Nylon-6 and Montmorillonite-Layered Silicate (MLS) Nanocomposites

Abstract

Reducing the high gas permeability of plastic packaging is of serious concern for a variety of applications in food packaging and microelectronics arena. In the development of high altitude scientific balloons, the potential for unmanned mission success is critically related to the improvement in helium barrier capability. Separately, the introduction of expandable smectite clays, such as montmorillonites, into polymers has resulted in improved barrier properties. Here we investigate the mechanical properties and helium permeability of dispersed montmorillonite-layered silicates (MLS) in nylon-6 nanocomposite films. A 20 wt% MLS in nylon-6 master batch was prepared in a twin-screw extruder and then mixed with nylon to produce nylon MLS nanocomposites with MLS content ranging from 1 to 5% for testing. The nylon nanocomposites were extruded into films. A highly exfoliated dispersion in different films was determined using X-ray diffraction. Nylon-6 nanocomposites showed formation of -crystalline form, which was absent in neat nylon-6. Differential Scanning Calorimetry (DSC) confirmed the crystallinity change and the role of MLS as an additional nucleation contributor. The glass transition and mechanical properties were related to the nucleation capabilities of MLS. Increase in the degree and type of crystallinity together with tortuous path development due to exfoliated dispersion were the primary reasons behind the improvement in gas barrier properties of exfoliated nylon-6 nanocomposites.