4. Product Shaping / Secondary
Operations
EXTRUSION
Shaping
through die
Final Product (pipe, profile)
Secondary operation
Fiber spinning (fibers)
Cast film (overhead
transparencies,
Blown film (grocery bags)
Preform for other molding
processes
Blow molding (bottles),
Thermoforming (appliance
liners)
Compression molding
(seals)
5. Fibers
• A Fiber is a long, thin thing!
– Aspect ratio >100
– At diameters > 75 m, the fiber is a rod
• Long means:
– > 1 kilometer
• At a density of 1.4 and a denier of 5, 1 kilometer weighs less than 5 grams
– > 1 kilogram
• 1.5 kilograms at 5 dpf is 20,000 miles
• Few commercial fibers are produced at a scale of less than 500 tons
– The length at 5 dpf is ~ .01 lightyear
• Typical melt spinning speeds are in excess of 100 miles/hour
– To be viable, polymer to fiber conversions must be ~ 90%
• Minimum property CVs are < 10%
• Real fibers are hard to make!!
6. MACROSCALE vs MICROSCALE
Griffith’s experiments
with glass fibers (1921)
Strength of bulk
glass: 170 MPa
Extrapolates to
11 GPa
FIBER DIAMETER (micron)
3
2
1
TENSILE STRENGTH (GPa)
0
0 20 40 60 80 100 120
7. Griffith’s equation for the strength of materials
2
s g a = length of defect
1 2
E
p
ö çè
÷ø
= æ
a
g = surface energy
• Thus, going from the macroscale to the atomic scale (via the
nanoscale), defects progressively become smaller and/or are
eliminated, which is why the strength increases (see equation).
• Note that the Griffith model predicts that defects have no
effect on the modulus, only on strength
• But note: the model also predicts that defects of zero length
lead to infinitely strong materials, an obvious impossibility!
8. Fibers
1000 X longer than diameter
Often uniaxial strength
Kevlar-strongest organic fiber
• M elt spinning technology can be applied to polyamide (Nylon),
polyesters, polyurethanes and polyolefins such as PP and HDPE.
• The drawing and cooling processes determine the morphology and
mechanical properties of the final fiber. For example ultra high
molecular weight HDPE fibers with high degrees of orientation in the
axial direction have extremely high stiffness !!
• Of major concern during fiber spinning are the instabilities that arise
during drawing, such as brittle fracture and draw resonance. Draw
resonance manifests itself as periodic fluctuations that result in
diameter oscillation.
9. TABLE 4.2. Fiber Propertiesa
Fiber Type
Natural
Cotton
Wool
Synthetic
Polyester
Nylon
Aromatic polyamide
(aramid)c
Polybenzimidazole
Polypropylene
Polyethylene (high strength)
Inorganicc
Glass
Steel
Tenacityb
(N/tex)
0.26-0.44
0.09-0.15
0.35-0.53
0.40-0.71
1.80-2.0
0.27
0.44-0.79
2.65d
0.53-0.66
0.31
Specific
Gravity
1.50
1.30
1.38
1.14
1.44
1.43
0.90
0.95
2.56
7.7
aUnless otherwise noted, data taken form L. Rebenfeld, in Encyclopedia of Polymer Science and Engineering (H. f. Mark,
N. M. Bikales, C. G. Overberger, G. Menges, and J. I. Kroschwitz, Eds.), Vol. 6, Wiley-Interscience, New York, 1986,
pp. 647-733.
bTo convert newtons per tex to grams per denier, multiply by 11.3.
cKevlar (see Chap. 3, structure 58.)
dFrom Chem. Eng. New, 63(8), 7 (1985).
eFrom V. L. Erlich, in Encyclopedia of Polymer Science and Technology (H.F. Mark, N. G. Gaylord, and N. M. Bikales,
Eds.), Vol. 9, Wiley-Interscience, New Uork, 1968, p. 422.
10. Polymer fibers
Organic
polymers
Flexible
molecules
Stiff
molecules
Melt
spinning
Wet
spinning
Dy
spinning Cellulose
Melt
spinning
Wet
spinning
Normal
spinning
Super
stretching
Nylon
PP, PE
HMW
PE
UHMW
PE
Acetate
Aromatic
polyesters
Aramides
11. Fibers
Dry Spinning:
From solution
Melt Spinning:
From Melt
Cellulose Acetate Nylon 6,6 & PETE
Wet Spinning:
From solution into
solution
Kevlar, rayon, acrylics,
Aramids, spandex
12. Fiber Spinning: Melt
Fiber spinning is used to
manufacture synthetic fibers.
