Synthetic Fiber Creation “Spinning”

Fiber overview Spring 2001 ISAT 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

Spinnability Hydrodynamic instability Jet distortion & growth Cohesive fracture Spinnable Spring 2001 ISAT 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

Spinning2 Piece of cake! Except…. The solvent may be toxic, corrosive, or explosive The temperatures may be in the 300 - 400 ºC range The fiber residence time from extrusion to cell exit may range from seconds to milliseconds. Spring 2001 ISAT 430 Dr. Ken Lewis

Things Common to all Spinning Even Crylex® has these!! Spinnerets Spin Cells Metering Pumps Spring 2001 ISAT 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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)

Spinneret Like a shower head Holes are called capillaries. Depending on the process 8 capillaries up to 1000 capillaries Spring 2001 ISAT 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

Spin Cell Assembly Metering pump & polymer supply Spinneret Spin Cell filaments Spring 2001 ISAT 430 Dr. Ken Lewis

Examples Later we will examine a few in some detail Spring 2001 ISAT 430 Dr. Ken Lewis

Melt Spinning

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 430 Dr. Ken Lewis

+ Nylon Nylon 6, 6 Hexamethylamine Adipic acid Spring 2001 ISAT 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

Wet Spinning

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

Kevlar® Viscosity Wet Spinning Isotropic solution produces amorphous low strength filaments anisotropic solution produces Kevlar® The concrete wall Spring 2001 ISAT 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

Dry Spinning

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

Lycra Polymer + Lycra® spandex Poly tetramethylene ether glycol 4,4’-methylenebis(4-phenylisocyanate) Lycra® spandex Spring 2001 ISAT 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

Dry Spinning Gas is made uniform The gas heats the solvent, and Hot Nitrogen (300 - 450 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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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

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

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 430 Dr. Ken Lewis

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

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis

Fiber Tenacities Spring 2001 ISAT 430 Dr. Ken Lewis

Fiber Elongation Spring 2001 ISAT 430 Dr. Ken Lewis

Fiber overview Spring 2001 ISAT 430 Dr. Ken Lewis

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 430 Dr. Ken Lewis