Polymer fibres

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<ul><li><p>Polymer Fibers</p></li><li><p>Polymer ProcessingShaping PolymersExtrusionMoldingFibersCoatings</p></li><li><p>Product Shaping / Secondary OperationsEXTRUSIONShaping through dieFinal Product (pipe, profile)Preform for other molding processesBlow molding (bottles),Thermoforming (appliance liners)Compression molding (seals)Secondary operation Fiber spinning (fibers) Cast film (overhead transparencies, Blown film (grocery bags)</p></li><li><p>FibersA Fiber is a long, thin thing!Aspect ratio &gt;100At diameters &gt; 75 , the fiber is a rodLong means:&gt; 1 kilometerAt a density of 1.4 and a denier of 5, 1 kilometer weighs less than 5 grams&gt; 1 kilogram1.5 kilograms at 5 dpf is 20,000 milesFew commercial fibers are produced at a scale of less than 500 tonsThe length at 5 dpf is ~ .01 lightyearTypical melt spinning speeds are in excess of 100 miles/hourTo be viable, polymer to fiber conversions must be ~ 90%Minimum property CVs are &lt; 10%Real fibers are hard to make!!</p></li><li><p>Griffiths equation for the strength of materialsa = length of defectg = surface energy</p><p>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 strengthBut note: the model also predicts that defects of zero length lead to infinitely strong materials, an obvious impossibility!</p></li><li><p>Fibers1000 X longer than diameterOften uniaxial strengthKevlar-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.</p></li><li><p>Polymer fibers OrganicpolymersFlexiblemoleculesStiffmoleculesMeltspinningWetspinningMeltspinningWetspinningNormalspinningSuperstretchingNylonPP, PEUHMWPEHMWPEAromaticpolyestersAramidesDyspinningCelluloseAcetate</p></li><li><p>FibersDry Spinning: From solutionMelt Spinning: From MeltNylon 6,6 &amp; PETECellulose AcetateWet Spinning: From solution into solutionKevlar, rayon, acrylics, Aramids, spandex</p></li><li><p>Fiber Spinning: MeltFiber 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 &amp; PETE</p></li><li><p>Dry Spinning of Fibersfrom a SolutionCellulose Acetate</p></li><li><p>Wet Spinning (e.g. Kevlar)Kevlar, rayon, acrylicsAramids, spandexfeedlinetake-upgodetfilamentsspinneretdrawingelementscoagulation bathplastisizing bath</p></li><li><p>Melt spinning</p></li><li><p>Acrylic Fibers85% acrylonitrileWet spunAcrylic's benefits are:Superior moisture management or wickabilityQuick drying time (75% faster than cotton)Easy care, shape retentionExcellent light fastness, sun light resistanceTakes color easily, bright vibrant colorsOdor and mildew resistant</p></li><li><p>Nanotube effecting crystallization of PPSandler et al, J MacroMol Science B, B42(3&amp;4), pp 479-488,2003</p></li><li><p>Why are strong fibers strong?The source of strength: van der Waals forcesFlexible molecules,normally spunFlexible moleculesultra stretchedRigid moleculesliquid crystallinity</p></li><li><p>Fiber orientationHigh 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-ExtinguishingKevlar</p></li><li><p>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-ExtinguishingKevlar or Twaron </p></li><li><p>Polypropylene elastomers</p></li><li><p>Aramide fibersthe complete spinning lineH2SO480 wt%H2OPPD-T20 wt%icemachineH2SO4 icemixerextruderspinneretWashingcsulf.ac. &lt; 0.5 %neutralisingdrying2000CwindingH2SO4 + H2Oair gapLong washing traject(initially difficult to control)Sometimes post-strech of 1%to enhance orientation</p></li><li><p>Strong fibers from flexible chainsSuper-stretched polyethylene:Mw = 105 (just spinnable)conventional melt spinningadditional stretching of 30 to 50 timesbelow the melting point Wet (gel) spinning of polyethyleneMw = 106 (to high elasticity for melt spinning)decalin or parafin as solventformation of thick (weak) fibers without stretchingremoval of the solventstretching of 50 to 100 times close to melting point </p></li><li><p>POLYETHYLENE (LDPE)Molecular Weights: 20,000-100,000; MWD = 3-20 density = 0.91-0.93 g/cm3Highly branched structureboth long and short chain branches15-30 Methyl groups/1000 C atomsTm ~ 105 C, Xlinity ~ 40%Applications: Packaging Film, wire