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# Polymer fibres

Published on: Mar 4, 2016
Published in: Engineering

#### Transcripts - Polymer fibres

• 1. Polymer Fibers
• 2. Polymer Processing Shaping Polymers Extrusion Molding Fibers Coatings
• 3. 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)
• 4. 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!!
• 5. 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
• 6. 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!
• 7. 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.
• 8. 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.
• 9. 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
• 10. 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
• 11. 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
• 12. 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
• 13. Wet Spinning (e.g. Kevlar) Kevlar, rayon, acrylics Aramids, spandex feed line take-up godet spinneret filaments drawing elements coagulation bath plastisizing bath
• 14. Melt spinning
• 15. 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
• 16. • Nanotube effecting crystallization of PP • Sandler et al, J MacroMol Science B, B42(3&4), pp 479- 488,2003
• 17. 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
• 18. 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
• 19. 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
• 20. Polypropylene elastomers H e-beam 99n R n 99n R n 99n R n R
• 21. 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
• 22. 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
• 23. 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
• 24. 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
• 25. UHMWPE fibers: Dyneema or Spectra Gel spinning process Structure of UHMWPE, with n = 100,000-250,000 http://www.dyneema.com
• 26. 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
• 27. 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
• 28. O O O O m n Vectran Vectran fiber is thermotropic, it is melt-spun, and it flows at a high temperature under pressure
• 29. 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
• 30. 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
• 31. 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
• 32. Electrospun polymers Human hair (.06mm)
• 33. Fibers 1000 X longer than diameter Often uniaxial strength Kevlar-strongest organic fiber tensile strength 60GPa Young’s modulus 1TPa)
• 34. Making Carbon Nanotubes
• 35. Carbon Nanotube Fibers 1cm Nature 423, 703 (12 June 2003); doi:10.1038/423703a
• 36. 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
• 37. SWNT Fiber after drawing 25 mm
• 38. 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)
• 39. 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