Rotary jet spinning review – a potential high yield future for polymer nanofibers

Abstract

Polymeric nanofibers have been the focus of much research due to their continually evolving applications in fields such as biomedicine, tissue engineering, composites, filtration, battery separators, and energy storage. Although several methods of producing nanofibers have shown promise for large scale production, none have yet produced large enough volumes at a low cost to be the front runner in the field, and therefore the preferred choice for industrialization. Rotary jet spinning (RJS) could be the answer to high throughput, low cost, and environmentally friendly nanofiber production. Being exploited in only the last decade, it is a technology that has seen relatively little research, but one which could potentially be the answer to large scale manufacturing of polymer nanofibers. In this review, we focus on fundamental processing characteristics and initial application driven research. A comparison between existing nanofiber production methods is drawn with the key differences noted. Two methods of utilizing RJS in nanofiber production are discussed, namely spinning from a polymer melt, and solution-based spinning as is typically used in more traditional methods such as electrospinning. Modeling of the process is introduced, in which material selection and processing parameters play an important role.

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Introduction
Polymer nanober research is a topical eld in the materials world
today
1
and is made up of many dierent types of production and
assembly methods based around the development and pace
of the technology being introduced. Within each novel way of
manufacturing nanobers, a myriad of uses for each type exists. It
is this demand for varying uses which provides the driving force
behind the research into newer, better technologies. Each new
iteration or technology jump tries to overcome the aws of their
predecessors. This constant innovation and continuing research
is looking toward the use of nanobers to complement the exist-
ing burgeoning microber industry. Nanobers, which are bers
typically less than one micrometer in diameter, are slowly being
introduced into the market as technologies to successfully man-
ufacture them in large volumes become available.
The manufacturing techniques that are available to pro-
duce nanobers, as well as microbers, vary greatly, with some
techniques oering benets that supersede others in either
volume, cost, or environmental qualities, etc. While some
techniques produce vast amounts of material in a short space
of time, others are only capable of producing insignicant
amounts not suitable for industrial scale applications.
Why polymer nanofibers?
There exist many reasons why it is benecial for certain appli-
cations to prefer nanobers over microbers, largely due to
their ability to oer advantages due to their reduced diameter.
Within this nanoscale, the bers have a greater surface area
to volume ratio and tunable porosity,2 making them attrac-
tive for applications such as ltration and composites, where
lters may benet from increased eciency by reducing the
ber diameter,3 and nanocomposites may show potentially
enhanced properties, notably toughness, due to an increase
in surface area.4–6 In a typical ltration application of nanober
mats as can be seen in Figure 1, the pollen spore is incapable
of traveling through the nanober mat, rendering it a suitable
air ltration application for a variety of objects (Figure 2).
Currently, nanoscale bers can be produced using exist-
ing techniques such as electrospinning,8–10 melt blowing,11,12
island-in-the-sea spinning13–15 and template synthesis16 to
Review
Rotary jet spinning review – a potential
high yield future for polymer nanofibers
James J. Rogalski, Cees W. M. Bastiaansen and Ton Peijs*
School of Engineering and Materials Science, and Materials Research Institute, Queen Mary University of London,
Mile End Road, E1 4NS London, UK
*Corresponding author, email t.peijs@qmul.ac.uk
Abstract
Polymeric nanofibers have been the focus of much
research due to their continually evolving applications in fields
such as biomedicine, tissue engineering, composites, filtration,
battery separators, and energy storage. Although several
methods of producing nanofibers have shown promise for
large scale production, none have yet produced large enough
volumes at a low cost to be the front runner in the field, and
therefore the preferred choice for industrialization. Rotary
jet spinning (RJS) could be the answer to high throughput,
low cost, and environmentally friendly nanofiber production.
Being exploited in only the last decade, it is a technology that
has seen relatively little research, but one which could potentially be the answer to large scale manufacturing of polymer
nanofibers. In this review, we focus on fundamental processing characteristics and initial application driven research. A
comparison between existing nanofiber production methods is drawn with the key differences noted. Two methods of
utilizing RJS in nanofiber production are discussed, namely spinning from a polymer melt, and solution-based spinning
as is typically used in more traditional methods such as electrospinning. Modeling of the process is introduced, in which
material selection and processing parameters play an important role.
Keywords Polymer nanobers, Rotary jet spinning, Electrospinning, Processing, Properties, Applications, Modeling
Cite this article James J. Rogalski, Cees W. M. Bastiaansen and Ton Peijs; Nanocomposites, doi: 10.1080/20550324.2017.1393919
Received  July ; accepted  October 
DOI: 10.1080/20550324.2017.1393919

Rogalski et al.
Rotary jet spinning review
Nanocomposites 2017 VOL. 3 NO. 4
98
name a few. These methods and others like them, which will
only be described in limited detail in this review, have been
the primary method of nanober production for some time.
There exist drawbacks to many of these methods, be it low
production rates or having to using large quantities of energy
for ber production. A more ecient method is needed to
create nanobers which would increase production rates and
reduce power consumption. One such method that could
answer these requirements is rotary jet spinning (RJS).
Introduction to rotary jet spinning
RJS is known by a few names within the research community;
however, the RJS title sums up the process better than most,
and will be used in this review. RJS is also known as centrif-
ugal spinning, rotor spinning, and Forcespinning™. This last
term was introduced as a brand name by FibeRio® Technology
Co. (Acquired by Clarcor Inc. in 2016, who were subsequently
acquired by Parker Hannin in 2017), for what appeared to
be the only commercial enterprise specializing in the devel-
opment and production of RJS machinery on the market. It
was at the University of Texas where the initial patents were
led by Lozano and Sarkar before being commercialized by
FibeRio.17,18
Since the granting of FibeRio’s RJS patents in the last dec-
ade,17,19–25 a urry of research relating to this eld has started
to emerge. Around a third of publications utilizing RJS as a
primary nanober production method have used equipment
produced by FibeRio in some way, but the majority do not,
opting to create their own RJS machines instead. Although
the mechanics behind RJS are simple, and resemble candy
oss making machines that have been around for decades,
developing a device that is capable of precision control for
the benet of tunable ber morphology is key.
To gage the scale of recent interest in centrifugally spun
bers, results from a patent search into characteristic patent
code D01D 5/18, which classies any patent relating to natural
or articial threads or bers created by means of rotating spin-
nerets, shows an increase in the ling of patents since the year
2000 (Figure 3). Under this classication, which is included as
one of multiple classications in a patent registration, all the
equipment or processes that are being patented are directly
related to polymer nanober manufacturing or applications.
More patent categories exist which give an overview of
the rise of this technology, however this classication code
search depicts the trend well enough to consider only one
type for illustration purposes.
The highest number of patent registrations come from China
and the United States (Table 1), with a steady rise in patents relat-
ing to ber spinning occurring since 2007, with a slight reduction
from both the USA and China in 2012 and 2013. Recent years
account for the highest registrations, indicating a continued
Figure 1 Nanober scale (human hair, pollen grain, nanober
mat). Photograph courtesy of Elmarco [7]
Figure 2 Comparison of the sizes of typical objects relevant for air ltration with ber diameters of RJS and electrospun
(ES) bers

