A Preliminary Investigation on Recycled PET-Derived Polyurethane Films: Role of NCO/OH Ratio in Film Development

This study presents the synthesis of polyurethane (PU) films using recycled polyethylene terephthalate (rPET) as a sustainable substrate. The rPET was depolymerized through the glycolysis reaction to produce a polyol, which was then reacted with polymeric methylene diphenyl diisocyanate (PMDI) via solution polymerization to form Polyurethane Film. The effect of varying NCO/OH molar ratios (1.00, 1.25, and 1.50) on the properties of the resulting films was investigated, with a focus on enhancing mechanical performance. The PU films were characterized by their physical appearance, FT-IR spectroscopy, and mechanical properties. At the NCO/OH ratio of 1.00, the PU remained in the form of sticky substance like glue and was unable to form into a solid film. However, increasing the ratio to 1.25 and 1.50 resulted in continuous, flexible films with significantly improved mechanical strength. FT-IR analysis confirmed the formation of urethane linkages, as evidenced by a clear reduction in –OH and –NCO functional groups after the film forming. The best performance was observed at an NCO/OH ratio of 1.50, yielding a PU film with a Young’s modulus of 0.528 N/mm², tensile strength of 1.289 N/mm², and elongation at break of 496.587%. These results highlight the importance of the NCO/OH ratio in tailoring films with suitable properties and support the potential of rPET-based PU as a sustainable material for advanced applications.