Effects of the Size and Loading of Chrome-Tanned Leather Shavings on the Properties of Styrene–Butadiene Rubber Compounds

Among the proposed leather recycling options, the incorporation of leather waste in rubber has been the subject of multiple studies, where the effects of leather content on the mechanical and rheological properties of the composites are usually studied. However, the effects of leather size have never been addressed in a systematic way. The reasons to study this parameter are twofold: it affects the physicochemical properties and processing conditions of the composites, and leather grinding is a costly and time-consuming process. In this work, leather waste (LW) with particle sizes ranging from ≤0.5 mm to ≤3 mm was incorporated in styrene-butadiene rubber (SBR) in contents of up to 50 phr. It was concluded that the composites with finer leather sizes exhibited a more uniform particles dispersion, and tensile strength was not significantly affected by the presence of LW, especially for the finer granulometries. However, there is a remarkable increase in the stiffness with the increase in leather content, particularly with the finer particles. The abrasion increased with the incorporation of leather across all particle sizes, especially for the ≤0.5 mm leather particles. The thermal stability of the composites was not affected by either the particle size or the amount of LW, except for high contents.