Mechanical properties of a bio-sourced epoxy resin for composite applications

The use of composite materials such as fiber reinforced polymers has become more and more popular during recent years. In particular, epoxy resins are often selected as polymer matrix due to their excellent mechanical properties. Nevertheless, their use is related to significant environmental concerns, which is the reason why bio-sourced epoxy resins with lower carbon footprint are subject of research. Together with natural fibers, the development of bio-sourced composite materials becomes possible. This work investigates mechanical properties of the partially bio-sourced InfuGreen810 epoxy resin. Samples provided by different curing cycles are tested using uni-directional compression and tensile tests. In this way, the stress-strain response of the material is obtained. The cycles are categorized according to their curing degree, measured with a DSC-analysis. Different strain rates are performed. Stiffness and yield stress are higher for lower degrees. A better packing of chains leading to stronger secondary interactions could be identified as physical origin. In tension, samples with low curing degrees are more brittle than fully-cured ones, showing an unusual high ductility. The fracture surfaces are investigated with a SEM. Mechanical properties are further related to the glass transition temperature Tg by studying incomplete cures. The yield drop and the stiffness both decrease linearly with Tg. Finally, the creep behavior under uni-axial compression is studied for different loads, all below yield stress. No tertiary creep, i.e. no failure due to static fatigue could be observed. The findings in this study could be a step forward in the development of bio-sourced fiber reinforced composites.