Polymer Fibers

1. Polymer Fibers

2. Polymer Processing Shaping Polymers Extrusion Molding Fibers Coatings

4. Product Shaping / Secondary Operations EXTRUSION Final Product (pipe, profile) • Secondary operation • Fiber spinning (fibers) • Cast film (overhead transparencies, • Blown film (grocery bags) Shaping through die • 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 , 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 Extrapolates to 11 GPa 3 Griffith’s experiments with glass fibers (1921) TENSILE STRENGTH (GPa) 2 Strength of bulk glass: 170 MPa 1 0 20 40 60 80 0 100 120 FIBER DIAMETER (micron)

7. 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! Griffith’s equation for the strength of materials • a = length of defect • g = surface energy

8. 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.

9. TABLE 4.2. Fiber Propertiesa Specific Gravity 1.50 1.30 1.38 1.14 1.44 1.43 0.90 0.95 2.56 7.7 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 Fiber Type Natural Cotton Wool Synthetic Polyester Nylon Aromatic polyamide (aramid)c Polybenzimidazole Polypropylene Polyethylene (high strength) Inorganicc Glass Steel 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 Nylon PP, PE Normal spinning Melt spinning Super stretching HMW PE Wet spinning UHMW PE Flexible molecules Dy spinning Cellulose Acetate Organic polymers Melt spinning Aromatic polyesters Stiff molecules Wet spinning Aramides

11. 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

12. Polymer Chips/Beads Melting Zone Heating Grid Pool Metered Extrusion (controlled flow) Pump Filter and Spinneret Air Diffuser Extruded Fiber Cools and Solidifies Here Moisture Conditioning Steam Chamber Lubrication by oil disk and trough Feed rolls Packaging Bobbin Yarn driver Bobbin drive 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. Nylon 6,6 & PETE

13. Cellulose Acetate Dry Spinning of Fibers from a Solution

14. Wet Spinning (e.g. Kevlar) take-up godet drawing elements feed line spinneret filaments Kevlar, rayon, acrylics Aramids, spandex plastisizing bath coagulation bath

16. Melt spinning

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

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. 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

23. Polypropylene elastomers

25. Aramide fibersthe complete spinning line H2SO4 80 wt% ice machine Long washing traject (initially difficult to control) Sometimes post-strech of 1% to enhance orientation H2SO4 ice PPD-T 20 wt% mixer extruder air gap H2O spinneret Washing csulf.ac. < 0.5 % neutralising winding drying 2000C H2SO4 + H2O

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) 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% 15-30 Methyl groups/1000 C atoms Applications: Packaging Film, wire and cable coating, toys, flexible bottles, housewares, coatings

28. Polyethylene (HDPE) 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

29. UHMWPE fibers: Dyneema or Spectra Gel spinning process Structure of UHMWPE, with n = 100,000-250,000 http://www.dyneema.com

30. Comparison of mechanical properties • Strength Modulus stretch • (Gpa) (Gpa) (%) • Classical fibres • nylon 1.0 5.6 18 • glass 2.7 69 2.5 • steel 2.8 200 2 • Strong fibres • superstretched PE 0.7 4.7 • wet spun PE (Dyneema) 2.2 80 3.4 • melt spun PE (Vectran) 3.2 90 3.5 • wet spun aramide 2.7 72 3.3 • idem with post-stretch 3.6 130 2.3

31. Aramide fibersthe spinning mechanism polymer in pure sulfuric acid at 850C Specific points: solvent: pure H2SO4 polymer concentration 20% generalorientation in the capillary extra orientation in the air gap coagulation in cooled diluted sulfuric acid platinum capillary 65 air gap 10 mm with elongational stretch (6x) coagulation bath at 100C removal of sulfuric acid

32. Vectran Vectran fiber is thermotropic, it is melt-spun, and it flows at a high temperature under pressure

39. Carbon Fibers: Pyrolyzing Polyacrylonitrile Fibers Young’s Modulus 325 Gpa Tensile Strength 3-6 GPa

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  [Voltage]-1 • “Inexpensive” and easy to form nanofibers from a solution of practically any polymer (Formhals 1934) • Only small amount of material required

44. Electrospun polymers Human hair (.06mm)

46. Fibers 1000 X longer than diameter Often uniaxial strength Kevlar-strongest organic fiber tensile strength 60GPa Young’s modulus 1TPa)

47. Making Carbon Nanotubes

49. Carbon Nanotube Fibers 1cm Nature 423, 703 (12 June 2003); doi:10.1038/423703a