TEXTILE FIBER 2 MAN MADE FIBER.ppt

Polyamide
 Polyamides are polymers which contain recurring
amide groups as integral parts of the polymer
backbone.
– CO – NH –
Amide Group
 Naturally occurring polyamides include the
protein fibers e.g. silk and wool. Synthetic
polyamide fibers form one of the most important
of all classes of textile fiber, which we know
today as nylon.

Two types of Polyamide Fiber
 Aromatic polyamide fiber
 Aliphatic polyamide fiber

Aromatic Polyamide
 A manufactured fiber in which the fiber forming substance
is a long chain synthetic polyamide in which at least 85
percent of the amide linkages (-CO-NH-) are attached
directly to two aromatic rings. Example-Aramid
 The first fiber of this class to be developed was Nomex
from DuPont. This yarn is of only medium tenacity, but is
non-flammable and widely used for the production of
fireproof clothing, etc.

Aliphatic Polyamide
 A manufactured fiber in which the fiber forming substance is a
long chain synthetic polyamide in which less than 85% of the
amide linkages (–CO – NH–) are attached directly to two aliphatic
groups.
 Aliphatic polyamides with structural units derived predominantly
from aliphatic monomers are members of the generic class of
nylons.
 The word nylon was introduced to signify the fineness of the
filament i.e. a pound of nylon could be converted to the length
equal to the distance between New York (NY) and London (LON).

Polyamide Composition
Straight-chain aliphatic nylons are commonly identified either as
nylon X,Y or nylon Z, where X, Y, and Z signify the number of
carbon atoms in the respective monomeric units. The pair X,Y
refers to the AA---BB-type nylons, where the first number X is
equal to the number of carbon atoms in the diamine unit and the
second number Y represents the number of carbon atoms in the
corresponding diacid unit. The number Z refers to the A---B-type
nylons and is equal to the number of carbon atoms in the amino
acid unit.

 Thus, nylon-6,10 is the polyamide produced from the 6-
carbon hexamethylene diamine and the 10-carbon sebacic
acid, whereas nylon-6 is obtained from the 6-carbon
caprolactam and nylon-11 from the 11-carbon
aminoundecanoic acid.
 The coding of nylons derived from ring structures usually
includes either a single letter or a combination of letters
representing the ring containing unit.
 Nylon-6,T refers to a polyamide produced from
hexamethylene diamine and terephthalic acid
 Nylon-mXD,6 is derived from m-xylene diamine and
adipic acid.

Nylon 66
 Nylon 66 types are synthesized from a diacid and diamine. For nylon
66, hexamethylene diamine (H) and adipic acid (A) are reacted to
form H-A salt. The salt is polymerized to produce nylon 66 in the
following manner.
NH2 (CH2)6NH2 + HOOC (CH2)4 COOH
Hexamethylene Diamine Adipic Acid
↓
--CONH (CH2)6 NHCO (CH2)4CONH (CH2)6 NHCO (CH2)4 CO---
Nylon 66
Polyhexamethylene Adipamaide

Conditions for Nylon 66 production
 Hexamethylene diamine should be in the
crystalline form with melting point of 40˚C and
boiling point of 204˚–205˚C.
 Adipic acid is in the white crystalline form with acid
number of 368, with melting and boiling point of 152˚
and 216˚C.
 The color, iron and water content are also controlled. In
the production process, the two monomers of nylon 66
are taken in the molar ratio of 1: 1.

 Nylon 6 is a nylon Z type of polymer, where the Z
represents the number of carbon atoms in the
monomer. Nylon 6 is typically produced from
caprolactam in the following manner.
Nylon 6

Condition for Nylon 6 production
 The purity of the caprolactam is critically assessed for
the production of nylon 6 polymer. The specificities of
the monomer are freezing point 69˚C; permanganate
number 71; iron content as 0.5 ppm.
 Caprolactam requires a catalyst, which converts small
amounts of caprolactam to ε-aminocaproic acid which
helps in polymerization process. The catalyst could be
water, where the control of reaction is easy.

Molecular weight of Nylon 6 in water
catalyst system
 In a water catalyst system the critical parameters
during reaction are temperature of 225˚–285˚C,
amount of water 5–10% and stabilizer content of
1% and time of polymerization.

