Quasi-static and dynamic response of cardanol bio-based epoxy resins: effect of different bio-contents

In recent years, the European Community regulations are promoting the use of sustainable and green materials to lower the overall carbon footprint, especially in the automotive sector. The majority of structural composite materials use petrol-based epoxy matrices which are not easily recyclable, thus representing a negative impact on the environment. The most promising and ready-to-use technology to lower the carbon footprint in composite materials is the use of bio-based resins partially derived from renewable resources since this replacement is not affecting the manufacturing processes. Two commercial resins, a cardanol-based epoxy resin (27% bio-content) and an epoxy novolac resin (84% bio-content), were mixed to obtain four different resin mixtures. In particular, the higher bio-content novolac resin was mixed with the cardanol epoxy resin in different weight percentages to reach a total bio-content higher than 27%. The resins obtained by this procedure are characterized by total bio-contents of 27%, 31%, 41% and 51%, calculated on biomass used in production. Quasi-static and dynamic tensile tests have been carried out to assess the mechanical behavior of the different resins at increasing bio-contents. The strain has been acquired by using Digital Image Correlation (DIC) system to determine the failure modes with respect to the bio-content. The tests have shown that the increase of bio-content lead to lower Young’s modulus and lower ultimate strengths both decreasing with a linear trend in static and dynamic conditions. The glass-transition temperatures (Tg) of each mixture have been also studied by means of Differential Scanning Calorimetry (DSC) analyses to assess the effect of the bio-content on the Tg values.