A Comprehensive Overview of Conventional and Bio-Based Fillers for Rubber Formulations Sustainability

In recent years, there has been a significant increase in literature regarding the development of sustainable rubber composites. This is due to the widespread use of rubber and the need to transition towards a circular economy, which addresses environmental concerns such as global warming and pollution. Extensive research has been conducted to replace conventional fillers like silica and petroleum-based fillers in rubber composites with eco-friendly and sustainable alternatives, namely bio-based fillers. These biofillers present diverse fundamental characteristics, making them promising substitutes for carbon black or inorganic mineral-based fillers, reducing reliance on petroleum. They possess biodegradable properties, resulting in a reduced environmental footprint, as well as lower density and cost compared to conventional counterparts. Furthermore, their unique properties, such as high specific strength and stiffness, render them well-suited for various rubber applications. The performance of reinforced rubber composites is influenced by factors including the matrix polymer, as well as the source, size, shape, chemical composition, and volume fraction of fillers. Rubber composites incorporating biofillers offer the dual advantages of economic efficiency and environmental sustainability. This article provides a comprehensive review of recent research in rubber composite development, with a specific focus on utilizing various fillers. Additionally, it examines the characterization of both conventional and bio-based fillers and their effects on the behaviour and performance of rubber composites, including morphology, thermal properties, and mechanical properties.