Preparation, Characterization and Mechanical Properties of Bio-Based Polyurethane Adhesives from Isocyanate-Functionalized Cellulose Acetate and Castor Oil for Bonding Wood

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.

Recent advances in vegetable oil-based polyurethanes

Polyurethanes are among the most versatile polymers because of the wide range of monomers, particularly diols or polyols, that can be utilized in their synthesis. This Review focuses on the most recent advances made in the production of polyurethane materials from vegetable oils. Over the past several years, increasing attention has been given to the use of vegetable oils as feedstocks for polymeric materials, because they tend to be very inexpensive and available in large quantities. Using various procedures, a very broad range of polyols or diols and in some cases, poly- or diisocyanates, can be obtained from vegetable oils. The wide range of vegetable oil-based monomers leads to a wide variety of polyurethane materials, from flexible foams to ductile and rigid plastics. The thermal and mechanical properties of these vegetable oil-based polyurethanes are often comparable to or even better than those prepared from petroleum and are suitable for applications in various industries.