Rogalski et al.
Nanocomposites 2017 VOL. 3 NO. 4 99
interest in the technology, with 2016 being the largest number
to date.
Publications relating directly to RJS, the primary focus of
this review, can be seen in Figure 4. These illustrate the number
of scientic publications per year according to Web of Science
(WoS) since this technology started to gain traction.
The fundamental principle behind RJS is relatively straight-
forward although the technology does require some knowl-
edge of polymer chemistry, processing, and uid mechanics.
The basic concept of RJS is illustrated in Figure 5 and is, as men-
tioned earlier, not too dissimilar to the well-known method
used in the catering industry for the manufacture of candy
oss.
Basic requirements in RJS are a reservoir to hold the pol-
ymer, which is in either solution or melt form, and a nozzle
through which the polymer is spun once it is rotated at a high
enough angular velocity to initiate jet expulsion. In addition
to this, a collector to “catch” the bers after they are spun and
stretched in the air vortices as they make their way from the
nozzle is also needed. This can take many forms, but the most
common method used is a radial array of vertical collector bars.
Comparisons with other techniques
Many techniques other than RJS can be used to create poly-
meric nanobers, but none with as high capacity for industrial
scaling using such low power consumption. Other nanober
production methods include drawing,27,28 template synthe-
sis,16,29,30 phase separation,31 self-assembly,32–34 islands in the
sea,
14,35
electrospinning,
8–10,36–41
and melt-blown spinning.
12,42–44
Each of these processes has distinct advantages and disadvan-
tages, which have been summarized by Nayak et al.45 andare
presented in Table 2.
Although RJS is sometimes labeled as environmen-
tallyfriendly, the process can only be credited as such if the
solvent is recycled or not used at all, such as with melt RJS.
However, alternative methods used to produce bers from
the melt can use signicantly more energy, thus making them
less environmentally friendly. In all of these melt processing
techniques thermal degradation is a possibility, but can be
overcome by using thermal stabilizers.46
Electrospinning
Electrospinning (ES) is a method that relies on an electro-
static force to spin a fiber from a polymer solution drop-
let suspended from a capillary by overcoming the surface
tension in the droplet to form fibers on a counter elec-
trode.39,47–51 This can be conducted through a single nee-
dle approach (Figure 6), or multiple needles can be used
to increase production rate of fibers. Needleless systems
such as Elmarco’s Nanospider™ technology also exist, allow-
ing semi-industrialized volumes of fiber to be produced
on a scale of <200g h−1 using polyvinyl alcohol (PVA) for
example.7,50
When comparing electrospinning with RJS, we can demon-
strate the variance in parameters such as ber diameter with
some ease. In comparing the production of poly(ethylene
oxide) (PEO) bers from these two systems, similarity can be
gaged and discussed. Son et al.52 produced beadless nano-
bers through the electrospinning of a PEO/water solution at
concentrations of 3, 4 and 7wt%. The average ber diameters
were between 0.36 and 1.96μm, with the larger diameters a
result of other solvents such as ethanol, chloroform, and DMF.
This can be directly compared with PEO/water solutions rang-
ing between 6 and 10wt% produced by Padron et al. using
Figure 3 Patents issued for ber creation relating to rotating spinnerets since 2000. Data compiled from Espacenet.com.26
Table 1 List of countries with the highest number of pat-
ents led for devices relating to the manufacture of bers
from rotating spinnerets from 2000 to 2016
Country Total
China 126
United States of America 88
Korea (South) 56
World Intellectual Property Organization (WIPO) 50
Japan 39
European Patent Office 35
Germany 16
Spain 13
Austria 10
Canada 9
Australia 7

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Figure 5 Schematic illustration of rotary jet spinning (RJS), comprised of an electric motor driven rotating spinneret with
polymeric bers being ejected outwards toward the vertical collector bars in this typical setup. Photographs (top left to bottom)
of the FibeRio Cyclone™ L10 00M laboratory machine, with ber spinning demonstration, and the Fibre Engine FX System
which is congurable for 1.1m (FX1100) or 2.2m (FX2200) line widths, achieving an output of up to 200g/min and compatible
with line speeds of up to 200m/min. Photographs courtesy of FibeRio
Figure 4 RJS publications by year 2010–2016 according to WoS

Rogalski et al.
Nanocomposites 2017 VOL. 3 NO. 4 101
Other methods
Template synthesis is a method that consists of creating nanow-
ires by lling a porous template that contains a large number of
straight cylindrical holes with a narrow size distribution. Although
scientically interesting, it is however not suited for large-scale
industrial production.16 Drawing, phase separation and self-as-
sembly are also not suitable for large-scale applications and will
not be discussed further here as a comparison to RJS.
The island-in-the-sea method of nanober creation is how-
ever a method that can be scaled toward mass production,
but does not produce continuous bers. It is based on the
use of two incompatible polymers which are melt blended
together to form a morphology replicating that of islands in
the sea, where the islands are the nanobers and the sea is
the sacricial matrix used to aid in the drawing of the bers.55
Eciency and yield
RJS shows promise toward market adaptability when com-
bined with considerations such as energy eciency. In RJS
we do not require the high voltages that come with electro-
spinning or the high velocity air jets that are required in melt
blowing – both of which are relatively large contributors to
the overall cost of ber production. Another benet aorded
to RJS is that (when melt spinning) we do not have to rely on
the use of harmful solvents, resulting in a “greener” product – a
feature which is however also possible with most other ber
production methods.
Lab scale versions of RJS machines can already pro-
duce more than 50 times the rate (60g h−1 per orice53 vs.
0.11 g h−150,53) of a single needle lab scale electrospinning
setup if only comparing one orice. The standard number of
orices on a RJS machine would be at least 2, some with many
more, dependant on design, meaning a 100 fold increase in
production rate for a lab scale RJS machine over a single nee-
dle electrospinning machine. RJS spinnerets can in turn be
RJS53 in which ber diameters obtained were 0.13–0.32μm
dependant on angular velocity of the spinneret. A conclusion
can be drawn from this simple comparison that the diameters
achievable from electrospinning are comparable to RJS.
Melt blowing
Although we will not cover all techniques in this review, it
is important to compare RJS with other techniques such as
melt blowing (Figure 7). This technology utilizes fast owing
heated air and dies to extrude a polymer melt, where after the
produced ber is carried along in the stream of hot air, which is
typically the same temperature as the die, before being depos-
ited on a collection device.11 This stream of heated air ows
at very high velocities which is very energy consuming due
to the high velocity and temperatures which are required.42
Table 2 List of nanober production methods. After Nayak et al.45
Manufacturing
process
Scope for
scaling-up Repeatability
Control of fiber
dimension Advantages Disadvantages
Electrospinning
(solution)
Yes Ye s Yes Long and continuous
fibers
Solvent recovery issues, low
productivity, jet instability
Electrospinning (melt) Yes Ye s Yes Long and continuous
fibers
Thermal degradation of
polymers, electric discharge
problem
Melt blowing Yes Ye s Yes Long and continuous
fibers, high productivity,
free from solvent recov-
ery issues
Polymer limitations, thermal
degradation of polymers
Island in the sea
spinning
Yes Ye s Yes Long and continuous,
relative uniformity
Solvent recovery and extra
processing
Template synthesis No Yes Yes Easy to vary diame-
ter by using different
templates
Complex process
Drawing No Yes No Simple process Discontinuous process
Phase-separation No Yes No Simple equipment
required
Only works with selective
polymers
Self-assembly No Yes No Easy to obtain smaller
nanofibers
Complex process
Rotary jet spinning Yes Ye s Yes Free from very high
voltage, eco-friendly
Requirement of high tem-
peratures
Figure 6 Typical electrospinning setup showing the polymer
solution being delivered through a needle to a capillary tip,
before being caught in the electrostatic attraction of the
counter electrode, drawing a ber across the void into the
whipping zone before being deposited as a ber mat

Rogalski et al.
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Nanocomposites 2017 VOL. 3 NO. 4
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Fluidnatek (Spain). These systems are complex to provide
direct production rate comparisons for as the manufacturers
quote various ber diameters, polymers, solutions and deposi-
tion thicknesses, and in some cases only machine speed capa-
bilities. All systems except the RJS FX2200 are electrospinning
machines. The only real alternative contender for micro and
nanoscale ber production is melt blowing, which is capable
of production rates of around 1500gh−1,45 but does not pro-
vide continuously uniform ber diameters in the nano scale.
Fiber diameters
Figure 8 shows the ber diameters of published RJS data from a
range of studies.
53,61–85
The large variability in diameters is gener-
ally due to dierent processing settings (e.g. rotational velocity,
orice size, temperature) and material characteristics (e.g. viscos-
ity, molar mass), rather than statistical variability. Viscosity aects
the ber diameter in RJS and Figure 8 shows a wide variety of
ber diameters for studies that have reported a range of sizes
for certain materials. Where only a small diameter variance is
shown, the publication often did not specify an upper and lower
diameter range, but rather mentioned only a single value.
These ber diameters illustrate the typical values that can
be achieved with the materials shown. Data shown do not nec-
essarily represent the smallest diameters that are possible with
this technology, but are however an indication of what has so
far been achieved. Comparing the smallest diameters of 10
materials from RJS and ES indicated that reported diameters
for ES are on average around 10% smaller. However, electros-
pinning has been around for much longer and these smaller
diameters could be simply the result of a better understanding
of the ES process, rather than some intrinsic limitation of the
RJS process.For example, one clear dierencecan be seen by
comparing polyamide 6,where electrospinning has produced
bres in the region of 50-100 nm, whereas rotary jet spinning
has only reported diameters as low as 450-500nm (Figure 8).
There is however a larger variation in the uniformity of ber
diameter in RJS compared with ES. This is shown by Krifa and
positioned in parallel to create a system which covers a larger
area for creating continuously fed nonwoven mats.
Exploring the production rates of processes capable of pro-
ducing industrial volumes of nanobers highlights even more the
dierences between methods when considering the commercial
future of polymer nanobers. FibeRio’s Cyclone™ Fibre Engine FX
System, which is designed with a modular and expandable archi-
tecture congurable for 1.1m (FX1100) or 2.2m (FX2200) line
widths, can achieve continuous outputs of up to 12,000gh
−1
with
line speeds of up to 200mmin
−1
and controllable ber diameters
of around 500nm.
56
In comparison, the highest production rates
of the leading electrospinning systems are 210gh−1 for inoven-
so’s Nanospinner416 1m line width needleless electrospinning
system, depending on polymer solution used (see Table 3).
In addition to the Nanospider™ needles systems, multi-jet
systems have been developed and are now commercialized
by companies such as 4SPIN (Czech Republic), MECC Co.
Ltd (Japan), inovenso (Turkey), SPUR (Czech Republic), and
Figure 7 Schematic of the melt blowing process where heated air moves at speed past a polymer melt to create bers (top).
Image of the melt blowing process and produced ber. Reprinted from Hiremath and Bhat,
54
available under a Creative Commons
attribution 3.0 license
Table 3 Industrial nanober production system compar-
ison, showing manufacturer ’s quoted production rates of
continuous nanober deposition on substrates, with the
FX2200 RJS system being the highest
Manufacturer
Output width
(mm)
Quoted produc-
tion rates
Nanospider™
(NS 8S1600U) by
Elmarco (Czech
Rep.)
1600 78gh−1
1680mh−1
2640m2h−157
NW-101 by MECC
Co. Ltd (Japan)
600 600mh−158
Nanospinner416
by inovenso
(Turkey)
1000 210gh−1
210m2h−159
SPIN line by
SPUR® (Czech
Rep.)
1200 186gh−1
300m2h−160
Fluidnatek LE-1000
by Bioinicia (Spain)
3000 Not available
FX2200 by Fiber-
Rio (US)
2200 12,000gh−1
12,000mh−156

