This document discusses the production process of polypropylene fibers. It begins with an introduction to polypropylene and its uses. It then describes the two main polymerization methods used - Ziegler-Natta catalyst polymerization and metallocene catalyst polymerization. The final section discusses the melt spinning process used to produce polypropylene fibers from the polymer, including extrusion of the melt, quenching and drawing of the fibers.

1. DIRE DAWA INSTITUTE OF TECHNOLOGY
DIRE DAWA UNIVERSITY
Chemistry of Man Made Fiber production
BY : TAAME BERHANU
2018

2. Outline
 Introduction
 Polymerization methods of polypropylene
 Polypropylene fiber production process
 References

3.  Polypropylene is a material of moderately high melting temperature
(176 °C) that can be melt-spun into fibers useful for several types of
clothing, upholstery, carpets, and nonwoven fabrics.
 Synthetic Fiber: are made of polymers that do not occur
naturally.
 They are produced entirely in the laboratory, almost always from
by-products of petroleum.
 The general chemical formula for olefins can be represented as
CH2=CHR, with R representing any of several possible atoms or
groups of atoms.
INTRODUCTION

4. What are olefins ?
Class of hydrocarbons produced from the refining of petroleum
and natural gas —contains one double bond between two carbon
atoms.
and chemical formula CnH2n.
Ethylene and propylene are most important olefins
produced from Petro chemicals
Have highly reactive double bond helps Easley
conversion to many useful end products.
Can produce by steam cracking of natural gas liquids
like ethane and propane.
as solvents, detergents and adhesives.

5. Polymerization methods of PP

6. 1. Ziegler-Natta catalyst polymerization
1953 polymerized ethylene catalytically to polyethylene.
In 1973 the 2nd generation Ziegler-Natta catalysts were
introduced with β-TiCl3 at lower temperatures.
In 1980 3rd generation catalysts supported on MgCl2 were
commercialized by many companies.
In 1991 4th generation Ziegler-Natta catalysts based on
aluminoxane activated metallocene complexes were used.
TiCl4
1 atm
20-70 C
Al(Et)3 + CH2CH2
"linear"
Mw = 10,000 - 20,00,000

8. What is Ziegler-Natta catalyst?
Is a Catalyst used for Polymerization of Ethylene and Propylene
 Group III metallic compounds , such as (AlEt3,
AlEt2Cl, Al(OEt)Et2, As co- catalyst and
Group IV transition metal halide, such as (TiCl4, TiCl3,
VCl4, ZrCl4, NiCl2, MnCl2) as main catalyst
• Most commonly used are -triethylaluminium (AlEt3) and
titanium tetrachloride (TiCl4)

9. Mechanism of Ziegler Natta catalyst polymerization of PP
 Ziegler Natta works by combination of G4 Metallic
compounds(as a main catalyst) Like TiCl3 & TiCl4 with
G3 metallic compounds (as co-catalyst) like ,
Al(C2H5)2Cl & Al(C2H5)3 Respectively.
 Most of the time catalyst/co-catalyst pair are TiCl3 and
Al(C2H5)2Cl, or TiCl4 with Al(C2H5)3.

10.  Transition metals(Ti) , have six empty orbitals
(resulting from one 4s and five 3d-orbitals)
Structure of α-TiCl3
TiCl3 can arrange itself into a number of crystal
structures.
each titanium atom is coordinated to six chlorine
atoms, with octahedral geometry.
Free active site of α-TiCl3
Deficiency of e-in the Outermost shale
(Empty orbital on the surface)

11.  Al(C2H5)2Cl (co-catalyst) donates one of its ethyl groups to
the needy titanium, but kicks out one of the chlorines in
the process & it also coordinates itself to one of the
chlorine atoms adjacent to the titanium. But still Ti have
an empty orbital.

