Water Sorption in Glassy Polyvinylpyrrolidone-Based Polymers.

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Polyvinylpyrrolidone (PVP)-based polymers are crucial stabilizers in food supplements and pharmaceuticals.
• These polymers exhibit high hygroscopicity, impacting their performance and stability.
• Understanding water sorption is essential for optimizing their application.

Purpose of the Study:

• To measure and model water-sorption isotherms and kinetics in PVP and PVP-co-vinyl acetate (PVPVA) films.
• To investigate the distinct sorption behaviors in glassy and rubbery polymer states.
• To develop accurate predictive models for water diffusion in these polymers.

Main Methods:

• Experimental measurement of water sorption isotherms at 25 °C across a relative humidity (RH) range of 0 to 0.9.
• Modeling of water sorption using perturbed-chain statistical associating fluid theory (PC-SAFT) for rubbery states.
• Integration of non-equilibrium thermodynamics of glassy polymers (NET-GP) with PC-SAFT for glassy states.

Main Results:

• Combined NET-GP and PC-SAFT modeling demonstrated excellent agreement with experimental water-sorption data.
• Transitions between modeling approaches correlated well with the glass transition of polymer-water systems.
• Fickian water diffusion coefficients were determined, showing non-monotonous concentration dependency.

Conclusions:

• The combined NET-GP and PC-SAFT model accurately describes water sorption in both glassy and rubbery states of PVP and PVPVA films.
• Water diffusion coefficients can be predicted using free-volume theory coupled with PC-SAFT and NET-GP.
• This study provides valuable insights for the formulation and stability of PVP-based materials in humid environments.