Rogalski et al.
Nanocomposites 2017 VOL. 3 NO. 4 103
market growth increasing from $3.7bn in 2013 to $4.3bn in
2015 alone. With this continued growth, it is predicted to reach
$6.5bn in 2021 which signies a compound annual growth
rate of 7% between 2016 and 2021 as per a market report
produced by BCC Research.97 These statistics cover all man-
ufacturing methods related to nonwoven lter media, both
micro and nanober. Actual data on nanober markets alone
are not easilyavailable; however, as future applications begin
to develop within the marketplace, correlations with the grow-
ing microber industry should potentially be seen.
Biomedical
A commonly published nanober application in RJS is based
around biomedicine. This application exploits the ability of
the nanobers to oer signicantly increased surface area
to volume ratios than any other material, which is a highly
desirable property in this eld. Pelipenko et al.98 describe that
these novel materials can be employed in the treatment of var-
ious diseases as well as in the eld of regenerative medicine.
The promise is that biological function lost in host tissues will
be able to be restored and maintained by tissue engineer-
ing through the use of RJS nanobers.99–102 A common goal
Yuan,79 where PA6 bers spun with properties and process-
ing settings that would guarantee bead free continuous bers
were compared in both electrospinning and RJS (referred to
as FS in Figure 9).
The increase and spread in ber diameters for RJS in com-
parison to ES can be attributed to, but not limited to, the
phenomenon that occurs during the start-up process. For
example, in the solution spinning of polycaprolactone (PCL) in
dichloromethane (DCM), the rst 30 s of RSJ showed a reduc-
tion in the ber diameter to an equilibrium point (Figure 9).
Taking these initial larger diameter bers into account when
measuring the average diameter will increase reported values
and skew like for like comparisons. In almost all reported RJS
ber diameters, this phenomenon is not considered. It should
be noted that the diameters achievable in a continuous RJS
device would reach the equilibrium state at a much smaller
diameter to that of the start, as demonstrated below.
Potential nanofiber applications
The ber industry is a global marketplace with many man-
ufacturers having a large stake in the industry. The industry
sub category of nonwoven lter media is a contributor, with
Figure 8 A comparison of reported ber diameter ranges for rotary jet spinning53,61–85 and electrospinning41,52,86–96

Rogalski et al.
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Nanocomposites 2017 VOL. 3 NO. 4
104
Nanocomposites
Another interesting application area for nanobers is their
use within nanocomposites. This area has seen research from
nanober production areas such as electrospinning112–115
and vapor grown carbon bers (VGCF)116,117 in the past, with
multiple reviews written on their promising future4,118–120
Engineering composites typically consist of high modulus
(>50GPa) and high strength (>1GPa) bers embedded in
a low modulus polymer matrix, which through the interac-
tion between the two, leads to improved mechanical prop-
erties of both materials to a level more than which would
be expected from each material individually. Increased
mechanical strength from nanobers will be a requirement
should nanober based composites be successful, with only
limited success seen to date as reviewed in detail by Yao et
al.
8
and Peijs.
121
Various polymeric materials have been trialed
as composite reinforcement, with higher modulus materials
such as glass115,122 and carbon115,123 nanobers being among
them. Polymer nanobers, most often produced by electros-
pinning, typically have Young’s moduli of less than 3GPa and
tensile strengths below 300MPa,
8
which renders them rather
ineective as reinforcement for bulk engineering plastics such
as epoxies, polyesters, polyamides, or polypropylenes.121
However, it has been shown that such bers can be eective
as reinforcements for biomedical engineering purposes when
combined with hydrogels.124.
Manufacturing bers in the nano scale is of great interest
for composites, as these bers have a high aspect ratio and
large available ber surface area, potentially leading to high
in the design of tissue engineering scaolds is to mimic the
natural interfaces that interact selectively with a specic cell
type through biomolecular recognition.103,104
Similar to tissue scaolds, wound dressings are another
biomedical application which has seen much focus, exploiting
high surface areas within the nanobers to foster the perfect
conditions for cell growth, embryologic development, organo-
genesis, and wound repair.105,106
Using RJS nanofibers in direct contact with the human
body is only one aspect of the biomedical applications of
nanofibers. Zhu et al.107 for example, have investigated
affinity absorption materials by functionalizing poly(vi-
nyl alcohol-co-ethylene) (PVA-co-PE) with Cibacron Blue
F3GA to evaluate their effectiveness. Affinity membranes
can selectively remove bacteria, endotoxins, and viruses
from biologically active liquids and water, and if it becomes
cheaper to manufacture these types of products, it could
benefit developing nations battling against waterborne
disease.
Another interesting biological application for RJS nanob-
ers is that of controlled drug release.104,108–111 By being able to
provide a predictable and controlled drug release over time by
exploiting the high volume to surface area of nanobers, one
such study by Wang et al. using RJS has shown that producing
aligned ber mats are preferable when designing for a slower
and more controlled release of drugs, rather than a more rapid
release for random oriented bers due to the increased aque-
ous interaction. In their research, a lab-built device was used
to produce polyvinylpyrrolidone (PVP) bers between 6 and
19 microns in size via electro RJS.110
Figure 9 Comparison of RJS and ES ber diameter variance, showing a marked increase in the ber diameter based on
polymer concentration in solutions, with RJS showing exponentially higher outliers and extreme values compared with the
average. Reprinted with permission from Krifa and Yuan,79 Copyright 2016, Sage Publications

