Copolyamide based nanocomposite films as innovative solution of packaging materials.

Polymer layered silicate nanocomposites represent nowadays a very interesting opportunity to enhance the properties of unmodified resin and produce high-performances plastics. With the adding of very low silicate contents, generally less than 6ww%, not only structural properties but also functional properties are strongly improved [1,2]. It is well known that the final properties are strictly correlate with the nanoscale arrangement of the silicate layers inside the polymer matrix as well as the entity of polymer-clay interactions. In particular, the exfoliation of the silicate inside the polymer matrix is the key for obtaining the highest performance improvements. The field of packaging is one for which the application of nanocomposites is highly attractive, and improvements in mechanical and gas barrier properties could allow such materials to be employed as innovative solutions to satisfy the demanding requirements that a modern-day package must fulfill, such as protection, mechanical and thermal resistance, low cost, recycling, etc. This, coupled with the potential to process such materials with the conventional processing equipments, such as extrusion, can lead to a net improved performance/cost ratio. In this frame, great industrial and scientific attention is paid to polyamide-based nanocomposites prepared by melt compounding either because polyamides are inexpensive, available and widely used in packaging applications either because their hydrophilic nature is the base for a good compatibility with the silicate [3-4]. Nevertheless, the difficulty in conveniently tuning materials and processing parameters to control the developed nanomorphology (clay dispersion, exfoliation and orientation degrees, matrix crystallinity) represents a great limit for the application of polyamide based nanocomposites on industrial scale. This work focuses on the possibility to improve performance properties of polyamide layered silicate nanocomposite films 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 nylon 6 and copolyamide matrices. Oxygen barrier and mechanical properties were investigated on the nanocomposite films and correlated to their morphology through transmission electron microscopy (TEM), rheological analyses and theoretical models. The properties of copolyamide based films were compared to nylon 6 based ones in order to examine the effect of polymer molecular structure on the extent of silicate exfoliation and to establish the relationship between nanomorphology and properties, crucial in predicting and optimizing the end performances.