Layered silicate‐polyamide‐6 nanocomposites: Influence of silicate species on morphology and properties

The effect of two different species of layered silicates on the morphology, mechanical properties, and methanol vapor barrier properties of polyamide‐6 (PA6) nanocomposites was examined using identical experimental conditions for both species. The layered silicate species used were natural montmorillonite (MMT) and synthetic expandable fluoro‐mica (FM), the chemical compositions of which were Na_0.43(Al_1.56Mg_0.31Fe²⁺ _0.09)(Si_3.95Al_0.05)O₁₀(OH)₂ and Na_0.66Mg_2.68(Si_3.98Al_0.02)O₁₀F₂, respectively. The layered silicates were modified with a dodecylammonium salt (DDA) using an ion‐exchange method. The resulting organically modified layered silicates were melt‐kneaded with PA6 in a twin‐screw kneader at 260 °C. By quantitative analysis of the silicate layers dispersed in the PA6, the number‐average aspect ratio was estimated to be 76 for DDAMMT‐PA6 and 85 for DDAFM‐PA6. This confirmed that the primary particle size of the initial silicate did affect the aspect ratio. The rigidity and gas barrier properties of the nanocomposites appeared to depend upon the morphology of the nanocomposite. On the other hand, the elongation at break of the nanocomposites decreased as the amount of silicate increased. This reduction in ductility was ascribed to the difference in morphology of the nanocomposites, that is, distribution of silicate nanolayers in the polymer matrix. The homogeneity of the particle fraction of exfoliated nanolayers was clearly an important factor affecting the properties of the nanocomposites. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 583–595, 2009