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Nanocomposites 2017 VOL. 3 NO. 4 105
equal to 300nm in diameter in an air ow rate between 3
and 10ms−1 (as dened by the United States Department of
Energy, DoE, or a range between 85 and 99.999995% in Europe
(European Norm EN 1822:2009). There is also a specication of
minimal pressure drop over the lter of around 300Pa.
Fiber-based lters are at the low to mid-range price com-
pared to other materials such as paper, with new technologies
such as RJS hoping to introduce new methodologies for old
technologies, with the intention of potentially reducing the
sale price to market. According to data published in the Filters
and Filtration Handbook,
130
the retail price of spunbound ber
lters range from $0.065 to $6.50/m2, whereas paper lters are
the cheapest at $0.20 to $0.33/m2.
Among the most prominent concerns when developing
ltration media is the ability of the lter to maintain its use-
fulness and prevent further harm to users when used as an
air ltration device. Because polymer nanobers are contin-
uous, there is very little chance of them becoming airborne
and entering the body. In addition to this benet, a primary
advantage of using nanobers in ltration applications is their
high surface to volume ratio which increases particulate ltra-
tion eciency, and by nature of the design, results in surface
loading instead of depth loading as is typical of other nonwo-
ven substrates.131 This is achieved by increasing the number
of overlapping bers that exist which will limit the ow of
particles by trapping them. Therefore, a smaller diameter and
hence more bers result in a higher ratio of blockage points
for traveling particulate matter.
Figure 11 shows a standard HEPA lter test of varying air
ow rates conducted on polyamide (PA) 6 nanober mats,
comparing with the industry standard HEPA lter.132 Samples
1 and 2 were 10 and 5 times thinner, respectively, than the
standard HEPA lter being tested, and pressure drop data
suggested that the HEPA lter had the lowest pressure drop
compared to the PA6 lters. Although this shows superior e-
ciency from the HEPA lter, the potential to use signicantly
less material in the PA6 lter versus the HEPA lter, for similar
ltration eciencies, is promising.
A real world study of nanobers for use in air ltration
was conducted at Kaufman North Pit in Cleareld Country,
Pennsylvania, USA, where a mining vehicle had a comparable
cellulose lter tested against a cellulose+ nanober lter.3.
The result was a reduction in dust particles from 86 to 93%,
concluding in a successful trial of the retrotted nanober air
lters.
In an attempt to improve the eciency of lters, Podgorski
et al. demonstrated that there is an increase of up to 2.6 times
the quality factor (QF) of nanober-based lters versus those
created using microbers.133 QF is a method to evaluate lter
performance by measuring the lter eciency as well as the
pressure drop over the lter.
Additional potential applications
Although a subset of potential nanofiber applications has
already been listed, it is important to note a few more
which are currently being researched. One such appli-
cation, in a bid to improve sensor technology, is in the
development of polyaniline (PANI) nanofiber gas sensors
by utilizing the ability of conducting polymers to display a
energy absorption mechanisms through debonding and pull-
out. As a simple example, a 10μm diameter microber has the
same cross sectional area as 10,000 nanobers with diameter
100nm – resulting in much more surface area to interact with
a composite matrix to aid in energy absorption processes as
mentioned above.125
Papkov et al.
126
found that by reducing the diameter of elec
-
trospun polyacrylonitrile (PAN) bers from 2.8μm to ~100nm
increased the elastic modulus from 0.36 to 48GPa, with the
largest increase in bers below 250nm (see Figure 15). This
increase was also commented on by Yao et al.8 in their review
of high strength and high modulus electrospun nanobers,
where it is noted that this is not the only method of achieving
increased mechanical properties. Flexible chain polymers gen-
erally achieve chain alignment (and thereby higher modulus
and strength) through post-drawing, whereas rigid-chain pol-
ymers oer the ability to chemically guarantee higher chain
alignment during the spinning process.
Two examples of rigid chain polymers being used to
produce high mechanical strength nanobers for use in
composites has been investigated using poly(p-phenylene
terephthalamide)38 and also polyimide.127 A composite of
electrospun co-polyimide nanobers within a styrene-buta-
diene-styrene (SBS) triblock copolymer (Kraton®) matrix was
produced, where a Young’s modulus ranging from 2.5 to 7GPa
was achieved for ber volume fractions ranging from 21 to
62%, respectively. These values were in good agreement with
predictions made using the rule of mixtures.127 For this, the
ber orientation in the composite laminates was measured,
showing an average misalignment angle of 14°. By back cal-
culating the values obtainable for a fully aligned ber mat a
Young’s modulus of 26.5GPa was estimated for a perfectly
aligned UD laminate, yielding a co-polyimide ber modulus
of around 60GPa, similar to commercial high-performance
bers like Kevlar 29.
During electrospinning, albeit on a smaller scale, it is possi-
ble to obtain good levels of ber alignment using the rotating
disc method, but an equivalent of such method has not been
produced for RJS yet. Badrossamay et al.,128 Erickson et al.129
and Wang et al.110 have developed their own RJS systems to
produce aligned bers, although these studies combined
both electrospinning and RJS to achieve this. No reported
study has yet achieved a high level of ber alignment using
RJS alone.
Filtration media
The physical separation of matter occurs predominantly in
one of two methods, ltration or sedimentation. Fibers work
extremely well when it comes to ltration in order to sepa-
rate matter, as they are able to be scaled according to the
size required. The size of the nonwoven ber mat porosity
required depends on the droplet or particle size that needs
to be prohibited from passing through. Filters can be made of
many materials, with the most common being natural bers,
synthetic polymers, metals, carbon, ceramics, and paper-like
materials.130
A typical high performance lter such as a high eciency
particulate air (HEPA) lter is required to have a minimum
removal eciency of 99.97% of particles greater than or

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106
Melt spinning materials
Conversely to solution spinning and like electrospinning, RJS
in the melt phase has not seen as much research due to the
diculty in processing bers from the relatively viscous melt
(see Table 5). There is unfortunately very little information on
unpublished or failed experiments in RJS and thus on materi-
als which did not work. As literature suggests, melt spinning
would seem to be more limited in the materials choices facing
it, with only a few materials available in the list below from
published works:
In the publications listed in Table 5, three were using RJS
with a very specic application in mind, while the others were
studies of the RJS process itself for specic polymers. These
specic application focused studies were successfully able to
use the RJS process for the creation of tissue scaolds as well
as drug delivery systems.
Processing and properties
The method by which RJS research has been conducted is all
based on the same principle of a rotating spinneret (dened
as an enclosed material container with multiple orices) and
some collection device – be that vertical collector bars, a solid
cylindrical collector or a at surface. In almost all cases, bers
were produced by altering the rotational velocity from 2,000 to
16,000rpm, with some opting for higher rotational velocities
due to smaller spinneret geometries where a similar centrifu-
gal force would be required.
Altering the processing parameters in RJS yields a variation
in ber diameter. Processing variables within RJS include tem-
perature, rotational velocity, collector distance, orice diame-
ter, and duration. Spin duration mainly aects the volume of
the bers yielded, but is nonetheless a basic parameter that
is used in lab scale research. For continuous ber production
only the rst group of variables needs to be considered. Other
parameters that aect ber properties and diameters will be
related to the polymer material itself, depending on whether
it is spun from solution or melt. Considering the material’s
spinnability, a certain upper (blockage) and lower (beading)
limit for viscosity will exist for each combination of polymer
solution concentration, or temperature for polymer melts.
Rotational velocity is what drives the process, and increas-
ing this will yield a greater centrifugal force with which to eject
the polymer from the orice. This basic premise of RJS is uti-
lized by Mellado et al. in their equation derived for the critical
rotational velocity threshold as given below.169
Equation (1) signies that for a given polymer, each thresh-
old will dier based on measurements of stress (σ), density
(ρ), orice diameter (a) and distance from centerline to orice
opening (S
0
). With these measurements obtained beforehand,
the theory predicts that a critical rotational velocity should be
selected for a chosen polymer melt/solution.
As mentioned, the viscoelasticity of the material aects the
ability for a ber to be spun. A study by Shanmuganathan et
al. has shown the variance in ber diameter of polybutylene
(1)
Ω
th =
√𝜎
a2S
0
𝜌
transition between insulating and conducting states which
may occur due to chemical treatments with redox agents.
This method can be used to develop optical, chemical, and
biosensors.134
Flexible solar cell technology has been investigated by
creating nanostructured lms from poly(3-hexylthiophene)
bers by mixing them with a molecular acceptor such as
[6,6]-phenyl C61-butyric acid methyl ester in solution. By
using this process, one could produce an ecient layer of an
organic solar cell.135
Further potential applications being studied include super-
capacitors based on exible graphene/polyaniline nanober
composite lms [136], graphene/polyaniline nanober com-
posites as supercapacitor electrodes,137 lithium-ion battery
separators from PAN,77,138 polystyrene (PS) nonwoven fabrics
featuring radiation induced color changes,
139
nanober hydro-
philic studies70,140,141 and anionic dye adsorption techniques
[142] to name but a few.
Materials used in rotary jet spinning
Many polymeric materials have been considered for RJS
of nanofibers, with material choice driven by specific fiber
characteristics stemming from research goals or end-user
applications. Applications and future research directions
into nanofibers including RJS fibers are attributed to a few
key areas of interest, namely filtration,
3
healthcare, environ-
mental engineering, biotechnology, composites,121 defense
and security and the energy sectors.143
Many researchers have started studies into RJS nanobers
driven by applications within specic sectors such as medicine,
where bers resemble cellular topographies63 or are capable
of targeted outcomes such as drug delivery.68 Others have
focused on using conjugated polymers in the RJS process for
areas such as photovoltaic cells, light-emitting diodes, and
biocompatible materials.
64
The bers that are created for these
purposes are spun from either a melt state or a solution state,
all of which are listed below.
Solution spinning materials
As a relatively new technique for producing bers, RJS is still
undergoing an interesting period of initial research, whereby
the materials that are being selected are seemingly either for
general research into the RJS technique itself, or they target
potential end use applications. The materials chosen are for a
relatively broad range of potential applications, but the most
common theme amongst specic research is in the eld of
biomedicine (see Table 4).
In these studies, the bers produced were evaluated in
one of two ways. Firstly, in terms of the RJS process, and
secondly in the specic capability toward an intended
application. The results showed that application specic
publications found favorable quantitative results based on
initial objectives, while publications which focused more on
the general process of RJS mainly focused on diameters or
physical properties of bers to further understand the RJS
process. Several, more recent publications on RJS have con-
tinued to focus on processing and application specic rese
arch.15,47,104,106,138,142,158–167