Influence of catalyst system in Nylon 6 production

The DP of Nylon 6 governed by the following relation
 Here X0 and X represents the carboxyl
group concentration at the start of
polymerization and after some time, t,
respectively. Y0 and Y represent the
amino group concentrations at the
initial and final stage, respectively. X00
represents the initial concentration of
carboxyl group of a monofunctional
acid acting as a stabilizer. Acetic acid
is typically used as a stabilizer.

Molecular weight suitable for filament production
With appropriate molecular weights, it is possible to
produce filaments through melt spinning process.
Typically the number average molecular weight used
for fiber production process is 18,000–20,000.
Technical grade nylons are made from 24,000–26,000
number average molecular weight polymers. These
high molecular weight nylons are produced by solid
state polymerization from low molecular weight chips
obtained through melt polycondensation process.

Melt spinning process of Nylon

Polymer chain structure of nylon
 The crystal structure of polyamides results from the
conformation of the macromolecules and their lateral
packing. Generally, the packing of polymer chains will be
such that the occupied volume is at a minimum, thereby
minimizing the potential energy of the structure, but
maintaining appropriate distances for intermolecular
forces between adjacent chain segments. In polyamides,
these intermolecular forces are both van der Waal’s bonds
and hydrogen bonds. The latter, involving the NH and CO
moieties, cause the formation of sheet-like arrangements
between adjacent chains.

 The stacking of these hydrogen-bonded sheets controls the
size and shape of the unit cell. Since the nature of the bonds in
the chain direction is different from that of the lateral bonds,
the unit cells of polyamides are generally characterized by
monoclinic, triclinic, and rhombic lattices. Hexagonal lattices
indicate usually metastable mesomorphic modifications. The
general conformation of the chain segments in the unit cell
and their mode of packing are the basis for classification with
regard to the crystalline forms of various polyamides. One is
characterized by fully extended chain segments and is referred
to as the α -structure; the other γ -structure consists also of
extended segments, which however are twisted or contain
some kink, resulting usually from rotation about the
–CH2NHCO– unit.

 Polyamides of the nylon X,Y-type with even–even carbon atom
numbers crystallize mainly in the α -form, whereas those with
odd–odd, even–odd, and odd–even numbers crystallize usually in
the γ -form.
 Polyamides of the nylon Z type with even numbers crystallize
generally in the γ -form for Z>8.
 Nylon-4 and nylon-6 can crystallize in either the α- or the γ-form.
However, the predominant structure of these two polyamides is
the α -form. The two structures are interconvertible. The γ -form
can be converted to the α -form by either treatment with aqueous
phenol or the application of stress at high temperatures, whereas
the α -form can be converted to the γ -form by treatment with
aqueous iodine–alkali iodide solutions.

Unit cell of the monoclinic α -form of nylon-6

Characterization of structural parameters by X –ray
diffraction
 Information on physical parameters of the molecular
structure of polyamide fibers are usually obtained by x-
ray diffraction methods, electron and light microscopies,
infrared spectroscopy, thermal analyses such as
differential thermal analysis.
 X-ray diffraction provides detailed information on the
molecular and fine structures of polyamide fibers.
Although the diffraction patterns of polyamide fibers
show wide variation, they exhibit usually three distinct
regions:

 A generally well-defined crystalline pattern within
Bragg angles of about 20 to close to 900 by wide-
angle diffraction.
 Less well-defined diffuse bands due to scattering
from the amorphous phase.
 Diffraction pattern within Bragg angles of less
than about 20 of the primary beam by small-angle
diffraction, due to longer-range periodicities
entailing amorphous and crystalline phases in
meridional reflections, particle scattering, and
vacuoles that usually cause an equatorial
diffraction of continuously declining intensity.

Schematic diagram of x-ray diffraction pattern

 ‘‘Bragg angle’’ refers to the well-known relation
known as the Bragg equation λ=2dsinθ, where λ is
the wavelength of the x-rays, d the vertical
distance (spacing) of the lattice planes, and θ the
angle of the incident x-rays. The principal features
of the diffraction pattern are shown schematically
in the following figure together with the structural
information that may be derived from them.