and cable coating, toys, flexible bottles, housewares, coatings</p></li><li><p>Polyethylene (HDPE)Essentially linear structureFew long chain branches, 0.5-3 methyl groups/ 1000 C atomsMolecular Weights: 50,000-250,000 for molding compounds250,000-1,500,000 for pipe compounds &gt;1,500,000 super abrasion resistancemedical implants MWD = 3-20 density = 0.94-0.96 g/cm3Tm ~ 133-138 C, Xlinity ~ 80%Applications: Bottles, drums, pipe, conduit, sheet, film Generally opaque</p></li><li><p>UHMWPE fibers: Dyneema or Spectra</p><p>http://www.dyneema.comGel spinning processStructure of UHMWPE, with n = 100,000-250,000</p></li><li><p>Comparison of mechanical propertiesStrength Modulus stretch (Gpa) (Gpa) (%)Classical fibres nylon 1.0 5.6 18 glass 2.7 69 2.5 steel 2.8200 2Strong 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 3.6130 2.3</p></li><li><p>Aramide fibersthe spinning mechanismremoval ofsulfuric acidplatinumcapillary 65polymer inpure sulfuric acidat 850Cair gap 10 mm withelongational stretch (6x)coagulationbath at 100CSpecific points:</p><p>solvent: pure H2SO4</p><p>polymer concentration 20%</p><p>general orientation in the capillary</p><p>extra orientation inthe air gap</p><p>coagulation in cooled diluted sulfuric acid </p></li><li><p>VectranVectran fiber is thermotropic, it is melt-spun, and it flows at a high temperature under pressure</p></li><li><p>Carbon Fibers: Pyrolyzing Polyacrylonitrile Fibers Youngs Modulus 325 GpaTensile Strength 3-6 GPa</p></li><li><p>Electrospinning of FibersDriving force is charge dissipation, opposed by surface tensionForces are lowLevel of charge density is limited by breakdown voltage Taylor cone formationFiber diameter [Voltage]-1Inexpensive and easy to form nanofibers from a solution of practically any polymer (Formhals 1934)Only small amount of material required</p><p>5-30 kV</p></li><li><p>Human hair (.06mm)Electrospun polymers</p></li><li><p>Fibers1000 X longer than diameterOften uniaxial strengthKevlar-strongest organic fiber tensile strength 60GPaYoungs modulus 1TPa)</p></li><li><p>Making Carbon Nanotubes</p></li><li><p>Carbon Nanotube FibersNature 423, 703 (12 June 2003); doi:10.1038/423703a 1cm</p></li><li><p>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</p></li><li><p>SWNT Fiber after drawing25 mm</p></li><li><p>Fibers Large aspect ratio (length/diameter) &amp; strong (fewer defects) Common fibers: cellulose acetate, viscous cellulose, polyethylene, polypropylene, acrylics (acrylonitrile copolymers), nylons, 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)</p></li><li><p>Polymides (PI) - Vespel, Aurum, P84, and more. Polybenzimidazole (PBI) - CelazolePolyamide-imide (PAI) - Torlon Polyetheretherketone (PEEK) - Victrex, Kadel, and more. Polytetrafluoroethylene (PTFE) - Teflon, HostaflonPolyphenylene Sulfide (PPS) - Ryton, Fortron, Thermocomp, Supec and more. Polyetherimide (PEI) - UltemPolypthalamide (PPA) - Amodel, BGU, and more. Aromatic Polyamides - Reny, Zytel HTN, StanylLiquid Crystal Polymer (LCP) - Xydar, Vectra, Zenite, and more. Other Polymers - Nylon, Polyacetal, Polycarbonate, Polypropylene, Ultra High Molecular Weight Polyethylene, ABS, PBT, and mor</p><p>*Dyneema(r), the worlds strongest fiberDSM Dyneema is the inventor and manufacturer of Dyneema, the world's strongest fiber. Dyneema is a superstrong polyethylene fiber that offers maximum strength combined with minimum weight. It is up to 15 times stronger than quality steel and up to 40% stronger than aramid fibers, both on weight for weight basis. Dyneema floats on water and is extremely durable and resistant to moisture, UV light and chemicals. The applications are therefore more or less unlimited. Dyneema is an important component in ropes, cables and nets in the fishing, shipping and offshore industries. Dyneema is also used in safety gloves for the metalworking industry and in fine yarns for applications in sporting goods and the medical sector. In addition, Dyneema is also used in bullet resistant armor and clothing for police and military personnel.*Relative Flexlife: Dyneema 100, Vectran 55, Aramid 8.</p></li></ul>