Correlation between rheological, mechanical, and barrier properties in new copolyamide-based nanocomposite films

This work focuses on the possibility of improving performance properties of polyamide-layered silicate nanocomposite films for packaging applications by using, as alternative matrix, a statistical copolymer of the nylon-6 having a partially aromatic structure. Nanocomposites at different silicate loadings ( commercial organo-modified montmorillonite) were produced by cast-film extrusion using three polyamide matrices: nylon-6 and two copolyamides with similar chemical structure but different molecular weights. Oxygen barrier and mechanical properties of the produced films were investigated and correlated to their nanostructure through analytical techniques sensitive to different aspects of the same morphology, such as TEM, rheological, and dynamic-mechanical analyses. Permeability data were interpolated on the basis of different theoretical approaches, from which a quantitative indication on exfoliation and orientation levels of silicate layers in the matrices was obtained. TEM images at different magnifications were used to empirically evaluate the average length-thickness ratio of silicate platelets and to verify the correspondence with aspect ratios and order parameters calculated by data fitting. A strong correlation between nanomorphology and properties was observed in the different nanocomposite systems and all the three matrices exhibited performance improvement with increasing the silicate content. Nanocomposite films based on the copolyamide with higher molecular weight displayed more exfoliated regions and a preferential orientation of silicate layers, leading to the most significant oxygen barrier improvements and the best mechanical properties.