1. Synthetic Fiber Creation
“Spinning”

2. Fiber overview
Spring 2001
ISAT Dr. Ken Lewis

3. Plan of attack Synthetic Fiber History Spinning Fundamentals
Nomenclature
Things Common To All
Basic methods of spinning a fiber
Melt spinning
Wet spinning
Dry spinning
Some details of Lycra® spandex formation
Spring 2001
ISAT Dr. Ken Lewis

4. Fibers -- History Textiles predate recorded history
fabrics were made thousand of years before written records
All early fibers were from animals or plants
wool -- sheep
silk -- silk worms
cotton -- cotton plant
linen -- flax plant
All had problems...
shrinks
delicate
wrinkles
wrinkles
Spring 2001
ISAT Dr. Ken Lewis

5. Fibers -- History2 1664 1855 Robert Hooke predicted artificial silk
Nothing happened.
1855
Swiss chemist Audemars received first patent for artificial silk
dissolved the inner bark of a mulberry tree and made cellulose
Audemars never thought of emulating the silkworm and pushing the solution out through a small hole
Spring 2001
ISAT Dr. Ken Lewis

6. Fibers -- History3 1910 1938 1959 1974 First commercial rayon Nylon
Lycra® spandex
1974
Kevlar® aramid
Audemars never thought of emulating the silkworm and pushing the solution out through a small hole
Spring 2001
ISAT Dr. Ken Lewis

7. Nomenclature Spinning Today --- we are spiders. Fiber users
To mingle and make a continuous yarn from staple fibers (like spinning wool into yarn)
Fiber makers
To extrude and make a fiber in continuous form (much like a spider spins her silk)
Today --- we are spiders.
Spring 2001
ISAT Dr. Ken Lewis

8. Nomenclature Staple Filament Wool up to 20 inches long Staple
short fibers
Filament
long fibers
Silk
up to 450 yards long
Filament
Cotton
1 - 2 inches long
Staple
All synthetic Fibers
Filament
Spring 2001
ISAT Dr. Ken Lewis

9. Nomenclature2 Denier A measure of the fineness of a yarn
Denier = grams / 9000 meters
Linear density
Allows comparison of yarns of different densities
wool
cotton
nylon
etc.
Spring 2001
ISAT Dr. Ken Lewis

10. Nomenclature3 Tenacity Elongation
A measure of the strength of a fiber.
Measured as: Grams force / denier
Elongation
How much a fiber can be stretched before it breaks.
Measured as percent.
Spring 2001
ISAT Dr. Ken Lewis

11. Spinnability Hydrodynamic instability Jet distortion & growth
Cohesive fracture
Spinnable
Spring 2001
ISAT Dr. Ken Lewis

12. Spinnability continued
Let  be any scalar variable of interest
(denier, yarn temperature, solvent concentration…)
Essentially, the variable is independent of time for steady spinning.
The fiber is evolving but at any particular point in space it does not change with time.
Spinning implies steady state
Spring 2001
ISAT Dr. Ken Lewis

13. That is, the fiber is changing as it moves down the cell.
However:
That is, the fiber is changing as it moves down the cell.
Spring 2001
ISAT Dr. Ken Lewis

14. Spinning Fiber formation conditions are carefully controlled
Essentials
Start with a melted polymer or polymer/solvent solution
Extrude this liquid through one or more small orifices called spinneret capillaries
Perform the necessary transport processes
May be heat transfer, mass transfer, chemical reactions or a combination of all.
The more precise control of these variables the more uniform the fiber
Wind up the finished fiber
Spring 2001
ISAT Dr. Ken Lewis

15. Spinning2 Piece of cake! Except….
The solvent may be toxic, corrosive, or explosive
The temperatures may be in the ºC range
The fiber residence time from extrusion to cell exit may range from seconds to milliseconds.
Spring 2001
ISAT Dr. Ken Lewis

16. Things Common to all Spinning
Even
Crylex®
has these!!
Spinnerets
Spin Cells
Metering Pumps
Spring 2001
ISAT Dr. Ken Lewis