Rogalski et al.
Nanocomposites 2017 VOL. 3 NO. 4 107
as previously noted, due to the reduction in melt viscosity with
elevated temperatures. Zander
76
showed that with increasing
PCL melt temperature, the ber diameter initially decreased
before increasing at an even lower viscosity due to high tem-
peratures and potential polymer degradation (see Table 7).
A trend of a decreasing and then increasing ber diam-
eter was also shown for an increase in rotational velocity by
O’Haire et al.74 in which they attempted to melt spin bers
from a melt blowing grade polypropylene (Lyondell MF650Y,
MFI=1800gdmin−1) and a 1 wt% concentration of MWCNT
(multi-walled carbon nanotube) dispersion.
Reported in Table 8 is the proportion of bers with a
diameter greater than 5 μm. This is a phenomenon that
appears to show up in RJS as a by-product from the start of
the spinning cycle. By producing nanobers from a PCL solu-
tion, measurements taken by McEachin et al.63 at dierent
interval times (5, 10, 15, 30s) throughout the spinning cycle
demonstrated this issue (see Figure 10). Explaining this phe-
nomenon, the authors describe the eect of droplet elonga-
tion in the initial stages of ber drawing from the orice, in
which the initial bers that are collected have not had time to
fully elongate or have sucient solvent evaporation yet. This
leads to an equilibrium diameter being reached somewhere
after around 30s in the spinning cycle at 6,000rpm (see
Table 9). Due to this, many published mean ber diameters
from RJS will possibly have higher values due to the initial
non-equilibrium state at start-up being included, and not
accounted for.
O’Haire et al.74 corrects for this start-up phenomenon by
allowing bers that fall into this initial spin duration to be dis-
counted from the values of the averages quoted by setting a
size limit of 5μm. Once these values are removed, a far more
realistic mean value for the ber diameter is obtained.
In research completed by Padron et al.,53 the ber spinning
process was lmed at a high frame rate to view the polymer
jet leaving the orice (Figure 13). They investigated the eect
of the angle of the orice in comparison to the ber diameters
for a 6wt% PEO solution at 6,000rpm and concluded that the
smallest diameter ber was produced with a straight orice,
rather than 30° in the direction of rotation, or 89° against the
direction of rotation.
Another inuencing processing factor studied by Zander76
illustrates the change in ber diameter with collector distance
variation. In his research, PCL bers were collected at distances
of 10, 12 and 14cm from the orice, producing bers with
diameters of 8.2±5.8, 8.3±4.4 and 7.0±1.1μm, respectively.
Although this small amount of data is not conclusive, it does
indicate that there is indeed a variation of ber diameter with
collector distance.
Mechanical properties
Limited data are available in terms of mechanical properties
of nanobers produced by the RJS process, and nanobers
in general, due to the general diculty in testing individual
nanobers. Nanoscale mechanical testing requires extremely
small loads for deformation, along with expert handling of the
bers due to their size. According to Tan et al.,173, the practical-
ities of testing individual nanobers have the following ve
challenges: (1) Ability to manipulate extremely small bers,
terephthalate (PBT) when altering the processing tempera-
ture.65 Their data in Table 6 show that for a rotational speed
of 12,000rpm, the ber diameter changed from 1.64 μm at
280°C to 1.17μm at 320°C. This demonstrates that for PBT,
an increase in processing temperature leads to thinner bers.
This will typically be the case for all polymers, as viscosity is
reduced with temperature for thermoplastic polymers. It is
worth noting that the viscosity of the polymer melt will have
a great eect on spinnability, with low viscosity, Newtonian
uids being the best contenders as the standard systems are
generally not pressure driven. For pressure driven systems
see.153,170,171
Solution spinning does not rely on elevated temperatures
as they are typically spun at room temperature. Instead of tem-
perature, the reliance here will be on solution concentration
and how it aects morphology of the bers in the RJS process,
as shown by Badrossamay et al. in Figure 12.
Their research demonstrates that jet break-up and there-
fore ber quality may be estimated by the capillary number;
dened as the ratio of the Weber number
(We
=𝜌
U2a
𝛾)
to the
Reynolds number
(Re
=
𝜌Ua
𝜇)
, which characterizes the ratio
of the viscous force to surface tension force. ρ is density, μis
dynamic viscosity (which is directly related to the molecular
weight and solution concentration), γ is surface tension of the
polymer solution, U is the polymer jet exit speed based on a
stationary frame and a is the orice diameter. A lower capillary
number results in shorter jet lengths and earlier jet break-up
to isolated droplets. It therefore highlights the critical poly-
mer concentration for this polymer type, to produce the best
quality polylactic acid (PLA) bers.61
A study by Mohan et al.151 has also investigated, in some
detail, the ability of atactic-polystyrene (PS) to be melt spun
by pressurized RJS. Here, the authors were particularly inter-
ested in molecular anisotropy of RJS bers as compared to
electrospun bers with the highest level of anisotropy found
in ES bers. It was found that polymer solutions only yielded
bead-free bers between concentrations of 5–16wt%. This
type of range is a typical outcome for any study investigating
the process conditions for bead-free bers.
These types of analysis are a good methodology to employ
for considering the types of polymers suitable for RJS, as this
could potentially lead to further research whereby polymer
properties can be used to approve or discard their ability to be
spun without the time and eort expended on experimental
testing.
Fiber diameters
Fiber diameter measurements are a common and eective
characterization method which is typically conducted using
scanning electron microscopy (SEM),71,74,145 optical microscopy
(OM)
65
or transmission electron microscopy (TEM)
172
for imag-
ing purposes.
The ber diameters reported have several common inu-
encing factors. Initial observations report a reduction in ber
diameter with an increase in rpm (therefore centrifugal force).
In the case of PLA, anincrease in the rotation speed from 4,000
to 12,000rpm resulted in a reduction in ber diameter from
1143 (±50) to 424 (±41) nm.
61
In the case of melt spinning, ber
diameters were also reduced with an increase in temperature

Rogalski et al.
Rotary jet spinning review
Nanocomposites 2017 VOL. 3 NO. 4
108
indication of the force required and therefore mechanical
properties can be extrapolated.
In another method, Wang et al.177 performed a 3-point
bending test on electrospun PVA/MWCNT composite nano-
bers to establish mechanical properties. They used an AFM
cantilever to perform the test to measure ber deection,
from which they could calculate the Young’s modulus (Figure
14). These are however all time-consuming methods which
require a high degree of precision, coupled with the fact that
it remains dicult to manipulate single bers within these
test rigs.
(2) Finding a suitable mode of observation, (3) Sourcing of
an accurate and sensitive force transducer, (4) Sourcing of an
accurate actuator with high resolution, and (5) Preparing sam-
ples of single-strand nanobers.
The most common methods of nanober tensile test-
ing include the use of atomic force microscope (AFM) can-
tilevers,174–176 3-point bending testing177–179 or commercial
nano-tensile testing.38,127 The AFM testing method essentially
relies on the xing of bers to the ends of the AFM cantilever
before applying a tensile load. Measuring the angle of deec-
tion from the cantilever arm and ber extension provides an
Figure 10 Fiber diameter at various spinning times, showing a diameter reduction of RJS bers during initial 30s start up
time, demonstrating the potentially skewed data of reported ber diameter distributions if start up effects are not considered.
Reprinted with permission from McEachin et al.,63 Copyright 2012, JohnWiley and Sons
Figure 11 Filtration efficiency of PA 6 nanober lters. Standard HEPA lter compared with two base weight nanober mats
with average ber diameters of 200nm. Doubling the base weight led to a demonstrable increase in efficiency. Reprinted with
permission from Ahn et al.,132 Copyright 2006, Elsevier

Rogalski et al.
Nanocomposites 2017 VOL. 3 NO. 4 109
Figure 12 Nanober morphology reliance based on PLA concentration, showing that a critical concentration is needed to produce
continuous bead-free bers. Reprinted with permission from Badrossamay et al.,61 Copyright 2010, American Chemical Society
Figure 13 Analysis of the effect of orice direction during spinning, showing that a straight needle (e) produced the smallest ber
diameter compared to other needle angles. Reprinted with permission from Padron et al.,53 Copyright 2013, AIP Publishing LLC
Figure 14 Methods of mechanical testing on nanobers using AFM cantilevers. Reprinted with permission from Tan et al.,173
Copyright 2006, Elsevier

