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Manufacturing Of High Strength Kevlar Fibers



In this study, it is shown that Kevlar was developed in 1965 by two authors worked at DuPont research center. They were looking to create a fiber with exceptional strength, lightweight and flexible behavior the organic fiber in the aromatic polyamide family, also known as aramid is a sufficient polymer. Fibers of Kevlar consist of long molecular chains produced from poly-paraphenylene terephthalamide. The chains are highly oriented with strong interchanged bonding that results in an unusual combination of properties. General features include high tensile strength, low weight, high modulus of rigidity, high chemical resistance, high toughness, low elongation to break, low electrical conductivity, excellent dimensional stability and self-extinguishing flame resistance but it is bad machinability. Four types of spinning methods are explained which are: wet spinning, dry spinning, melt spinning and gel spinning. In order to manufacture Kevlar with specified properties, dry jet wet spinning method is used by forcing a viscous fluid or solution of the polymer through the small orifices of spinnerets and immediately solidifying or precipitating the resulting filaments.
Table of Contents
I-History and Development of Kevlar……………………………….….…………..1
II-DuPont's Kevlar Production Facility………..……………………..…………….2
III-Composition of Kevlar……………………………………………..…………….4
A) Grades of Kevlar……………………………………..…………….…………4
B) Mechanical Properties of Kevlar……………………………….……………4
C) Technical Properties……………...……………………………..……………6
D) Advantages and Disadvantages of Kevlar………….……….….…...………6
E) Applications of the Kevlar Fibers………………………………….………..7
F) A comprehensive list of Kevlar application………………..………………8
A) The Spinnerets………………………………………………………………….9
B) Types of Spinning Methods…………………...………..…………………….10
1- Wet Spinning…………………...……………..…………………………10
2- Dry Spinning…………………...……...…………………………………11
3- Melt Spinning……………………...…………………………………….12
4- Gel Spinning……………...….…….…………………………………….13
A) Affects of the Crystallinity of Kevlar……………...………….……………..14
B) Spinning Solvent………………………………….……..……………………..14
C) Dry Jet Wet Spinning Method………………………….…………………….15
Reference ………………………………………………….….…………………….16
Manufacturing Of High Strength Kevlar Fibers
All fibers used in polymer engineering composites can be divided into two
categories, namely synthetic fibers and natural fibers. Synthetic fibers are the most
common. Although there are many types of synthetic fibers, glass, carbon and aramid
fibers represent the most important.
Kevlar is an aromatic polyamide or aramid fiber introduced in early 1970s by
DuPont. It was the first organic fiber with sufficient tensile strength and modulus to
be used in advanced composites. It has approximately five times the tensile strength
of steel with a corresponding tensile modulus. Originally developed as a replacement
for steel in radial tires, Kevlar is now used in a wide range of applications. It is a trade
name of aramid fiber. [13]
The U.S. Federal Trade Commission gives a good definition of an aramid
fiber as "a manufactured fiber in which the fiber forming substance is a long chain
synthetic polyamide in which at least 85% of the amide linkages are attached directly
to two aromatic rings" [14].
History and Development of Kevlar
Kevlar's history goes back to 1948, when DuPont, with its invention of nylon
behind it, made a decision to pursue work in a broad area of fibers with unusually
high thermal, elasticity, and strength properties. [13]
The possibility of making polyaramid plastic was hypothesized in 1939. It was
synthesized and identified at DuPont in 1960, but polyaramid fiber could not be
produced until 1965, when Stephanie Kwolek, a chemist at DuPont, discovered a
practical solvent. At about the same time, a team at Akzo, Inc., a multinational firm
headquartered in Holland, independently discovered a practical solvent and applied
for a patent for the manufacture of polyaramid fiber, which DuPont named Kevlar®
and Akzo later (1984) named Twaron®. DuPont contested the patent. A consent
decree of the International Trade Commission settled the dispute; terms of the
settlement included cross-licensing but barred Akzo from marketing Twaron® in the
United States until late 1990.
