© 2014 Akadémiai Kiadó, Budapest, Hungary. A silica-supported bis(n-butylcyclopentadienyl) zirconium dichloride [( n BuCp)2ZrCl2] catalyst was synthesized. This was used to prepare an ethylene homopolymer and an ethylene-1-hexene copolymer. The active center multiplicity of this catalyst was modeled by deconvoluting the copolymer molecular mass distribution and chemical composition distribution. Five different active site types were predicted, which matched the successive self-nucleation and annealing temperature peaks. The thermo-oxidative melt stability, with and without Irganox 1010 and Irgafos 168, of the above polyethylenes was investigated using nonisothermal differential scanning calorimetric (DSC) experiments at 150 °C. This is a temperature that ensures complete melting of the samples and avoids the diffusivity of oxygen to interfere into polyethylene crystallinity and its thermo-oxidative melt degradation. The oxidation parameters such as onset oxidation temperature, induction period, protection factor, and S-factor were determined by combining theoretical modeling with the DSC experiments. Subsequently, these findings were discussed considering catalyst active center multiplicity and polymer microstructure, particularly average ethylene sequence length. Several insightful results, which have not been reported earlier in the literature, were obtained. The antioxidant effect, for each polymer, varied as (Irganox + Irgafos) ≈ Irganox > Irgafos > Neat polymer. The as-synthesized homopolymer turned out to be almost twice as stable as the corresponding copolymer. The antioxidant(s) in the copolymer showed higher antioxidant effectiveness (AEX) than those in the homopolymer. Irganox exhibited more AEX than Irgafos. To the best of our knowledge, such findings have not been reported earlier in the literature. However, mixed with Irganox or Irgafos, their melt oxidation stability was comparable. The homopolymer, as per the calculated S-factor, showed Irganox-Irgafos synergistic effect five times that of the copolymer. This illustrates how the transition in backbone structure, from exceedingly high to low ethylene sequence length, influences antioxidant synergistic performance. Finally, this study shows a DSC-aided approach that can elucidate the effect of polyethylene structural backbone on its thermo-oxidative melt degradation as well as antioxidant synergism in a facile fashion.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The authors acknowledge the financial supportprovided by King Abdulaziz City for Science and Technology(KACST) via the Science and Technology Unit at King Fahd Uni-versity of Petroleum and Minerals (KFUPM) through Project Number08-PET90-4 as part of the National Science and Technology Inno-vation Plan. The technical assistance provided by the followingKFUPM centers—Center of Refining and Petrochemicals (CRP) andCenter for Engineering Research at Research Institute, and the Centerof Research Excellence in Petroleum Refining and Petrochemicals(CoRE-PRP)—at Dhahran, Saudi Arabia; NMR Core Laboratory,Thuwal, King Abdullah University of Science and Technology(KAUST), Saudi Arabia; the Department of Chemical Engineering atKFUPM and the Department of Chemical Engineering at KasetsartUniversity, Thailand; and Institute of Physical Chemistry andChemical Physics, Slovak University of Technology, Slovak Republicis also gratefully acknowledged. Messrs. Anwar Hossaen and SarathP. Unnikari are appreciated for technical support
This publication acknowledges KAUST support, but has no KAUST affiliated authors.