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chemical spinning
Chemical spinning is the process of converting a fiber-forming substance into a viscous fluid that is extruded through spinneret holes and then solidified. The most widely used chemical spinning method is melt spinning, which is used for polymers that can be melted safely. A spinneret must have corrosion-resistant holes of controlled dimensions to produce uniform fibers and withstand high pressures. Melt spinning is the fastest chemical spinning method. Dry spinning fibers often have deformed cross-sectional shapes due to uneven solidification from the exterior to interior layers. Solvent recovery is essential for dry spinning to minimize environmental and economic costs. Wet spinning poses the highest pollution risks of the three methods discussed.
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chemical spinning
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- 2. Content Chemical Spinning Melt Spinning DrySpinning Wet Spinning Fiber Forms
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- 4. ReviewQuestions • Define chemicalspinning. •What is the most widely used method for manmade fiber spinning? • Mention three important features of aspinneret. • What is the requirement of apolymer for melt spinning? • Why dry-spun fibers have deformed cross-sectional shape? • Why is solvent recovery installation essential in dry spinning? • Which spinning method may causeserious environmental pollution? • Compare speeds of different chemical spinning methods? • Which form of manmade fiber is frequently used during blending with other fibers?
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- 6. ChemicalSpinning Man-made fibers are producedby convertingthe fiber forming substanceto a viscous fluid that is extruded through theholes of aspinneret and then solidified by coagulation or evaporation or cooling.
- 7. ChemicalSpinning This process is knownaschemical spinning to distinguish it from mechanical spinning.
- 8. Methods of Production Extrusionthrough spinneret to get solid fiber Conversion to viscous fluid state Solid polymer Fiber forming substance Dissolving ≈30% Dry Spinning Wet Spinning Gel Spinning Melting ≈70% Melt Spinning
- 9. Properties required forFibre forming polymer: 1. Molecular weight should be high. 2. Crystallinity – high not suitable. 3. Resistance to different chemical. 4. Orientation – Physical and chemical symmetry. 5. Straight chain structure. 6. Glass Transition Temperature (Tg) – Should be near to Room Temp. 7. Crystalline Melting Point (Tm) - 200o – 300o c is suitable. 8. Polymer should be soluble in some solvent from which it can be spun. 9. Hygroscopic nature – Should be hydrophobic.
- 10. Modifying the spinningsolution: • Delusturing agent: TiO2, it prevents the reflection of the surface of the fiber. Variation in the amount of pigment will control the degree of luster to produce semi dull or dull fibers. • Solution dyeing: Addition of colored dyeing / pigments or certain dyes to the spinning solution or to the resin polymer. It is also called spun dyeing or dope dyeing.
- 11. Modifying the spinningsolution: • Whitening agent: To resists the yellowing and to make whiter fiber fluorescent whitening compounds (dyes) added to the solution. This whiteness is permanent to washing and dry cleaning. • Light stabilized: To make light resistant.
- 12. • A nozzleor plate provided with fine holes or slits through a fiber forming solution or melt is extruded in fiber manufacturing is called spinneret. • The number of holes, sizes and shapes vary with the filament desired. • Spinneret was 1st invented by OZANAM at 1862 A.D. Spinneret
- 13. Spinneret • Similar toashowerhead. • Stainless steel orprecious metal alloys e.g. nickel, iridium, platinum, gold, titanium, vanadiumetc. • Corrosion-resistant and withstand highpressure.
- 14. Control of FilamentDiameter •Equal hole dimensionsare maintained. • Breakage or cloggingof holes areprevented.
- 15. Filtration andCleaning • Spinneretholes arevery sensitive to impurities. • Thorough filtration ofthe fluid prior tospinning. • Spinnerets are cleanedat regular intervals.
- 16. Spinneret cleaning process: 1.Salt bath method 2. Sample burning method 3. Vacuum cleaner method 4. Solvent cleaning method 5. Fluidized bed system
- 17. Spinneret Holes For meltspinning,a spinneret hole may be of 0.1mm diameter.
- 18. Spinneret Holes For wetspinning, the hole size is much smallerwith large number of holes.
- 19. Spinneret Holes For dryspinning, holes are widely spaced so that evaporation of the solvent can be faster.
- 20. Different shapes ofspinneret hole:
- 21. Flow chart ofMMF production: Manufacture of the fiber forming polymer. Spinning (extrusion through spinneret) Stretching/Drawing (improving strength and crystallinity) Texturing/Crimping (developing natural fiber properties) Intermingling/Interlacing (applied instead of twisting) Heat setting (made dimensionally stable)
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- 23. 28,50000-1-4,8,50000 m/min >6,000m/min BasicPrinciple • Used forpolymers that can be melted safely (Td–Tm>30oC). • Molten polymer is pumped through a spinneret which subsequently gets cooled andsolidified. FOY
- 24. Process Flowchart ofMelt Spinning:
- 25. Cross-sectionalShapeof Fibers Melt-spun fibers canbe forced through the spinneret in different cross- sectional shapes which give different qualities to thefabrics.
- 26. Cross-sectionalShapeof Fibers Filaments areof compact structure with smooth surface.
