Transcript Polymer Processing - Loy Research Group

Polymer Fibers
Polymer Processing
Shaping Polymers
Extrusion
Molding
Fibers
Coatings
Product Shaping / Secondary
Operations
EXTRUSION
Final Product (pipe, profile)
Shaping
through die
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)
Fibers
•
A Fiber is a long, thin thing!
– Aspect ratio >100
– At diameters > 75 , 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!!
TENSILE STRENGTH (GPa)
MACROSCALE vs MICROSCALE
Extrapolates to
11 GPa
3
Griffith’s experiments
with glass fibers (1921)
2
1
0
0
Strength of bulk
glass: 170 MPa
20
40
60
80 100 120
FIBER DIAMETER (micron)
Griffith’s equation for the strength of materials
 2 E 
 

 a 
1
2
a = length of defect
 = 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!
Fibers
1000 X longer than diameter
Often uniaxial strength
Kevlar-strongest organic fiber
• Melt 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.
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
aUnless
Tenacityb
(N/tex)
Specific
Gravity
0.26-0.44
0.09-0.15
1.50
1.30
0.35-0.53
0.40-0.71
1.80-2.0
1.38
1.14
1.44
0.27
0.44-0.79
2.65d
1.43
0.90
0.95
0.53-0.66
0.31
2.56
7.7
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.
Polymer fibers
Melt
spinning
Wet
spinning
Flexible
molecules
Organic
polymers
Stiff
molecules
Dy
spinning
Normal
spinning
Nylon
PP, PE
Super
stretching
HMW
PE
UHMW
PE
Cellulose
Acetate
Melt
spinning
Aromatic
polyesters
Wet
spinning
Aramides
Fibers
Dry Spinning:
From solution
Melt Spinning:
From Melt
Wet Spinning:
From solution into
solution
Kevlar, rayon, acrylics,
Aramids, spandex
Cellulose Acetate
Nylon 6,6 & PETE
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 m 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.
Polymer
Chips/Beads
Melting
Zone
Metered
Extrusio
n
(controll
ed flow)
Extruded Fiber
Cools
and Solidifies Here
Heating Grid
Po
ol
Pump
Filter and
Spinneret
Air
Diffuser
Moisture
Conditioning
Steam
Chamber
Lubricati
on by oil
disk and
trough
Packagi
ng
Feed
rolls
Yarn
driver
Bobbin
Bobbin drive
Nylon 6,6 & PETE
Dry Spinning of Fibers
from a Solution
Dry Spinning
Filtered
polymer
solution
Feed
Metered
extrusion
Pump
Cellulose Acetate
Filter and
spinneret
Solidification
by solv ent
evaporation
Heated
chamber
Feed roll
and guide
Lubric ation
Air
inlet
Yarn driv ing
Balloon guide
Packaging
Ring and traveler
Bobbin transverse
Spindle
Wet Spinning (e.g. Kevlar)
feed
line
take-up
godet
spinneret
drawing
elements
filaments
Kevlar, rayon, acrylics
Aramids, spandex
coagulation bath
plastisizing bath
Melt spinning
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
• Nanotube effecting crystallization of PP
• Sandler et al, J MacroMol Science B, B42(3&4), pp 479488,2003
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
Kevlar
O
N
H
N
O
H
O
N
H
N
O
H
O
N
H
N
H
O
•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
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
Polypropylene
elastomers
R
H
e-beam
n
99n R
n
99n R
n
99n R
H2SO4
80 wt%
PPD-T
20 wt%
Aramide fibers
the complete spinning line
ice
machine
H2SO4 ice
mixer
extruder
H2O
Long washing traject
(initially difficult to control)
Sometimes post-strech of 1%
to enhance orientation
air gap
spinneret
Washing
neutralising
csulf.ac. < 0.5 %
H2SO4 + H2O
drying
2000C
winding
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
POLYETHYLENE (LDPE)
R
H2C
CH2
20-40,000 psi
150-325° C
H2C CH2
x
Molecular Weights: 20,000-100,000; MWD = 3-20
density = 0.91-0.93 g/cm3
H3C
Highly branched
structure—both long and
short chain branches
Tm ~ 105 C, X’linity ~ 40%
H3C
CH3
H3C
H3C
C
H2
H3C
H3C
15-30 Methyl groups/1000 C atoms
Applications: Packaging Film, wire and cable coating, toys,
flexible bottles, housewares, coatings
CH3
CH3
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
density = 0.94-0.96 g/cm3
Tm ~ 133-138 C, X’linity ~ 80%
Generally opaque
Applications: Bottles, drums, pipe, conduit, sheet, film
UHMWPE fibers: Dyneema or
Spectra
Gel spinning process
Structure of UHMWPE,
with n = 100,000-250,000
http://www.dyneema.com
Comparison of mechanical properties
Strength
(Gpa)
Classical fibres
• nylon
• glass
• steel
Strong fibres
• superstretched PE
• wet spun PE (Dyneema)
• melt spun PE (Vectran)
• wet spun aramide
• idem with post-stretch
Modulus
(Gpa)
stretch
(%)
1.0
2.7
2.8
5.6
69
200
18
2.5
2
0.7
2.2
3.2
2.7
3.6
4.7
80
90
72
130
3.4
3.5
3.3
2.3
Aramide fibers
the spinning mechanism
polymer in
pure sulfuric acid
at 850C
platinum
capillary 65
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
Vectran
O
O
O m
O n
Vectran fiber is thermotropic, it is melt-spun, and it flows at a high temperature under pressure
O
O
O
O
O m
n
HN
NH
HN
n
O n
Ultra High Molecular Weight Polyethylene
Vectran
Aramid
O
N
N
O
n
poly(p-phenylene benzobisoxazole)
Zylon
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
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  [Voltage]-1
–“Inexpensive” and easy to form nanofibers from a solution of practically any
polymer (Formhals 1934)
–Only small amount of material required
Electrospun
polymers
Human hair (.06mm)
Fibers
1000 X longer than diameter
Often uniaxial strength
Kevlar-strongest organic fiber
tensile strength 60GPa
Young’s modulus 1TPa)
Making Carbon Nanotubes
Carbon Nanotube Fibers
1cm
Nature 423, 703 (12 June 2003); doi:10.1038/423703a
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
SWNT Fiber after drawing
25m
Fibers
• Large aspect ratio (length/diameter) & strong (fewer defects)
• Common fibers: cellulose acetate, viscous cellulose,
polyethylene, polypropylene, acrylics (acrylonitrile
copolymers), nylon’s, polyester (PETE), PMMA (optics),
urethane (Spandex).
• High performance fibers: polyaramides (Kevlar), Uniaxially
oriented gels (UHMWPE), Liquid crystals (Vectran)
• Carbon fibers (Black Orlon or pitch based), carbon nanotubes
• Methods for preparing:
-Dry spinning
-Wet spinning
-Melt spinning
-Gel spinning
-electrospinning
-growing (self-assembly)
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