Kevlar 29, introduced in the early 1970s, was the first generation of bullet
resistant fibers developed by DuPont and helped to make the production of flexible,
concealable body armor practical for the first time. In 1988, DuPont introduced the
second generation of Kevlar fiber, known as Kevlar 129. According to DuPont, this
fabric offered increased ballistic protection capabilities against high energy rounds
such as the 9mm FMJ. In 1995, Kevlar Correctional was introduced, which provides
puncture resistant technology to both law enforcement and correctional officers
against puncture type threats.
The newest addition to the Kevlar line is Kevlar Protera, which became
available in 1996 by DuPont. DuPont contends that the Kevlar Protera is a high-
performance fabric that allows lighter weight, more flexibility, and greater ballistic
protection in a vest design due to the molecular structure of the fiber. Its tensile
strength and energy-absorbing capabilities have been increased by the development of
a new spinning process. [17]
Before Kevlar® was used for body armor, it was used as a substitute for steel
in the manufacture of radial tires, including those designed for police cars. “Kevlar” is
a registered trademark of DuPont de Nemours and Co., Inc. “Twaron” is a registered
trademark of Akzo, Inc.
DuPont's Kevlar Production Facility
DuPont will expand its Kevlar para-aramid fiber production facility in
Richmond, Va., by adding a new production line at the site, increasing its capacity by
the end of 2002. Total investment for this expansion is expected to be roughly $50
million. [5]
The company has already completed the first phase of an expansion begun
early in 2001 and has increased global production capacity for Kevlar fiber by 15
percent. The second expansion will address a two year trend of growing demand for
high-performance, high strength para-aramid fibers, which has exceeded global
manufacturing capabilities. The capacity expansion is based on technology developed
and patented by DuPont and used in the company's European operations for the past
four years [5]. For example, Toray Industries Inc. of Japan and E.I. DuPont de
Nemours of the U.S. said they have agreed to build a joint plant in Japan to
manufacture Du- Pont's kevlar fiber [7].
Composition of Kevlar:
The chemical composition of Kevlar is poly para-phenyleneterephthalamide
(PPD-T) and it is more properly known as a para-aramid. It is oriented para-
substituted aromatic units. Aramids belong to the family of nylons. Common nylons,
such as nylon 6,6 do not have very good structural properties, so the para-aramid
distinction is important. Aramid fibers like Nomex or Kevlar, however, are ring
compounds based on the structure of benzene as opposed to linear compounds used to
make nylon. The aramid ring gives Kevlar thermal stability, while the para structure
gives it high strength and modulus. Like nylons, Kevlar filaments are made by
extruding the precursor through a spinneret. The rod form of the para-aramid
molecules and the extrusion process make Kevlar fibers anisotropic--they are stronger
and stiffer in the axial direction than in the transverse direction. In comparison,
graphite fibers are also anisotropic, but glass fibers are isotropic. [14]
Figure1: Chemical composition of Kevlar [17]
It is made from a condensation reaction of para-phenylene diamine and
terephthaloyl (PPD-T) chloride. The resultant aromatic polyamide contains aromatic
and amide groups which makes them rigid rod like polymers. The rigid rod like
structure results in a high glass transition temperature and poor solubility, which
makes fabrication of these polymers, by conventional drawing techniques, difficult
Instead, they are melt spun from liquid crystalline polymer solutions as described
later. The Kevlar fiber is an array of molecules oriented parallel to each other like a
package of uncooked spaghetti. This orderly, untangled arrangement of molecules is
described as a crystalline structure. Crystallinity is obtained by a manufacturing
process known as spinning, which involves extruding the molten polymer solution
through small holes. [14]
When PPD-T solutions are extruded through a spinneret and drawn through an
air gap during fiber manufacture, the liquid crystalline domains can orient and align in
the flow direction. Kevlar can acquire a high degree of alignment of long, straight
polymer chains parallel to the fiber axis. The structure exhibits anisotropic properties,
with higher strength and modulus in the fiber longitudinal direction than in the axial
direction. The extruded material also possesses a febrile structure. This structure
results in poor shear and compression properties for aramid composites. Hydrogen
bonds form between the polar amide groups on adjacent chains and they hold the
individual Kevlar polymer chains together [8]. It is shown as in the following figure:
Figure 2: Hydrogen bonds form between the polar amide groups
Grades of Kevlar
There are three grades of Kevlar available: Kevlar 29, Kevlar 49, and Kevlar
149. Tensile modulus is a function of molecular orientation. As a spun fiber, Kevlar
29 (a high toughness variant) has a modulus of 62 GPa (9 Mpsi). Heat treatment under
tension increases crystalline orientation. The resulting fiber, Kevlar 49, has a modulus
of 131 GPa. [14]
Mechanical Properties of Kevlar:
The tensile strength of Kevlar ranges from about 2.6 to 4.1 GPa. This is more
than twice that for conventional fibers like Nylon 66. Tensile failure initiates at the
fibril ends and propagates via shear failure between the fibrils. The table below shows
the differences in material properties among the different grades. Kevlar cloth is most
likely to be Kevlar 49.
