Thermal Characterization of Kraft Lignin Phenol-Formaldehyde Resin for Paper Impregnation

Both kraft lignin phenol-formaldehyde (KLPF) and phenol-formaldehyde (PF) resins were synthesized and the curing kinetics of the resins was determined using thermal analysis data. The kinetic parameters were predicted using two popular model-free kinetic (MFK) methods: the advanced form of the Vyazovkin method and the Kissinger–Akahira–Sunose method. From the experimental and predicted values, the rate of kraft lignin phenol-formaldehyde curing was less compared to the phenol-formaldehyde resin. To increase the cure rate different cure additives were tried. Among these, only potassium carbonate (KC) showed a positive effect: An increase in additive concentration to 4% reduced the curing time to almost 50% as compared to pure KLPF resin at 160°C. Comparison of the predicted values from MFK calculations with isothermal experimental data showed that both MFK approaches were suitable to predict the curing characteristics.