The influence of humidity on the protective performance of a membrane based on poly(vinyl alcohol)

Abstract

A solid-state NMR study has been used to rationalize the way humidity affects the barrier properties of a polyvinyl alcohol-based membrane. Polymer blends composed of polyvinyl alcohol–polyethyleneimine (PVOH–PEI) and polyvinyl alcohol–polydiallyldimethyl ammonium chloride (PVOH–PDADMAC) were investigated. At 90% relative humidity the PVOH–PEI material retains a PVOH-rich component that is detected in a cross-polarization NMR experiment and is therefore assumed to be relatively immobile. The barrier properties of this material are also largely retained at this relative humidity. Under the same conditions of humidity no signal is detected in the cross-polarization NMR experiment for the PVOH–PDADMAC system and the barrier properties of the PVOH–PDADMAC system are compromised. The persistence of the more rigid domains in the PVOH–PEI material is used to explain the barrier properties of this blend at high relative humidity. For the PVOH–PDADMAC system the cross-polarization signal is recovered and the barrier properties of the blend are restored to their original level as the humidity is lowered.