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- 28. Features andCharacteristics • Simpleand less expensivetechnology • Filaments with all possible X-sections can be produced • No toxic hazards • Solvent not required, no purification problem • Highest speed (up to 10,000 m/min) • Not suitable for thermally unstable polymer
- 29. TypicalMelt-spun Fibers • Polyester •Polyamide • Polypropylene • Polyethylene • Glass
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- 31. BasicPrinciple • Used forpolymers that need to be dissolved in avolatile solvent. • Hot air/gas is used to evaporate the solvent to get the solid fiber. ~1,200m/min
- 32. Process Flowchart ofDry Spinning
- 33. Dry spinning solvent FibreSolvent Cellulose Acetone + (2-6) % water Triacetate Methylene chloride (40%) + Methanol (10%) Poly acrylonitrile Di-methyl formamide or Dimethyl acetamide Spandex DMF, DMAC Mod acrylic Acetone
- 34. Cross-sectionalShapeof Fibers Dry-spun fibersusually have- • deformed cross-sectional shapes. • The filaments are of microporous structure with compact surface.
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- 36. Features andCharacteristics • Dryspinning is used in caseswhere the polymer may degrade thermally if attempts to melt. • The process necessarily introduces another species and its removal causes the cost to rise. • The cost can be minimized by using an efficient solvent recovery system.
- 37. Features andCharacteristics • Filamentsolidification takes place faster on the external layers and slows down towards the interior. • Asaconsequence of massexchange, the original round filament undergoes acontraction generating a deformed cross-section.
- 38. Features andCharacteristics • Cumbersometechnology • Flammable and toxic solventhazards • Yarn does not requirepurification • Medium speed (up to1,500m/min) • Solvent recovery system must be used
- 39. TypicalDry-spunFibers • Acrylic • Modacrylic •Acetate • Triacetate • Elastane/Spandex
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- 41. BasicPrinciple • Used forpolymers that have to be dissolved in anon- volatile solvent. • The spinneret is immersed in a chemical bath that precipitate & solidify the fiber. ~400 m/min
- 42. Process flow chartof Wet Spinning
- 43. Wet spinning solvent& coagulant: Fibre Solvent Coagulant Viscose Alkaline water Diluted H2SO4 + Na2SO4 + ZnSO4 PVA Water Aqueous NaOH PAN DMF + 60% ZnCl2 Aq DMF + 40% ZnCl2
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- 45. Features andCharacteristics • Cumbersometechnology • Environmental pollution hazards • Purification of the filaments required • Slow speed (up to 500 m/min) • Suitable for tow production combining all operations • Solvent and chemical recovery system may be used
- 46. TypicalWet-spunFibers • Acrylic, Modacrylic •Viscose • Modal, Cupro &Lyocell (dry-jet) • Elastane/Spandex • Aramid • Carbon
- 47. Comparison among melt,dry and wet spinning Parameter Melt Spinning Dry Spinning Wet Spinning 1. Investment cost Low High Low 2. Hazard Non toxic Toxic Toxic 3. Heat of spinning High Low Low 4. Spinneret hole 2 to many thousands 300 – 900 20000 – 75000 5. Spinningspeed High speed, up to 10,000 m /min Moderate High up to 1500 m/min Low speed upto 500 m/min 6. Application Filament or staple Filament Filament or staple 7. Solvent Not required Only volatile organic solvent Both organic and inorganic non volatile solvent can be used.
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- 49. BasicPrinciple • Used forhighstrength fiber through agel state asintermediate. • Extruded solution is cooled down byagas or aliquidmedium. ~1500m/min
- 50. BasicPrinciple During extrusion, the polymerchains are bound together at various points producing strong inter-chain forces that can significantly increase the strength of fibers.
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- 53. Filament • Filament fibersare spun from spinnerets with 350 holes or less is determined by the size of the yarn to be made. • Eachindividual strand is continuous in length. • Filaments are of two types o Monofilament 2-5 o Multifilament: apparel 10-240, technicaltextiles 100-1500
- 54. Staple • Staple fibersare made from filaments which are spun from large spinnerets with as many as 3000 holes. • Cut fiber of predetermined lengths depends on its use. • Easier to blend with otherfibers. • Cotton type 30-50 mm, wool type 60- 120mm.
- 55. Tow • The productof 100 or more spinnerets is collected into a large rope of fibers called Tow. • Continuous filaments drawn loosely together. • Used to produce staples by breaking or cutting. • Up to 100,000 filaments.
- 56. Fiberfill • It isthevoluminous form. • Used in pillows, quilts and outerwear.
- 57. Differentiate between Naturalfiber & MMF: Natural Fiber Man Made fiber The fibre which we get from nature is natural fiber. The fibers made by regeneration system. Number of molecular weight is not limited. Limited. Hygienic fabric made from Natural Fibre. Non-hygienic. Comfortable to wear. Uncomfortable. It cannot be made as our expected form. It can be made. The no of molecules controlled by nature. The no of molecules controlled by man. Dependent on climatic condition. Independent production from climatic condition.
- 58. ReviewQuestions • Define chemicalspinning. •What is the most widely used method for manmade fiber spinning? • Mention three important features of aspinneret. • What is the requirement of apolymer for melt spinning? • Why dry-spun fibers have deformed cross-sectional shape? • Why is solvent recovery installation essential in dry spinning? • Which spinning method may causeserious environmental pollution? • Compare speeds of different chemical spinning methods? • Which form of manmade fiber is frequently used during blending with other fibers?