Applications of Coupled Rheology–FTIR to Polymer Analyses

• Dr. Sara Reynard, Arkema (& President-elect of NATAS (North American Thermal Analysis Society) and Dr. Dana Garcia, consultant (& Arkema retired)
• Sponsored by the Golden Gate Polymer Forum
• 5-6pm, Online via Zoom, Free/$5 Donation, Registration required (Registration Deadline: Tuesday, February 15, 1:00 pm)

Abstract

The advancement of coupled rheological spectroscopic techniques opens wide opportunities to study in situ structure-property-processing-performance relationships of polymers under dynamic conditions. At Arkema, we explored the use of combined Rheo-IR in the attempt to understand the mechanisms behind phenomena such as shear instability, preferential crystallization pathways, structural changes under processing conditions, and more. This presentation summarizes our initial feasibility studies on temperature-dependent structural transitions in Styrene-Butadiene Copolymers and Polymethylmethacrylate-Polylactic acid (PMMA-PLA) blends. The collection of real time IR spectra allows identification of chemical changes within the polybutadiene blocks during isothermal rheological experiments. The partial irreversibility of the chemical changes indicates a possible crosslinking of the copolymer when processed at high temperatures. In the case of PMMA-PLA blends, the variation of the IR spectra suggests the formation of a metastable morphology formed at high temperatures, which was difficult to detect by the rheology alone.

In a more recent study, we describe the mechanisms of internal lubrication due to the addition of polymer process aids (PPAs) to polyethylene. In particular, we will focus on commercial fluoropolymer-based polymer processing additives, Kynar® PPAs, used to help melt fracture during film extrusion. We show that addition of ppm levels of Kynar® PPAs into PE drastically improves the quality of extrusion. The lubrication phenomenon is due to the migration of PPA particles to the metal surface of the die, which promotes wall slippage. Although the PPA migration mechanism at high shear rates is well understood in the industry, very little is known about the effect of PPA on the flow behavior of the molten polymer when processed at relatively low shear rates. Our Rheo-IR findings indicate a good correlation between the transient viscosity and the evolution of the CH2 band in presence of PPA. Based on the conformational changes and the increase in PE mobility observed in the IR spectra when shearing PE with Kynar® PPA, we suggest a new internal lubrication mechanism that involves the diffusion of PPA droplets across the polymer matrix instead of migrating to surface. This work explains why a small amount of Kynar® PPA is also beneficial for low shear rate processing such as pipe and cable extrusion. Further experiments are undergoing to investigate lubrication and migration phenomena in other commercial systems.

Speaker Background

Dr. Sara Reynaud joined Arkema in 2012, where she is a Senior Research Scientist. She leads research projects on rheological behavior and mechanical properties of polymers, and works on the implementation of new analytical methodologies. Sara is a co-author of 30+ technical publications including a highly cited review paper on boron carbide, a book chapter on carbon nanotubes; and 3 patents. Prior to joining Arkema, Sara was a postdoctoral associate at the Center for Ceramic Research at Rutgers University. She holds a Ph.D. degree in Material Science and Engineering from Rutgers and a combined BS/MS degree from the University of Naples in Italy. She has been actively involved with ASTM International where she is second vice-chairman of E37. Dr. Reynaud is a NATAS Fellow, and she is currently serving as NATAS President for 2022.

Dr. Dana Garcia received her BS degree in chemistry from Stockton State University (NJ) and her Ph.D. in physical-organic chemistry from Brandeis University (MA). Dana retired in Dec. 2021 from Arkema Inc., where she was a Principal Scientist at the Arkema King of Prussia (Pa.) Research Center, responsible for the vibrational spectroscopy laboratory. Prior to joining Arkema in 1987 she held industrial positions in the areas of polymer crystallization & nucleation and adhesive & composite characterization using FTIR, thermal, and rheological techniques. Dr. Garcia is a Fellow of the American Chemical Society and a Fellow of the American Chemical Society, POLY Division.