Synthesis of Renewable Thermoset Polymers through Successive Lignin Modification Using Lignin-Derived Phenols

An approach to lignin-based epoxy networks from both organosolv lignin and lignin-derived phenol (dihydroeugenol) are developed using multiple chemical modifications including demethylation, phenolation, and a phenol-formaldehyde reaction. Structures of lignin-incorporated novolac polyphenols and epoxy networks (LINENs) were characterized using proton nuclear magnetic resonance and infrared spectroscopy. Compared to a common synthesis route in which lignin was epoxidized prior to blend with comonomers, LINEN derivatives exhibited improved cross-link density, α-relaxation temperature and storage modulus in a glassy region as obtained from dynamic mechanical analysis, and increased thermal stability measured by thermogravimetric analysis. This study widens the routes of lignin modification. Renewable epoxy networks derived from both lignin and lignin derivatives are economically and ecologically attractive.