Grade Density
29 1.44 83 3.6 4.0
49 1.44 131 3.6--4.1 2.8
149 1.47 186 3.4 2.0
Table 1: Differences in material properties among the different grades of Kevlar. [14]
The tensile modulus and strength of Kevlar 29 is roughly comparable to that
of glass (S or E), yet its density is almost half that of glass. Thus, to a first
approximation, Kevlar can be substituted for glass where lighter weight is desired.
Kevlar 49 or 149 can cut the weight even further if the higher strength is accounted
for. Of course, Kevlar's weight savings does come at a price: Kevlar is significantly
more expensive than glass [13]. DuPont sees kevlar as a replacement for steel cable
on offshore oil rigs [12].
Kevlar behaves elastically in tension. In compression, it shows nonlinear,
ductile behavior. It exhibits yield at compression strains of 0.3 to 0.5%. This
corresponds to formation of structural defects known as kink bands. These bands are
related to compressive buckling of the aramid molecules. Aramid fibers are noted for
toughness and general damage tolerance. Kevlar 29 has the lowest modulus and
highest toughness and the tensile elongation of Kevlar 29 is about 4%. The fibrillar
structure and compression behavior contribute to composites that are less notch-
sensitive and which fail in a ductile, non-catastrophic manner, as opposed to glass and
carbon. [8]
The aromatic structure gives the fibers a high degree of thermal stability. They
decompose in air at about 425°C and are inherently flame resistant. Aramids have a
slight negative longitudinal coefficient of thermal expansion of about -2 x 10-6/K and
a positive transverse expansion of 60 x 10-6/K. They also have a low thermal
conductivity that varies by about an order of magnitude in the longitudinal versus
transverse direction. [8]
Technical Properties:
Technical properties claimed of kevlar can be summarized as follows:
* High strength to weight ratio.
* Low ductility.
* High modulus of rigidity (structural rigidity).
* Low electrical conductivity.
* High chemical resistance.
* Low coefficient of thermal expansion.
* High toughness (work-to-break).
* Excellent dimensional stability.
* Low machinability.
* Flame retardant, self-extinguishing. [3]
Advantages and Disadvantages of Kevlar:
Advantages are:
It has the lowest specific gravity.
It has the highest tensile strength-weight ratio.
Only fiber for structural application.
Disadvantages are:
Low compressive strength.
Difficult to machine (Low machinability). [9]
Applications of the Kevlar Fibers:
Because of its chemical nature and linearly oriented polymer structure, kevlar
claims an excellent combination of physical properties. High tensile strength, high
stiffness and damage tolerance, and high thermal stability with self-extinguishing
properties (kevlar fiber does not melt), make kevlar fibers ideal for a huge range of
demanding applications. These exceptional properties, particularly its high strength to
weight ratio, temperature resistance and versatility, are thought responsible for kevlar
being used in a huge range of demanding applications ranging from deep sea
umbilical lines and premium sports goods to high performance structural composites
in boat hulls, aircraft components and high-performance cars. [3]
The kevlar fiber is suggested to be used in flywheel of a commuter car because
the kevlar fiber glass flywheel has a greater strength-to-weight ratio so that it can spin
much faster than flywheels made of other materials which would shatter. [1]
Kevlar is now being used to produce lightweight bulletproof body armor, and
kevlar vests are currently being worn by many of the country's policemen. However,
kevlar's main chance seems to lie in markets created by the energy problem.
