chemical spinning

Content
Chemical Spinning
Melt Spinning
Dry Spinning
Wet Spinning
Fiber Forms

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?

CHEMICALSPINNING
Definition andSpinneret

ChemicalSpinning
Man-made fibers are
produced by convertingthe
fiber forming substanceto a
viscous fluid that is
extruded through theholes
of aspinneret and then
solidified by coagulation or
evaporation or cooling.

ChemicalSpinning
This process is
known aschemical
spinning to
distinguish it from
mechanical
spinning.

Methods of Production
Extrusion through
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

Properties required for Fibre 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.

Modifying the spinning solution:
• 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.

Modifying the spinning solution:
• 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.

• A nozzle or 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

Spinneret
• Similar to ashowerhead.
• Stainless steel orprecious
metal alloys e.g. nickel,
iridium, platinum, gold,
titanium, vanadiumetc.
• Corrosion-resistant and
withstand highpressure.

Control of FilamentDiameter
• Equal hole dimensionsare
maintained.
• Breakage or cloggingof
holes areprevented.

Filtration andCleaning
• Spinneret holes arevery
sensitive to impurities.
• Thorough filtration ofthe
fluid prior tospinning.
• Spinnerets are cleanedat
regular intervals.

Spinneret cleaning process:
1. Salt bath method
2. Sample burning method
3. Vacuum cleaner method
4. Solvent cleaning method
5. Fluidized bed system

Spinneret Holes
For melt spinning,a
spinneret hole may
be of 0.1mm
diameter.

Spinneret Holes
For wet spinning,
the hole size is
much smallerwith
large number of
holes.

Spinneret Holes
For dry spinning,
holes are widely
spaced so that
evaporation of the
solvent can be
faster.

Different shapes of spinneret hole:

Flow chart of MMF 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)

MELTSPINNING
Basic Principle andFeatures

28,50000-1-4,8,50000
m/min
>6,000m/min
BasicPrinciple
• Used for polymers
that can be melted
safely (Td–Tm>30oC).
• Molten polymer is
pumped through a
spinneret which
subsequently gets
cooled andsolidified.
FOY

Process Flowchart of Melt Spinning:

Cross-sectionalShapeof Fibers
Melt-spun fibers
can be forced
through the
spinneret in
different cross-
sectional shapes
which give
different qualities
to thefabrics.

Filaments are of
compact structure
with smooth
surface.

Features andCharacteristics
• Simple and 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

TypicalMelt-spun Fibers
• Polyester
• Polyamide
• Polypropylene
• Polyethylene
• Glass

DRYSPINNING

BasicPrinciple
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

Process Flowchart of Dry Spinning

Dry spinning solvent
Fibre Solvent
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

Dry-spun fibers usually have-
• deformed cross-sectional
shapes.
• The filaments are of
microporous structure with
compact surface.

• Dry spinning 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.

• Filament solidification 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.

• Cumbersome technology
• Flammable and toxic solventhazards
• Yarn does not requirepurification
• Medium speed (up to1,500m/min)
• Solvent recovery system must be used

TypicalDry-spunFibers
• Acrylic
• Modacrylic
• Acetate
• Triacetate
• Elastane/Spandex

WETSPINNING

BasicPrinciple
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

Process flow chart of Wet Spinning

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

• Cumbersome technology
• 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

TypicalWet-spunFibers
• Acrylic, Modacrylic
• Viscose
• Modal, Cupro &Lyocell (dry-jet)
• Elastane/Spandex
• Aramid
• Carbon

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.

BasicPrinciple
• Used for highstrength
fiber through agel
state asintermediate.
• Extruded solution is
cooled down byagas
or aliquidmedium.
~1500m/min

BasicPrinciple
During extrusion, the
polymer chains are
bound together at
various points producing
strong inter-chain forces
that can significantly
increase the strength of
fibers.

TypicalGel-spunFibers
• UHMW-PE
• Aramid
• PVA
• PAN

FIBERFORMS
Forms ofManmade Fiber

Filament
• Filament fibers are 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

Staple
• Staple fibers are 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.

Tow
• The product of 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.

Fiberfill
• It is thevoluminous
form.
• Used in pillows,
quilts and
outerwear.

Differentiate between Natural fiber & 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.

chemical spinning

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