UHMW Ziegler–Natta polyethylene: Synthesis, crystallization, and melt behavior
KAUST DepartmentImaging and Characterization Core Lab
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AbstractThe fabrication of normal and UHMW PE end-products involves melting and crystallization of the polymer. Therefore, the melt behavior and crystallization of as-synthesized UHMW PE, and NMW PE and E-1-hexene copolymer have been studied using a new nonisothermal crystallization model, Flory's equilibrium theory and ethylene sequence length distribution concept (SLD), Gibbs–Thompson equation, and DSC experiments. By using this approach, the effects of MW, 1-hexene incorporation, ethylene SLD, the level of undercooling θ, and crystal surface free energy D on crystallite stability, relative crystallinity α, instantaneous crystallinity χ, the crystallization kinetic triplet, crystallization entropy, and lamellar thickness distribution (LTD) have been evaluated. Consequently, this study reports insightful new results, interpretations, and explanations regarding the melting and crystallization of the aforementioned polymers. The UHMW PE results significantly differ from the NMW PE and E-1-hexene copolymer ones. Ethylene sequences shorter than the so called minimum crystallizable ethylene sequence length, irrespective of E-1-hexene copolymer MW, can also crystallize. Additionally, the polymer preparation shows that the catalyst coordination environment and symmetry, as well as achiral ethylene versus prochiral α-olefin steric encumbrance and competitive diffusion affect the synthesis of UHMW PE, particularly the corresponding UHMW copolymers.
CitationAtiqullah M, Adamu S, Emwas A-HM (2017) UHMW Ziegler–Natta polyethylene: Synthesis, crystallization, and melt behavior. Journal of the Taiwan Institute of Chemical Engineers. Available: http://dx.doi.org/10.1016/j.jtice.2017.04.011.
SponsorsThe authors greatly acknowledge the financial support provided for this study by King Abdulaziz City for Science and Technology (KACST) via the Science & Technology Unit at King Fahd University of Petroleum & Minerals (KFUPM) through Project Number 14-PET-283-04 as part of the National Science and Technology Innovation Plan (MAARIFAH). The technical assistance provided by the Center for Refining & Petrochemicals (CRP) at the Research Institute, KFUPM, Dhahran, Saudi Arabia; and NMR Core Laboratory, Thuwal, King Abdullah University of Science & Technology (KAUST), Saudi Arabia is also gratefully acknowledged. The support offered by Prof. J. C. Santamarina, Energy GeoEngineering Laboratory, KAUST to NMR assay is highly appreciated. The technical assistance of Mr. Anwar Hossaen and the gift of the experimental α-olefins by United Petrochemicals, an affiliate of Saudi Basic Industries Corporation (SABIC), are thankfully appreciated.