Development and Thermo-Mechanical Analysis of Bio-based Epoxy Resin/Cardanol Blends as Matrices for Green Composites Manufacturing

Abstract

This study explores the development of recyclable and bio-based epoxy resin/cardanol blends with varying cardanol content (25, 50, and 75%wt) using a cleavable amine hardener to achieve full recyclability. This approach offers a significant advantage by addressing two critical aspects of the epoxy resin life cycle—feedstock selection and end-of-life recyclability. Blends with over 28% bio-based content were developed and their recyclability was demonstrated through chemical dissolution tests. The most performing formulations in terms of thermo-mechanical properties were identified through thermo-mechanical characterizations (such as TGA, DSC, DMA, and flexural tests). The obtained results showed that, by selecting the most suitable curing cycle and cardanol content, it was possible to achieve promising properties. In fact, glass transition temperatures (\(\:{T}_{\text{g}}\)), ranging between 67 and 79 °C, were found enabling most of the common applications for these formulations. Flexural strength values reaching 77.3 ± 1.3 and 73.4 ± 1.5 MPa were found for formulations containing 25 and 50%wt cardanol, respectively. These formulations also exhibited good flexural modulus values (up to 2.50 ± 0.06 GPa) and stiffness, attributed to higher cross-linking densities. Generally, the findings of this study suggest the potential for developing eco-composites with good thermo-mechanical properties, high bio-based content, which are also fully-recyclable through a chemical approach, thus enhancing the overall sustainability of these materials. The latter class of materials is finding industrial applications in the automotive, sports and wind turbine fields, such as for the manufacturing of the first generation of fully-recyclable wind turbine blade.