Isocyanate curing of novolac-type ligno-phenol–formaldehyde resins

This work proposes the use of a diisocyanate as curing agent for novolac-type lignin–phenol–formaldehyde (LPF) resins, instead of typical hexamethylene–tetraamine (HMTA), with the aim of overcoming the loss of reactivity of lignophenolic resins resulting from the introduction of lignin. Curing LPF resins with methylene–diisocyanate (MDI) and HMTA has been investigated through Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC) and rheological analysis. The analysis of experimental results shows that the proposed curing reaction with MDI gives similar results to those for HMTA-cured systems. However, MDI curing is faster than HMTA one and proceeds easier at lower temperatures.