Ellagic acid as stabilizer in the thermo-oxidative degradation of thermoplastic polyurethane

Ellagic acid (EA) is a plant polyphenol with strong antioxidant properties. The stabilizing effect of EA on the \nthermo-oxidative degradation of the commercial thermoplastic poly(ester-ether urethane) (TPU) was studied for \nthe first time and compared with effect of kraft lignin (KL), butylated hydroxytoluene (BHT) and pentaerythritol \ntetrakis (Irganox 1010). TPUs doped with antioxidants (ca. 20,000 ppm), were analysed for their oxidation in- \nduction time (OIT) at 200 ◦C and the oxidation onset temperature (OOT). The extent of TPU degradation with \nand without addition of antioxidants was studied by head space-gas chromatography-mass spectrometry (HS-GC- \nMS) at 200 ◦C under aerobic atmosphere. The highest stabilizing effect of EA was attributed primarily to its \nstronger antioxidant capacity when compared to KL and synthetic polyphenolic antioxidants (BHT and Irganox), \nwhich was corroborated by antiradical power studies with 2,2-diphenyl-1-picrylhydrazyl (DPPH). The analysis of \nthe volatile products released under thermo-oxidative degradation showed the suppressive effect of EA on the \nthermally induced depolymerization of TPU occurring via homolysis. Furthermore, it has also been proposed that \nEA affects TPU degradation with the cleavage of urethane bonds in carbamates due to eventual coordination with \nthe intermediate cyclic intramolecular transition complex involved in thermally induced depolymerization. \nFurther studies in this area can prompt the performance improvements of TPU products, allowing them to be \nused in a wider range of durable goods applications.