Synthesis, curing kinetics, thermal and mechanical behavior of novel cardanol-based benzoxazines

To improve the crosslink density of bio-polybenzoxazines a series of cardanol-based benzoxazine monomers with different amine compounds (aniline, furfurylamine and 4,4'-methylenedianiline) were synthesized, cured and characterized. The epoxidation of aniline-cardanol-based benzoxazine was another approach to achieve a higher crosslink density of the resulting thermoset. The nuclear magnetic resonance and Fourier transform infrared spectroscopy were used to analyze the chemical structure and purity of synthesized benzoxazine monomers. The influence of different functionalization on the curing, thermal and viscoelastic properties of cardanol-based benzoxazines was studied systematically. The curing kinetics was studied by differential scanning calorimetry and by applying Kissinger, Flynn-Wall-Ozawa and Crane methods. Thermal and mechanical properties were investigated by differential scanning calorimetry and dynamic mechanical analysis. The introduction of additional polymerizable groups (oxazine, epoxy or furan ring) into benzoxazine molecule increased the activation energy and reaction enthalpy of curing. After curing, the crosslink density, glass transition temperature and storage modulus of functionalized thermosets were considerably enhanced, especially those of epoxidized cardanolaniline-based benzoxazine. (C) 2015 Elsevier Ltd. All rights reserved.