Properties Nylon 66 Nylon 6
Tensile Strength g/d
Dry 5.0-6.5 4.8-6.4
Wet 4.5-6.0 4.2-5.9
Tensile Elongation % 25-38 28-45
Dry 28-45 36-52
Wet
Young’s Modulus g/d 30-52 20-45
Elastic Recovery %
at 3% elongation
98-100 98-100
Specific Gravity 1.14 1.12-1.15
Specific Heat J/gK 1.67 1.6
Water Absorption %
65% RH 3.5-4.5 3.5-4.5
100% RH 9-10 9-10
Physical properties of nylon 6 and nylon 66

Difference between Nylon 6 and Nylon 66
 Nylon 66 and nylon 6 differ from each other in
various ways. The difference in the structural
composition in these two fibers are reflected to
their physical as well as chemical behavior that
lead them to be used in different areas of
application according to the requirements of a
particular end use.

 First of all, nylon 6 is only made from one kind of
monomer, a monomer called caprolactum. Nylon 66
is made from two monomers, adipic acid and
hexamethylene diamine.
 The chemical structures of nylon 66 and nylon 6 are
virtually identical. They differ only in the arrangement
of the carbonyl and NH groups between the
hydrocarbon chains of the polymer.
 In nylon 66 their order is alternatively reversed and
the order might be designated AB----BA (A
representing amine groups and B representing
carboxyl groups).

 Nylon 6 does not have the same functional groups
at each end of the monomer unit like nylon 66 and
can be written as AB----AB structure.
 Nylon 66 fiber has a tighter molecular structure
than nylon 6 due to higher level of hydrogen
bonding and maximum alignment between the
molecular chains.
 Type nylon 6 does not have this level of internal
bonding resulting in a more random and open
structure

Crystallinity
 Nylon 66 is more crystalline than the nylon 6. This more crystalline
structure of type nylon 66 helps the fiber to retain its shape better
and gives the enhanced resilience properties. The higher degree of
crystallinity and tighter molecular structure of nylon 66 results,
however, a poor dye affinity than nylon 6 fibers.
Melting point
The melting point determines thermal resistance, safe ironing
temperature and heat setting temperature. Nylon 66 has a higher
melting temperature (about 2500C) than nylon 6 (about 2150C) due to
its molecular structure. The higher melting point of nylon 66 allows it
to be used in some particular cases, where the melting point of nylon 6
can not meet the requirements of application.

Dye affinity and color fastness
 Nylon 6 has a greater affinity for certain dyestuffs than nylon 66.
 Dye together with acid dyes in the same dyebath, nylon 6 will dye
to a shade several times deeper than that attained by nylon 66.
 The dye diffusion rate for nylon 66 is not as fast as for nylon 6.
 Therefore it is more difficult to dye nylon 66.
 Two tone (multi tone) colorings may be obtained by dyeing fabrics
constructed from both fibers.
 On the other hand, it is also difficult to strip out the color from
type 66 because the dye more closely combines with the fiber.
 Consequently, nylon 66 possesses better colorfastness properties
than nylon 6.

Polyester
 The word ester is the name given to salts formed
from the reaction between an alcohol and an acid.
Esters are organic salts and polyester means
many organic salts.
 Polyester is a man made, synthetic polymer,
filament or staple fiber. The most common
polyester apparel filament or staple fiber is usually
composed of polyethylene terephthalate polymers.
-C-OH + -COOH = -CO-OC- + H20H

 Polyester is a term often defined as “long-chain polymers
chemically composed of at least 85% by weight of an
ester and a dihydric alcohol and a terephthalic acid”.
 In other words, it means the linking of several esters
within the fibers.
 Reaction of alcohol with carboxylic acid results in the
formation of esters.
 Polyester also refers to the various polymers in which the
backbones are formed by the “esterification condensation
of polyfunctional alcohols and acids”.

Raw materials for polyester fiber
 The fiber-forming polyester may be obtained from
dicarboxylic acids with diols.
 Commercially, aromatic polyester is applied using
ethylene glycol (EG) and dimethyl terephthalate (DMT),
or ethylene glycol and terephthalic acid (TPA) to produce
polyethylene terephthalate (PET).
 Before 1970, polyester was exclusively produced on a
commercial scale from ethylene glycol and dimethyl
terephthalate.

Production of ethylene glycol
 Direct oxidation process
This process involves direct oxidation of ethylene to
ethylene oxide according to the following reaction.
The reaction uses metal catalysts (e.g., silver oxide)
and the reaction temperature is approximately
250°C.

Required properties of EG for polyester production
 Boiling point: 195–198°C.
 Density: 1.110–1.112 (at 20°C).
 OH number: greater than 1750.
 Water content: less than 0.1%.
 Ester interchange value: greater than 90.

