Nanoclay-modified polyisoprene latexes for reinforcing natural rubber thin films

Abstract

Nanoclay-modified polyisoprene latexes were prepared and then used as a reinforcing component in natural rubber (NR) thin films. The synthesizing efficiency of three emulsion polymerization techniques was first compared so that an adequate technique could be selected for further investigations. Results demonstrate that starve- fed emulsion (SFE) polymerization is the most appropriate synthesizing method compared to conventional and mini-emulsion techniques i.e. batch process. This is attributed to the SFE provides a smaller average polymer particle size which in turn results in a greater polymerization locus, promoting the reaction rate. The addition of organo-nanoclay during synthesizing polyisoprene significantly lessens polymerization efficiency because the nanoclay has a potential to suppress nucleation process of the reaction. It also intervenes stabilizing efficiency of the surfactant - SDS or sodium dodecyl sulfate, giving enlarged average sizes of the polymer particles suspended in the latexes. TEM images show that nanoclay particles are attached on and/or inserted in the polymer particles. XRD and thermal (DSC and TGA) analyses were employed to assess the d-spacing of nanoclay structure in NR nanocomposite films, respectively. Based on the overall results, 5 wt% of nanoclay relative to the monomer content utilized to alter polyisoprene during emulsion polymerization is an optimum amount since the silicate plates of nanoclay in the composite exhibit the largest d-spacing which maximizes the extent of immobilized polymer constituent, giving the highest mechanical properties to the films. The excessive amounts of nanoclay used, i.e. 7 and 10 wt% relative to the monomer content, reduce the reinforcing power due to re-agglomeration effect. Investigation of the influence of Clay-PIP contents on properties of NR thin films reveals that there are three crucial parameters affecting reinforcement mechanism of the composites: 1) nanoclay, 2) molecular characteristics of polyisoprene and 3) material heterogeneity. These influencing factors play a competitive role on reinforcement efficacy in the system. The best possible formulation for a NR thin film based on Clay- PIP as a reinforcing component is NR/Clay-PIP at 90/10 phr using the Clay-PIP containing 5 wt% of nanoclay relative to the monomer content.