Rotor speed and mixing time investigation of internal mixing for fabricating vibration-damping compounds of waste rubber powder in natural rubber

Vibration-damping elastomers are widely used to reduce mechanical vibrations and improve the durability of engineering systems. This study investigates the effects of internal mixing parameters on the structure and performance of natural rubber composites filled with waste rubber powder and carbon black, with an emphasis on establishing relationships among processing, structure, and properties. The results reveal that composite performance is governed by the balance between shear-assisted dispersion of filler particles and processing-induced deterioration of network integrity under excessive mixing conditions. Increased shear promotes filler distribution, interfacial continuity, and stress-transfer efficiency, whereas overly severe processing adversely affects structural stability. Consequently, an intermediate mixing regime produces a more homogeneous microstructure while preserving effective network integrity, resulting in improved mechanical properties, reduced solvent swelling, and stable vibration-damping performance. The optimally processed composite exhibited a damping efficiency of approximately 76.7% and a tensile strength of approximately 15 MPa, together with favourable ageing resistance and dimensional stability. These findings provide a mechanistically grounded framework for understanding how competing dispersion and degradation phenomena govern the behaviour of filled elastomer systems and offer generalizable insights for the design of sustainable rubber composites.