Sustainable lignin-based epoxy resins cured with aromatic and aliphatic amine curing agents: Curing kinetics and thermal properties

• Lignin-based epoxy resins cured with aromatic and aliphatic amine curing agents.
• Curing behavior was monitored by using DSC and evaluated by isoconversional models.
• The mechanism of curing process was influence by the type of curing agents.
• The thermal stability of epoxy resins depended on the type of curing agents and lignins.

Lignin-based epoxy resins were synthesized by reacting de-polymerized organosolv lignin (DOL) or de-polymerized Kraft lignin (DKL) with epichlorohydrin under an alkaline condition in the presence of a phase transfer catalyst. The synthesized lignin-based epoxy resins were cured with 4,4′-diaminodiphenyl methane (DDM, an aromatic amine) and diethylenetriamine (DETA, an aliphatic amine) to generate a 3-dimentional cross-linked structure. The effects of curing agents on the curing process were investigated by non-isothermal differential scanning calorimetry (DSC). The dependency of activation energy of the curing reaction on the extent of curing (conversion) was determined in this study by model-free kinetics based on the DSC results. In addition, it was found that the thermal stability of the cured lignin-based epoxy resins was also influenced by the type of curing agents and the types of lignin used in the synthesis of the bio-based epoxy resins.