Optimal Entanglement of Polymers Promotes Formation of Highly Oriented Fibers

TL;DR

This study uses large-scale simulations and theory to identify an optimal level of polymer entanglement that maximizes chain orientation and fiber strength, revealing a universal optimal entanglement number around 100.

Contribution

It introduces a microscopic analytical theory and simulation results showing an optimal entanglement level for fiber formation, challenging previous assumptions.

Findings

Optimal entanglement number is about 100 for maximum fiber orientation.

Both too many and too few entanglements lead to less oriented fibers.

A new theoretical framework explains fiber formation and disentanglement processes.

Abstract

Polymer fibers consist of macromolecules oriented along the fiber axis. Better alignment of chains leads to an increased strength of the fiber. It is believed that the key factor preventing formation of a perfectly oriented fiber is entanglement of polymers. We performed large-scale computer simulations of uniaxial stretching of semicrystalline ultrahigh molecular weight polyethylene. We discovered that there is an optimal number of entanglements per macromolecule necessary to maximize chain orientation in a fiber. Polymers that were entangled too strongly formed less oriented fibers. On the other hand, when polymers had too few entanglements per chain, they disentangled during stretching, and the strong fiber was not formed. We constructed a microscopic analytical theory describing both the fiber formation and disentanglement processes. Our work presents a novel view on the role of entanglements during fiber production and predicts the existence of a single universal optimal number of entanglements per chain maximizing the fiber quality: approximately $10^2$ entanglements.