A filament is continuously
extruded through an orifice
and stretched to diameters
of 100 mm and smaller. The
molten polymer is first
extruded through a filter or
“screen pack”, to eliminate
small contaminants. It is
then extruded through a
“spinneret”, a die composed
of multiple orifices (it can
have 1-10,000 holes). The
fibers are then drawn to their
final diameter, solidified (in a
water bath or by forced
convection) and wound-up.
Heating Grid
Po
ol
Moisture
Conditioning
Steam
Chamber
Bobbin
Melting
Zone
Metered
Extrusio
n (controll
ed flow)
Extruded Fiber
Cools
and Solidifies Here
Polymer
Chips/Beads
Pump
Filter and
Spinneret
Air
Diffuser
Lubricati
on by oil
disk and
trough
Packagi
ng
Bobbin drive
Yarn
driver
Feed
rolls
Nylon 6,6 & PETE
13. Feed
Filtered
polymer
solution
Metered
extrusion Pump
Filter and
spinneret
Solidification
by solvent
evaporation
Heated
chamber
Lubrication
Air
inlet
Feed roll
and guide
Yarn driving
Balloon guide
Packaging
Ring and traveler
Bobbin transverse
Spindle
Dry Spinning
Dry Spinning of Fibers
from a Solution
Cellulose Acetate
17. Acrylic Fibers
• 85% acrylonitrile
• Wet spun
• Acrylic's benefits are:
– ･Superior moisture management or wickability ･
– Quick drying time (75% faster than cotton) ･
– Easy care, shape retention ･
– Excellent light fastness, sun light resistance ･
– Takes color easily, bright vibrant colors ･
– Odor and mildew resistant
18.
19. • Nanotube effecting crystallization of PP
• Sandler et al, J MacroMol Science B, B42(3&4), pp 479-
488,2003
20. Why are strong fibers strong?
The source of strength: van der Waals forces
Flexible molecules,
normally spun
Flexible molecules
ultra stretched
Rigid molecules
liquid crystallinity
21. N
N
O
O
H
H
N
N
O
O
H
H
N
N
O
O
H
H
Kevlar
Fiber orientation
•High Tensile Strength at Low Weight
•Low Elongation to Break High Modulus (Structural Rigidity)
•Low Electrical Conductivity
•High Chemical Resistance
•Low Thermal Shrinkage
•High Toughness (Work-To-Break)
•Excellent Dimensional Stability
•High Cut Resistance
•Flame Resistant, Self-Extinguishing
22. Kevlar or Twaron
•High Tensile Strength at Low Weight
•Low Elongation to Break High Modulus (Structural Rigidity)
•Low Electrical Conductivity
•High Chemical Resistance
•Low Thermal Shrinkage
•High Toughness (Work-To-Break)
•Excellent Dimensional Stability
•High Cut Resistance
•Flame Resistant, Self-Extinguishing
25. Aramide fibers
the complete spinning line H2SO4
80 wt%
PPD-T
20 wt%
H2O
ice
machine
H2SO4 ice
mixer
extruder
spinneret
Washing
csulf.ac. < 0.5 %
neutralising
drying
2000C
winding
H2SO4 + H2O
air gap
Long washing traject
(initially difficult to control)
Sometimes post-strech of 1%
to enhance orientation
26. Strong fibers from flexible chains
Super-stretched polyethylene:
Mw = 105 (just spinnable)
conventional melt spinning
additional stretching of 30 to 50 times
below the melting point
Wet (gel) spinning of polyethylene
Mw = 106 (to high elasticity for melt spinning)
decalin or parafin as solvent
formation of thick (weak) fibers without stretching
removal of the solvent
stretching of 50 to 100 times close to melting point
27. POLYETHYLENE (LDPE)
H2C CH2
R
H2C CH2
20-40,000 psi x
150-325°C
Molecular Weights: 20,000-100,000; MWD = 3-20
density = 0.91-0.93 g/cm3
Highly branched structure
—both long and short chain
branches
Tm ~ 105 C, X’linity ~ 40%
H3C
C
H2
15-30 Methyl groups/1000 C atoms
CH3
Applications: Packaging Film, wire and cable coating, toys,
flexible bottles, housewares, coatings
CH3
H3C
CH3
H3C
H3C
H3C
H3C
28. Polyethylene (HDPE)
CH3
Essentially linear
