Layered silicates (sodium montmorillonite) based elastomer nanocomposites

Abstract

Two novel techniques known as freeze-drying and electrolytic admicellar polymerization were herein conducted for fabricating the natural rubber (NR)-based composites. These approaches were considered to be ideal for creating various types of NR-based materials that stood out as good candidates for a wide variety of applications ranging from thermal insulation till actuator or sensor. By utilizing a freeze-drying, the granular appearance of pristine clay (sodium montmorillonite, Na+- MMT) was converted into a monolith ‘house of cards’ structure with a bulk density of typically 0.05 g cm'3. This was originated from the parallel alignment of clay bundles along the ice crystal through electrostatic interactions between edge and face (EF) of clay particles. As the neat clay aerogel was relatively fragile, natural rubber (NR) latex was then introduced, followed by the cross-linking process to increase the materials structural integrity without harming the bulk density and microstructure. This reinforcement was illustrated by a good connectivity between each single sheet through a web of the NR matrix, thus promoting the load transfer under the applied stress. Further, to enable the production of semiconducting materials based on NR and Na+-MMT, polypyrrole (PPy) was introduced and served as a path for an effective charge transportation (electron hopping). This was accomplished by conducting an electrolytic admicellar polymerization of the corresponding aqueous solution. It was seen that the morphological characteristics as well as mass fractions of both PPy and Na+-MMT were crucial in determining the composites electrical conductivity, mechanical, and thermal performances.