Development of Bio-based Polyurethane Wood Adhesives from Agroindustrial Waste

Polyurethanes (PUs) are among the most produced type of polymers in the world due to their wide field of applications. However, most commercial PUs are still prepared from non-renewable sources. In this study, we report for the first time, the preparation of PUs from the direct valorization of cashew nutshell liquid (CNSL) without any further purification. First, two polyols were synthesized through epoxidation of CNSL double bonds followed by ring-opening reaction, using ethanol and ethylene glycol. Then, PUs were prepared from the reaction between the synthesized polyols and toluene diisocyanate at different NCO:OH ratios (1.0, 1.5 and 2.0), and subsequently applied onto wood surfaces. All formulations were evaluated by Fourier-transform infrared spectroscopy, gel content, and thermogravimetric analysis. The adhesion efficiency of PUs was investigated by lap shear strength test. The results showed that PUs with lower NCO:OH ratio presented the highest values of tensile strength. This study presents the direct usage of CNSL as an efficient and eco-friendly alternative towards the development of bio-based polyurethanes.