Effect of cenosphere size and loading on silicone rubber composites

This study investigated the influence of fly ash-derived aluminosilicate cenospheres on the structure and performance of silicone rubber composites. The silicone matrices were filled with cenospheres of two representative particle sizes (average diameters of 46 and 106 µm) at concentrations of 10, 25, and 50 phr. A comprehensive characterization was conducted, including SEM analysis, mechanical and thermal testing, ESR spectroscopy, FTIR analysis, TGA/DTG, specific heat capacity evaluation, and swelling resistance in various media. The results showed that the incorporation of cenospheres at low to moderate loadings (10–25 phr) led to improved mechanical retention and thermal stability. In particular, composites filled with smaller cenospheres (46 µm) at 10 phr retained high elongation at break (up to 650%) while exhibiting enhanced tear resistance (up to 32.8 kN·m -1 ) compared to the neat silicone rubber. Thermogravimetric analysis revealed delayed thermal degradation and a significant increase in inorganic residue, exceeding 65% at 800°C for filled composites. Accelerated thermal aging at 250°C for 72 h demonstrated that cenosphere-filled systems preserved their elastomeric character, whereas the unfilled rubber became brittle. Overall, the quantitative results confirm that aluminosilicate cenospheres act as effective functional fillers, enhancing the mechanical durability and thermal-protection performance of silicone rubber composites.