# Melt Spinning of Thermoplastic Polyurethane-Based Bulk Ionofibers Filled with Carbon Nanotubes

## TL;DR

This paper explores a method to create conductive fibers using thermoplastic polyurethane and carbon nanotubes for ionotronic textiles.

## Contribution

The study introduces an industrial-compatible melt-spinning process using ionic liquids and carbon nanotubes to enhance fiber conductivity.

## Key findings

- Melt-spun fibers with ionic liquid and carbon nanotubes achieved conductivities of 10–2 μS cm dtex–1.
- The segregated network of carbon nanotubes doubled fiber conductivity compared to fibers without ionic liquid.
- Optimal ratios of ionic liquid and carbon nanotubes were identified for efficient melt-spinning.

## Abstract

Ionotronic textiles or i-textiles offer in-air electrochemical
applications and sensing due to their ionic character, mimicking phenomena
of organisms. To manufacture different i-textiles with unique functions
and characteristics, it is necessary to have a range of ionically
conductive textile fibers or ionofibers to choose from. However, their
means of production are not sufficiently explored to provide knowledge
that meets the fabric manufacturing needs. For a textile application,
surface functionalization is usually explored as a convenient way
to build upon an already known textile material. In contrast, bulk
functionalization allows for superior production rate, versatility,
and durability. Additionally, the use of the synergy between ionic
liquids and carbon nanotubes is seldom explored. Therefore, in this
study, melt spinning is investigated regarding the use of an ionic
liquid (IL) initially without and ultimately with multiwalled carbon
nanotubes (CNTs) for the tailoring of the electrical and mechanical
properties of ionofibers. Based on thermoplastic polyurethane (TPU)
elastomers, IL-containing pellets are prepared using 1-ethyl-3-methylimidazolium
trifluoromethanesulfonate (EMIm OTf) at different weight ratios. About
the melt-spun monofilaments, their extrusion temperatures, their morphology
through scanning electron microscopy with energy-dispersive X-ray,
their fiber conductivity through electrochemical impedance spectroscopy
and cyclic voltammetry, and their tensile properties are investigated.
An optimum of the ratios of IL and CNTs is observed for the melt-spinning
process, which results in fiber conductivities within the range of
10–2 μS cm dtex–1. Compared
to a monofilament melt-spun with no IL and a CNT weight ratio above
percolation threshold, the fiber conductivity is twice higher due
to its intricate segregated network. Thus, this industrial textile-compatible
process offers an alternative within the development of ionotronic
fabrics.