Morphological characterization and effect of diatomaceous earth on the cure characteristics and tensile properties of natural rubber vulcanizates

Abstract

This study aims to discover the fundamental morphological properties of Diatomaceous Earth (DE) and its impact on the curing characteristics and primary tensile properties of natural rubber vulcanizates to substitute commercial silica. The methodology involved detailed characterization of DE and commercial silica using Scanning Electron Microscopy (SEM), Dynamic Light Scattering (DLS), X-ray Diffraction (XRD), X-ray Fluorescence Spectroscopy (XRF), and Fourier-Transform Infrared Spectroscopy (FTIR). Rubber composites were formulated using 55 parts per hundred parts of rubber (phr) of DE and silica, incorporating DE in proportions of 25%, 50%, and 75% of filler by weight. Cure properties were determined using a Moving Die Rheometer (MDR) at 150 °C, and ultimate tensile strength was assessed with a Universal Testing Machine. The findings revealed that the 100% DE-filled composite demonstrated poor curing characteristics, evident from its low cure rate index and reduced cross-link density. Composites containing 25% DE blended with silica exhibited superior ultimate tensile strength compared with those containing only silica as a filler, attributed to the advantageous synergistic effect arising from particle size and the enhanced surface area of DE. Nonetheless, loadings exceeding 25% of DE resulted in diminished tensile properties due to low density of the DE filler. These discoveries may facilitate the implementation of DE as a bio-based material in polymer composites.