Replacing heavier materials with Kevlar in airplanes, for instance, saves on fuel. Du
Pont also sees kevlar as a replacement for steel cable on offshore oil rigs. [12]
Kevlar fiber and butacite laminated glasses that make buildings safer, more
durable and more efficient. Kevlar is a lightweight, synthetic fiber, five times stronger
than steel on an equal weight basis, used to protect buildings from blasts. [6]
Wheels made with a single carbon fiber and Kevlar spoke can run
continuously from rim to rim, wrapping around, but not ending at the hub. The Kevlar
and carbon fibers are manipulated into an airfoil shape and coated with a thin layer of
clear thermoplastic resin. The spokes are then shaped to pass through the carbon-
composite hub shell and span across the wheel. The spokes are joined to a standard
rim with stainless steel fasteners and a standard alloy nipple.
Carbon fiber components are used in manufacturing of motorcycles. Baxter, a
textile engineering graduate of Clemson University, went on to invent Draggin' Jeans,
which use 100% Kevlar in denim jeans. About 11 inches of the protective fabric is
used in the knees, seam to seam, and the entire rear is covered with it. [2]
A comprehensive list of Kevlar applications
A comprehensive list of Kevlar applications includes :
•Adhesives and sealants — Thixotropes;
•Ballistics and defense — Anti-mine boots, cut-resistant gloves, composite helmets,
and bullet- and fragmentation-resistant vests;
•Belts and hoses — Automotive heating/cooling systems, industrial hoses, and
automotive and industrial synchronous and power transmission belts;
•Composites — Aircraft structural body parts and cabin panels, boats, and sporting
•Fiber optic and electromechanical cables — Communications and data transfer
cables; ignition wires; and submarine, aerostat and robotic tethers;
•Friction products and gaskets —Asbestos replacement, automotive and industrial
gaskets for high-pressure/high-temperature environments; brake pads; and clutch
•Protective apparel — Boots; chain-saw chaps; cut-resistant industrial gloves;
helmets (both for firefighters and consumer bicyclists); and thermal- and cut-
protective aprons, sleeves, etc.;
•Tires — Aircraft, automobiles, off-road, race vehicles and trucks; and
•Ropes and cables — Antennae guy wires, fishing line, industrial and marine utility
ropes, lifting slings, mooring and emergency tow lines, netting and webbing, and
pull tapes. [19]
Most synthetic and cellulosic manufactured fibers are manufactured by
“extrusion” forcing a thick, viscous liquid (about the consistency of cold honey)
through the tiny holes of a device called a spinneret to form continuous filaments of
semi-solid polymer.
In their initial state, the fiber-forming polymers are solids and therefore must
be first converted into a fluid state for extrusion. This is usually achieved by melting,
if the polymers are thermoplastic synthetics (i.e., they soften and melt when heated),
or by dissolving them in a suitable solvent if they are non-thermoplastic cellulosics. If
they cannot be dissolved or melted directly, they must be chemically treated to form
soluble or thermoplastic derivatives. Recent technologies have been developed for
some specialty fibers made of polymers that do not melt, dissolve, or form appropriate
derivatives. For these materials, the small fluid molecules are mixed and reacted to
form the otherwise intractable polymers during the extrusion process. [16]
The spinnerets:
The spinnerets used in the production of most manufactured fibers are similar,
in principle, to a bathroom shower head (see figure 3). A spinneret may have from
one to several hundred holes. The tiny openings are very sensitive to impurities and
corrosion. The liquid feeding them must be carefully filtered (not an easy task with
very viscous materials) and, in some cases, the spinneret must be made from very
expensive, corrosion-resistant metals. Maintenance is also critical, and spinnerets
must be removed and cleaned on a regular basis to prevent clogging.
Figure 3: Spinnerets
As the filaments emerge from the holes in the spinneret, the liquid polymer is
converted first to a rubbery state and then solidified. This process of extrusion and
solidification of endless filaments is called spinning, not to be confused with the
textile operation of the same name, where short pieces of staple fiber are twisted into
yarn. There are four methods of spinning filaments of manufactured fibers: wet, dry,
melt, and gel spinning. Table 1 lists the different types of spinning methods with the
fiber types produced by each method. [16]
Table 2: Types of spinning methods and fiber types produced.