12. So then a vinyl monomer like propylene comes along.
There are two electrons in the π-system of a carbon-carbon
double bond. Those electrons can be used to fill the empty
orbital of the titanium. We say that the propylene and the
titanium form a complex, and we draw it like this:

13. How Alkene-metal complexes formed?
 A carbon-carbon double bond, is made up of a σ bond
and a π bond.
 consists of two π-orbitals, One is the π-bonding orbital
(two lobes sitting between the carbon atoms) and the
other is the π-anti bonding orbital (out away from the
two carbon atoms)
 π-anti bonding orbital is
too high in energy,

14. In Ti side
 Empty orbital in Ti is
going to look for a pair
electrons.
 It knows that the
alkene's π-bonding
orbital has a pair that it
will share.
 So the alkene's π-
bonding orbital and the
titanium's d-orbital
come together and
share a pair of
electrons.
Pink-filled
Green-empty

15. But once they're together, that other orbital (the pink one)
comes might close to that empty π-anti-bonding orbital. So
the titanium orbital and the π-anti-bonding orbital share a
pair of electrons, too.

16. Isotactic Polymerization
Breaking, shifting &
reformation of bonds
Shifting of pairs of electrons during
polymerization processAlkene-metal complexes 1st step
 The first to move is that pair from the carbon-carbon p-bond that is complexed
with the titanium. It's going to shift to form simple titanium-carbon bond.

17. Unknown rotation & migration process will happened .
Rotation about a single bond of c-c atom in a space of storio -isomer
Independent of special change
 The aluminum is now complexed
with one of the carbon atoms from
our propylene monomer and also
see, titanium is back where it
started, with an empty orbital,
needing electrons to fill it.
 So when another propylene molecule comes along, the
whole process starts all over, and the end result is
something like this:

18.  more and more propylene molecules react, and our polymer
chain grows and grows and get isotactic polypropylene.

19. 2. metallocene catalysts polymerization
 Metallocene is a positively charged metal ion sandwiched between two
negatively charged cyclopentadienyl anions. Used to make isotactic and
syndiotactic polymers, depending on what you need.
 most of the carbon atoms have one
hydrogen, but one carbon atom has
two hydrogens. One of those two
hydrogens are acidic, that is, one will
fall off/drop very easily. When this
happens, it leaves its bonding
electrons (that is, an electron pair)
behind. So the carbon it left now
has only one hydrogen, just like the
others, plus an extra pair of
electrons.

21. Zirconocenes are a little different from ferrocene. those extra
ligands( chlorines, take up space). So to make room for the
chlorines, the rings become tilted with respect to each other,
opening like a clam shell. This gives the chlorines space to
breathe.

22. To make our zirconocene complex catalyze a polymerization it is
mandatory to add methyl alumoxane polymer 1000 times the
amount of catalyst to the process
The main purpose of MAO is to replace the chlorines
(labils) with some of its methyl groups like this:
By un known reason 1
methyl groups becomes fall
off and get a complex that
looks like this:

23. Once the positively-charged zirconium is stabilized with
electrons from the carbon-hydrogen bond are shared with
the zirconium what we called α-agostic association. But still,
the zirconium is lacking in electrons.
When we add propylene, Its carbon-carbon double bond is
shares a pair of e- with the zirconium to become zirconium is
stabilized.

24. Breaking, shifting &
reformation of bonds

28. Properties required for Fiber forming polymer:
• Molecular weight should be high.
• Crystallinity – high not suitable.
• Resistance to different chemical.
• Orientation – Physical and chemical symmetry.
• Straight chain structure.
• Glass Transition Temperature (Tg) – Should be near to Room
Temp.
• Crystalline Melting Point (Tm) - 200o – 300o c is suitable.
• Polymer should be soluble in some solvent from which it can be
spun.
• Hygroscopic nature – Should be hydrophobic

29. Different Types of Spinning
A. Dry Spinning: the fiber-forming substance is dissolved in a
solvent before the solution is extruded. As the jets of solution emerge from the
spinneret, a stream of hot air causes the solvent to evaporate from the spinning
solution, leaving solid filaments. Acetate is dry spun by extruding acetone
solutions of cellulose acetate into hot air.

