Synthesis of nano-silica from natural resources and applications

Abstract

A fast growing interest in applying nanomaterials in various fields has been observed in recent years. Nano-silica is one of the widely used nanomaterials in adhesives, fiber optic strands, sealants, surface coatings, defoamers, cosmetics, food additives, cement-based building materials and rubber composites. As an agricultural country, Sri Lanka produces tones of paddy husk annually. The benefit of using paddy husk has been identified in many applications. Paddy husk is burnt to generate energy resulting paddy husk ash (PHA). PHA is rich in silica (-60 %) and can be an economically viable raw material for the production of nano-silica through chemical method as a value added product. Also Sri Lanka has highly pure vein quartz (~98%) which can be converted in to nano-silica. In this research, nano-silica was prepared by precipitation method from both PHA and vein quartz and characterized by various analytical techniques. Scanning electron micrographs showed that nano-silica particles from both resources were in the agglomerated form (primary particle size 50-70 nm). The particle shape was found to be spherical. X-ray diffractograms showed a strong broad peak at 22 ° (2G) indicating that the obtained products from both starting materials were amorphous and also the Infrared spectra data supports the presence of hydrogen bonded silinol groups and siloxane groups in silica. Silica nanoparticles were surface modified by oleic acid and characterized using TGA and FT-IR techniques. Reinforcing ability of the synthesized nano-silica from PHA (NS) in natural rubber composites (NRNS) was investigated. Cure characteristics and mechanical properties of the NRNS nanocomposites were compared with that of commercial grade silica (PS) reinforced natural rubber composites (NRPS) and it was found that NS has lower reinforcing ability compared to that of PS.