Natural rubber-clay nanocomposites: mechanical and structural properties

TL;DR

This study investigates how clay nanocomposites enhance the mechanical properties of natural rubber, emphasizing the role of exfoliated clay lamellae and the effects of removing auto-reinforcing molecules.

Contribution

It demonstrates that removing auto-reinforcing molecules improves clay reinforcement efficiency and characterizes the morphology and mechanical behavior of natural rubber-clay nanocomposites.

Findings

Exfoliated clay lamellae significantly reinforce rubber.

Tactoids coexist with exfoliated lamellae without reducing reinforcement.

Clay alignment under strain shows increased anisotropy with higher clay content.

Abstract

The mechanical properties of non-vulcanized natural rubber and dialyzed natural rubber-clay nanocomposites have been studied by uniaxial deformations to evaluate the reinforcement efficiency of the clay. We show that while non-rubber molecules contribute to auto-reinforcement, removal of these molecules improves significantly the performance of clay as reinforcement agent. These mechanical properties are discussed in relation to morphological aspects of the clay characterized by TEM and SANS. The nanocomposites prepared by "latex-mixing" with aqueous dispersions of clay are found to contain completely exfoliated clay lamellae in coexistence with tactoids. Improved mechanical properties of the nanocomposites can be modeled by the high aspect ratio of exfoliated clay platelets coupled with immobilized rubber matrix. Interestingly, presence of tactoids does not appear to compromise the excellent reinforcement properties of the exfoliated platelets. At high deformations, strain-induced alignment of the clay exhibits anisotropic scattering, with anisotropy increasing with clay concentration and stretching.