Viscose rayon fibre

A PRESENTATION ON:
1
VISCOSE RAYON FIBRE

Presented by-
Ashish Kumar Dua 2012TTF2406
INDIAN INSTITUTE OF TECHNOLOGY, DELHI

Introduction:
2

 It is oldest regenerated cellulose fibre.
 It is biodegradable & renewable polymer.
 Comman sources wood pulp & cotton lint.
 Highly purified wood pulp consists of of 90-95% cellulose called
chemical cellulose & dissolving pulp.
 The process used to make viscose either continuous or batch process.


PROCESS TO MAKE ORDINARY RAYON:
3
Cellulose pulp 13”X18” or 20X30” & cellulose :87-98% are
Steeping vertically stacked in 3”-6” apart to each other.
& tank contain 17-18% NaOH.
(C6H10O5)n + nNaOH -- (C6H9O4ONa)n + nH2O

Shredding To make cellulose in fluffy crumbs by mechanical action

Ageing De-polymerization

Add CS2: 32-35%,1-3 h,20-30 0c 1-4 rev.
Xanthation (C6H9O4ONa)n + nCS2 ----> (C6H9O4O-SC-SNa)n


CONTINUED... 4

Dissolution Add 4-6% NaOH +agitators and total sulphr-2 to 2.5%

Storage at 15-25 0 c for 1-3 days.
In this time redistribution of xanthate take place.
Ripening (C6H9O4O-SC-SNa)n + nH2O ---> (C6H10O5)n + nCS2 +
nNaOH

Filtration & Blending Remove undissolved material, bubble air


CONTINUED… 5
H2SO4-8-10%
Spinning Na2SO4-16-24%
ZnSO4-1-2%
(C6H9O4O-SC-SNa)n + (n/2)H2SO4 --> (C6H10O5)n + nCS2 +
(n/2)Na2SO4 Spinning speed may be high as 120m/min
Spinning Bath

Neutralization

Drying & Winding


PROPERTIES OF RAYON: 6
 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 fibre 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 tenacity 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.


CONTINUED: 7
 Thermal properties: Viscose rayon loses strength above 149 C; chars
and decomposes at 177 to 204 C. It does not melt or stick at elevated
temperatures.

 Chemical properties: Hot dilute acids attack rayon, whereas bases do
not seem to significantly attack rayon. Rayon is attacked by bleaches
at very high concentrations and by mildew under severe hot and
moist conditions. Prolonged exposure to sunlight causes loss of
strength because of degradation of cellulose chains.

 Abrasion resistance is fair and rayon resists pill formation. Rayon has
both poor crease recovery and crease retention.


ROLE OF ZINC IN SPINNING BATH: 8


SPINNING WITH MODIFIERS: 9
 Modifiers enhance the action of zinc in the spinning bath without effecting
the viscose.
 Formation of semipermeable membrane by the combined action zinc ions
by the product trithocarbamate ions viscose & modifiers and makes an
barrier which retards the diffusion of both Zn+ & H+.
 So the acidification boundary shift further away from the nozzle in the
presence of modifiers.
MODIFIERS
Tertiary amine
Quaternary ammonium salt
Polyoxyalkylene derivative
Polyoxyhydroxy polyamide
Dithiocarbamates

CONTINUED: 10
Tyre yarn-

A viscose solution of viscosity 100 poise containing modifiers 1-3% by
weight of cellulose and with a CS2 content of 40% is spun underripe into
a aqueous spinning bath containing –

H2SO4 8-10%

Na2SO4 16-24%

ZnSO4 6%

The spin bath temperature is kept around 550c and the spinning speed is
between 40 and 60 m/min. The stretch applied is 75-125%


CONTINUED: 11
Modified high wet-modulus yarns-

The condition of viscose solution and spinning bath composition are
generally similar to those tyre yarns.

 Spinning bath temperature 350c is kept lower because it gives more
deformable gel necessitating a slower spinning speed 20-40 m/min The
result is that gel fibres are stretched at an earlier state of the gel
dehydration and decomposition when the gel is more plastic and can be
stretched more(125%-150%).

Polynosic fibre-It is similar to rayon process but with-outing having the step of
ageing and ripening stage, with dilute acid concentration & zinc sulphate.

 Its having the high crystallinity & orientation, ,chemical resistance ,high
wet modlus and more dimension stable.