30. C. Wet Spinning: the solution of fiber-forming material is extruded into
coagulating bath that causes the jets to harden as a result of chemical or physical
change. Viscose, for example, is wet spun. The solution of cellulose xanthate is
extruded into an aqueous solution of acids and salts, in which the cellulose is
regenerated to form solid filaments

31. B. Melt spinning is the preferred method of manufacture for
polymeric fibers. The polymer is melted and pumped through a
spinneret (die) with numerous holes (one to thousands). The molten
fibers are cooled, solidified, and collected on a take-up wheel.
Stretching of the fibers in both the molten and solid states provides
for orientation of the polymer chains along the fiber axis. Polymers
such as poly(ethylene terephthalate) and nylon 6,6 are melt spun in
high volume.

33. Advantage and dis advantages of Melt spinning
Advantage:
– Can be used for both staple and continuous filament.
– Direct and simple process.
– No environment pollution.
– No solvent required.
– Non toxicity and no risk of explosion.
– High production speed (2500 – 3000 ft/min)
– Low investment cost.
• Disadvantage:
– Required more proper maintenance of the m/c.
– Heat of input is high.

34. Typical melt spinning:
Polymer Melting point
Nylon – 6, 6 264oC
Nylon – 6 220oC
PET 264oC
Polypropylene 167oC
Poly ethylene 125oC

35. Comparative features of melt, dry and wet spinning
Features Melt Dry Wet
Investment Cost Low High Low
Hazard Non-toxic
Toxic
(Risk of explosion)
Toxic
Heat of Spinning High High Low
Spinneret Hole
2 to many
thousand
300-900 20,000-75,000
Spinning Speed 2500-3000
ft/min
2500-3000 ft/min 150-300 ft/min

38. Polypropylene chips can be converted to fiber/filament by melt
spinning, though the operating parameters need to be adjusted
depending on the final products.
The general scheme of a spinning line for thermoplastic polymers
(pp) consists of:
• screw extruder
• distribution system (manifold)
• spinning head or spinning position
• metering pumps
• spinnerets (up to 8 or 8x2 per position)
• spinning pipes
• take-up units (winders for up to 8 bobbins)

40. Additional comments and description of the above figure
 Extrusion: L/D=30, compression ratio=1:3.5
 Metering: one or more spinning gear pumps receives the molten
polymer and sends it through the spinning pack to homogenize the
product, feed the spinning pack at a constant rate, and prevent
fluctuation due to screw extruder.
 Spinning: the spinning pack consists of three parts-filters, distributor
(which distributes the molten polymer over to die surface) and the die.
The diameter of the die varies from 0.5 to 1.5mm, depending on the
denier required.
 Quenching: newly extruded filaments are cooled in a good ―box" which
will distribute 3 m3/min of cool air without damaging the filaments.

41.  Finishing: to improve antistatic and reduce abrasion.
 Hot Stretching: to enhance the physicomechanical properties.
 Crimping: to improve the bulk.
 Thermosetting: it is a treatment in hot air or steam that removes
the internal stresses and relaxes fibers. The resultant fibers are
heat-set with increased denier.
 Cutting: fibers are cut into 20 to 120 mm length depending on
whether they are intended for cotton or woolen system.

42. BIAXIALLY ORIENTED POLYPROPYLENE (BOPP):
When polypropylene film is extruded and stretched in both the
machine direction and across machine direction it is called biaxially
oriented polypropylene. Biaxial orientation increases strength and
clarity. BOPP is widely used as a packaging material for packaging
products such as snack foods, fresh produce and confectionery. It is
easy to coat, print and laminate to give the required appearance and
properties for use as a packaging material. This process is normally
called converting. It is normally produced in large rolls which are slit
on slitting machines into smaller rolls for use on packaging
machines.

43. Continues filament pp formation

44. Yarns produced with high speed spinning (HOY and FOY) show some qualitative
and technological problems and found therefore up to now a limited diffusion at
processing and application level.
An advanced form of LOY, which needs to be submitted to a drawing process in
order to be usable, is POY, a yarn characterized by about 100-120% elongation at
break. This yarn is widely used thanks to its good stability to ageing and, although
not directly usable in the production of textile items, to its suitability to
intermediate processes which combine a specific
process (warping, sizing, etc.) with a complementary drawing process; in fact this
yarn finds wide use in draw-texturization, but also in draw-warping and in draw-
sizing.
Yarns originated by a specific drawing process performable either directly in
spinning or successively in a separate phase, are named ―fully drawn yarns‖
(FDY).