Rogalski et al.
Rotary jet spinning review
Nanocomposites 2017 VOL. 3 NO. 4
110
and ber diameter in these bers. Although ber modulus
generally increases with decreasing ber diameter this eect
is typically only observed for diameters below ~250nm,126
which is much lower than the 1.4μm of the bers tested by
Tan et al. Arinstein et al.,181 for example, showed that a reduc-
tion in diameter of electrospun PA 6,6 bers lead to a consid-
erable increase in mechanical properties of these ber due
to improved molecular orientation and chain connement
(Figure 15).
Another option available in testing nanobers is to test a
bundle of multiple bers together in a micro tensile tester. Yao
et al.
182
tested electrospun co-polyimide nanober bundles of
30 nanobers and reported a Young’s modulus of 38 GPa and
tensile strength of 1.6 GPa. The bundle data were evaluated
using Daniels’ theory183 based on Weibull statistics in order to
calculate individual ber strengths.
Figure 16 shows the testing procedure of a single nanober
using the framing method as proposed by Chen et al.184 In
their paper they discussed the mechanical properties of single
electrospun polyimide nanobers with a diameter of ~250nm
and reported a record high tensile modulus of 89GPa.
In the case of RJS, only a handful of publications have
considered the mechanical properties of the materials pro-
duced. In one of these publications, Teon nanober yarns
were tested. The polymer solution was prepared by dissolving
the Teon in Fluorinert FC-40, before RJS and subsequently
collecting and assembling as yarns. Tensile testing of these
twisted yarns produced a modulus of 348MPa.70
Tensile testing using commercially available equipment
can be conducted by collecting aligned bers on a ready-
made frame, for use in a universal tensile testing machine.
Electrospun PCL and PLA nanobers have been successfully
tested in this way.180 The single PCL ber used in this exper-
iment measured 1.4 ± 0.3 μm, with a tensile modulus of
120±30 MPa and a tensile strength of 40± 10 MPa being
observed. This publication also commented on the fact that
there was no apparent correlation between Young’s modulus
Figure 15 Relative Young’s modulus of PA 6,6 bers as a
function of diameter. These results show a denite increase
in mechanical properties with reducing ber diameters.
Reprinted with permission from Arinstein et al.,181 Copyright
2007, Nature Publishing Group
Table 4 RJS (solution) materials choices from published data
Polymer Application Refs.
Poly(lactic acid) (PLA) Biomedical, tissue engineering [61]
Polyethylene oxide (PEO)
Gelatine
Poly(2,5-bis(20-ethyl-hexyl)-1,4-phenylenevinylene) (BEH-
PPV)
Photo-luminescent qualities for applications in light emit-
ting diodes
[64]
Polyethylene oxide (PEO)
Polycaprolactone (PCL) Study of RJS process [63,144]
Polyvinylidene fluoride (PVDF) Study of RJS process [66]
Polytetrafluoroethylene (PTFE) Super-hydrophobic properties for anti-fouling applications [70]
Polyacrylonitrile (PAN) Carbon fiber precursor [67,145]
Poly(vinyl butyral) (PVB) Study of RJS process [84]
Polyvinylpyrrolidone (PVP) Sacrificial polymer in fabrication of tin-doped indium oxide
nanofibers
[62]
Polyvinylpyrrolidone (PVP) Biomedical applications, drug delivery vehicle [68,110]
Polycaprolactone (PCL)
Poly(L-lactic acid) (PLLA) Biomedical, tissue engineering [71]
Polyvinylpyrrolidone (PVP)
Polyvinylchloride (PVC) Study of RJS process [146]
Polyethylene glycol (PEG)
Chitosan
Gelatine
Polyurethane (PU)
Polyamide 6 (PA6) Study of RJS process [147,148]
Bacterial cellulose (BC) Biomedical, tissue engineering [149]
Polymethyl methacrylate (PMMA) Battery applications [85,138,150]
Polyacrylonitrile (PAN)
Polystyrene (PS) Composite reinforcement, refractory filtration systems,
molecular anisotropy study
[81,151]
Polystyrene (PS) Silicon carbide precursor [152]
Polycarbomethylsilane (PCmS)
Thermoplastic polyurethane (TPU) Switchable hydrophobicity applications for oil-water sepa-
ration, graphene composite filler study
[141,153]
Polyvinylpyrrolidone (PVP) Gas sensing membranes [154]
SnCl4·5H2O
Polyvinyl alcohol (PVA) Composite nanofiber for lithium-ion battery anodes [155,156]
SnO2/PAN (Carbon)
Polyvinylpyrrolidone (PVP) Electrostatic-assisted RJS process [157]

Rogalski et al.
Nanocomposites 2017 VOL. 3 NO. 4 111
it would ensure more accurate mechanical testing data using
the frame method (see Figure 16). Upson et al. however used
this method to test a nanober web produced by RJS, aligning
the testing frame (and thereby the tensile testing direction)
with the spinning direction of the bers.164
Simplied methods of testing mechanical properties of
polymer nanobers are essential for future developments,
although existing methods do provide some data which
allows us to compare mechanical properties of nanober
yarns,185 bundles, and in rare occasions even single polymer
nanobers.
Modeling the rotary jet spinning
process
With any of the material’s processing techniques available, mod-
eling has a lot to oer to further rene and optimize the process.
Knowledge that is gained from modeling is used to improve
and understand the process in more detail, which is sometimes
simply not possible through experimental techniques alone.
Modeling the RJS process involves the use of basic parameters
such as polymer viscosity, centrifugal force, Coriolis force, air
drag on the ber and also the evaporation time of a solvent
in the collector during spinning.53 Several publications investi-
gating viscoelastic properties and production methods163,186–191
provide great insight into the complexity of the RJS process, and
will provide useful directions for future RJS models.
Models which focus on electrospinning have been pub-
lished recently,49,192 and these would naturally include addi-
tional properties such as the volumetric charge density and
electrical potential during processing. One property which
is obviously absent in electrospinning models are rotational
velocities, but in many of these electrospinning models there
is good agreement between predicted ber morphology and
that obtained through experimentation.
Figure 17 shows a basic representation of the forces
involved in the RJS process in agreement with assumptions
made by Mellado et al.169
There have been one-dimensional studies that have investi-
gated related parameters such as spiraling slender jets emerging
from a rapidly rotating orice in both a viscous model by Decent
As mentioned earlier, so far RJS research has not been
able to develop a deposition methodology that allows for
ber alignment in a similar way as the rotating drum or disc
method does in electrospinning. By collecting oriented bers,
Table 6 PBT ber diameter variance with processing tem-
perature, showing little variation with rotational velocity,
but dened change from temperature affecting the polymer
viscosity65
Rotational
speed
(rpm)
Process
ing tem-
perature
(°C)
Average
diameter
(μm)
Std.
deviation
% Nano-
fibers
10,000 300 1.35 0.78 36
12,000 300 1.31 0.68 40
15,000 300 1.38 0.68 28
12,000 280 1.64 0.90 26
12,000 320 1.17 0.92 55
Table 7 PCL ber diameter with varying viscosity76
Temperature (°C) Viscosity (Pas) Fiber diameter (μm)
120 158.1 9.7±4.9
140 130.4 8.8±3.1
200 43.3 7.0±1.1
250 17.8 12.8±8.4
Table 8 Melt processing effect on ber diameter, showing the PP/MWCNT nanocomposite ber variation in diameter with
increasing spinneret speed74
Compound Spinneret speed
(rmin−1)
Mean fiber diameter
(μm)
Proportion of fib-
ers<1μm (%)
Mean fiber diameter
(nm)
Proportion of fib-
ers>5μm (%)
Pure PP 12,000 0.51 91.5 439 0
13,000 0.63 88.3 502 0.7
PP/MWCNT 13,000 1.87 53.7 702 6.4
14,000 1.05 56.7 633 0.6
16,000 1.75 63.5 621 9.7
Table 9 PCL ber diameter variation with RJS time63
Average fiber diameter of 16% PCL @ 6,000rpm. Collected after 5, 10, 15, 30s.
Sample Average diameter (nm) Standard deviation (nm)
15% – 5s 2105 ±1004
16% – 10s 1239 ±895
16% – 15s 509 ±256
16% – 30s 326 ±112
Table 5 RJS (melt) materials choices from published data
Polymer Application Refs.
Polypropylene (PP) Study of RJS process,
Hydrophilic nonwoven
applications
[69,74,140]
Polybutylene tereph-
thalate (PBT)
Study of RJS process [65]
Polycaprolactone
(PCL)
Biomedical applica-
tions
[76,168]
Polyethylene tereph-
thalate (PET)
Study of RJS process [78]
Polyvinylpyrrolidone
(PVP)
Crystalline Olanzapine Biomedical applica-
tions (Drug delivery)
[109]
Crystalline Piroxicam
Crystalline Sucrose

