Study of Soybean Oil-Based Non-Isocyanate Polyurethane Films via a Solvent and Catalyst-Free Approach

Synthesizing polymeric materials that are both sustainable and practical has become a priority. Polyurethanes (PUs) are becoming more popular because of their countless applications and exclusive properties in many sectors. While considering the current issue of environmental problems and the excessive use of petroleum products, nonisocyanate PU (NIPU) are favored due to their sustainability and low toxicity compared to conventional PU. In this work, flexible NIPU films were made using a green and facile method. For that, soybean oil (SBO) was used as the starting material and converted into epoxide SBO, followed by its chemical conversion into carbonated SBO (CSBO) using carbon dioxide gas. Following that, the CSBO reacted with three different aliphatic amines, namely, 1,2-ethylenediamine, 1,4-butylenediamine, and 1,6-hexamethylenediamine, in a solventless and catalyst-free system. The films were cast and cured at 85 °C for different curing times. The effects of the aliphatic diamines and curing times on the NIPU films were evaluated. The individual materials were confirmed with Fourier transform infrared, ¹H nuclear magnetic resonance, and gel permeation chromatography. To analyze the thermal and mechanical properties, thermogravimetric analysis, dynamic mechanical analysis, and differential scanning calorimetry were performed. Furthermore, mechanical tests such as hardness and tensile strength were also performed along with the degree of swelling, gel content, and contact angle by using several solvents. This study elucidated the structure-property relationship based on the effect of curing time and aliphatic chain size of diamines in the properties of a NIPU film. The satisfactory thermal and mechanical properties, accompanied by a green and facile approach, displayed the potential scalability of the NIPU films.