Synthesis of green-based carbon-doped nanosilica for enhanced mechanical properties of coconut oil-based rigid polyurethane foam

High-strength, bio-based rigid polyurethane foam (RPUF) was synthesized using coconut oil-based polyol reinforced with green silica nanoparticles (SNP) derived from rice husk ash (RHA). The SNPs were carbon-doped using κ-carrageenan to enhance their functional properties. Comprehensive characterization of the synthesized SNP and SNP-enhanced RPUF was conducted using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), dynamic light scattering (DLS), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). X-ray photoelectron spectroscopy (XPS) confirmed successful κ-carrageenan-mediated carbon doping, improving SNP reactivity. The incorporation of SNP (up to 0.3% by mass) significantly enhanced the compressive strength of RPUF by 92.42%, attributed to hydrogen bonding and induced crosslinking interactions between the SNP and amine groups in the bio-polyol, as evidenced by FTIR, SEM, and pycnometric analyses. Thermogravimetric analysis (TGA) demonstrated that SNP integration improved the thermal stability of RPUF without compromising its thermal conductivity, meeting industrial standards. This study highlights the potential of sustainably derived nanomaterials to improve the mechanical and thermal properties of bio-based composites. Furthermore, the SNP-reinforced RPUF offers promising applications in environmentally friendly materials for thermal insulation, structural components, and environmental remediation, contributing to the development of high-performance, sustainable materials for various industrial applications.