Phosphorus acid: an asset for flame-retardant sustainable vitrimers

Abstract

Three biobased epoxy resins from vanillic alcohol, linseed oil and cardanol were crosslinked with phosphoric acid to prepare vitrimers. The reactivities of the different types of epoxy towards phosphoric acid were assessed by ¹H and ³¹P NMR spectroscopy on model molecules. The resulting phosphate esters constitute the nodes of the network, which can exchange with free hydroxy groups upon heating, thus conferring reshaping capability to the materials. Additionally, the phosphate groups endow flame retardant properties to the materials. When exposed to fire a char layer is formed, which insulates the inner part of the material and slows down its combustion. Finally, mixtures of the three epoxy resins led to dynamic materials with both fire retardancy properties and low T_g.