Types of Spinning Methods
(1) Wet Spinning:
Wet spinning is the oldest process. It is used for fiber-forming substances that
have been dissolved in a solvent. The spinnerets are submerged in a chemical bath
and as the filaments emerge they precipitate from solution and solidify. [16]
The process begins by dissolving polymer chips in a suitable organic solvent,
such as dimethylformamide (DMF), dimethylacetamide (DMAc), or acetone, or in a
weak inorganic acid, such as zinc chloride or aqueous sodium thiocyanate. In wet
spinning, the spinning solution is extruded through spinnerettes into a precipitation
bath that contains a coagulant (or precipitant) such as aqueous.
Because the solution is extruded directly into the precipitating liquid, this process for
making fibers is called wet spinning. Acrylic, rayon, aramid, modacrylic and spandex
can be produced by this process. [10]
Figure 4: Wet spinning
(2) Dry Spinning:
Dry spinning is also used for fiber-forming substances in solution. However,
instead of precipitating the polymer by dilution or chemical reaction, solidification is
achieved by evaporating the solvent in a stream of air or inert gas. The filaments do
not come in contact with a precipitating liquid, eliminating the need for drying and
easing solvent recovery. [10]
The dry spinning process begins by dissolving the polymer in an organic
solvent. This solution is blended with additives and is filtered to produce a viscous
polymer solution, referred to as "dope", for spinning. The polymer solution is then
extruded through the spinnerets as filaments into a zone of heated gas or vapor. The
solvent evaporates into the gas stream and leaves solidified filaments, which are
further treated using one or more processes (See Figure 5.) [10]
Figure 5: Dry spinning
This process may be used for the production of acetate, triacetate, acrylic,
modacrylic, PBI, spandex, and vinyon. [16]
(3) Melt Spinning
In melt spinning, the fiber-forming substance is melted for extrusion through
the spinneret and then directly solidified by cooling. Nylon, olefin, polyester, saran
and sulfur are produced in this manner. [10]
Melt spinning uses heat to melt the polymer to a viscosity suitable for
extrusion. This type of spinning is used for polymers that are not decomposed or
degraded by the temperatures necessary for extrusion. Polymer chips may be melted
by a number of methods. The trend is toward melting and immediate extrusion of the
polymer chips in an electrically heated screw extruder. Alternatively, the molten
polymer is processed in an inert gas atmosphere, usually nitrogen, and is metered
through a precisely machined gear pump to a filter assembly consisting of a series of
metal gauges interspersed in layers of graded sand. The molten polymer is extruded at
high pressure and constant rate through a spinneret into a relatively cooler air stream
that solidifies the filaments. Lubricants and finishing oils are applied to the fibers in
the spin cell. At the base of the spin cell, a thread guide converges the individual
filaments to produce a continuous filament yarn, or a spun yarn, that typically is
composed of between 15 and 100 filaments. Once formed, the filament yarn either is
immediately wound onto bobbins or is further treated for certain desired
characteristics or end use. [10]
Melt spun fibers can be extruded from the spinneret in different cross-
sectional shapes (round, trilobal, pentagonal, octagonal, and others). Trilobal-shaped
fibers reflect more light and give an attractive sparkle to textiles. Pentagonal-shaped
and hollow fibers, when used in carpet, show less soil and dirt. Octagonal-shaped
fibers offer glitter-free effects. Hollow fibers trap air, creating insulation and provide
loft characteristics equal to, or better than, down. [16]
(4) Gel Spinning
Gel spinning is a special process used to obtain high strength or other special
fiber properties. The polymer is not in a true liquid state during extrusion. Not
completely separated, as they would be in a true solution, the polymer chains are
bound together at various points in liquid crystal form. This produces strong inter-
chain forces in the resulting filaments that can significantly increase the tensile
strength of the fibers. In addition, the liquid crystals are aligned along the fiber axis
by the shear forces during extrusion. The filaments emerge with an unusually high
degree of orientation relative to each other, further enhancing strength. The process
can also be described as dry-wet spinning, since the filaments first pass through air
and then are cooled further in a liquid bath. Some high-strength polyethylene and
aramid fibers are produced by gel spinning. [16]
Although the specific details of the manufacturing of aramid fibers remain
