Ultrafine calcium carbonate-filled natural rubber latex film: mechanical and post-processing properties

This study aims to improve the dispersion of treated calcium carbonate (CaCO3) in natural rubber latex (NRL) films. Ball mill and ultrasonic methods were used to break down the particle size of CaCO3, and the combined effect of ball mill/ultrasonic and ultrasonic/ball mill methods with their optimum processing times was applied to re-agglomerate and further break down the particle size of CaCO3. The particle size and dispersibility of treated CaCO3 were characterized by particle-size analysis, transmission electron microscopy (TEM), and Zeta-potential measurement. The particle-size analysis and TEM results revealed that the particle size of CaCO3 reduced down to 1.4 µm with less agglomeration using ultrasonic for 120 min and ball mill for 72 h. Zeta--potential measurement also indicated that the ultrafine-treated CaCO3 with a broad particle-size distribution was compatible with NRL particles. The treated CaCO3 loadings from 5 to 20 phr were filled in the NRL compounds. NRL/CaCO3compounds showed decrease in viscosity and cross-link density, but increase in swelling index. It was found that tensile strength, modulus at 100% elongation, elongation-at-break, swelling index, and cross-link density of the films were improved with addition of 10 phr of CaCO3. At 20 phr of filler loading, the increment rate of tensile strength of NRL/CaCO3 films was 44% after leaching, and their retention percentage was 62% after heat aging. Therefore, ultrafine CaCO3-incorporated NRL can withstand under accelerated heat-aging condition.