Silica extracted from rice husk (silica nanoparticles, Si-NP RHA) has great potential for industrial use, particularly as filler in the rubber industry. However, silica is poorly dispersed in the matrix and needs to be modified by a silane linking agent (bis-(3-triethoxysilylpropyl) tetrasulfane (TESPT)) to improve its mixing properties. As a result, a large amount of used solvent containing silane TESPT is produced. This study aimed to evaluate the surface modification of silica nanoparticles from rice husk employing this used solvent and to characterize the particles’ physical properties. Silica nanoparticles were extracted from rice husk using a sol-gel method. FTIR spectography demonstrated that the TESPT on fresh solvent and the used solvent were successfully grafted onto the surface of Si-NP RHA. Si-NP RHA modified by Two Step Modification (TSM) employing used solvent had strong absorption peaks at wave numbers of 2927.94 cm-1 and 1446.61 cm-1, which are associated with vibration of the ‑CH2 group and deforming vibration of the -C-H group in TESPT compounds. Likewise, Si-NP RHA modified with One Step Modification (OSM), either using fresh solvent or the used solvent, exhibited absorption peaks at wave numbers 2935.66 cm-1 and 1404.18 cm-1. The result showed that the used solvent still effectively modified the silica nanoparticle surface.

Biosilica from rice husks has a potential that can be used as a reinforcing filler in the production of rubber finished goods displace mine silica. But it’s difficult to disperse homogenetically into a rubber finished goods, so it needs to modify the surface using a coupling agent sign. The capacity for the production of modified-biosilica would need to be at a great level to meet the needs of the rubber industry. The purpose of the research is to identify the characteristics of the modified-biosilica by silane TESPT (bis-(3-triethoxysilylpropyl) tetrasulfane) that resulted from increasing the weight of biosilica in the production process and the application as reinforcing filler on the rubber. Increasing of weight in the production process was done gradually on a scale of 0.5; 1; 2; and 5 kg of biosilica per process using a mixer-propeller. The technique on surface modifications was using a one-step modification (OSM) and two-step modification (TSM). Surface modification treatment using TESPT has increased the uniformity of the particle size distribution of the biosilica. Unmodified-biosilica has an average particle size of 717.1 nm (PDI 0.600), while modified-biosilica has an average particle size of 574.6 nm (PDI 0.585). Applications for reinforcing filler in the soles rubber industry are performed in PT Triangkasa Lestari Utama. Research indicates that increasing the weight of biosilica on the surface modifications did not significantly affect the density, lightness, crystallinity, and purity. The applications as reinforcing fillers have increased the quality of rubber finished goods compared with unmodified-biosilica. The best rubber finished goods quality approaching shoes-sol standards is a product that used modified-biosilica by OSM technique. This rubber finished goods has a tensile strength of 5.80 MPa, elongation at break of 425%, tear strength of 23.25% and abrasion resistance of 251.5 mm3 .