17. Spin Cell Essentially the cell provides control and containment.
Polymer solution
or melt in
Essentially the cell provides control and containment.
Control
temperature
fiber components
Contain
Fluids
Solvents
Gases
Toxins
The Cell
Filaments out
Spring 2001
ISAT Dr. Ken Lewis

18. Metering Pumps Sit at the top of the cell
Deliver precisely the correct amount of polymer to the spinneret.
Positive Displacement pumps
Can be single stream or many streams
Allow precise control of the filament size (denier)

19. Spinneret Like a shower head Holes are called capillaries.
Depending on the process
8 capillaries up to 1000 capillaries
Spring 2001
ISAT Dr. Ken Lewis

20. The Spinneret Function
Converts the polymeric liquid from a homogeneous mass into discrete filaments
Controls the molecular alignment of the polymer molecules
Imparts shear energy into the system from the shear stresses in the capillaries.
These are critical
Spring 2001
ISAT Dr. Ken Lewis

21. Capillaries The actual capillary diameter may be a small as 0.05 mm.
Shear rates may be as high as 100,000 sec-1
Can cause
shear fracture
loss of continuity
disruption of properties.
Spring 2001
ISAT Dr. Ken Lewis

22. Spin Cell Assembly Metering pump & polymer supply Spinneret Spin Cell
filaments
Spring 2001
ISAT Dr. Ken Lewis

23. Examples Later we will examine a few in some detail Spring 2001
ISAT Dr. Ken Lewis

24. Melt Spinning

25. Melt Spinning Melt spinning Not the oldest spinning method
More straight forward
removal of heat
no solvents to worry about.
Example -- nylon
Spring 2001
ISAT Dr. Ken Lewis

26. + Nylon Nylon 6, 6 Hexamethylamine Adipic acid Spring 2001
ISAT Dr. Ken Lewis

27. Nylon Melt spinning Either cross flow or radial gas flow.
staple yarn uses radial
filament yarn uses crossflow
Uniformity of the air flow is critical
Minimum air necessary is used to reduce turbulence.
Three forces resist the feed roll
Resistive inertial
Rheological stresses
Aerodynamic or drag forces (important for spinning speeds > 5000 m/min
Spring 2001
ISAT Dr. Ken Lewis

28. Wet Spinning

29. Wet Spinning Wet Spinning If a polymer We wet spin
does not melt
dissolves only in non-volatile or thermally unstable solvents
We wet spin
Polymer solution is extruded into a liquid bath
miscible with the solvent
does not solvate the polymer.
Example: Kevlar®
Spring 2001
ISAT Dr. Ken Lewis

30. Kevlar® Wet Spinning Kevlar® is intractable and insoluble
except in 100+ wt % H2SO4
which is miscible in H2O.
PPD-T / H2SO4 becomes liquid crystalline in concentrations above 12%
Shear stress then aligns the molecules.
Spring 2001
ISAT Dr. Ken Lewis

31. Kevlar® Viscosity Wet Spinning
Isotropic solution produces amorphous low strength filaments
anisotropic solution produces Kevlar®
The concrete wall
Spring 2001
ISAT Dr. Ken Lewis

32. Kevlar® Spinning Wet Spinning Traditional wet spinning did not work
As soon as the solution exited the spinneret, it coagulated.
It would not draw
Remained low strength, and friable
Then in 1970 Herb Blades made a mistake
He left the spinneret in air!
Spring 2001
ISAT Dr. Ken Lewis

33. Kevlar® Air Gap Spinning
Wet Spinning
Kevlar® Air Gap Spinning
Metering pump
Spinneret
To drying and constant tension winder
4 ºC water
Neutralization & Washing bath
Spring 2001
ISAT Dr. Ken Lewis

34. The Air Gap Difference between success and failure.
Allows the molecules to align
almost no further draw once the filament hit the water.
A 2” diameter spinneret may extrude 1000 filaments at once.
Constant tension winders used
strength to 30 g/denier
Spring 2001
ISAT Dr. Ken Lewis

35. Dry Spinning

36. Dry Spinning Dry Spinning Some polymers do not melt efficiently
They may decompose
The melt viscosity may be too high to process
May be able to find a low molecular weight solvent
Which allows a reasonable concentration of polymer
Which has a reasonable volatility
Spring 2001
ISAT Dr. Ken Lewis