Manufacturing of terephthalic acid and dimethyl
terephthalate
 Material from p-xylene
Conversion of p-xylene mainly occurs by oxidation.
Terephthalic acid and dimethyl terephthalate are
produced from p-xylene according to the following
formula:

Polymerization process of polyester fiber in industry

 In industrial practice, the polymerization processes of
aromatic polyethylene terephthalate are produced via a two
step process.
 The first step is esterification and preliminary
condensation, while the second is polycondensation or
melt polymerization.
 Esterification and preliminary condensation proceed in two
paths:
a. Transesterification and preliminary condensation
b. Direct esterification and preliminary condensation.

 In the first path, the DMT is transformed, with the assistance
of one or more catalysts and EG at temperatures ranging
from 150 to 200°C, into BHET (bis-(2-hydroxyethyl)
terephthalate) (also called di glycol terephthalate, DGT) with
the elimination of methanol.

Transesterification & preliminary condensation

The reaction condition of transesterification and preliminary
condensation are;
 Catalysts: metal oxides (PbO, MgO, Sb2O3, etc.), metal
acetates (Co, Mn, Zn, etc.), or mixtures of oxides and acetates
metals (CH3COO)2CO-Sb2O3, (CH3COO)2CO-PbO, etc.).
 Concentration of catalyst: 0.05% (to the amount of DMT).
 Monomer ingredient for DMT: EG =1: (2-2.5) (mole ratio).
 Reaction temperature: falls in the range of 150–200°C
(gradually increases).
 Reaction time: 3–6 hours.

Direct esterification and preliminary condensation
 In the second path (direct esterification and
preliminary condensation), terephthalic acid
(TPA) is converted, with EG and the aid of one or
more catalysts at temperatures ranging from 250
to 280°C, into BHET with the elimination of
water.

Reaction of direct esterification

The reaction condition of directesterification
and preliminary condensation are;
 Catalysts: metal oxides (Sb2O3, PbO, etc.).
 The concentration of catalysts: should be less than
0.05% (to the amount of TPA).
 Monomer ingredient for TPA: EG =1: (1.1–2) (mole
ratio).
 Reaction temperature: 250–290°C (increases
gradually).

Polycondensation
 This step starts by the BHET produced by
esterification and preliminary condensation.
Then, by condensation reaction, the
intermolecular BHET releases EG and produces
PET. The reaction is:

Reaction conditions of polycondensation
 Catalysts: metal acetates (e.g., Co, Mn, Zn, Mg,
Pb, Cd, etc.) or mixtures of oxides and acetate
metals; such as (CH3COO)2Mn +Sb2O3,
(CH3COO)2Co +Sb2O3, etc.
 The concentration of catalysts: 0.02–0.03% (to the
amount of TPA or DMT).
 The thermal stabilizer of PET: phosphor
compounds.
 The concentration of the thermal stabilizer of PET:
0.015–0.03% (to the amount of TPA or DMT).

 Nitrogen under pressure is needed to place
BHET into the condensation vessel.
 Reaction temperature: 265–285°C (stable
temperature).
 Reaction pressure: below 1 mm/Hg.

Advantages of PTA route over DMT route
 PTA gives higher production output to about 15
per cent higher, due to the faster rate of
esterification and reduced raw material weight to
product ratio.
 Capital investment to construct a polyester fiber
plant based on PTA is at least 20 percent less
than one based on DMT route.
 PTA has higher bulk density than DMT and
hence requires less storage space compared
with DMT.

 The PTA process needs less MEG as compared with DMT
(1: 1.15 vs. 1: 2). Thus less MEG is to be recovered during
polycondensation resulting in lower investment for MEG
recovery and recycle system. This in turn promotes energy
conservation.
 PTA process is safe, as methanol is not evolved during
esterification while in DMT process; methanol is produced
as a by-product. Methanol is highly inflammable and can
cause explosion.
 Higher molecular weight is reached in less time in the PTA
process than with the DMT process.

Characteristics of polyester
 Polyester fabrics and fibers are extremely strong.
 Polyester is very durable: resistant to most
chemicals, stretching and shrinking, wrinkle
resistant, mildew and abrasion resistant.
 Polyester is hydrophobic in nature and quick
drying. It can be used for insulation by
manufacturing hollow fibers.
 Polyester retains its shape and hence is good for
making outdoor clothing for harsh climates.
 It is easily washed and dried.

