Valorization of Bio- and Coal-Based Ash in Rigid Polyurethane Foams: Thermomechanical Performance and Decomposition Under Pyrolytic Conditions

This study investigates the pyrolytic processes and thermomechanical properties of polyurethane (PU) foamed composites filled with ashes obtained after sunflower husk combustion and conventional coal combustion, as well as their silanized derivatives. The results indicate that an improvement in thermal stability during the initial stages of pyrolysis was observed only for PU composites containing silanized ash generated from conventional coal combustion (a difference of 5 °C). At later stages of the thermal decomposition, a significant increase in temperature resistance was observed for the remaining composites. Kinetic studies of degradation using isoconversional methods revealed that composites containing sunflower husk ash exhibit degradation mechanisms different from those of the reference material, as observed by the changes in the activation energy particularly within the conversion range of 0.40–0.65. Dynamic mechanical analysis (DMA) demonstrated that all composites show improved mechanical response over a broad temperature range, with the highest mechanical performance observed after ash silanization (doubled E′ at the initial stage of the study compared to the reference). The analysis of evolved gases, performed using the Py-GC/MS technique, proved the existence of a different degradation path for composites with sunflower husk ash by a change in the amount of evolved gases during the pyrolysis process.