Electrically conductive nanocomposites produced by in situ polymerization of pyrrole in a natural rubber latex medium

Authors: SANTIM, RICARDO HILDAGO - Universidade Estadual Paulista (UNESP); SANCHEZ, ALEX OTAVIO - Universidade Estadual Paulista (UNESP); DA SILVA, MICHAEL JONAS - Universidade Estadual Paulista (UNESP); McMahan, Colleen; MALMONGE, JOSE ANTONIO - Universidade Estadual Paulista (UNESP)

Submitted to: Polymer Composites
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2022
Publication Date: 3/22/2022
Citation: Santim, R., Sanchez, A., da Silva, M., McMahan, C.M., Malmonge, J. 2022. Electrically conductive nanocomposites produced by in situ polymerization of pyrrole in a natural rubber latex medium. Polymer Composites. 43(5):2972-2979. https://doi.org/10.1002/pc.26591.
DOI: https://doi.org/10.1002/pc.26591

Interpretive Summary: The purpose of this study was to identify solutions to a growing need for flexible elastic materials that provide sufficient conductivity for wearables, electronics, and military applications. Polymerization of pyrrole (Py) in a natural rubber latex medium can be used to create electrically conductive PPy/NR composites. The poly(pyrrole) in the composite provides electrical conductivity, while the natural rubber provides soft, flexible, elastic properties needed in many applications. Usually, the natural rubber is used as purchased. But pre-vulcanized natural rubber latex can be made by addition of appropriate chemistry. In this work, for the first time, nanocomposites of natural rubber/polypyrrole were produced by the polymerization of Py into the pre-vulcanized natural rubber latex at different NR/Py monomer ratios. All composites were made in a green, solvent-free process. The result was electrically conductive soft, flexible materials with unique structures at the molecular level.

Technical Abstract: Flexible conductive polymeric nanocomposites were produced by in situ polymerization of polypyrrole (PPy) in a natural rubber (NR) latex medium. Pre-vulcanized and non-pre-vulcanized natural rubber latex, with varying NR/pyrrole (Py) monomer ratio was studied. The resulting nanocomposites were characterized by scanning electron microscopy (SEM), Fourier Transform Infrared spectroscopy (FTIR), dc electrical conductivity and mechanical properties. The electrical conductivity increased as the NR/Py ratio decreased reaching a maximum of 1.0 x 10-2 S/cm for a vulcanized nanocomposite with NR/PY = 4 mass ratio. In terms of mechanical properties, it was observed that tensile strength at break also increased with decreasing of NR/Py mass ratio, and for the same proportion of Py, the nanocomposites obtained from vulcanized latex presented higher strength. SEM analysis revealed that unlike non-pre-vulcanized latex, PPY nanoparticles tend to be distributed in the pre-vulcanized matrix in circumferential patterns, with an average diameter of 1 micron, indicating that the rubber microparticles have been encapsulated by the conductive polymer. This engineered morphological structure has been shown to significantly influence the final properties of the nanocomposites, compared to those prepared from non-vulcanized latex, changing not only the distribution of PPy in the matrix, but also changing the coalescence behavior of natural rubber particles, as well as influencing the percolation threshold.