Rigidity Percolation Dictates Rheological Hysteresis Regime in Polypropylene during Crystallization and Melting
Paul Roberts, Chad R. Snyder, Anthony P. Kotula
TL;DR
This study shows how the rigidity of polypropylene changes during crystallization and melting, revealing two distinct hysteresis regimes linked to percolation thresholds.
Contribution
The paper introduces a new framework linking rigidity percolation to rheological hysteresis in polypropylene using simultaneous rheology and Raman spectroscopy.
Findings
Polypropylene exhibits different rheological behavior during crystallization and melting at the same crystallinity due to thermal pathway.
Hysteresis onset aligns with the percolation threshold calculated by the GEM model.
Two hysteresis regimes are identified: one with limited hysteresis before percolation and one with large hysteresis after percolation.
Abstract
Understanding structure–property relationships during polymer crystallization and melting has been limited by challenges in the simultaneous measurement of crystallinity and rheological properties. Consequently, rheological models overlook the fundamental asymmetry between crystallization and melting processes. Here, we use simultaneous rheology and Raman spectroscopy to directly measure rheological behavior as a function of crystallinity. We find that polypropylene’s rheological behavior can differ significantly between crystallization and melting at identical crystallinity values depending on thermal pathway. Using a generalized effective medium (GEM) model, we show that the onset of hysteresis aligns with the calculated percolation threshold. We quantify hysteresis through a normalized hysteresis parameter ΔG̃ and show that the maximum value of ΔG̃ occurs at the percolation threshold…
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Taxonomy
TopicsPolymer crystallization and properties · Material Dynamics and Properties · Polymer Nanocomposites and Properties