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

• High-performance bio-based polymers from largely available renewable feedstock. • Benzoxazine synthesis processes were eco-friendly as confirmed by sustainable metrics. • Cured polymers presented elevated degradation temperatures higher than 350 °C. • Glass transition temperatures of cured polymers reached 250 °C. • Cured polymers had elevated flexural strains compared to traditional thermosets. 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 (1H and 13C 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 °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. [ABSTRACT FROM AUTHOR]