Rayon fiber
 Rayon is a manufactured fiber composed of
regenerated cellulose in which substituents have
replaced note more than 15 percent of the hydrogen
of the hydroxyl groups.

Types of regenerated cellulose fiber
 Depending of the production methodology, type of
solvent used and fiber properties, the regenerated
cellulose fiber or rayon fiber can be classified mainly
in four groups. At present the following methods are
used to produce cellulose based man made fiber;
a. Viscose process – viscose fiber
b. Cuprammonium process – cupro fiber
c. Lyocell process – lyocell fiber
d. Acetate process – acetate fiber

Manufacturing process of viscose
 The process of manufacturing viscose rayon consists of
the following steps mentioned, in the order that they are
carried out:
Steeping: Cellulose pulp is immersed in 17-20%
aqueous sodium hydroxide (NaOH) at a temperature in
the range of 18 to 25C in order to swell the cellulose
fibers and to convert cellulose to alkali cellulose.
(C6H10O5)n + nNaOH ---> (C6H9O4ONa)n + nH2O
Pressing: The swollen alkali cellulose mass is pressed
to a wet weight equivalent of 2.5 to 3.0 times the original
pulp weight to obtain an accurate ratio of alkali to
cellulose.

Shredding: The pressed alkali cellulose is shredded
mechanically to yield finely divided, fluffy particles called
"crumbs". This step provides increased surface area of
the alkali cellulose, thereby increasing its ability to react
in the steps that follow.
Aging: The alkali cellulose is aged under controlled
conditions of time and temperature (between 18 and 300
C) in order to depolymerize the cellulose to the desired
degree of polymerization. In this step the average
molecular weight of the original pulp is reduced by a
factor of two to three. Reduction of the cellulose is done
to get a viscose solution of right viscosity and cellulose
concentration.

Xanthation: In this step the aged alkali cellulose crumbs are
placed in vats and are allowed to react with carbon
disulphide under controlled temperature (20 to 30C) to form
cellulose xanthate.
(C6H9O4ONa)n + nCS2 ----> (C6H9O4O-SC-SNa)n
Side reactions that occur along with the conversion of alkali
cellulose to cellulose xanthate are responsible for the orange
color of the xanthate crumb and also the resulting viscose
solution. The orange cellulose xanthate crumb is dissolved in
dilute sodium hydroxide at 15 to 20 C under high-shear
mixing conditions to obtain a viscous orange colored solution
called "viscose", which is the basis for the manufacturing
process. The viscose solution is then filtered (to get out the
insoluble fiber material) and is deaerated.

 Dissolving: The yellow crumb is dissolved in aqueous
caustic solution. The large xanthate substituents on the
cellulose force the chains apart, reducing the interchain
hydrogen bonds and allowing water molecules to solvate
and separate the chains, leading to solution of the
otherwise insoluble cellulose. Because of the blocks of un-
xanthated cellulose in the crystalline regions, the yellow
crumb is not completely soluble at this stage. Because the
cellulose xanthate solution (or more accurately,
suspension) has a very high viscosity, it has been termed
"viscose".

Ripening: The viscose is allowed to stand for a period of
time to "ripen". Two important process occur during ripening:
Redistribution and loss of xanthate groups. The reversible
xanthation reaction allows some of the xanthate groups to
revert to cellulosic hydroxyls and free CS2. This free CS2 can
then escape or react with other hydroxyl on other portions of
the cellulose chain. In this way, the ordered, or crystalline,
regions are gradually broken down and more complete
solution is achieved. The CS2 that is lost reduces the
solubility of the cellulose and facilitates regeneration of the
cellulose after it is formed into a filament.
(C6H9O4O-SC-SNa)n + nH2O ---> (C6H10O5)n + nCS2 + nNaOH
Filtering: The viscose is filtered to remove undissolved
materials that might disrupt the spinning process or cause
defects in the rayon filament.

Degassing: Bubbles of air entrapped in the viscose must be removed
prior to extrusion or they would cause voids, or weak spots, in the fine
rayon filaments.
Spinning - (Wet Spinning): Production of Viscose Rayon Filament: The
viscose solution is metered through a spinnerette into a spin bath
containing sulphuric acid (necessary to acidify the sodium cellulose
xanthate), sodium sulphate (necessary to impart a high salt content to
the bath which is useful in rapid coagulation of viscose), and zinc
sulphate (exchange with sodium xanthate to form zinc xanthate, to cross
link the cellulose molecules). Once the cellulose xanthate is neutralized
and acidified, rapid coagulation of the rayon filaments occurs which is
followed by simultaneous stretching and decomposition of cellulose
xanthate to regenerated cellulose. Stretching and decomposition are
vital for getting the desired tenacity and other properties of rayon. Slow
regeneration of cellulose and stretching of rayon will lead to greater
areas of crystallinity within the fiber, as is done with high-tenacity rayons.