37. Dry Spinning Solution is extruded into a hot gas
As the filaments pass down the cell, the hot gas causes the solvent to vaporize
This process is complex
Heat transfer
Mass transfer
through the filament
into the gas
Gas - solvent management
Example: Lycra®
Spring 2001
ISAT Dr. Ken Lewis

38. Lycra Polymer + Lycra® spandex Poly tetramethylene ether glycol
4,4’-methylenebis(4-phenylisocyanate)
Lycra® spandex
Spring 2001
ISAT Dr. Ken Lewis

39. A word on the gas management
Dry Spinning
A word on the gas management
Note what happens when the volume percent oxygen > 10%
Kablooie!!!
So careful isolation is essential
safety
environment
Spring 2001
ISAT Dr. Ken Lewis

40. Dry Spinning Gas is made uniform The gas heats the solvent, and
Hot Nitrogen ( ºC)
inserted
The gas heats the solvent,
driving it from the
filaments.
Gas is made uniform
and
passes
into the filaments
down
the
cell
Polymer is dissolved in dimethylacetamide (DMAc) and then pumped to the top of the cell
Solution passed into the
spinneret assembly
extruded into the
spin cell
Spring 2001
ISAT Dr. Ken Lewis

41. Dry Spinning Near the bottom of the cell there is a vacuum box.
The solvent rich gas is extracted.
The solvent is recovered.
Just at the cell exit
Recycle gas is inserted into the cell
DMAc >15% flammable
Keeps solvent/gas from the room
Acts as a curtain
The fibers exit the cell and pass to the winders.
Long cell
Vacuum Box
Recycle
Spring 2001
ISAT Dr. Ken Lewis

42. Dry Spinning The fibers fully formed exit the cell.
Pass to the feed rolls
actually pull the yarn from the cell
two are used for tension control
Finish is applied
Passes to the winders
Feed
rolls
The
winders

43. (diisocyanate and ureas) (tetramethylene glycol)
Lycra® Polymer
Hard segment
(diisocyanate and ureas)
Soft segment
(tetramethylene glycol)

44. Lycra® Polymer
During polymerization and polymer solution transport, the hard segments begin to associate
in Kevlar ® the liquid crystalline molecules are held together with Van der Waal forces
in Lycra ® hydrogen bonding holds the hard segments together
Spring 2001
ISAT Dr. Ken Lewis

45. Molecular Orientation
Spinneret
Capillary
Lead in
Shear rate increasing
Capillary
High Shear rate
High Orientation
Barus Bulge
Zero Shear rate
Partial deorientation
Neck down
Elongational Flow
High Orientation
To winders

46. Drying the filaments Drying rate limitations
how fast we can transfer heat into the filaments
Is the limitation
how fast solvent can diffuse through the filament and across the surface
the persistence of the solvent / gas boundary layer.
Spring 2001
ISAT Dr. Ken Lewis

47. Yarn Temperature DMAc begins to leave the filament
temperature of the filament is restrained by the boiling point of the DMAc.
At cell exit, the threadline temperature is ~200 C
Spring 2001
ISAT Dr. Ken Lewis

48. Yarn Velocity Initially threadline is in freefall
During this time of solvent removal tensile force from the feed roll are not transmitted.
At solvent levels ~10% the threadline can transmit information and it accelerates up to feed roll speed.
Spring 2001
ISAT Dr. Ken Lewis

49. Cell limits Drying rate limitations
How fast we can transfer heat into the filaments and mass out of the filaments.
Is the limitation
How fast solvent can diffuse through the filament and across the surface
The persistence of the solvent / gas boundary layer.
Spring 2001
ISAT Dr. Ken Lewis

50. Fiber Tenacities
Spring 2001
ISAT Dr. Ken Lewis

51. Fiber Elongation
Spring 2001
ISAT Dr. Ken Lewis

52. Fiber overview
Spring 2001
ISAT Dr. Ken Lewis

53. At long last...
We have seen the similarities in the different ways of manufacturing synthetic fibers
We have seen some of the difficulties
And we have seen a little of the beauty of science.
Spring 2001
ISAT Dr. Ken Lewis