Crystallization and Entanglement of Ultra-High Molecular Meight Polyethylene

Laboratory of Catalysis, Polymerization, Processes and Materials. We are located at the CPE-Lyon engineering school on the campus of the DOUA in Villeurbanne, and are supported by the CNRS, CPE-Lyon, and the Université Claude Bernard-Lyon. The CP2M is recognized for its expertise in polymerization catalysis and processes: development and implementation of advanced organometallic complexes and materials for different applications (of which homogeneous and heterogeneous catalysis), advanced polymerization chemistries and processes, reaction engineering, reactor design and process automation, and new approaches to the study of chemistry.

State of the art
Ultra-high molecular weight polyethylene (UH) is an exceptional material with a molecular weight exceeding one million g/mol, offering remarkable physical properties, including high resistance to abrasion, impact, and fatigue. While extensive entanglement of these exceedingly long UH chains enhances the polymer's toughness it also presents a challenge, as it leads to elevated melt viscosity, making the processing of entangled UH a challenging task. To address this, processing methods include using high pressure to provoke a reorganization of the entangled chains or disentangling the polymer chains through dilution with solvents (decalin) which involves large amounts of poisonous solvents such as decalin. An alternative route involves the direct synthesis of disentangled UH reactor powder.[1]

Project position
Recently the CP2M have developed the synthesis of “slightly” disentangled UH in gas phase on Ziegler-Natta supported catalysts in the presence of induced condensing agents (ICAs). Notably, using vaporized n-pentane as ICA, “slightly” disentangled UH with a draw ratio of 60-100 was obtained which puts them on a par with commercially interesting products (DR ≥ 100).[2-3] This method offers a solvent-free route for manufacturing disentangled UH, however, more in-depth study is required to explain the role of the ICA. Preliminary molecular dynamics simulations confirmed that n-alkanes like n-pentane reduce interchain entanglement by adsorbing onto polyethylene macromolecules and diminishing attractive interactions between them. These simulations enabled us to screen various ICA and identifies the best candidates which now need to be tested experimentally. Beyond the role of ICAs, a better understanding of the relationship between entanglement and crystallization is required in order to propose an optimal process.

Objectives :
• Test the selected ICA candidates in a gas phase process with a Ziegler-Natta catalyst to produce UH with a focus on improved drawability.
• Characterize the UH microstructure using SAXS/WAXS experiment
• Analyze the melting/crystallization kinetics of UH by Flash-DSC
• Study the entanglement kinetics using rheological measurements and HR-MAS solid-state NMR spectrometry

Reference
[1] Kurtz, The UHMWPE Handbook, 2004 (DOI :10.1016/B978-0-12-429851-4.X5000-1)
[2] Roberta Lopes do Roasario, PhD thesis UCBL
[3] Lopes do Rosario et al. J. Polym. Sci. 2022 (DOI :10.1002/pol.20230038)

Students with a master's degree or an engineer in materials science, chemistry, physical chemistry. Experience in chemical engineering and polymer chemistry is desired. Experience with catalysis and polymer chemistry will be a plus. Finally, the candidate must demonstrate great curiosity and an interest in process engineering.