Rogalski et al.
Rotary jet spinning review
Nanocomposites 2017 VOL. 3 NO. 4
112
also measured and compared with a simulation derived value,
showing a correlation based on rotational velocity variation.
In a separate publication by Valipouri et al.194 regarding
the numerical study of RJS and the eect of angular velocity,
they investigated the inuence of non-dimensional numbers
such as the Rossby number on ber diameter. Here it was con-
cluded that a decrease in Rossby number (which in real terms
indicates an increase in angular velocity) reduces the size of
the ber diameter, contracts the trajectory, and increases the
tangential velocity. This further enhances the experimental
proof of reduced ber diameter with increasing angular veloc-
ity, of which some qualitative agreement with experimental
data has been established.
When investigating a new technique and possible ways to
numerically evaluate its behavior, it may be possible to arrive
at the same conclusions from dierent models, thus conrm-
ing each other’s ndings.
To this end, Mellado et al.
169
produced what they called “A sim-
ple model for nanober formation by rotary jet spinning”. In it they
establish three key moments in the lifecycle of nanober forma-
tion, namely (1) jet initiation, (2) jet elongation, and (3) solvent
evaporation (Figure 19). It is in these three areas that experimental
et al.186 and an inviscid model by Wallwork et al.193 This research,
and other related studies have set the initial basis for RJS models.
Valipouri et al.83,194 performed experiments using both air-
sealed (isolated) and open air (non-isolated) ow RJS setups
to evaluate the prediction from a numerical model. The reason
for this is due to the complexity of the addition of air resistance
to the model once the system accounts for drag forces on the
drawing ber as it spins.
Based on coordinate systems from Wallwork et al.193 and
Decent et al.,186 Valipouri et al.83 established a model to evalu-
ate the process. The main forces considered were centrifugal,
Coriolis and viscous forces in a comparison between isolated
and non-isolated models.
The model could accurately predict the experimental
trajectory proles for the isolated jets based on simulations
(Figure 18), but was not able to accurately predict the trajec-
tories of the non-isolated ow experiments, when using water
as a test uid.
The conclusion that Valipouri et al. reached was that an
increase in trajectory curvature was found in the non-isolated
open air system due to the increase in air resistance/turbu-
lence within the spinning area. Fiber diameters of PAN were
Figure 16 Tensile testing of a single polymer nanober using the paper frame method
Figure 17 Schematic of RJS process with magnied views. Reprintedwith permission from Badrossomay et al.,61 Copyright
2010,American Chemical Society

Rogalski et al.
Nanocomposites 2017 VOL. 3 NO. 4 113
the collector and the radius of the orice, which are all shown
to be parameters in the model prediction for ber radius.
While studying the interaction of the RJS process with
various material property variations, Badrossamay et al.61
experimented with polymer concentrations in solution as a
benchmark for ber quality. In their publication, they reviewed
the eect of a change in polymer concentration on molecular
chain entanglement, and the critical concentration at which
the presence of a sucient amount of entanglements dramat-
ically alters the viscoelastic properties of the spinning solution
to facilitate bers of a higher quality (those without beading).
As with RJS, electrospinning also relies on chain entan-
glements. A detailed study by Shenoy et al.195 has shown this
to be the case for several polymer/solvent systems in which
distinct zones are present, namely good ber formation,
ber and bead formation, or beads or droplets only. In their
research, Shenoy et al. calculated that for stable ber forma-
tion to occur, a minimum of 2.5 entanglements per chain
should exist.
A PVP/poly(L-lactic acid) (PLLA) and DCM solution was
chosen to evaluate this phenomenon, with concentrations
and theoretical studies produce a phase diagram, which can with
some certainty predict the production rates and quality of bers.
The nal ber radius and threshold rotational velocity for
ber production is calculated using the following equations,
as proposed by Mellado et al.169:
where r is radius of ber, a is orice diameter, U is exit velocity
of polymer, ν is kinematic viscosity dened at viscosity/density,
Rc is radius to collector and Ω is rotational velocity.
where Ωc is critical rotational velocity, ρ is density, Rc is radius
to collector, γ is surface tension, a is orice diameter and μ is
viscosity.
This study highlighted the fact that the formation of bers
using RJS is inuenced by a few key factors. The tuning of ber
radii is essentially controlled by varying viscosity, angular veloc-
ity (which directly aects the polymer exit velocity), distance to
(2)
r
∼
aU 0.5
𝜐
0.5
R
3∕2
c
Ω
(3)
Ω
c∼𝜌
R2
c𝛾
2
a
2𝜇−
3
Figure 18 Experimental vs. model behavior of H20 (left) and polyacrylonitrile (PAN) (right). The model prediction of trajectory
(left) shows the isolated jet and model having near identical values, whereas the real world non-isolated jet will experience air
resistance, altering the trajectory which cannot be accounted for in the model. Fiber radius predictions (right) of PAN using a
dimensionless value over the arc length show good correlation with measured experimental diameters, prediction only very
small variances with speed. Reprinted with permission from Valipouri et al.,83 Copyright 2015, Elsevier
Figure 19 Phase diagram illustrating ber prediction by Mellado et al.
169
showing: (a) Fiber radius measurements based around
processing parameters (see publication for more details). (b) A phase diagram divides the scaled angular velocity-viscosity plane
into regimes I, II, III. (c, f) Beady bers. (d, g) Fine continuous bers. (e, h) Large continuous bers collected from regime I. Scale
bars are 4μm (c)–(e) and 20μm (f)–(h). Reprinted with permission from Mellado et al. [169], Copyright 2011, AIP Publishing LLC

Rogalski et al.
Rotary jet spinning review
Nanocomposites 2017 VOL. 3 NO. 4
114
the parameters studied included angular velocity, material
properties, collector diameter, orice size and solvent evap-
oration rate. This model is however 2D which assumes that
the gravitational forces are much smaller than the centrifugal
forces produced in the system.
Non-dimensional numbers provide ratios between vari-
ous forces in the system being studied. Padron et al.64 reviews
some of the most important ones in Table 10.
Padron et al. produced comparable solutions to those of
Wallwork et al.193 where the trajectory and diameters of beads
formed using the prilling process are studied. This process is
similar to RJS and based on viscous material ejected from a
rotating surface, typically used to create pellets from materi-
als heated to low viscosity melting points such as fertilizers
or detergent powders.200 The steady state solutions that were
obtained were then used to compare similarly derived equa-
tions for time-dependant parameters with constant angular
velocity, transforming the equations into partial dierential
equations.
Padron et al.’s work clearly displays an ability to model
and predict the variation in ber diameter along its axis with
respect to time, including information on the trajectory of
such bers. However, their work does not include a viscous
element, and could therefore be misleading when comparing
with experimental data. However, with a viscoelastic compo-
nent included in such a model, a powerful prediction tool
would become available.
Such a model was presented in a further publication by
Padron et al.53 in which they study the ber forming process
from a material property point of view, along with high speed
photography to capture the physics of the jet as it leaves the
orice. This work once again summarized the importance of
all of the processing parameters including viscoelastic prop-
erties, viscosity and relaxation time of the polymeric material.
As discussed by Padron et al.,53 it is important to consider the
large deformations that are present in the RJS process, and
to choose appropriate viscoelastic models which will be able
to approximate the solution or material properties such as
a Pipkin diagram,201 which separates a materials’ viscoelastic
ranging from 0.1 to 10%. In Figure 20, the gradient change of
the zero shear viscosity versus polymer concentration signies
the alteration in molecular entanglements. There are usually
three distinct regimes observed in these graphs, indicating
a step change in the overlapping of polymer chains from a
dilute, semi-dilute disentangled state to a semi-dilute entan-
gled state. These gradients can vary depending on the dif-
ferent chain lengths, chain congurations, polydispersity and
molecular weight of the PLLA and PVP in this study.71
It is typical in non-branched linear polymer melts for the
zero shear viscosity to scale with the molecular weight to the
power of ~3.4 above the critical entanglement molecular
weight, Me,196 however polymer solutions can deviate from
this gradient.197
It is this overlapping of polymer chains, with increase in
polymer concentration, which results in a critical concentra-
tion being reached. In the case of RJS of PLA/chloroform, this is
in the region of 8wt%. At this concentration, there are enough
chain entanglements to create a viscoelastic solution that can
produce bead-free bers at sucient rotational velocities. As
shown in Figure 12, the critical concentration may indicate
when a polymer solution is likely to produce a good quality
ber, but the angular velocity must still be sucient to over-
come the surface tension in the drawn ber so as not to induce
malformations such as beading.
As with previous modeling examples in RJS, non-dimen-
sional numbers are often the key to understanding the limita-
tions of the process. In Badrossamay’s evaluation of them,
61
the
Capillary number (dened as the ratio of the Weber number to
the Reynolds number) indicates whether a ber would be of
better quality by possessing a higher value. They state that the
Capillary number could estimate jet break-up, whereby lower
Capillary numbers result in shorter jet lengths and earlier jet
break-up to isolated droplets.61,198
The two-dimensional (2D) inviscid model for RJS focuses on
determining the ber radius and trajectories as a function of
arc length and was produced by Pardon et al.199 This model is
geared toward predicting nal ber diameters, with the hope
of reducing experimental time and material waste. To do this,
Figure 20 Zero shear viscosity versus polymer solution concentration for polyvinylpyrrolidone/poly(L-lactic acid) (PVP/PLLA)
blends with varying PLLA content (left) and PVP/PLLA ber quality (right), showing how the critical entanglement ratio affects
the quality of the ber throughout all spinning speeds. Reprinted with permission from Ren et al.,71 Copyright 2013, Royal
Society of Chemistry

