Facile exfoliation method for improving interfacial compatibility in montmorillonite-natural rubber nanocomposites: A novel charge inversion approach

Abstract

Montmorillonite (Mt) is a widely researched nano-filler in rubber compounds. Although, many methods have been reported to disperse Mt at nanoscale, up-to-date obtaining highest interfacial properties between the rubber matrix and the inorganic filler remains a challenge due to the lack of suitable preparation method to make stable dispersions of Mt. This study reports a novel, scalable and simple method to reinforce natural rubber (NR) with Mt achieving the highest degree of exfoliation and subsequently, offering high surface area for interactions between the filler and the rubber matrix. Stable cationic latex of NR was prepared by a charge inversion approach where NR latex was first treated with a quaternary ammonium surface active substance, n-hexadecyltrimethylammonium bromide (CTAB). Cationic NR latex thus prepared was directly coagulated using Mt aqueous dispersion as the coagulant. This coagulation approach facilitated the in-situ formation of a Mt-NR nanocomposite containing exfoliated and intercalated clay mineral platelets. Interfacial and stress-stain behavior of the un-vulcanized nanocomposite were further studied and compared with those of a nanocomposite prepared by the conventional latex compounding method (LCM). The results of powder X-ray diffraction (PXRD) and transmission electron microscopic (TEM) imaging of Mt-NR nanocomposite prepared via this process, confirmed that Mt platelets are exfoliated with in the rubber matrix. Further studies carried out using Mooney viscosity and green strength measurements proved that the interfacial interaction between the cationic latex and Mt was significantly improved compared to those of the nanocomposites prepared via latex compounding method.