High gas barrier properties of poly(vinyl alcohol) nanocomposite films with various equibiaxial stretching ratios

Abstract

The enhancement of barrier properties in composites depends on several factors such as the quantity, length, and width of the clay particles, as well as their orientation and dispersion. Numerous studies have shown that the aspect ratio of exfoliated clay particles plays a critical role in controlling the microstructure of polymer-clay nanocomposites and their gas barrier performance. Although polymer-clay nanocomposites have displayed enhanced gas barrier properties relative to conventional composite systems, the dependence of these properties on factors such as the extent of clay aggregation and dispersion is not well understood. There are many types of clays, including kaolinite, montmorillonite, hectorite, saponite, synthetic mica, and so on. Among these, saponite (SPT) consists of stacked silicate layers with lengths of about 160-170 nm. The thickness of these layers is the same, i.e., 1 nm. SPT has a high swelling capacity, which is essential for efficient intercalation of a polymer, and its stacked silicate layers provide good thermal, tensile, and molecular barrier properties, as do its hybrid polymer-containing materials. SPT has been used widely as a reinforcing filler in polymeric matrices because of its excellent mechanical, electrical, and thermal properties, and its low price. Poly(vinyl alcohol) (PVA) is a water-soluble polymer that is extensively used in paper coatings, textile sizing, and the production of flexible water-soluble packaging film. Such applications have stimulated interest in improving the mechanical, thermal, and permeability properties of thin nanocomposite films while retaining the optical clarity of PVA. PVA nanocomposite materials may offer a viable alternative to heat-treated or conventionally filled PVA materials in commercial applications. In our previous study, the variations in the dispersion, morphology, and gas permeability of nanocomposites with clay contents in the range 0 to 10 wt% were examined. For clay loadings up to 5 wt%, the clay particles were found to be highly dispersed in the PVA matrix without agglomeration of the particles. However, some agglomerated structures formed in the polymer matrix above 7 wt% SPT. In this paper, we report the optical transparency and the oxygen transmittance rate (O2TR) in PVA hybrid films containing 5 wt% SPT. The resulting optical transparencies and gas barrier properties are discussed in terms of the relative equibiaxial stretching ratios (150% to 300%) in the PVA hybrid films.