[Paper Review] Natural rubber-clay nanocomposites: mechanical and structural properties

Camila A. Rezende, Fábio C. Bragança+4 more|arXiv (Cornell University)|Jun 27, 2010

Polymer Nanocomposites and Properties3 citations

TL;DR

This study investigates non-vulcanized natural rubber-clay nanocomposites fabricated via latex-mixing, demonstrating that clay platelets significantly enhance mechanical properties through high aspect ratio exfoliation and rubber matrix immobilization. Removal of non-rubber impurities boosts clay's reinforcement efficiency, with strain-induced alignment of exfoliated platelets driving anisotropic scattering and superior performance even in the presence of tactoids.

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.

Motivation & Objective

• To evaluate the reinforcement efficiency of clay in non-vulcanized natural rubber nanocomposites.
• To investigate the impact of removing non-rubber molecules on clay's effectiveness as a reinforcement agent.
• To correlate mechanical performance with morphological features of clay, including exfoliation and tactoid formation.
• To understand the role of clay dispersion state and alignment under deformation in determining mechanical response.

Proposed method

• Preparation of nanocomposites via 'latex-mixing' using aqueous clay dispersions.
• Use of transmission electron microscopy (TEM) to characterize clay morphology and dispersion.
• Employment of small-angle neutron scattering (SANS) to probe nanoscale structure and alignment under deformation.
• Uniaxial deformation tests to assess mechanical properties under varying clay concentrations.
• Dialysis of natural rubber to remove non-rubber molecules prior to nanocomposite formation.
• Modeling mechanical enhancement based on high aspect ratio of exfoliated clay platelets and matrix immobilization.

Experimental results

Research questions

• RQ1 How does the removal of non-rubber molecules affect the reinforcement efficiency of clay in natural rubber?
• RQ2 To what extent do exfoliated clay platelets contribute to mechanical reinforcement compared to tactoids?
• RQ3 How does clay concentration influence strain-induced alignment and anisotropic scattering in the nanocomposite?
• RQ4 What is the role of matrix immobilization in enhancing mechanical performance of clay-reinforced natural rubber?
• RQ5 Can mechanical properties be effectively modeled using the high aspect ratio of exfoliated clay platelets?

Key findings

• Removal of non-rubber molecules significantly improves the reinforcement efficiency of clay in natural rubber.
• Nanocomposites exhibit a coexistence of fully exfoliated clay lamellae and tactoids, with exfoliated platelets driving mechanical enhancement.
• Exfoliated clay platelets with high aspect ratio contribute to superior mechanical properties through matrix immobilization.
• Strain-induced alignment of clay leads to anisotropic scattering, with increasing anisotropy at higher clay concentrations and greater deformation.
• The presence of tactoids does not compromise the overall reinforcement performance, as exfoliated platelets dominate mechanical response.
• Mechanical performance can be effectively modeled by considering the high aspect ratio of exfoliated platelets and their interaction with the immobilized rubber matrix.