Toward Sustainable Phenolic Thermosets with High Thermal Performances

Abstract

This paper proposes more sustainable alternatives for the synthesis of high thermal performances phenolic networks. Terephthalaldehyde (TPA), a nontoxic aromatic dialdehyde, was selected to replace formaldehyde. Phenol was, in turns, replaced with biobased and nontoxic phenolic building blocks: resorcinol as a model for tannins, guaiacol which is easily accessible from lignin, and tyrosol from olive oil mill wastewaters. The prepolymerization was performed under mild conditions (ethanol, T ≤ 100 °C). The liquid prepolymers were characterized by NMR, IR, MALDI-ToF, and rheology. The curing behavior of these formulations was assessed by DSC and IR spectroscopy. An advanced isoconversional analysis of the DSC data allowed for the determination of cross-linking activation energies. Furthermore, a multistep mechanism of TPA cross-linking was proposed with strong evidence. The thermo-mechanical properties of cured networks were characterized using DMA, showing high cross-link densities and glass transition temperatures. Finally, these new thermosets displayed very high thermal performances under pyrolysis conditions (TGA).