Free Volume and the Mechanism of Plasticization in Water-Swollen Poly(vinyl alcohol)

Abstract

Poly(vinyl alcohol), PVOH, films have been studied as a function of water content. The states of water present in the polymer (bound or free) have been characterized and are a function of water content. The effects of water content (and hence state) on the free volume, chain mobility, and glass transition (T g) behavior have been studied by positron annihilation lifetime spectroscopy, 13C solid state nuclear magnetic resonance, and dynamic mechanical analysis. The addition of approximately 30 wt % water results in a marked increase in free volume cavity size and polymer chain mobility and a corresponding decrease in T g. The water is in a molecular, nonfreezable state for water additions up to approximately 30 wt %, hence it is postulated that nonfreezing water is responsible for the majority of the plasticization in this system. The plasticization is attributed to the increasing free volume and lubrication provided as the water swells the polymer and disrupts polymer−polymer hydrogen bonding. A limited equivalence between the action of water on the polymer and the action of temperature (thermal energy) is proposed.

Compositional dependence of free volume in PAN/LiCF3SO3 polymer-in-salt electrolytes and the effect on ionic conductivity

“…The enormous increase in 3 from 1.4 ns to 2.1 ns on uptake of 6 wt % water is similar to that observed when dry PVOH (T g ϭ 86°C) is plasticized with 28 wt % water (T g ϭ Ϫ28°C). 25 The other notable feature of these diagrams is the complete reversibility obtained after drying the "wet" sample at 40°C under vacuum. Clearly the absorption and desorption of water do not appear to change the PALS free volume characteristics of the sample.…”

Molecular modelling of oxygen and water permeation in polyethylene

“…Experimental studies provide valuable understanding of the macroscopic [4][5][6][7][8][9] and microscopic [10,11] properties of polymers and their transport properties. Michaels and co-workers [4,5] found that there is a slight increase in the solubility of oxygen in polyethylene between 285 and 315 K, and that a further increase in temperature results in a far larger solubility.…”

PVA / Montmorillonite Nanocomposites: Development and Properties

“…I n p u r e P V A , t h e h y d r o g e n bonds are the dominant interaction responsible for both structure and molecular dynamics. As a consequence of these bonding interactions, water is capable to destroy inter-and intra-chain hydroxyl bonds, affecting PVA's crystalline regions and acting as a plasticizer, increasing the free-volume of the amorphous phase (Hodge et al 1996). On the other hand, in PVA/MMT nanocomposites, the interactions of the surface of the clay with the polymer can be attributed to the formation of hydrogen bonds between the PVA hydroxyl groups and the negatively charged clay surface (Grunlan et al, 2004), (Hernández et al, 2008).…”