Integration of silica with benzoxazine to improve particle dispersion and thermal performance of composites

Abstract

The concentration gradient and non-uniform dispersion of the most commonly used filler (silica) in the polymer matrix is one of the main reason for the inferior performance of the polymer composite. The present work utilizes surface chemistry to integrate the surface of silica particles with benzoxazine moieties in order to improve the dispersion of silica particles in bio-based benzoxazine resin with a generic aim to develop polybenzoxazine composites with improved thermal performance. In view of the same, co-condensation of tetraethoxysilane (TEOS) and 3-aminopropylltriethoxysilane (APTES) at room temperature has been performed, resulting in amine functionalized silica (AFS) particles. The feed concentration of the reactants has been optimised to prepare least agglomerated particles. The organic functionalization on silica particles has been evidenced using Fourier transform infrared (FTIR), 13C solid state NMR, X-ray photoelectron (XPS) spectroscopies and thermogravimetric analysis (TGA). The free primary amine groups of amine functionalized silica (AFS) particles has been utilized as amine co-reactants which undergoes Mannich like condensation with various bio-based phenols to integrate oxazine functionality on the surface of silica particles. The presence of oxazine moieties on the surface of silica particles has been confirmed using various thermal techniques including differential scanning calorimetry (DSC) and TGA. The improved dispersion of benzoxazine functionalized silica (BFS) particles in a bio-based benzoxazine resin based on cardanol-aniline (C-a) as well as the polybenzoxazine thermoset has been demonstrated using digital and SEM images. Thermogravimetric results shows the influence of improved dispersion in terms of relatively higher thermal stability of the polybenzoxazine composite prepared using modified silica particles.