Antagonism between transition metal pro-oxidants in polyethylene films

Nikolic, Melissa, Gauthier, Emilie, George, Karina, Cash, Gregory, de Jonge, Martin D., Howard, Daryl L., Paterson, David, Laycock, Bronwyn, Halley, Peter J. and George, Graeme (2012) Antagonism between transition metal pro-oxidants in polyethylene films. Polymer Degradation and Stability, 97 7: 1178-1188. doi:10.1016/j.polymdegradstab.2012.03.036


Author Nikolic, Melissa
Gauthier, Emilie
George, Karina
Cash, Gregory
de Jonge, Martin D.
Howard, Daryl L.
Paterson, David
Laycock, Bronwyn
Halley, Peter J.
George, Graeme
Title Antagonism between transition metal pro-oxidants in polyethylene films
Journal name Polymer Degradation and Stability   Check publisher's open access policy
ISSN 0141-3910
1873-2321
Publication date 2012-07
Sub-type Article (original research)
DOI 10.1016/j.polymdegradstab.2012.03.036
Volume 97
Issue 7
Start page 1178
End page 1188
Total pages 11
Place of publication Oxford, United Kingdom
Publisher Elsevier
Collection year 2013
Language eng
Formatted abstract The oxidation of linear low density polyethylene (LLDPE) films containing the combination of pro-oxidants titanium (IV) dioxide (TiO 2) with either cobalt (II) stearate (CoSt) or iron (II) stearate (FeSt) have been evaluated under accelerated photo- and thermo-oxidative conditions as well as on outdoor weathering. LLDPE containing only surface-compatibilised nano-TiO 2 rapidly photo-whitens and embrittles at a low apparent extent of oxidation (as measured by carbonyl index) due to formation of microscopic voids of ∼150 nm. When CoSt was also included in the film, antagonism occurred shown by embrittlement times longer by ∼90%, higher carbonyl index and absence of film whitening. In contrast, films containing TiO 2/FeSt whitened during photo-oxidation and exhibited lower antagonism with only 44% longer times to embrittlement and lower carbonyl index. Antagonism between pro-oxidants was not observed under dark thermo-oxidative conditions. X-ray Fluorescence Microspectroscopy elemental maps revealed that the TiO 2 nanoparticles were spatially correlated with iron and cobalt metal ions allowing scavenging of electrons and holes through cycling of the redox states of the metal without producing radical species to initiate polymer oxidation. It is suggested that the antagonism differences between TiO 2/CoSt and TiO 2/FeSt pro-oxidants is related to the respective reduction potentials of Co 3+/2+ and Fe 3+/2+ and their effect on the UV conduction and valence band edges of the TiO 2 particle. In these ways the photochemistry of TiO 2 is suppressed and the photo-oxidative lifetime is governed by the chemistry of the transition metal pro-oxidant.
Keyword Polyethylene
Pro-oxidant
Transition metal
Photo-oxidation
Thermo-oxidation
TiO2
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ
Additional Notes Available online 30 March 2012.

 
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