Towards bio-based high-performance polybenzoxazines: Agro-wastes as starting materials for BPA-free thermosets via efficient microwave-assisted synthesis

In this work is described the use of Cashew Nutshell Liquid (CNSL) and the lignin-derivative catechol as widely available renewable starting materials for the synthesis of BPA-free benzoxazines. The bio-based resins were obtained through an efficient eco-friendly method using microwave-irradiation as a heating source, producing resins with good yields. After characterization by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance Spectroscopy (H-1 and C-13 NMR) and differential scanning calorimetry (DSC), these resins were combined in different ratios and then thermally (co)polymerized to obtain fully bio-based polybenzoxazines. These thermosets were studied by thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and three-point flexural test, which showed elevated char yield (up to 40%) and good mechanical properties (T-g above 200 degrees C). Sustainable metrics, E factor and Atom Economy, were also applied for the synthesis of the bio-based monomers demonstrating the greenness of this process and suggesting that these materials can be considered interesting high-performance alternatives to substitute BPA-based polybenzoxazines.