Plasticizer-level study of poly(vinyl chloride) ion-selective membranes

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Science

Background:

• Poly(vinyl chloride) (PVC) membranes plasticized with 200 phr are used in ion-selective electrodes (ISEs).
• Previous research identified an optimal plasticizer ratio (phr(exp)/phrmin) of 2.0 for membrane mechanical properties.

Purpose of the Study:

• To determine if the previously found optimal plasticizer ratio (phr(exp)/phrmin = 2.0) is necessary or sufficient for ISE function.
• To investigate the effect of different plasticizers on the mechanical and ion-selective properties of PVC membranes.

Main Methods:

• Dynamic mechanical analysis (DMA) was employed to study the mechanical properties of PVC membranes with five different plasticizers (DOS, PGDO, o-NPOE, ESO, ELO) across a range of temperatures and frequencies.
• Electromotive-force (EMF) measurements were conducted on membranes plasticized with o-NPOE at varying phr(exp)/phrmin ratios.
• The glass transition temperature (Tg) of PVC membranes was measured under different conditions.

Main Results:

• The addition of 200 phr of plasticizers significantly depressed the glass transition temperature of PVC.
• A 'transition window' for ion-selectivity was observed between phr(exp)/phrmin ratios of 2.0 and 3.3 for o-NPOE plasticized membranes.
• Optimal phr(exp)/phrmin ratios were determined for each plasticizer, ranging from 0.8 (ESO, ELO) to 3.0 (o-NPOE).

Conclusions:

• The optimal plasticizer ratio for PVC-based ISE membranes is plasticizer-dependent and not universally 2.0.
• A specific range of plasticizer ratios (2.0-3.3) is crucial for transitioning from polymer films to predictable ion-selective membranes.
• The findings provide optimized plasticizer ratios for various plasticizers, crucial for designing high-performance ISEs.