Apparent kinetics of nonisothermal high temperature oxidative degradation of ethylene homopolymers: effects of residual catalyst surface chemistry and structure

Journal of Polymer Research, January 2013, 20:56
Apparent kinetics of nonisothermal high temperature oxidative degradation of ethylene homopolymers: effects of residual catalyst surface chemistry and structure
Muhammad Atiqullah, Mohammad M. Hossain, Syed Masiur Rahman, Khurshid Alam, Hasan A. Al-Muallem, Abdulrahman F. Alharbi, Ikram Hussain, Anwar Hossaen
1. Center of Research Excellence in Petroleum Refining & Petrochemicals (CoRE-PRP); and Center for Refining & Petrochemicals, King Fahd University of Petroleum & Minerals, Dhahran, 31261, Saudi Arabia
2. Department of Chemical Engineering, King Fahd University of Petroleum & Minerals, Dhahran, 31261, Saudi Arabia
3. Center for Environment and Water, King Fahd University of Petroleum & Minerals, Dhahran, 31261, Saudi Arabia
4. Center for Refining & Petrochemicals, King Fahd University of Petroleum & Minerals, Dhahran, 31261, Saudi Arabia
5. Department of Chemistry, King Fahd University of Petroleum & Minerals, Dhahran, 31261, Saudi Arabia
6. Chemical Business, Saudi Aramco R&D Center, Dhahran, 31311, Saudi Arabia
Abstract
Researchers used TGA experiments and kinetic modeling to study the effects of two supported residual catalysts—one Ziegler-Natta and another metallocene—on the nonisothermal thermooxidative degradation of the resulting ethylene homopolymers.
They designed a rigorous constitutive kinetic model which, in contrast to the analytical Horowitz and Metzger model, fitted very well to the entire TGA curve, without distribution of activation energy Ea, for n (overall degradation order) = 1 for both polymers. Consequently, the proposed unified molecular level concept of surface chemistry and structure of the residual catalysts held all through the degradation process. The rigorous constitutive model-predicted apparent kinetic energy Ea, and frequency factor Z also support this finding. The proposed degradation mechanism suggests that the Zr residual catalyst more (i) decreased the activation energy required to decompose the −C−C− and the −O−O− bonds, and (ii) eliminated β-hydrogen (by the carbonyl functionalities) from the polymer chains. Study results present a rigorous constitutive kinetic model illustrating the influence of the characteristic surface chemistry and structure of the residual catalysts on the high temperature oxidative degradation of polyethylenes.
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