Biobased structural epoxy foams derived from plant-oil: Formulation, manufacturing and characterization

This paper is devoted to the description of the scientific method used for developing biobased structural foams derived from highly reactive epoxy resins. The chemical formulations were obtained from the mixing of two epoxidized plant oil-derivates (epoxidized linseed oil ELO and glycerol triglycidyl ether commonly named epoxidized glycerol EG) with an anhydride hardener and a non-toxic foaming agent. The optimization of the composition was achieved by studying the influence of many parameters such as the proportion of each epoxy molecule in the reactive formulation, the exact nature of the hardener or foaming agent retained by the use of different complementary experimental techniques. For instance, the reactivity of four cyclic anhydride compounds with ELO was investigated by differential scanning calorimetry and rheometry in dynamic or kinetic mode. Two different blowing agents were initially retained for the preparation of foams and their respective density and mechanical properties were evaluated and compared. The proportion of each epoxy molecule (ELO and EG) was also tuned to achieve a good equilibrium between the gelation and foaming mechanisms within a few minutes. The definition of an optimized composition made it possible the production of rigid foams using a short production time (i.e. lower than 3 min). These foams were characterized by a glass transition temperature close higher than 80 °C and an apparent density comprised between 0.05 and 0.08 g/cm3. Their specific mechanical properties were judged convenient for a possible valorisation as lightweight structural material.