Multi-criteria optimization of in-situ silica sol–gel modified palm sprout fiber-polypropylene thermoplastics composites for enhanced mechanical, thermal, and flame retardant properties

A sustainable technique was formulated to improve the mechanical, thermal, flammability, and moisture resistance characteristics of palm sprout fiber–reinforced polypropylene (PSF–PP) composites by in-situ silica sol–gel modification utilizing rice husk ash–derived silica (RHA–SiO 2 ). The sol–gel synthesis parameters were optimized using a Taguchi-based multi-criteria optimization approach to maximize silica content (SC) and silica residue (SR) simultaneously. The optimized condition improved silica deposition and interfacial compatibility within the polypropylene matrix. The proposed decision-making framework was further validated by Spearman’s correlation with the ranking outputs from existing MCDM methodologies, confirming its efficacy and robustness. According to the MCDM analysis, the optimal process parameters identified are a pH of 9, a soaking duration of 24 hours, a drying period of 90 min, and a RHA-SiO2/water ratio of 1:3, yield a maximum silica residue of 45.1% and a silica content of 39.5%. X-ray diffraction validated the emergence of crystalline silica with low-cristobalite phases in RHA–SiO 2 and maintained cellulose I crystallinity in palm sprout fibers, while FTIR analysis corroborated effective silica deposition via the detection of Si–O–Si and Si–OH functional groups. Silica-modified fibers were integrated into polypropylene using (MAgPP) maleic anhydride grafted polypropylene. Compared with untreated PSF–PP composites, the PSF-S-PP-MAgPP composite exhibited approximately 26.3% higher tensile strength and 44.8% greater Young’s modulus due to improved interfacial bonding and effective silica deposition. Furthermore, silica treatment markedly decreased the burning rate (about 52.44% relative to unmodified PP) and moisture absorption (around 68.15%), indicating enhanced flame retardancy and dimensional stability. The developed sol–gel modification utilized rice husk ash-derived silica as a sustainable bio-based precursor, reducing dependence on conventional synthetic silica sources while improving composite performance.