Photocurable Lignin Materials: Tuning Lignin Methacrylation to Tailor Photocuring Kinetics

ABSTRACT The methacrylation of Beech organosolv Lignin with methacrylic anhydride (MA) at 65°C under 4‐ (dimethylamino) pyridine (DMAP) base catalysis is monitored by the FTIR OH‐stretch at 3340cm −1 and the C═C vibrations associated with the methacrylate group at 780, 810, 945, and 1637 cm −1 . Methacrylation extent increases with the MA: lignin OH molar ratio, the DMAP: MA wt%, and their interactions. Monitoring these vibrations over 48 h suggests side reactions, liberating new OH functionalities and, in turn, new grafting sites. Under these conditions, zero‐ and second‐order kinetics fit the kinetics of lignin methacrylation equally well. Lignin methacrylate derivatives cure readily under UV light, and both the cure rate and full cure extent increase with increasing methacrylate conversion of lignin OH. The Sestak‐Berggren autocatalytic kinetic model successfully describes UV‐photocure, whereby the product autocatalytic (m) and reactant's exhaustion retardation (n) effects decrease with increasing methacrylation extent, from ca. 0.34 to 0.28 and from ca. 1.05 to 0.67, respectively. Lignin methacrylation can thus be tuned to adjust rheological and photocuring properties of methacrylate lignins for UV light induced processing, such as 3D printing.