In contrast to the traditional method of silica synthesis, green silica made from rice husk ash uses landfilling agricultural waste and exempts the requirement of higher temperatures for digestion, making the precipitation and functionalization processes sustainable. An energy-efficient method of functionalization has been optimized for the synthesis of functionalized silica from rice husk ash via co-condensation. Silica is employed as a filler in the manufacturing of composites due to its propensity to offer superior reinforcing. Three different types of silica samples have been made with nitroxide functionalized silica utilising various techniques to achieve a better silica-polymer interaction. The thiol-ene reaction between 4-acryloyloxy(2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) and mercaptopropyl functionalized silica particles produced the nitroxide functionalities. By post-modification and co-condensation over commercially available precipitated silica, commercially available rice husk ash silica, and silica produced in the lab from sodium silicate derived from rice husk ash, the mercaptopropyl functionalized silica was synthesized. It has been discovered by comparing the nitroxide and mercaptopropyl grafting densities that the nitroxide loading greatly depends on the type of functionalization and that the co-condensed samples had higher nitroxide loading than the post-modified samples. The effectiveness of surface nitroxide radicals in capturing the polymer radicals with respect to nitroxide loading was assessed after polystyrene grafting was performed on the nitroxide functionalized samples. It was shown that the grafting density was increased with an increase in conversion and the initiator-to-monomer ratio. Despite having a greater surface area and surface nitroxide radicals, the grafting density was found to be saturated at some point. Future applications can benefit from optimizing the surface nitroxide radical concentration and surface area through this work.

Potential of nitroxide-functionalized green silica for polymer grafting

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