The dilute sulphuric acid decomposes the xanthate and
regenerates cellulose by the process of wet spinning. The
outer portion of the xanthate is decomposed in the acid
bath, forming a cellulose skin on the fiber. Sodium and zinc
sulphates control the rate of decomposition (of cellulose
xanthate to cellulose) and fiber formation.
(C6H9O4O-SC-SNa)n + (n/2)H2SO4 --> (C6H10O5)n + nCS2 + (n/2)Na2SO4
Drawing: The rayon filaments are stretched while the
cellulose chains are still relatively mobile. This causes the
chains to stretch out and orient along the fiber axis. As the
chains become more parallel, interchain hydrogen bonds
form, giving the filaments the properties necessary for use
as textile fibers

Washing: The freshly regenerated rayon contains many
salts and other water soluble impurities which need to be
removed. Several different washing techniques may be
used.
Cutting: If the rayon is to be used as staple (i.e.,
discreet lengths of fiber), the group of filaments (termed
"tow") is passed through a rotary cutter to provide a fiber
which can be processed in much the same way as cotton

Process flowchart of viscose rayon

TYPES OF RAYON
Rayon fibers are engineered to possess a range of properties to meet
the demands for a wide variety of end uses. Some of the important
types of fibers are briefly described.
 High wet modulus rayon: These fibers have exceptionally high wet
modulus of about 1 g/den and are used as parachute cords and
other industrial uses. Fortisan fibers made by Celanese (saponified
acetate) has also been used for the same purpose.
 Polynosic rayon: These fibers have a very high degree of
orientation, achieved as a result of very high stretching (up to 300 %)
during processing. They have a unique fibrillar structure, high dry
and wet strength, low elongation (8 to 11 %), relatively low water
retention and very high wet modulus.

Viscose has lower tenacity in both wet and conditioned state than cotton

Viscose has lower tenacity in both wet and conditioned state than cotton– more care
is necessary to prevent fabric breakages and tears in wet processing

Viscose has greater elongation in both wet and conditioned state than cotton –
it will be stretched or distorted more under tension.

 Flame retardant fibers: Flame retardnce is achieved by
the adhesion of the correct flame- retardant chemical to
viscose.
Examples of additives are alkyl, aryl and halogenated alkyl
or aryl phosphates, phosphazenes, phosphonates and
polyphosphonates. Flame retardant rayons have the
additives distributed uniformly through the interior of the
fiber and this property is advantageous over flame
retardant cotton fibers where the flame retardant
concentrates at the surface of the fiber.
Specialty of rayon fiber

 Super absorbent rayons: This is being produced in
order to obtain higher water retention capacity (although
regular rayon retains as much as 100 % of its weight).
These fibers are used in surgical nonwovens. These
fibers are obtained by including water- holding polymers
(such as sodium polyacrylate or sodium carboxy methyl
cellulose) in the viscose prior to spinning, to get a water
retention capacity in the range of 150 to 200 % of its
weight.
 Micro denier fibers: rayon fibers with deniers below 1.0
are now being developed and introduced into the market.
These can be used to substantially improve fabric
strength and absorbent properties.

PROPERTIES OF RAYON
Variations during spinning of viscose or during drawing of
filaments provide a wide variety of fibers with a wide
variety of properties. These include:
 Fibers with thickness of 1.7 to 5.0dtex, particularly those
between 1.7 and 3.3 dtex, dominate large scale
production.
 Tenacity ranges between 2.0 to 2.6 g/den when dry and
1.0 to 1.5 g/den when wet.
 Wet strength of the fiber is of importance during its
manufacturing and also in subsequent usage.
Modifications in the production process have led to the
problem of low wet strength being overcome.

 Dry and wet tenacities extend over a range
depending on the degree of polymerization and
crystallinity. The higher the crystallinity and
orientation of rayon, the lower is the drop in
tenacity upon wetting.
 Percentage elongation-at-break seems to vary
from 10 to 30 % dry and 15 to 40 % wet.
Elongation-at-break is seen to decrease with an
increase in the degree of crystallinity and
orientation of rayon.

