Electrospinning

From Basic Research to Commercialization

Erich Kny, Kajal Ghosal, Sabu Thomas, Erich Kny, Kajal Ghosal, Sabu Thomas

• Publisher: Royal Society of Chemistry
• Year: 2018
• ISBN:
  9781788014915
• Edition: 1
• Topic: Technik & Maschinenbau
• Subtopic: Werkstoffwissenschaft

Electrospinning is a technique used to produce nanofibres from a polymer solution using an electrostatic force. The technology is now being used to create materials for a wide variety of uses from tissue engineering and 3D printing to packaging materials and electronic sensors.

This new book focusses on the recent developments in their design, process parameters and polymers-selection to enable the commercial applications of electrospinning. The initial chapters introduce the technique and then specific chapters focus on the different application areas showing the various approaches for successful implementation of this fabrication process towards commercialization from basic research and development.

The book will be suitable for graduate students, academics and industrial entrepreneurs in materials science, polymer science and chemical engineering as well as those interested in the energy and health applications of the materials.

CHAPTER 1

Electrical Spinning to Electrospinning: a Brief History

K. Ghosal^*a, C. Agatemor^b, N. Tucker^c, E. Kny^d and S. Thomas^a

^aMahatma Gandhi University, Department of Chemical Science, Priyadarshini, Kottayam, 686560, India

^bHarvard University, Harvard John A. Paulson School of Engineering and Applied Sciences, 29 Oxford Street, Cambridge, MA 02138, USA

^cUniversity of Lincoln, School of Engineering, Lincoln LN6 7TS, UK
^dCEST GmbH, 2700 Wiener Neustadt, Austria
^*E-mail: [email protected]

Fine fibers made by electrostatic force have been discussed, investigated, and patented since the late 18th century. However, until the 1980s, potential applications for such fibers were restricted by various technological limitations. In 1995, Doshi and Reneker reworked and simplified the electrical spinning process. This book begins with this journey, and describes how the invention fueled applications. It also presents a short account of the current status of electrospinning in diverse fields of application.

1.1Introduction to Early Concepts, Phenomena and Technology Related to Electrospinning

1.1.1Initial Identity of Triboelectric Charge and the Consequences for Electrohydrodynamic Processes

Electrospinning technology has progressed a long way, from certain fundamental concepts to substantial industrial applications. Electrospinning is an electrohydrodynamic process resulting in the movement of a fluid by means of the application of an electrostatic field. This movement of liquids by electrostatic force was first observed by William Gilbert, sometime personal physician to Queen Elizabeth I of England and president of the Royal College of Physicians. In about 1600, Gilbert¹ first recorded the movement of liquid under the influence of a triboelectric field produced by rubbing amber. Due to friction-induced charge separation, the amber is electrified. The rubbing or friction of some material with another material to produce a separated charge was widely known, having said to have been first observed by the Greek philosopher, Thales of Miletus.² The use of amber (in ancient Greek ἤλεκτρον or ēlektron) gave rise to the coinage by Gilbert of the word ‘electricus’, which in turn lead to the terms ‘electric’ and ‘electricity’. When the rubbed amber was placed in proximity to a water droplet placed on a dry surface, the water droplet distorted under the influence of electric charge into a diagnostic conical shape that later became known as the Taylor cone.³ William Gilbert observed:

Indeed it plainly does draw the body itself in the case of a spherical drop of water standing on a dry surface; for a piece of amber applied to it at a suitable distance pulls the nearest parts out of their position and draws it up into a cone; otherwise, if it were drawn by means of the air rushing along, the whole drop would have moved.¹

Before the invention of reliable methods of generating low-voltage, high-current electricity, a considerable amount of fundamental work on electricity using high-voltage electrostatics was undertaken by workers such as Otto von Guericke, Stephen Gray, Charles Francois Dufay and Georg Mathias Bose.

In 1749, French clergyman and physicist Jean-Antoine Nollet⁴ observed another electrohydrodynamic phenomenon, namely how electrifying water can cause the formation of droplets, a process now known as electrospraying. None of this early work resulted in the development of recognizable processing technology for either electrospraying or electrospinning. The efforts of these early workers were focused on the description and understanding of these phenomena. The concept of an artificial fiber dates from this period, being proposed by the natural philosopher Robert Hooke. Hooke⁵ said that to succeed in producing artificial fibers from an unnamed ‘glutinous composition’, “very quick ways of drawing it out into small wires for use could be found”.

