# Ultrasonic-Assisted Extrusion Processing for Enhancing Physical Properties of High-Density Polyethylene by Flow-Induced Crystallization

## TL;DR

This paper explores using ultrasonic-assisted extrusion to improve the crystallinity and properties of high-density polyethylene films.

## Contribution

The novel use of ultrasonic fields during extrusion to induce crystallinity and enhance polymer properties without additives.

## Key findings

- Ultrasonic shear rates significantly influence lamellar spacing and amorphous fraction redistribution in HDPE.
- Ultrasonic-assisted extrusion improves mechanical and oxygen barrier properties of monolayer films.
- Regression models correlate HDPE structure, processing, and performance effectively.

## Abstract

The evolution of crystallinity resulting from stress
imposed on
a melt, known as flow-induced crystallinity, can strongly influence
the mechanical and physical properties of semicrystalline polymers.
This study investigates shear-induced crystallization by applying
an ultrasonic field to the melt flow as it passes through dies with
various geometries. A custom-built sonication die is employed for
controlling the dynamic temperature and shear environment, resulting
in molecular alignment and potential for flow-induced crystallization.
Application of both conventional and ultrasonic shear rates at the
equilibrium melt temperature of high-density polyethylene (HDPE) was
investigated to accelerate crystallinity and manipulate the crystal
morphology across the film in pursuit of improved mechanical and gas
barrier properties without the need for additives or other polymer
layers. The relationships among ultrasonic-assisted extrusion processing,
polymer structure, and performance were analyzed using wide- and small-angle
X-ray scattering (WAXS and SAXS), tensile testing, and oxygen transmission
rate (OTR) analysis. Multiple linear regression models were implemented
to predict the correlation among HDPE structure, process, and properties.
Structural analysis revealed that both conventional and ultrasonic
shear rates had the most significant influence on lamellar spacing
and redistribution of rigid and soft amorphous fractions within the
crystalline domains, ultimately dictating the mechanical and physical
properties of the films. The goal is to explore the potential of the
ultrasonic-assisted high crystallinity monolayer that can replace
some of the functionality of complex, heterogeneous multilayer packaging
with a single-material film having enhanced oxygen barrier properties.