46. Main components of melt spinning machine
EXTRUDER

47. METERING PUMP
Metering pump has a very important function in spinning as
it regulates the through put of the polymer from the
spinneret.
Mass flow rate = volume between teeth x no. of teeth in a
gear x 2x rpm x density of melt

48. SPIN PACK
heart of the spinning system
It consists :-
 melt resolver- reserve for continues
delivery
 Filter pack – to filter the solid
materials
 Distributor – distribute the molten
polymer to each spin hole

49. Spinneret: This is the most important part of a MMF producing m/c. The
number of holes, sizes and shapes vary with the filament desired.
Shape of holes
Spinneret
Shape of holes

50. QUENCH CHAMBER
The extruded filament from the spinneret is subjected to pass through an
air quench zone (or chamber) at a low temperature (~15- 30 °C) with low
to moderate relative humidity.
This cool air facilitates solidification of the extruded filament by lowering
the temperature below the TG of the polymer.
Cross flow
Radiant flow
outflow
in-flow

51. The process needs to be completed by an additional operation of
mechanical drawing. The process entails winding the yarns on rollers
or cylinders running at high speed and can be carried out
continuously on filaments coming from the spinning room (single-
phase process) or on filaments coming from a phase subsequent to
spinning (two-phase process). The speed ratio between the delivery
or drawing rollers and the feeding rollers is the draft ratio R. The
mechanical configuration of the rotating devices and the filament
path are designed in order to ensure the equivalence of fibre speed
with the speed of contact organs.
Drawing

53. Drawing principle

54. Optimal conditions for fiber drawing are attained when the molecular chains show
high mobility and creep; this result is in practice attained by increasing
temperature to levels higher than glass transition and by introducing plasticizers
which can make the structure more deformable and can reduce glass transition
temperature (generally by acting upon the system water/humidity or using
spinning solvents).
From an operational point of view, the draft zone can operate at room temperature
(cold
drawing) or at heated conditions (warm drawing) and consists of rollers, contact
plates, heated air chambers or steam chambers and of immersion baths.
In order to provide the drawn fibers with thermal stability, usually these fibers
undergo also a treatment at temperature higher than drawing temperature, under
controlled tensions or in a free state, with the objective of eliminating internal
tensions through readjustment of intermolecular chemical links and of the
crystallization degree.

55. WINDER

56. Technologies for the production of continuous filament
yarns and of discontinuous fibers (staple fibers)
polyester, polypropylene and viscose are produced in both forms,
that is as continuous filament and as staple, whereas acrylic is
produced almost exclusively in staple form.
Although the production principles are identical for continuous
filament and for staple fiber, the two processes differ considerably
in terms of plant engineering shown below.

59. ADVANTAGES OF POLYPROPYLENE FIBERS:
 PP is a light fiber, its density (.91 gm/cm³) is the lowest of all
synthetic fibers.
 It does not absorb moisture. This means the wet and dry properties of
the fiber are identical. Low moisture regain is not considered a
disadvantage because it helps in quick transport of moisture as is
required in special applications like babies’ ever-dry nappies.
 It has excellent chemical resistance.
 PP fibers are very resistant to most acids and alkalis.
 The thermal conductivity of PP fiber is lower than that of other fibers
and may be used in applications as thermal wear.

60. DISADVANTAGES OF POLYPROPYLENE FIBERS:
 The main drawbacks of PP fibers are listed below:
 Low melting temperature which prevents it from being ironed like cotton, wool,
nylon etc.,
 Hard to be dyed after manufacturing, except after substantial treatment and
modification,
 High crystallinity and poor thermal conductivity leads to limited texturizability.
[Drawn polypropylene requires a contact time of 2 seconds in the heater
compared to PET (POY) which requires only 0.4 seconds]
 Poor UV and thermal stability which requires addition of expensive UV
stabilizers and antioxidants to overcome this problem,
 Poor resilience compared to PET and Nylon,
 Creeping due to its low Tg(-15 to -20°C),
 Poor adhesion to glues and latex, and
 Flammable which melts and burns like wax.