Towards the development of uniform closed cell nanocomposite foams using natural rubber containing pristine and organo-modified nanoclays

Abstract

A closed cell rubber foam, based on a natural rubber (NR)/nanoclay nanocomposite, was produced using a one-step foaming process with compression molding. The effects of three different nanoclays on the properties of the NR/nanoclay nanocomposite foam were examined: an un-modified nanoclay (Cloisite Na⁺) and two organo-modified nanoclays (Cloisite 20A and Cloisite 30B). We examined their curing behavior, foam morphology, sound absorption, and their mechanical and thermal properties. The morphological results from X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) showed that the Cloisite Na⁺ agglomerated in the NR matrix while an intercalated-exfoliated/fully-exfoliated morphology was seen in the Cloisite 30B and the Cloisite 20A, respectively. The rheometry results showed that all three nanoclay types increased the NR's curing rate, and also accelerated its scorch and curing time. Other results showed that the organo-modified nanoclays, which were the ammonium-salt modified nanoclays (Cloisite 30B and Cloisite 20A), improved the foam's curing behavior more than the pristine Cloisite Na⁺. Using the one-step foaming process kept the nanocomposite foam density and expansion ratio constant in all of the samples, independent of the nanoclay type. Meanwhile, the scanning electron microscopy (SEM) results showed that the nanoclay increased the cell density and decreased the cell size, depending on the nanoclay type. The mechanical properties of NR nanocomposite foams including the hardness and the modulus were improved by incorporating the nanoclays. At the same time, there was a gradual deterioration in the foams' sound absorption and thermal stability behavior.