Lyocell Fiber
 Lyocell is a manmade fiber derived from cellulose, better
known in the United States under the brand name Tencel.
 Though it is related to rayon, another cellulosic fabric, lyocell
is created by a solvent spinning technique, and the cellulose
undergoes no significant chemical change.
 It is an extremely strong fabric with industrial uses such as in
automotive filters, ropes, abrasive materials, bandages and
protective suiting material. It is primarily found in the garment
industry, particularly in women's clothing.

Lyocell Process
The production of regenerated cellulose fibers with
NMMO as a cellulose solvent is a modern, highly efficient,
nonpolluting process. The production of regenerated
cellulose fibers with NMMO(N-METHYLMORPHOLINE-
N-OXIDE) fconsists of the following steps:
 Preparation of a homogeneous solution (dope) from
cellulose pulp in NMMO–water solution
 Extrusion of the highly viscous spinning dope at elevated
temperatures through an air gap into a coagulation bath
(dry-jet wet-spinning process)
Coagulation of the cellulose fibers
Washing, drying, and post treatment of the cellulose fibers
Recovery of NMMO (N-METHYLMORPHOLINE-N-OXIDE)
from coagulation baths

Flowchart of lyocell production

Properties of NMMO
 The NMMO is a highly polar compound with the N–O group
having the dipole moment that can form hydrogen bonds with
the hydroxyl groups of cellulose. Consequently the aqueous
solutions of NMMO dissolve the cellulose.
 NMMO can be produced from morpholine (1-oxa-4-
azacyclohexane). Morpholine (M) is a colorless liquid having
boiling point of 129–1300C. The compound is a weak organic
base and can be synthesized from ammonia and ethylene
oxide.
 The oxidation of N-methylmorpholine (NMM) is accomplished
by using a 35% excess of H2O2 and carrying out the reaction
at 67–720C for 4–5 h.

Advantages of NMMO technology
 NMMO process has a short production cycle. The dissolution and
spinning process is usually done within 5 h. Currently, full continuous
dissolution of cellulose is implemented in the Lyocell process.
 NMMO process is eco-friendly. No toxic gases or by-products are
formed. The recovery of NMMO can be as high as 99.5%.
 NMMO process can be utilized to obtain highly concentrated
cellulose solutions (25–35%).
 NMMO fibers can be spun at a relatively high spinning speed in the
range of 150–300 m/min.
 NMMO technology allows regenerated cellulose fibers to be modified
by spinning fibers from the solutions containing cellulose and some
other polymers including cellulose acetate, cellulose derivatives,
polyvinyl alcohol, and some other natural polymers.
 NMMO technology can be utilized to make cellulose membranes and
films

Properties of lyocell fiber
 Much higher dry and wet strength
 2. Much higher dry and wet Young’s modulus
 3. Higher knot- and loop-strength
 The strength of lyocell fibers in the wet state is significantly
higher than that of other celluloses, losing only 15% from
the dry state.
 Also of significance is the very high modulus of the fibers,
much higher than for the other fibers shown.
 A high initial wet modulus gives lyocell fibers very low
potential shrinkage in the wet state.

Ester Cellulose Fiber
 Textile fibers which are composed of ester cellulose are
called acetate fibers.
 There are two types: acetate and triacetate.
 The term acetate is derived from acet and ate.
 The former comes from acetic acid (the acid of vinegar),
whilst the latter denotes a chemical salt.
 Acetate means a salt of acetic acid. To make acetate
fibers, cellulose is treated to form cellulose acetate; that
is, the cellulose salt of acetic acid.
 In organic chemistry, a salt is known as ester. As a result
acetate fibers are at times referred to as cellulose ester
or ester cellulose fibers.

Two Types of Acetate Fiber
 Acetate – a man made, natural polymer based
secondary cellulose acetate filament or staple
fiber.
 Triacetate – a man made, natural polymer based
primary cellulose acetate filament or staple fiber.

Acetate & Triacetate
 Acetate and triacetate are mistakenly referred to as the
same fiber; although they are similar, their chemical
compounds differ. Triacetate is known as a generic
description or primary acetate containing no hydroxyl
group. Acetate fiber is known as modified or secondary
acetate having two or more hydroxyl groups.
 The Federal Trade Commission definition for acetate fiber
is "A manufactured fiber in which the fiber-forming
substance is cellulose acetate. Where not less than 92
percent of the hydroxyl groups are acetylated, the term
triacetate may be used as a generic description of the
fiber."