proprietary secrets, it is believed that the processing route involves solution
polycondensation of diamines and diacid halides at low temperatures. [15]
Affects of the Crystallinity of Kevlar
The most important point is that the starting spinnable solutions that give high
strength and high modulus fibers have liquid crystalline order. Various states of
polymer in solution depend on the type of polymer chain. Two-dimensional, liner,
flexible chain polymer in solution is called random coils. If the polymer chain can be
made of rigid units, that is, rod like, they can be represented like a random array of
rods. Any associated solvent may contribute to the rigidity and to the volume
occupied by each polymer molecule. With increasing concentration of rod like
molecules, one can dissolve more polymers by forming regions of partial order, that
is, regions in which the chains form a parallel array. This partially ordered state is
called a liquid crystalline state. When the rod like chains become approximately
arranged parallel to their long axes but their centers remain unorganized or randomly
distributed, we have what is called a nematic liquid crystal. It is this kind of order that
is found in the extended chain polyamides. [15]
Liquid crystal solutions, because of the presence of the ordered domains, are
optically anisotropic, that is birefringent. The parallel array of polymer chains in the
liquid crystalline state becomes even more ordered when these solutions are subjected
to shear. It is this inherent property of liquid crystal solutions which is exploited in the
manufacture of aramid fibers (trade name of kevlar). The characteristic fibrillar
structure of aramid fibers is due to the alignment of polymer crystallites along the
fiber axis. [15]
Spinning Solvent
Organic Fibers Researchers at DuPont discovered a spinning solvent for poly
p-benzamide (PBA) and were able to dry spin quite strong fibers from
tetramethylurea-LiCI solutions. This was the real breakthrough. The modulus of these
as spun organic fibers was greater than that of glass fibers. P-Oriented rigid diamines
and dibasic acids give polyamides that yield, under appropriate conditions of solvent,
concentration, and polymer molecular weight, the desired nomadic liquid crystal
structure. One would like to have, for any solution spinning process a high molecular
weight to obtain improved mechanical properties, a low viscosity to ease processing
conditions, and a high polymer concentration to achieve a high yield. For para aramid,
poly p-phenyleneterephthalamide (PPD-T), trade name Kevlar, the nematic liquid
crystalline state is obtained in 100% sulfuric acid at polymer concentration of about
20%. The polymer solution is often referred to as the dope. The various spinning
processes available are classified as dry, wet and dry jet-wet spinning process
(mentioned earlier). [15]
Dry Jet Wet Spinning Method
For aramid fibers, the dry jet wet spinning method is employed. It is believed
that solution-polycondensation of diamines and diacid halides at low temperatures
(near 00C) gives the aramid forming polyamides. Low temperatures inhibit by product
generation and promote linear polyamide formation. The resulting polymer is
pulverized, washed, and dried. This is mixed with a strong acid (e.g., concentrated
sulphuric acid) and extruded through spinnerets at 100 0C through about 1-cm air
layer is to cold water (0-4 0 C). The fiber precipitates in the air gap and the acid is
removed in the coagulation bath. The spinneret capillary and air gap cause rotation
and alignment of the domains resulting in highly crystalline and oriented as-spun
fibers. At the end of this process, the Kevlar is produced. [15]
In this report, it is shown that fibers are formed by forcing a viscous fluid or
solution of the polymer through the small orifices of spinnerets and immediately
solidifying or precipitating the resulting filaments. This prepared polymer may also be
used in the manufacture of other nonfiber products such as the enormous number of
extruded plastic and synthetic rubber products.
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... Process of, for instance, Kevlar fabric creation requires to boil petroleum (also known as crude oil) and sulphuric acid (a mineral acid composed of the sulfur, oxygen and hydrogen) at temperature of 750 o C, which contributes to large quantities of toxic waste. After that the mixture should be pressed to organize molecules in a proper order (Algahtani A., 2006). The whole process demands extreme conditions, such as enormous temperature and high pressure and in addition produces lots of dangerous waste, when at the same time spiders manage to achieve the same results at ambient temperature, with a bit of water and dead flies (Harris. ...
