Paper Number
SM28 

Session
Polymers Solutions, Melts and Blends

Title
Dilution rheology allows for the determination of the molecular weight distribution of ultra-high molecular weight polyolefins

Presentation Date and Time
October 11, 2022 (Tuesday) 2:50

Track / Room
Track 2 / Sheraton 3

Authors (Click on name to view author profile)

  1. Ianniello, Vincenzo (University of Naples, DICMaPI)
  2. Costanzo, Salvatore (Federico II University, Department of Chemical, Materials and Production Engineering)
  3. Pasquino, Rossana (DICMaPI, Università degli Studi di Napoli Federico II)
  4. Ianniruberto, Giovanni (Federico II University, Department of Chemical, Materials and Production Engineering)
  5. Tervoort, Theo A. (ETH Zurich, Department of Materials)
  6. Grizzuti, Nino (University of Naples Federico II, Chemical, Materials and Industrial Production Engineering)

Author and Affiliation Lines (in printed abstract book)
Vincenzo Ianniello1, Salvatore Costanzo1, Rossana Pasquino1, Giovanni Ianniruberto1, Theo A. Tervoort2 and Nino Grizzuti1
1Chemical, Materials and Industrial Production Engineering, University of Naples Federico II, Naples, Naples 80125, Italy; 2Department of Materials, ETH Zurich, Zurich, ZH 8093, Switzerland

Speaker / Presenter 
Grizzuti, Nino

Keywords
experimental methods; theoretical methods; polymer melts; polymer solutions

Text of Abstract
Ultra-High Molecular Weight Polyolefins (UHMWPOs), such as Polyethylene (PE) and Polypropylene (PP) are high performance materials used in many industrial and biomedical applications. Their high molecular weight improves some mechanical properties as well as the wear resistance but makes processing more difficult due to the very large melt viscosity. The latter may be even impossible to determine, due to a somewhat negative combination of instrument limits and viscoelasticity-driven instabilities. Furthermore, some relevant molecular properties, such as the Molecular Weight Distribution (MWD), are intrinsically difficult to measure by standard methods. In this paper, we explored the idea of diluting the UHMWPO with a suitable solvent, in order to both minimize the above-mentioned experimental limitations and widen the window of linear viscoelasticity towards the longest relaxation times. To this end, we prepared solutions of UHMW PE and PP into their corresponding oligomers of molecular weight below the entanglement threshold, thus avoiding issues related to unfavourable solvent-polymer interactions. We measured the linear viscoelastic response by a combination of oscillatory and creep experiments and we verified that the scaling laws of the main rheological parameters (plateau modulus, relaxation time, zero-shear viscosity) as a function of concentration were well obeyed. In this way, using a time-concentration superposition approach, we were able to build master curves for the pure melt over a wide range of frequencies, thus uncovering the terminal relaxation regime. The rheological results were then elaborated by using the time-dependent diffusion/double reptation model introduced by van Ruymbeke et al., which allowed to finally obtain the MWD of the polymer. The latter was found to satisfactorily agree with the MWD (when available) independently obtained by other measuring techniques.