On a bio-based epoxy vitrimer from a cardanol derivative

Abstract

The development of this work lies in the relevant interest in epoxy resins, which, despite their wide use, do not meet the requirements for sustainable materials. Therefore, the proposed approach considers the need to develop environmentally friendly systems, both in terms of the starting material and the synthetic method applied, as well as in terms of end-of-life. The above issues were taken into account by: i) using a monomer from renewable sources, ii) promoting the formation of dynamic covalent bonds, allowing for material reprocessing, and iii) evaluating the degradability of the material. Indeed, an epoxy derived from cardanol was used, which for the first time was applied in the development of a vitrimer system. The exploitation of a diboronic ester dithiol ([2,2′-(1,4-phenylene)-bis[4-mercaptan-1,3,2-dioxaborolane], DBEDT) as a cross-linker allowed the cross-linking reaction to be carried out without the use of solvents and catalysts, through a thiol-epoxy “click” mechanism. The dynamicity of the network was demonstrated by gel fraction experiments, rheological and DMA measurements. In particular, the formation of a vitrimer was highlighted, characterized by low relaxation times (around 4 seconds at 70°C) and an activation energy of ca. 50 kJ/mol. Moreover, the developed material, which is easily biodegradable in sea water, was found to show promising flame reaction behavior. Preliminary experiments demonstrated that, unlike an epoxy resin prepared stating from the same monomer and using a classical cross-linker, our boron-containing material exhibited no dripping under combustion conditions, a phenomenon that will allow this novel bio-based system to be widely used.