Nowadays, different types of natural carbohydrates such as sugars, starch, cellulose and their derivatives are widely used as renewable raw materials. Vegetable oils are also considered as promising raw materials to be used in the synthesis of high quality products in different applications, including in the adhesive field. According to this, several bio-based formulations with adhesion properties were synthesized first by inducing the functionalization of cellulose acetate with 1,6-hexamethylene diisocyanate and then mixing the resulting biopolymer with a variable amount of castor oil, from 20% to 70% (wt). These bio-based adhesives were mechanically characterized by means of small-amplitude oscillatory torsion measurements, at different temperatures, and standardized tests to evaluate tension loading (ASTM-D906) and peel strength (ASTM-D903). In addition, thermal properties and stability of the synthesized bio-polyurethane formulations were also analyzed through differential scanning calorimetry and thermal gravimetric analysis. As a result, the performance of these bio-polyurethane products as wood adhesives were compared and analyzed. Bio-polyurethane formulations exhibited a simple thermo-rheological behavior below a critical temperature of around 80-100 • C depending on the castor oil/cellulose acetate weight ratio. Formulation with medium castor oil/biopolymer weight ratio (50:50 % wt) showed the most suitable mechanical properties and adhesion performance for bonding wood.

On account of the irreversible environmental damage caused by the utilization of non-renewable raw materials in industrial production, since the end of the twentieth century, the interest in replacing the traditionally applied petroleum-based starting compounds in the polyurethane production by more sustainable feedstocks has grown enormously. Such pursuit of Green Chemistry has been fostered by the implementation of a set of national and international initiatives and stricter regulations, especially in the field of adhesives. In this respect, the latest advances in the production of bio-based polyurethanes are collected in this review. Thus, after a brief introduction to this subject and main tendencies towards the production of more sustainable polyurethanes, the first section reviews the feasibility of manufacturing polyurethanes from a range of natural platforms, including lignocellulosic biomass and vegetable oils, whether modified or in their original form, along with some industrial wastes. Afterwards, the hitherto considered synthetic routes for the preparation of greener polyurethanes are assessed, encompassing waterborne, radiation-curable and non-isocyanate polyurethane techniques. Finally, the last section focuses on the research advancement on the synthesis, properties and different uses of bio-based polyurethanes specifically implemented in the field of adhesives.

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