structure
Few long chain branches, 0.5-3
methyl groups/ 1000 C atoms
Molecular Weights: 50,000-250,000 for molding
compounds
250,000-1,500,000 for pipe compounds
>1,500,000 super abrasion resistance—medical implants
MWD = 3-20
dTemn s~it y1 3=3 -01.9348- C0.,9 X6 ’gli/ncmity3 ~ 80%
Generally opaque
Applications: Bottles, drums, pipe, conduit, sheet, film
29. UHMWPE fibers: Dyneema or
Spectra
Gel spinning process
Structure of UHMWPE,
with n = 100,000-250,000
http://www.dyneema.com
31. Aramide fibers
the spinning mechanism
polymer in
pure sulfuric acid
at 850C
platinum
capillary 65m
air gap 10 mm with
elongational stretch (6x)
coagulation
bath at 100C
removal of
sulfuric acid
Specific points:
solvent: pure H2SO4
polymer concentration 20%
general orientation
in the capillary
extra orientation in
the air gap
coagulation in cooled
diluted sulfuric acid
32. O
O
O
O
m
n
Vectran
Vectran fiber is thermotropic, it is melt-spun, and it flows at a high temperature under pressure
33.
34.
35. O
O
HN NH HN
n
Aramid
n
Ultra High Molecular Weight Polyethylene
O
O
O
O
m
n
Vectran
O
N
N
O
n
poly(p-phenylene benzobisoxazole)
Zylon
36.
37.
38.
39. Carbon Fibers: Pyrolyzing
Polyacrylonitrile Fibers
N N N N N N N N
Young’s Modulus 325 Gpa
Tensile Strength 3-6 GPa
N N N N N N N N
C C C C C C C
N N N N N N N
40.
41. Electrospinning of Fibers
5-30 kV
–Driving force is charge dissipation, opposed by surface tension
–Forces are low
–Level of charge density is limited by breakdown voltage – Taylor cone
formation
Fiber diameter a [Voltage]-1
–“Inexpensive” and easy to form nanofibers from a solution of practically any
polymer (Formhals 1934)
–Only small amount of material required
51. Fig. 4. Scanning electron micrograph of a dry ribbon deposited on a
glass substrate. The black arrow indicates the main axis of the
ribbons, which corresponds to the direction of the initial fluid velocity.
Despite the presence of a significant amount of carbon spherical
impurities, SWNTs bundles are preferentially oriented along the main
axis. Scale BAR=667 nm
54. Polymides (PI) - Vespel®, Aurum®, P84®, and more.
Polybenzimidazole (PBI) - Celazole®
Polyamide-imide (PAI) - Torlon®
Polyetheretherketone (PEEK) - Victrex®, Kadel®, and more.
Polytetrafluoroethylene (PTFE) - Teflon®, Hostaflon®
Polyphenylene Sulfide (PPS) - Ryton®, Fortron®, Thermocomp®, Supec®
and more.
Polyetherimide (PEI) - Ultem®
Polypthalamide (PPA) - Amodel®, BGU®, and more.
Aromatic Polyamides - Reny®, Zytel HTN®, Stanyl®
Liquid Crystal Polymer (LCP) - Xydar®, Vectra®, Zenite®, and more.
Other Polymers - Nylon, Polyacetal, Polycarbonate, Polypropylene, Ultra
High Molecular Weight Polyethylene, ABS, PBT, and mor
Editor's Notes
Dyneema(r), the worldﾕs strongest fiberDSM Dyneema is the inventor and manufacturer of Dyneemaｨ, the world&apos;s strongest fiber. Dyneemaｨ is a superstrong polyethylene fiber that offers maximum strength combined with minimum weight. It is up to 15 times stronger than quality steel and up to 40% stronger than aramid fibers, both on weight for weight basis. Dyneemaｨ floats on water and is extremely durable and resistant to moisture, UV light and chemicals. The applications are therefore more or less unlimited. Dyneemaｨ is an important component in ropes, cables and nets in the fishing, shipping and offshore industries. Dyneemaｨ is also used in safety gloves for the metalworking industry and in fine yarns for applications in sporting goods and the medical sector. In addition, Dyneemaｨ is also used in bullet resistant armor and clothing for police and military personnel.
