Cure Behavior, Thermal Degradation and Kinetic Analysis of Sustainable Polyurethanes

To reduce dependence on fossil resources and limit the use of harmful isocyanates, researchers are increasingly developing polyurethanes (PUs) using renewable building blocks like bio-based polyols and diisocyanates. In this work, new PUs were produced using poly(ethylene glycol) (PEG), isosorbide (ISO), and pentamethylene diisocyanate (PDI) to create more sustainable materials. Various compositions were prepared with ISO levels ranging from 0 % to 70 % in a vacuum reactor fitted with a condenser and magnetic stirring. The resulting polymers were analyzed using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TG). The DSC data showed exothermic peaks in the 100–200 °C range, revealing active crosslinking reactions. Increasing ISO content made the curing reaction faster, with the T_0.01 shifting from 95 °C at 50 % ISO to 91 °C at 70 % ISO, and the maximum rate constant (Cmax) rising slightly as well (0.2750 to 0.2964 min^-1, respectively). FTIR confirmed the chemical bonding between hydroxyl (OH) groups in ISO/PEG and isocyanate (NCO) groups in PDI, showing full NCO conversion at the 2267 cm⁻¹ band. Formulations with higher ISO content (>50 %) exhibited an excess of hydroxyl groups, increasing the system’s reactivity through both covalent and hydrogen bonding, which promoted more extensive crosslinking. For samples with 70 % ISO, the NCO groups were completely reacted at 126 °C, while the 50% ISO variant reached near-total (99 %) curing at 192 °C. TG results indicated that higher ISO levels caused earlier weight loss due to degradation, starting around 146–151 °C for 50 and 70 % ISO, respectively. The curing and thermal degradation processes were modeled with Friedman, Kissinger–Akahira–Sunose, and Ozawa–Flynn–Wall methods, confirming that moderate ISO content (i.e., 30 – 50 %) enhances both curing speed, degradation activation energy and thermal stability.