Effect of imine-containing phenolic hardeners with different chain lengths and epoxy functionalities on thermal, mechanical, and healing properties of bio-based epoxy vitrimers

Mixtures of polyglycerol polyglycidyl ether (PGPE) and poly(ethylene glycol) diglycidyl ether (PEGDGE) with different molar ratios were cured with imine-containing phenolic hardeners prepared by the reactions of vanillin with ethylene glycol bis(3-aminopropyl) ether, diethylene glycol bis(3-aminopropyl) ether, and a polyetheramine (JEFFAMINE® ED-600) to produce bio-based epoxy cured products. Fourier-transform infrared spectroscopy (FT-IR) of the cured products revealed that the curing reaction of the epoxy and phenolic hydroxy groups was almost complete. The cross-linking density, glass transition temperature, and mechanical strength of the cured products decreased with decreasing the PGPE/PEGDGE ratio and increasing the oligoalkyleneoxy chain length of the phenolic hardeners. All cured products were healed three times at 100 °C under 2 MPa for 2 h. The healing efficiency, in terms of tensile strength, increased with decreasing PGPE/PEGDGE ratio and increasing oligoalkyleneoxy chain length. The polyetheramine-based cured product with the lowest PGPE/PEGDGE ratio exhibited the highest healing efficiency (94–97%), which only slightly decreased following repeated healing treatments.