Lignins for phenol replacement in novolac-type phenolic formulations, part I: Lignophenolic resins synthesis and characterization

Several lignin (L)-based novolac-type phenolic prepolymers with two phenol (P) substitution degrees have been synthesized using three L from different origin (kraft pine L, soda/anthraquinone (AQ) flax L, and sulfonated kraft softwood L). These lignophenolic (LPF) resins have been characterized by means of free P and formaldehyde (F) analysis, viscosity, chemical structure (FTIR), and thermal behavior (DSC). Temperature at which curing reaction begins (DSC), hardening time at several curing temperatures (rheology) and volumetric changes (PVT) have also been determined for the curing process with 10 wt % hexamethylenetetraamine (HMTA). All the results have been compared to those obtained for a commercial novolac. Depending on the L type employed a homogeneous material with lower curing onset temperature and gelation time than reference PF can be obtained even at high P substitution level (45 wt %).