CONTINUED: 12
Spinning bath- H2SO4-2-3%
Na2SO4-4-6%
Temp-250c
Spinning speed-20-30m/min
Stretch-150-300%
-
Crystallinity(%) Birefringence
Standard 45.2 0.027
Viscose
Tyre yarn 41.5 0.037
Polynosic 55.2 0.046
Super high wet modulus rayon-By adding 1% formaldehyde to spin bath .
Stretch - 500-600%


Fibre variant for improvrd bulk & hsndle-: 13
 TO produce high performance crimped fibres where the bulk is due to the interaction
between the fibres, creating bulk in resultant yarns and fabric. The second approach
has been to produce an inherently bulky fibre using an inflation technique during fibre
production.
Composition Typical range(%)
Cellulose 7-7.5
NaOH 6-7.5
CS2 30-32
Modifiers: Dimetylamine .8-1.5
Polyethylene glycol .8-1.5
We can produced different types of fibres-
1. High performance crimped fibres.
2. Super absorbent fibres.
3. Flame retardant fibres.

Incorporation of carbon in viscose fibre: 14
(a) Incorporation of carbon black for antistatic properties-
Electrically conductive carbon is used for the production of
electrically conductive fibre. For the production of the electric
conductive fibre a slightly alkaline electric conductive carbon black
with a particle size 20 nm is dispersed in water and mixed in viscose
solution prior to spinning.

(b) Incorporation of graphite.-Incorporating 40% of lubricating
graphite with a purity 99.5% into viscose yields fibres with
excellent lubricating properties which as packing and sealing
for crankshafts. Packings from graphite containing viscose
fibres may be used to a temperature of 180-2000c.They are
stable in the Ph range 5-9 .


ALTERNATIVE METHOD TO DISSOLVE TO CELLULOSE: 15
1. N-Methylmorpholine N-Oxide And Water-

1. It is the best solvent to dissolve viscose fibre.
2.Its having strong oxidant property due to which it can
dissolve cellulose.


DOPE PREPAETION : 16
Its having high potential to dissolve cellulose up to 50%.

Mixture
transfer in air
Disadvantage- 1.During the dissolving step time
tight vessel and temp. are maintained properly otherwise
thermal degradation & explosion takes place.
Generally temp. is around 1300c.

Mix & stirred 2. .If the temp. is goes above 150 0 c ,DP of
cellulose goes down for this we add some
phenolic oxidant .It stabilize the solution and
finally oxidize the colour compound.
Heat it up to 130 O C
For 30 min


CONTINUED: 17
2. . N-N Dimethyl acetamide and lithium chloride-
1. It is another solvent which dissolve cellulose. It directly
linked with very high reproducible.
2. It was observed that fibres from wet spinning process
exhibited superior properties.
3. It makes an complex with OH-group of cellulose & help
to dissolve cellulose. solution is much stable in nature. It is
stable few years in room temperature.


CONTINUED: 18
Dope preparation-

DMAc + Cellu-OH
Of mixture

Distillated at 165 0c
In nitrogen
atmosphere,30 min

Reduce temperature Stirring continuously
at 80 0c for 40 min Solution is ready
at 100 0c +Licl

CONTINUED:
3. Ionic liquid 19

Salt that melt at temp. below 1000c called as ionic liquid or green solvent.

Properties-1. Chemically & thermally stability.
2.Non-flammability

Generally contain imidazoloium, pyridinum or organic ammonium cation.
The anion could be chloride ,bromide.
Room temp. have more stronger complex.


CONTINUED:
 Cellulose can be dissolved, solubility of cellulose and its properties can be easily 20
controlled by selection of ionic liquid compound.

 At high chloride concentration is responsible for breaking for hydrogen network .
Thus allowing to dissolve cellulose.
 Dope solution can be easily precipitated by the addition of water, ethanol or
methanol
 The regenerated cellulose is hardly degraded and has almost the same degree of
polymerization and polydispersity as the initial cellulose.
 The ionic liquids can be recovered and reused by various methods, such as
evaporation, ionic exchange, reverse osmosis and salting out.


Ammonia /ammonium thiocyanate : 21
Advantages-1. It has an excellent dissolving power as a solvent
for cellulose.

2.Low cost and readily available.

3.Due to boiling solvent 700c ,as a result it can handled easily.

