Rubber articles including tires are the materials that are very sensitive towards ozone attack, which induces accelerated aging and cracks and can lead to the failure of these articles. Considering the increasing amount of ozone in the troposphere, the topic of protection of rubber articles becomes more important. N-substituted p-phenyl diamines, also known as PPDs, are typically used as antiozonants to protect the tires from ozone attack as the nitroxyl radicals formed by PPDs or secondary aromatic amines enter the redox cycle, thus giving the tire a longer life. To work with a more simplified model, squalene was used in this work as it has a similar degradation mechanism as natural rubber. The main goals of this project are to monitor the degradation of squalene films which are doped with diphenylamine in the presence of gas-phase ozone and to evaluate the products formed with the help of Attenuated Total Reflectance - Fourier Transform Infrared Spectroscopy (ATR-FTIR). A thin film of about 1 micrometer of both squalene and diphenylamine was pipetted on the ATR crystal, which was then exposed to the ozone gas, and IR spectra of the reaction were recorded in real-time. The IR spectra showed the formation of new peaks around the carbonyl and alcohol region. Future work will characterize the kinetics of the reaction and determine the ratio of squalene and diphenylamine required to inhibit the oxidation of squalene.

Multiphase oxidation of squalene and diphenylamine with ozone gas by using ATR-FTIR spectroscopy

ACS Spring 2022

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