There were also parallel attempts to store the charge. The storing of electrostatic charge was first experimentally achieved using a glass jar (known as a Leyden jar), coated inside and out with metal foil. The Leyden jar form of the capacitor was developed by Pieter van Musschenbroek, Professor of Physics at Leiden University, but the credit for performing this experiment is often attributed to the German scientist, Ewald G. von Kleist, in 1745.⁶

In electrospinning, electrostatic charge provides the motive force for the production of fibers. The speed of a fiber in flight is commonly between 60 and 100 m s⁻¹, but the mass rate of production from a single spinneret is typically measured in mg per hour. The electrostatic charge that is engendered in the fluid by applying a high voltage causes the fluid to overcome the surface tension that holds a pendant droplet in shape. Ultimately the surface of the droplet fails and droplets or – if there is sufficient molecular cohesion – a fiber are ejected from the droplet. This form of use of electrostatic charge is applied in various fields in addition to electrospinning. Examples include photocopying, laser printing, electrostatic painting and acoustic transducers, including high-fidelity loudspeakers, particle separators, and electrostatic filters.⁶

1.1.2The Development of Industrial Spinning Processes

The establishment of the electrohydrodynamic process of electrospinning as a commercial application is the result of work by a number of researchers and manufacturers. It should be noted that the work by the academic community has been of most use in understanding the parallel efforts of commercial companies to develop the spinning process. Electrospinning is but one of a number of artificial fiber manufacturing processes that were developed during the 19th century.

The need for large quantities of reliable fiber for the production of woven and embroidered goods during the Victorian period was an early driver for the production of artificial fibers. At that time, machine embroidery was mainly used for decorative furnishings. In 1828, Josué Heilmann developed commercial machine fiber combing and stressed the importance of improvements to profitability that this process offered for large-scale production; the machine was patented in 1829 in England. Joshua Wordsworth, the owner of a weaving mill who took out a patent on the machine, and in turn established a parallel arrangement with Manchester silk manufacturer Louis Schwabe for fabricating embroidered goods. Louis Schwabe devised a process for spinning glass fiber, but was unable to find a more suitable spinning material for fabric production,⁷ although he put considerable work into “carrying out experiments which would lead to the discovery of a substance which would form a homogeneous mass possessing the quality of ductility and susceptible of being drawn out through fine holes, or otherwise, into filaments or fibers possessing suitable strength and other properties to adapt it for manufacturing purposes”.

The invention of a potential spinning formulation by George Audemars⁸ in 1855, of suitable strength and suitable for the manufacturing process, had been demonstrated in concept by Schwabe. Audemars dipped needles into a nitrocellulose solution, then drew it into air, obtaining a long durable thread as the solvent evaporated. The manually applied dragging force pulling the fibers from the polymer solution was low, but the process was very slow and hence only suitable for small-scale production. Cellulose was first nitrated to a high degree by the Swiss chemist Christian Schönbein, in 1845, who patented his process for the production of the explosive known as guncotton. In 1846 Louis-Nicolas Ménard and Florès Domonte dissolved cellulose nitrate in a mixture of ether (ethoxyethane) as the solvent and ethanol as a diluent to produce a solution that became known as collodion. The expedition of generating fibers continued. Count Hilaire De Chardonnet, a French engineer and industrialist, forced a solution of cellulose derivatives through small holes like a spinneret, then dried these in air and further treated the fibers with a coagulating medium: for this work he became known as the ‘father of the artificial silk industry’.⁹ His artificial silk was sold as ‘Chardonnet silk’. Chardonnet silk was the first artificial semi-synthetic fiber. The invention was exhibited by Chardonnet in 1889, but pre-dated in 1855 by Joseph Wilson Swan, the British chemist who produced fibers for electric light filaments from ‘parchmentized’ cotton, and who went on by 1881 to develop and patent a method for extruding nitrocellulose to form conducting fiber filaments – this material was used to produce incandescent light bulbs by the Edison & Swan United Electric Light Company.

The next significant development was cuprammonium silk. In 1857, Eduard Schweizer investigated the solubility of cellulose in an ammoniacal solution of copper hydroxide (cuprammonium hydroxide solution). This observation was applied to the fiber production process in 1890 by L. H. Despaissis, who regenerated a solution of cellulose into a solid¹⁰ by treating a cuprammonium solution of cellulose in a coagulating bath. Although the process was patented, it was not successfully commercialized. Two years later, in 1892, Dr Max Fremery and Johan Urban used a development of the process to make lamp filaments: the first profitable outcome of manufacturing cellulose fibers from a cuprammonium solution. At first only short discontinuous lamp filament fibers were produced. It took significant further work to produce continuous long fibers. Early in the market in 1908 with this material...