Rubber-Based Composites: Challenges in Reusing Waste and Nanostructures as Fillers

Dear Colleagues,

Rubber, classified as an elastomer, is a flexible material capable of being stretched multiple times its original length without undergoing plastic deformation. Due to its properties such as elasticity, and thermal and electrical insulation, it finds extensive applications across various industries. Notable uses include automotive components like tires, hoses, transmission belts, and cushions; industrial equipment (hydraulic and pneumatic systems) utilizing sealing rings and gaskets to prevent leaks; medical materials including gloves and catheters; footwear manufacturing for soles; rubber flooring in the construction industry; and electrical insulators for electronics and telecommunications.

To be utilized in these products, rubber undergoes vulcanization processes that enhance its mechanical strength and durability. Furthermore, the incorporation of reinforcing fillers can improve tensile and tear resistance. Commercial fillers, such as carbon black and silica, contribute to chemical and mechanical resistance, while the addition of fillers like calcium carbonate or talc reduces costs. These fillers decrease the polymer matrix mass without significantly compromising the material's properties. Other fillers can also enhance composite processing by reducing vulcanization time or improving molding and may impart new properties like electrical conductivity or flame resistance.

An alternative to replace—even partially—commercial fillers involves utilizing waste materials. Although many agricultural and industrial wastes are directed towards energy generation or by-products through pyrolysis processes, recycling and beneficiation methods remain complex, costly, and require improvement in product quality. Consequently, employing fillers in composites offers an environmental advantage by enabling proper disposal of these residues, reducing costs, and mitigating mineral resource exploitation.

However, challenges persist, such as ensuring that waste-derived fillers provide mechanical reinforcement surpassing that of commercial fillers, achieve homogeneous dispersion, promote cross-linking within the polymer matrix, and yield reproducible results. Reducing filler size to nanometric levels presents advantages in interaction with the polymer matrix, provided uniform distribution and phase compatibility are ensured. Nanoparticles, including graphene oxide, carbon nanotubes, nanoclays, titanates, and ceramics, have been integrated into composites. Future research correlating nanostructured with waste materials may facilitate the development of advanced engineering composites. With this, we are pleased to invite you to submit papers representing new reinforcing fillers, whether organic, fibrous or inorganic (industrial), originating from waste recycling or the synthesis of metallic or magnetic nanostructures, or prominent results with known commercial fillers such as carbon nanotubes, graphene oxide, etc.

This Special Issue aims to summarize recent advances regarding reinforcing fillers in rubber composites, reuse of waste as reinforcement, and nanostructures for the production of advanced engineering materials. Research articles and reviews are welcome.

Prof. Dr. Flávio Camargo Cabrera
Dr. Carlos Henrique Scuracchio
Guest Editors

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• recycling
• waste management
• nanomaterials
• filler
• reinforcement