Antioxidants from p-phenylendiamine in NBR Elastomers. Study of Thermooxidative Degradation Mechanism

The aim of this study is the determination of the influence of the N-isopropyl-N'-phenyl-p-phenylendiamine (IPPD) antioxidant agent when is incorporated to elastomers NBR. Particularly, it has been analyzed how the presence of antioxidant prevents the degrading process inhibiting it partially. NBR samples containing IPPD were exposed to an oxidizing atmosphere at 140 degrees C for different time periods (between 0 and 120 hours) to observe its performance. Besides, IPPD alone has been subject to the same ageing thermo-oxidizing process. The results show the presence of intermediate imines, oxims, aminoxyl radicals and nitro groups. Moreover, we suggest the IPPD mechanism that allows hindering the degradation process of NBR. At high temperatures NBR chains are broken to make alkyl and peroxide radicals. The alkyl radicals react with the aminoxyl radicals obtained during the degradation process to make the N-alcoxiimines. The last stage at long exposure time (more than 48 hours) is the forming of nitro group.