This paper presents a facile strategy to activate citric acid (CA) for room temperature curing.

Eutectic hardeners were prepared using mixtures of natural acids and liquefactor for increasing the curing speed and for improving the mechanical performances of biobased thermosets.

Coffee is one of the most popular beverages in the world but generates copious amounts of waste that is usually discarded. This discarded waste, the so-called spent coffee grounds (SCGs), can become a valuable resource if compelling use cases are found. Following a circular economy approach, one such use case can be employing SCGs as filler in polymer matrices, complementing conventional inorganic fillers such as kaolin clay. This work studies the effect of SCGs as filler in wholly natural thermosets, investigating changes in curing kinetics and final material properties. Different SCG content, for example, 25 to 35 wt% and various curing time and temperature is employed. SCGs are found to have a moderate catalytic effect on the curing reaction. Furthermore, SCGs are found to heavily increase stiffness of the final material, especially when oils present in SCGs are previously extracted, raising the rubber plateau modulus from around 5 MPa to 14 MPa. Extracted SCGs are most efficient during curing at room temperature, where they significantly improved the tensile strength, toughness, and hardness of the filled material compared to the pristine resin.