Preparation and performance characterisation of organosilicon-modified cardanol-phenolic resin

Abstract

This study presents the synthesis and characterisation of KH550-modified cardanol-based phenolic hybrid resins. The hybrid resins were prepared via a two-step process: (1) synthesis of cardanol-based phenolic resin (CPR) through the condensation of cardanol and paraformaldehyde (1:1.3 molar ratio of phenolic hydroxyl groups to aldehyde groups), followed by (2) ultrasound-assisted grafting of γ-aminopropyltriethoxy silane (KH550) at varying mass ratios (5 and 15 wt%, denoted as CPR-K5 and CPR-K15, respectively). Hydrolysis of KH550 generated silanol (Si–OH) groups, which underwent covalent grafting and condensation reactions with the phenolic hydroxyl groups (–OH) and hydroxymethyl groups (–CH2OH) of CPR to form Si–O–C crosslinked networks, as confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) revealed the homogeneous dispersion of the organosilicon phase within the resin matrix. Thermogravimetric analysis (TGA) demonstrated a significant enhancement in thermal stability, with the char yield at 800°C increasing from 7.8% (neat CPR) to 22.1% (CPR-K15). Stress-strain tests verified the enhanced mechanical performance, with the Young’s modulus of CPR-K5 reaching 104.7 MPa (representing a ~512% increase compared to neat CPR, 17.1 MPa) and that of CPR-K15 being 52.2 MPa (~205% increase vs neat CPR). This work provides a facile strategy for preparing sustainable hybrid resins with tailored thermomechanical properties, addressing the inherent brittleness and a low char yield of conventional cardanol-based phenolic resins. The resulting materials show potential for high-temperature structural applications and flame-retardant composites.