Water barrier properties of polyamide 12/montmorillonite nanocomposite membranes: Structure and volume fraction effects

The water barrier properties of polyamide 12/organo-modified montmorillonite nanocomposites were studied by differential permeation. The water permeability and diffusivity were calculated from permeation kinetics and discussed with respect to the composite compositions. Depending on the clay volume fraction in the 0-5% range and the rotation speed during the composite processing, two different structures were obtained: a partially intercalated structure and a partially exfoliated structure, characterized by a higher level of exfoliation for the higher speed. In agreement with the tortuous path model, the water permeability and the diffusivity decrease with increasing clay volume fraction, ϕ, up to 2.5%, for both structures. However, beyond ϕ = 2.5% for partially intercalated nanocomposites and ϕ = 4% for partially exfoliated nanocomposites, the permeability no longer decreases, but increases. This effect was larger for the partially intercalated structure than for the partially exfoliated structure. The singular variations in the water permeation properties of nanocomposite membranes were interpreted in considering not only the structural properties, including the polymer crystallinity, but also various nanocomposite/permeant interactions, taking into account the plasticization phenomenon, solubility and free volume variations. It was possible to well simulate the permeation data by considering a water concentration dependent diffusion coefficient. Tensile measurements have shown the influence of the preparation conditions of nanocomposite membranes (clay volume fraction and the rotation speed) on the mechanical properties. As for permeation tests, the best performances were obtained with partially exfoliated nanocomposites compared to partially intercalated ones.