Comparative Analysis of Aliphatic and Aromatic Isocyanates on Soy-Based Polyurethane Films Modified with Schiff Base Diol

Polyurethanes (PUs) are widely utilized in various industries due to their versatile properties. Traditionally, these polymers are synthesized using petrochemical-based polyols, which pose environmental concerns. To address this issue, there is a growing trend towards the use of bioresources in polymer manufacturing. This study explores the synthesis of a Schiff base diol derived from ethylene diamine (EDA) and vanillin, which can be obtained by depolymerization of lignin. Additionally, a soybean oil-based polyol (SOP) was employed as a sustainable alternative to traditional petroleum-based polyols. The synthesized Schiff base diol and SOP were used to prepare PU films, incorporating both aromatic and aliphatic diisocyanates which are methylene diphenyl diisocyanate (MDI) and hexamethylene diisocyanate (HDI), respectively. The primary objective was to investigate the impact of the aromatic and aliphatic nature of the isocyanates on the properties of the resultant PU films. The thermal stability and mechanical properties of the PU films were evaluated and compared. The results demonstrate that the bio-based PU films exhibit good thermal stability. However, contrary to expectations, the mechanical strength decreased with an increasing amount of Schiff base diol, while the elongation percentage increased. A flammability test was also performed to assess flame retardancy, and an unexpected trend was observed in HDI-containing PU films, which is discussed in detail in the manuscript. The study highlights the potential of using bioresources, such as vanillin and soybean oil, to produce sustainable and thermally stable PUs, paving the way for more environmentally friendly applications in the polymeric industry and beyond.