4. No degradation of cellulose.
5.Solvent preparation (NH3/NH4SCN 24.5/75.5) is very simple.


Dope preparation: 22
Require amount of
cellulose +Ammonia +
Ammonium thiocyanate
Mix it

Place it and
mixed with hand
& homogenized

mixture pass
The bag place in through shearing Increase temperature up
cool place at -33 force at room to 40 0c to make solution
0c for few mins
temperature


Amine salt: 23

Hydrazine Ethylenediamine

Two component system (amine salt) consisting of hydrazine or ethylenediaine and various
Thiocyanate salt such as LIScN, NaScN or KScN that dissolove cellulose pump.
A high concentration 40-50% salt is generally required to obtain high concentration up to
18-20% spinning dope.


Dope preparation : 24
Solvent
+cellulose in
polyethylene
bag

Place at -10 0c
for few hours

Apply shearing
Increase
force for 30 min
temperature
to dope
up to 50 0c
preparation

CONTINUED: 25

 Ethylenediamine/KSCN System is the best solvent.


Development in process technology &process 26
chemistry:
Difficulties-1. Old batch-wise process to continuous or semi-continuous
system. In the batch wise process the sequence of steeping ,pressing
and ageing took up to 40 hr. to produce alkali cellulose.

2.Difficulties in ensuring contact temp. and equal ageing time,
because a large no. of bins involved ,frequently resulted in a variable
degree of polymerization in the resultant viscose.

Process- 1. In the modern plants bales of wood pulp are auto-
matically fed into continuously sulrry.
2. By the use of catalyst and elevated temp during ageing have
reduced to time 4-5 hr.
3.Xanthation process has been improved with the use of wet churns.In
which both xanthation and mixing carried out.

CONTINUED: 27
4.More recently the introduction of back flush filters with non-woven metal
screens has improved the filtration efficiency with the new non woven metal
screens the filtration amount has increased 50 fold. Thus the filtration size
could be decreased.

5. Completely automatization.

Process chemistry- Reduction in chemical used such as
CS2,NaOH and H2SO4

Process-SINI process-Its also known as double steeping process
operation of aged alkali cellulose at lower alkali concentration
(10-12%).A second steeping after ages reduces the amount of
free alkali in the crumb with out changing the bound alkali. This
reduces the formation of by-product and improves distribution
of xanthate group to get a stable viscose

CONTINUED: 28
Other process-1.Activation of cellulose with liquid ammonia
prior to xanthation also reduces CS2 consumption by as
much as 33%.

2. Xanthation in the presence of surfactants like Berol spin
decreases CS2 consumption without effecting the quality of
rayon produced.The addition of urea to the steeping
solution result in change viscosity of viscose, the ripening
time decreases and a high degree of xanthate substitution
is obtained. It is presumed that compex with the alkali
cellulose is formed which control the side reactions
occurring during xanthation process.


CONTINUED: 29
 A reduction in viscosity of viscose allow for an increases in α-cellulose content &
leads to reduction in consumption of H2SO4 & also less amount of energy is required
for transport, filtration.

Advantages-1. This process yield a 30% reduction in CS2 useage,
reducing CS2 emission.

2.It is claimed that even interior-grade pulp can be used with this process
to yield a good quality of viscose fibre.

3.Due to removal of low molecular weight fractions. In the second
steeping as well as increased rate of swelling of alkali cellulose which
increases the reactivity to CS2 during xanthation with this process a
higher CS2:NaOH ratio(9:4.5) can be used in viscose solution which result
in a substantial reduction in H2SO4.

Conclusion: 30
 Development in process technology & process chemistry are much environment
friendly

 Polynosic fibre show high crystallinity ,high resistant ,high dimension stability.

 By different solvent ,spinning specifications ,modifiers . We can make end use
product.

 Solvent is very costly so need to recycle it.

 Ethylenediamine/KSCN System is the best solvent.


References: 31
1. Spinning of cellulose from N-methyl morpholine N-oxide in the presence of
additives, polymer 1990,vol 31,march.
2. Structure formation of regenerated cellulose materials from NMMO solutions,
progress in polymer science 26(2001).
3.Novel cellulose solvent system and dry jet wet spinning of cellulose ED/KSCN
solution, by hyun jik cel (thesis)
4. www.google.com
5. Life cycle assessment of man-made cellulose fibres, lenzinges berichte
88(2010)
5. Modified polynosic fibres.
6. Handbook of fibre chemistry, M lewin & E.M pearce.
7. V.B Gupta & V.K Kothari ,Manfacturing of fibre technology 481-513.


32


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