Rogalski et al.
Nanocomposites 2017 VOL. 3 NO. 4 115
where ρ is density, Vpd is volume of the pendant drop.
High speed imagery was used to establish the shape of the
pendant drop as it approaches the critical velocity thresh-
old, which results in ber jet initiation. After this point, when
the ber has commenced its extension, the velocity of the
jet increases due to the simultaneous pushing and pulling
momentum from both sides of the capillary (Figure 23). This
velocity is expressed in an equation by Padron et al.53 by add-
ing an additional term U
f
(ber velocity) into the above velocity
equation.
Padron et al.53 also experimented by varying both angular
velocities and solution viscosity, and were able to establish a
model of trajectories along the X and Z axis as seen in Figure
24.
Being able to accurately predict the nal radius and tra-
jectory for the RJS process is important in the long term as
industrial applications for nanobers become more rened.
When the basic morphology can be predicted to a reasonably
acceptable accuracy, the process becomes more commercially
viable. The current data available to achieve this are approach-
ing the point to which this would be possible.
Adaptations within rotary jet spinning
As RJS is still a relatively new technique for manufacturing pol-
ymer nanobers, there are dierent approaches in the design
and construction of the equipment used. These variations are
often based on a few key parameters which alter the spin-
neret size, collector distance and rotational velocity, with some
changing the number of jet orices and locations. According
to the centrifugal force equation (Fc= Mω2r), an equivalent
force can be obtained by either altering the rotational velocity
or by altering the distance from the axes of rotation – with the
rotational velocity being the more sensitive parameter.
Commercial versions of RJS hardware are available to
purchase from companies such as FibeRio® Technology Co. in
Texas, USA, and around a third of publications have used their
agship Cyclone™ spinner to conduct research into nanober
production. Current availability is unknown since acquisition
by CLARCOR in 2016, which in turn were acquired by Parker
Hannin in 2017. Alternatively, an extremely simple setup
could involve nothing more than an inverted motor with a
polymer vessel acting as a spinneret, surrounded by a collec-
tion device. In essence, a very simple setup – not very dier-
ent from a candy oss machine – should you wish to conduct
research on varying dimensional scales other than that which
is available commercially. However, accuracy and repeatability
would rely on the quality of equipment being used with safety
being another key consideration.
Other adaptations of the process by which to make bers
through centrifugal force have involved experiments using
nozzle-free approaches, such as the one used by Weitz et al.
203
in their study of poly(methyl methacrylate) (PMMA) solution
(7)
U
cr =− 8L𝜇
𝜌a
22
1
2






256

L𝜇
𝜌a
22

2
8𝜋

a
2

𝜇sin𝛼
𝜌Vpd S0R2
c2LS0−L
2

properties into regimes based on their dynamic response
(Figure 21).
In their research, Padron et al. dene RJS falling into the
non-linear viscoelastic regime in Figure 21. It goes on to
dene the coordinate system using a rotating reference, and
the governing equations used are described by the continuity
equation:
where u is the relative velocity of the ber jet.
And the Cauchy momentum equations:
where P is the pressure, g is the gravity vector, T is the stress
tensor, Ω is the angular velocity of the spinneret, and c is a
position vector describing a point along the ber.
Exit velocities for both continuous and non-continuously
fed spinnerets are calculated using the parameters from Figure
22.
Based on these calculations for velocity U, the critical angu-
lar velocity
Ωcr
and critical exit velocity Ucr of the system were
established.
(4)
∇⋅U=0
(5)
𝜕U
𝜕t
+(U⋅∇)U=−
∇P
𝜌
+g+
∇T
𝜌
−Ω
(Ωc)−2ΩU
(6)
Ω
cr =
√2
𝜋
a
2𝜇
sin
𝛼
𝜌V
pd
S
0
Table 10 Non-dimensional numbers used for prediction of
uid behavior. Adapted from Padron et al.64
Dimensionless number Ratio description
Reynolds number Inertial forces to viscous forces
Froude number Fibre’s inertial force to gravitational
force
Weber number Fibre’s inertial force to surface
tension
Rossby number Fibre’s inertial force to Coriolis
force
Deborah number Polymer relaxation time to flow
Capillary number Fibre’s viscous forces to surface
tension
Figure 21 Pipkin diagram showing demarcated areas of
viscoelastic behavior, evaluating strain amplitude (γ
0
) versus
dimensionless frequency (
𝜔
). Reprinted with permission from
Parthasarathy et al.,202 Copyright 1999, Elsevier

Rogalski et al.
Rotary jet spinning review
Nanocomposites 2017 VOL. 3 NO. 4
116
they investigated the eects on a viscoelastic jet and a single
nanober through this technique. Much emphasis was placed
on the viscoelastic behavior of the jets. Badrossomay et al.,128
Ericksson et al.129 and Wang et al.110 have also produced good
ber alignment by combining both RJS and electrospinning.
The benet of this process is to ensure that ber alignment
is maximized. If the ber is moving toward the collector in
electrospinning, a whipping motion is experienced, creating
a non-oriented mat on the collector. By introducing RJS to this
process, it greatly increases alignment, much in the same way
that a rotating disc collector in electrospinning ensures ber
alignment on collection.
Pressure can also be used as an added element to improve
RJS. If the spinneret is enclosed and pressurized, an addi-
tional force is introduced. This is exactly what Edirisinghe and
co-workers did when spinning several materials from solution
under a pressure of up to 300kPa and 36,000rpm, being the
capability of their in-house built system.
153,165,168,170,171,206–210
The
benets of this system include the use of a wider range of pol-
ymer viscosities due to added pressure forcing ow through
the spinneret dies, rather than relying purely on centrifugal
force generated by the rotation velocity. This system does not
however seem toproduce bers consistently in the nanoscale.
The future of rotary jet spinning
Rotary jet spinning has become prevalent in the last decade,
with research related to this topic increasing exponentially
since its inception. At present, the commercialization of this
technology for the nonwoven industry is starting, with the
introduction of larger industrial scale RJS machines capable of
spinning one meter wide continuous ber mats. Other meth-
ods of nanober production such as needless electrospinning
also oer large scale production, such as the Nanospider™
technology by Elmarco,7 as referenced previously. However,
with up-scaled nanober production, it is only a matter of time
behavior on the surface of a spin coater. They were interested
in this technique and established a procedure to create dis-
continuous bers in the diameter range of 25nm to 5μm.
Methods that incorporate electrospinning together with an
element of RJS have also been investigated. Angammana et
al.204 considered a charged rotary atomiser disc with polymer
solution that would eectively eject bers from the top of the
rotational arc toward a charged collector plate above, resulting
in nanober production. A similar technique was introduced
by Chang et al.
205
They combined electrospinning with RJS and
termed it electrostatic-centrifugal spinning, with the view of
removing the whipping instability experienced by electros-
pinning alone. It is said to be rst introduced by their lab, and
Figure 22 Forces on material with spinneret and pendant drop. Reprinted with permission from Padron et al.,53 Copyright
2013, AIP Publishing LLC
Figure 23 Evolution of jet at orice for ber production as
it accelerates to 4,500 rpm, with additional jet shapes for
varying speeds. This shows the changeover from pendant
drop to full ber producing ow. Reprinted with permission
from Padron et al.,53 Copyright 2013, AIP Publishing LLC

Rogalski et al.
Nanocomposites 2017 VOL. 3 NO. 4 117
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until RJS starts to compete with other more established meth-
ods of polymer nanober production such as melt blowing,
where unaligned non-woven mats and spunbound materials
are made.
Due to the lower production costs and potentially greener
credentials, a lower price to market should be achievable
which could make this a potentially disruptive technology in
the nanober race. However, it remains to be seen whether a
broad range of materials will be considered for diverse appli-
cations, or if more traditional polymeric materials such as
polypropylenes, polyamides or polyesters will take on specic
product applications. Since biomedicine is a large contributor
to the research bulk to date, it is possible that pharmaceutical/
biomedical interests may become the lead user of this tech-
nology for the development of tissue recovery and/or drug
delivery systems. Other applications at the forefront of this
technology will be in ber-based electronic devices like exi-
ble sensors, super capacitors or lithium ion batteries.
As with most technology, the more that is understood
about the ability to manipulate a certain production method,
the more attractive it is for investment within them. The cur-
rent body of knowledge available on RJS would suggest that
we can expect a step change to occur well within the next
decade.
Funding
The authors gratefully acknowledge DSM (the Netherlands)
for nancial support and actively supporting our research in
the eld of RJS.
Disclosure statement
No potential conict of interest was reported by the authors.
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