the effects of oxygen and argon plasma treatments on plasticizer migration and PVC surface chemistry.
• To assess the stability and potential risks associated with DEP and DBP in PVC formulations.

Main Methods:

• Sum frequency generation vibrational spectroscopy (SFG) to analyze surface molecular structure.
• Coherent anti-Stokes Raman spectroscopy (CARS) for bulk and surface molecular analysis.
• X-ray photoelectron spectroscopy (XPS) to determine surface elemental composition and chemical states.

Main Results:

• Higher plasticizer concentrations led to increased surface segregation of DEP and DBP.
• DEP plasticized PVC showed instability, with DEP leaching under vacuum, unlike the more stable PVC/DBP system.
• Oxygen plasma treatment enhanced PVC/DBP stability and altered surface chemistry (increased C=O/C-O, decreased C-Cl).
• Argon plasma treatment induced surface bond breaking, cross-linking, and chain scission.

Conclusions:

• DEP poses a potential risk due to its tendency to leach from PVC.
• DBP exhibits greater stability in PVC, and oxygen plasma treatment can further enhance this.
• Plasma treatments significantly modify the surface chemistry and stability of plasticized PVC films.