A novel approach in blending natural rubber latex with siliceous earth nanoparticles

Siliceous earth (SE), a kind of volcanic ash, was formed more than 100 million years ago with a special crystal structure and morphology. In this work, SE was first used as filler to blend with natural rubber (NR) latex, and then an improved process was employed to build up a kind of sacrificial bond to prepare NR composites with SE loadings 0–10 per hundred rubber (phr). X-ray diffractometry, Fourier-transform infrared spectroscopy and scanning electron microscopy were employed to determine the structure and morphologies of NR composite films. Furthermore, to investigate the effect of SE loading on mechanical properties of films, tear and tensile tests were applied. The NR latex, reinforced with 2–10 phr SE nanoparticles, showed 14.9–38.1% improvement in tensile strength and 109.2–345.3% improvement in 500% modulus when compared to pure NR film. The tensile strength and tear strength of NR composite films reached 34 MPa and 55 N/mm, respectively, when 6 phr SE was added. The results of thermogravimetric analysis indicated that thermal decomposition temperature of the NR composite films increased with increase in SE loading. The results of Mooney–Rivlin equation and Lorenze–Park equation showed that stronger filler/rubber interfacial interactions exist between SE particles and NR molecular chains. The improvement of NR properties was resulted from good filler–polymer interactions and uniformly dispersed SE particles.