Global consumption of wood adhesives is increasing every year. Due to the environmental and health concerns related to the most commonly used synthetic adhesives, biobased adhesives are gaining substantial interest. Tannins and lignins, as the most abundant renewable sources of polyphenolic compounds, are considered the most suitable alternative raw material that could completely replace the currently used synthetic adhesives. In this study, two biobased adhesives, tannin-hexamine (TH) and organosolv lignin non-isocyanate polyurethane (NIPU), were studied and compared with each other and with commercial urea-formaldehyde (UF) adhesive. The basic characterization in the liquid state and the final characterization of the studied adhesives were performed. All three adhesives tested were classified as C1 durability class, which means that they are suitable for non-structural interior applications. The curing process was studied using ABES, DSC, DMA, and DEA methods to monitor the curing process of the adhesive bond. Based on the results of different methods, it was found that the curing process of UF adhesive is the fastest, followed by TH adhesive and the NIPU adhesive curing process as the slowest. The optimum pressing times and temperatures were determined by considering the results of the ABES reference method. These were 4 min at 175 °C for the TH adhesive, 7 min at 200 °C for the NIPU adhesive, and 1.5 min at 100 °C for the UF adhesive. The existence of general models for predicting the adhesive bond strength development determined by the ABES reference method based on the results of indirect methods has not been proven. In general, it was found that the DEA method slightly overestimates the curing process determined by the ABES method; the DSC method underestimates it in the first part but determines its final cure adequately, while the DMA method underestimates it.
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