Naturally abundant silica-kaolinite mixed minerals as an outstanding reinforcing filler for the advancement of natural rubber composites

This study was undertaken to explore the reinforcing abilities of a bis 3-(triethoxysilyl) propyl tetrasulfide (TESPT) functionalized silica-kaolinite mineral (FSKM) in natural rubber composite formulations. Curing, mechanical, and aging resistance measurements showed that FSKM had strong reinforcing abilities. For example, FSKM-filled rubber composite having 70 phr (grams per hundred grams of rubber) of filler content achieved a 589% higher M300 (modulus at 300% elongation) value than unfilled rubber. The higher tensile strengths and shorter elongation at break values observed indicated that filler particles effectively bound to and restricted the movements of rubber chains. In most cases, the use of FSKM resulted in better physical properties than a conventional precipitated silica-filled rubber composite. Aging resistance properties were also found to be excellent for FSKM filled vulcanized rubber up to a filler loading of 60 phr. Improvements in the mechanical and aging resistance properties of natural rubber containing FSKM were considered to be due to excellent filler-polymer interactions and improved filler dispersions.