Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.785472
Title: The role and significance of singlet oxygen in the degradation of engine oils
Author: Davies, Rebecca
Awarding Body: Loughborough University
Current Institution: Loughborough University
Date of Award: 2017
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Abstract:
The potential role of singlet oxygen in the oxidation, and subsequent degradation, of engine oils was investigated using spectroscopic steady-state and singlet oxygen lifetime measurements. Three currently commercially available antioxidants; a sterically hindered amine (aminic), a sterically hindered phenol (phenolic) and sulfurized olefin, all provided by Lubrizol, were tested alongside previously documented singlet oxygen quenchers; atocopherol and squalene. Singlet oxygen quenching constants, kQ, were calculated via both methods in a polar, 1-butanol, and non-polar, hexadecane, solvents to assess any potential solvent effects on each antioxidant's efficiency. α-Tocopherol showed the highest quenching in 1-butanol; 2.87x108 and 1.19x108 dm3mol-1 s -1 , in both spectroscopic and lifetime testing respectively. Of the commercial antioxidants, the aminic showed significant quenching across spectroscopic and lifetime tests in both solvents; 1.03 – 2.54x107 dm3mol-1 s -1 in steady-state and 4.70 – 5.65x106 dm3mol-1 s -1 in lifetime tests. Two different methods were employed to test several combinations of the antioxidants for signs of synergistic or inhibitory behaviour. Of the combinations tested the combination of the aminic and phenolic antioxidants showed the most significant synergistic effects, with improved singlet oxygen quenching across all tests, while the addition of squalene to any of the commercial antioxidants showed little to no sign of synergies in the primary method. The spectroscopic method was also utilised to attempt to detect signs of chemical quenching by each of the antioxidants. The absorbance of a-tocopherol at 294nm was observed to decrease significantly over the testing period, decreasing by 40-64%, suggesting chemical quenching may be the primary quenching pathway. The phenolic antioxidant also showed signs of chemical quenching; however, further tests are required to confirm the extent of its effect. Overall it was clear that all three of the commercial antioxidants tested showed the ability to quench singlet oxygen. This coupled with the efficiencies of quenching following the same trend as that seen in internal oxidation tests at Lubrizol; aminic > phenolic > sulfurized olefin, suggests that singlet oxygen may indeed be a factor in the oxidation of engine oils and that measurement of singlet oxygen quenching could be used as a sign of overall antioxidant effectiveness.
Supervisor: Not available Sponsor: Lubrizol Ltd
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.785472  DOI: Not available
Keywords: Chemical Sciences not elsewhere classified ; Singlet oxygen ; Antioxidant ; Engine oils
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