Novel Mineral and Organic Materials from Agro-Industrial Residues as Fillers for Natural Rubber

Bio-based materials are being developed, increasingly, because of the need for sustainable, environmentally friendly, processes and products. We have made natural rubber composites containing low cost fillers derived from agro-industrial wastes, namely, eggshells, carbon fly ash, processing tomato peels and guayule bagasse. Composites manufactured with 35 phr (parts per hundred rubber) of carbon black (particle size 108 ± 31 nm) were used as a reference filled material. The amount of carbon black was gradually replaced by a specific waste-derived macro (<300 µm diameter) or micro (<38 µm diameter) filler. Despite differences in particle size distribution and surface chemistry, the tensile properties of micro sized tomato peels composite were similar to those of the carbon black reference composite. Composites manufactured using micro sized particles at low loadings (5 and 10 phr) of carbon fly ash and eggshells, as co-fillers with carbon black, also demonstrated comparable tensile results to those of composites manufactured solely with carbon black. Hierarchical cluster analysis partitioned the data into five groups of composites having statistically similar mechanical properties. Composites containing micro sized particles at low loadings (5 and 10 phr) were grouped in clusters 1, 2 and 5. These clusters gathered composites with the highest tensile strength and 300 % modulus. As the amount of non-carbon black filler increased above 10 phr and up to 35 phr (maximum filler loading used), the composites became weaker than the carbon black filled composites and modulus decreased.