Biodegradable and wood adhesive polyesters based on lignin-derived 2-pyrone-4,6-dicarboxylic acid

2-Pyrone-4,6-dicarboxylic acid (PDC) is a chemically stable metabolic intermediate of lignin, and its condensation polymers can be synthesized by utilizing the functionality of two carboxylic acids. In this study, biodegradable PDC-based polyesters, namely, P(PDC2) and P(PDC3), with strong adhesive properties toward wood were developed by polycondensation with diols. The adhesive properties of P(PDC2) and P(PDC3) were fully characterized by tensile lap shear strength measurements, X-ray photoelectron spectroscopy, and cross-sectional computed tomography. The biodegradability of P(PDC2) and P(PDC3) in natural pond water was also measured. Both P(PDC2) and P(PDC3) showed strong adhesive strengths to wood with the highest average adhesion of 5.55 MPa, which usually causes wood failure. In order to quantitatively investigate the adhesive strengths of P(PDC2) and P(PDC3), decomposition acceleration experiments were performed. The average adhesive strength of 2.57 MPa remained even after immersion in hot water at 60 degrees C for 4 h, which demonstrated the excellent adhesive strength and water resistivity of the PDC-based polyesters. P(PDC2) and P(PDC3) remained almost uniformly biodegraded after 60 days of incubation in a simulated natural environment and reached a biodegradation rate of about 54% and 52%, respectively. The excellent adhesive properties and biodegradability of the PDC-based polyesters provide a new strategy for preparing safe and environmentally-friendly bio-based adhesives. Lignin-derived 2-pyrone-4,6-dicarboxylic acid is a biodegradable polymer unit that is also useful as a strong adhesive to wood.