Effect of chemical treatment and biosilica fillers on the mechanical, thermal, and tribological properties of Ricinus communis stem fiber composites: a machine learning and RSM approach

This study explores the enhancement of mechanical, thermal, and tribological properties of Ricinus communis stem fiber (RCSF)-reinforced polyester composites by incorporating biosilica derived from Proso millet husk as a filler. The RCSF fibers were treated with 5 wt% NaOH to improve the fiber-matrix bonding. Biosilica was added at varying concentrations (1–5 vol%) into the polyester matrix. The tensile strength increased from 42.6 MPa to 61.5 MPa with 4% biosilica, and the flexural strength improved from 72.15 MPa to 93.65 MPa at the same filler content. The 4% biosilica sample also showed the highest impact strength at 80.71 kJ/m2. Thermal analysis indicated improved stability, with a significant increase in weight retention at higher temperatures, especially for composites with higher biosilica content. In tribological tests, the optimal biosilica content (3–4%) reduced the specific wear rate (SWR) to 1.56 × 10−5 mm3 /Nm and the coefficient of friction (COF) to 0.239. However, higher concentrations of biosilica led to agglomeration, reducing composite performance. The study highlights the potential of biosilica-reinforced RCSF composites as a sustainable material, providing a balance of mechanical strength, thermal stability, and wear resistance for engineering applications.