Acetate & triacetate Process
 Basic Principles
Cellulose triacetate is obtained by esterification of cellulose
with acetic anhydride.
The anhydroglucose unit contains three -OH sites for
acetylation. Therefore, the maximum degree of acetylation of
cellulose is a triacetate; however, the acetylation does not
quite reach the maximum of three units per glucose unit.
The extent to which the hydroxyl groups are substituted is
called the degree of substitution (DS). For cellulose
acetate, also called secondary cellulose acetate or
cellulose diacetate, the DS is about 2.4.

 The overall reaction in the conversion of cellulose to
cellulose triacetate is:
 Where Cell is the anhydroglucose ring (without -OH
groups) and Ac is an abbreviation for acetyl, -COCH3. The
above equation shows that 3 mol of acetic anhydride react
with 1 mol of cellulose to give 1 mol of cellulose triacetate
and 3 mol of acetic acid.

 During hydrolysis, some of the acetate groups are
hydrolyzed. This is represented approximately by the
equation:
 The above equation shows the formation of a
diacetate. Actually, the DS is higher at 2.4, which
means that less than one acetyl group per
anhydroglucose unit is hydrolyzed on an average, or
three acetyl groups are hydrolyzed for every five
anhydroglucose units.

Manufacturing process of acetate

Acetate and triacetate characterization
 Acetyl Value
Degree of acetylation or substitution (DS) is specified by two terms:
acetyl value (%) and combined acetic acid (%). The ratio of these
terms is determined by the molecular weight ratio of acetyl group to
acetic acid, (-CH3CO)/(CH3COOH), or 43/60.
Commercial cellulose triacetate has a DS of about 2.91–2.96, which
corresponds to an acetyl value of 44.0–44.4% acetyl and a combined
acetic acid of 61.4–62.0%. Note that a full triacetate with DS of 3 has
an acetyl value of 44.79% and a combined acetic acid of 62.50%.
Commercial cellulose acetate or secondary cellulose acetate has a DS
of about 2.4, which corresponds to an acetyl value of 39.3% and a
combined acetic acid of 54.8%. The values could be slightly higher or
slightly lower, depending on the particular manufacturer.

Solubility
 Cellulose triacetate is soluble in several organic solvents.
 Methylene chloride or the mixed solvent of 9/1 methylene
chloride–methanol by weight is used for preparing dopes
of cellulose triacetate for spinning.
 Methanol enhances the solubility of cellulose triacetate
in methylene chloride.
 Cellulose triacetate is also soluble in chloroform, sym-
tetrachloroethane, trichloroethanol, dimethylformamide,
trioxane, sulfane, dimethylacetamide, formic acid, and
acetic acid.

 The universal solvent for cellulose acetate is acetone.
 Spinning dopes are prepared by dissolving the flake in an
acetone–water solvent composition of about 95/5.
 The small amount of water significantly reduces the
viscosity of a concentrated solution of cellulose acetate
such as for a 25% solution.
 Other solvents for cellulose acetate are ethyl methyl
ketone, dioxane, pyridine, nitroethane, dimethylformamide,
dimethylacetamide, formic acid, and acetic acid.
 Although methylene chloride alone is not a good solvent for
cellulose acetate, 9/1 methylene chloride–methanol is a
good solvent.

Fiber properties
 Hand: soft, smooth, dry, crisp, resilient
 Comfort: breathes, wicks, dries quickly, no static cling
 Drape: linings move with the body linings conform to
the garment
 Color: deep brilliant shades with atmospheric dyeing
meet colorfastness requirements
 Luster: high luster
 Performance: colorfast to perspiration staining,
colorfast to dry cleaning, air and vapor permeable

 Tenacity: weak fiber with breaking tenacity of 1.2 to 1.4
g/d; rapidly loses strength when wet; must be dry
cleaned
 Abrasion: poor resistance
 Heat retention: poor thermal retention; no allergenic
potential (hypoallergenic)
 Dyeability: (two methods) cross-dying method where
yarns of one fiber and those of another fiber are woven
into a fabric in a desired pattern; solution-dying method
provides excellent color fastness under the effects of
sunlight, perspiration, air contaminants and washing

TEXTILE FIBER 2 MAN MADE FIBER.ppt

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