Insights into the thermal behavior and flammability of poly(limonene carbonate)

This study investigates the thermal behavior of poly(limonene carbonate) (PLimC), focusing on three main areas: molecular mobility, pyrolysis, and flammability. Considering its molecular structure, a key objective is to compare the properties of PLimC with those of conventional polyolefins (PO) and bisphenol A polycarbonate (PC), while also examining the role of the plasticizer in PLimC and the effect of molecular weight. Molecular mobility was analyzed using broadband dielectric spectroscopy (BDS) and differential scanning calorimetry (DSC); pyrolysis by thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy, and pyrolysis gas chromatography-mass spectrometry (Py-GC-MS); and flammability by cone calorimeter, bomb calorimeter, UL 94, and limiting oxygen index (LOI). Three relaxation processes were identified by BDS: γ (low temperature), β (intermediate), and α (near glass transition temperature). Higher molecular weight increased the cooperativity of the α relaxation mobility due to chain entanglements. Plasticizers counteract this effect by increasing free volume and reducing intermolecular interactions, leading to less cooperative molecular dynamics and stronger glass-forming behavior. PLimC resembles polyolefins in its lack of char formation and low LOI (17.2 vol.-% O₂), but its decomposition pathway and effective heat of combustion (29.3 MJ kg -1 ) are similar to those of PC, producing CO₂ and limonene oxide derivatives. Notably, PLimC has a lower decomposition temperature (242–243 °C). These findings provide a foundation for developing effective flame retardant strategies tailored to PLimC’s hybrid thermal behavior, sharing characteristics of both PO and PC.