Thermal Decomposition Behavior of Castor Oil-based Polyurethane Resin

The thermogravimetric analyzer (TGA), thermogravimetric analysis-Fourier transform infrared spectrometer (TG-FTIR) and thermal pyrolysis gas chromatography/mass spectrometry (PY-GC/MS) were used for the test and characterization of the thermal degradation process in the castor oil-based polyurethane resin, different non-isothermal kinetic methods were used to calculate the kinetic parameters of the resin and infer the thermal degradation mechanism of the resin. The results show that the castor oil-based polyurethane resin starts to degrade at 285 ℃ (5% mass loss), and the degradation is almost complete around 450 ℃ (95% mass loss). The thermal degradation process (take a heating rate of 10 ℃/min as an example) is divided into three stages: the first stage occurs at 285.23~345.25 ℃, the mass loss is 60%, mainly due to the rupture of the resin urethane bond and parts of the ester group decomposed into CO₂; the second stage starts at 345.25~389.17 ℃ with 20% mass loss, the carbamate segment is degraded into amines, CO₂ and small molecular organics containing CH₃ or -CH₂-; the third stage occurs at 389.17~450.00 ℃, the mass loss is 20%, mainly because the small molecular organic matter is further degraded into CO₂ and N-containing volatile gas. The degradation mechanism may have two ways: the first is the cleavage of the carbon-oxygen bond on the left side of the ester group -O- in the main bond carbamate structure to form isocyanates and alcohols. The isocyanates are partially split into amines, carbon dioxide, etc., and the alcohol part is dehydrated to generate aldehydes or to synthesize olefins, enoic acids; the second is the cleavage of the -O- right carbon-oxygen bond in the carbamate structure to generate carbamic acid and alcohols. The carbamate partially cracked to generate primary amines and carbon dioxide, and alcohols partially cleft into aldehydes and olefins, etc.