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Bionics is more than just an architectural movement, it is a process of learning from a perfect source that has been developing for more than three and a half billion years – the nature. Natural world has plenty of examples of organisms that have thrived among the others, that have solved thorniest problems and now represent success stories we can draw from. Mankind has been trying to emulate biological species in the vast array of scientific domains but in many cases, it is challenging to match the efficiency of natural life forms.
Materialien aus Biopolymeren sind aufgrund ihrer mechanischen und biochemischen Eigenschaften in Kombination mit ihrer nachhaltigen Gewinnung extrem interessant. Ihr Einsatzgebiet erstreckt sich von Verpackungsmaterialien über Verbundwerkstoffe für den Leichtbau hin zu biomedizinischen Anwendungen. Neben verbesserten mechanischen Eigenschaften sind Mikro- und Nanofasern durch ihre im Verhältnis zu ihrem Volumen und Masse vergrößerte Oberfläche für technische und medizinische Anwendungen von großer Bedeutung. Durch Nassspinnen wurden Filamente aus Celluloseacetat hergestellt. Die Deacetylierung der Filamente und anschließende Carbonisierung der entstandenen Cellulose-Filamente bei Temperaturen bis zu 2200 ◦C, ermöglichte die Herstellung von Carbon-Mikrofasern mit Durchmessern unter 10 μm und einer Zugfestigkeit von über 0,9 GPa. Für die Produktion von Nanofasern wurde die Eignung eines Hochdurchsatzverfahrens, welches Elektro- mit Zentrifugalspinnen vereint, untersucht. Ultradünne Nanofasern mit Durchmessern unter 100 nm konnten aus Lösungen von Polyethylenoxid, Polymilchsäure und biotechnologisch hergestellter Spinnenseide hergestellt werden. Die Produktivität des vorgestellten Zentrifugalelektrospinnverfahrens hinsichtlich Nanofaser-Vliesen aus wässriger und organischer Lösung war im Vergleich zu den traditionellen Herstellungsverfahren um Größenordnungen höher. Die Entwicklung einer Roll-to-Roll-Produktion ermöglichte die kontinuierliche Herstellung von Filterflachware mit Feinfiltrationsschicht aus artifizieller Spinnenseide. Die hergestellten Filtermaterialien zeichneten sich durch sehr hohe Filtereffizienz für Feinstaub mit Partikelgrößen unter 2,5 μm sowie extrem geringen Strömungswiderstand aus, sodass sehr gute Filterqualitäten erzielt wurden. Es konnten Filter hergestellt werden, die Partikel mit Durchmessern von 200 nm mit einer Effizienz von 99,3 % bei einer Luftpermeabilität von 517 l/m2 filtern konnten, sodass ein Qualitätsfaktor von 25 mPa-1 erzielt wurde
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Biopolymers show extraordinary mechanical and biochemical properties making them interesting materials for the production of bioplastics. Their field of applications ranges from packaging materials to composites for lightweight constructions, biomaterials, and biomedical applications. Beside their improved mechanical properties, the increased ratio of surface area to volume and mass makes micro- and nanofibers highly interesting for technical and medical applications. Filaments of cellulose acetate were produced using wet spinning. Deacetylation of cellulose acetate filaments followed by carbonization of the deacetylated cellulose filaments at temperatures up to 2200 °C, enabled the production of biopolymer-based carbon microfibers. The carbon microfibers show diameters below 10 μm and tensile strengths above 0.9 GPa. Nanofibers investigating the applicability of a high throughput production method were produced, combining solution-based electrospinning with centrifugal spinning. Ultrathin nanofibers with diameters below 100 nm made of polyethylene glycol, polylactic acid, and artificial spider silk, were obtained. The productivity of the established centrifugal electrospinning method in manufacturing highly interconnected nanofiber nonwoven meshes from aqueous and organic polymer solutions was several orders of magnitude higher compared to that of traditional electrospinning methods. Developing a roll-to-roll production, enabled the continuous manufacturing of nonwoven meshes made of recombinant spider silk proteins. The produced nanofiber filter layers showed high filtration efficiency for fine particulate matter below 2.5 μm and a low flow resistance resulting in excellent filter quality. The manufactured filter material showed a filtration efficiency of 99,3 % for the filtration of particles with 200 nm in diameter. The air permeability of the filter material was 517 l/m² resulting in a quality factor of 25 mPa-1.
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