1. health and fitness
2. weight loss

Indian Journal of Fibre & Textile Resea rch
Vol. 21, March 1996, pp. 79~89
Recent advances in the development of silk-like polyester fabrics
Pushpa Bajaj
Department of Textile Technology, Indian In stitute of Technology, New Delhi 110016, India
Silk-like po lyes ter fibres ha ve been one of the most important targets for the textile industry in the present
era. Key technologies starting from fibre engineering to finishing process have been illustrated for producing
silky polyester fabric s with bulk y hand touch and superior drape. Effects of polymer additives, delustrant s,
surfact a nt s, e tc. on a lkaline hydro lysis of polyester fabrics for improving silk-like characteristics have a lso
been highl ighted.
Keywords:
Alkaline hydrol ysis, Bicomponent fibres , Micro-crator pol yes ter, Microfibrcs. Shingosen,
Silk-like pol yes ter. Spinning tec hn o fogies
by simulating the characteristic features of silk fibre ,
I Introduction
Polyester fibre has conquered the leading position VIZ.
• The design of cross-sectional shape,
among the three major synthetics because of its
• Enhancement of drape characteristics through
excellent properties such as high strength, abrasion
resistance, wash and wear, and wrinkle-free
weight reduction of conventional pol yes ter
fibres or by the development offine denier fibres.
characteristics. However, polyester does have some
and
deficiencies, i.e. it is hydrophobic and oleophilic. Due
to this, 1t is easily soiled and accumulates the static
• Creation of moderate bulk and soft handle.
History of the progress made in silk-like pol yester
charge. Oily stains are also difficult to remove .
Polyester fabrics are, therefore, not as comfortable as fibres is given in Table I and the technologies
natural fibre fabrics.
developed for the production of Shin-Go sen (Shin =
On the basis of consumers' comments, Latta I has new & Gosen = synthetic fibre) in Japan are
. also mentioned the following limitations of illustrated in Fig.l .
synthetics:
In this review, the va rious processes developed for
• Unnatural hand and unfamiliar skin cqntact
sensations,
Table I- Histpry of the progress of silk-like polyester fibres9
• Unpleasant thermal sensations,
Generation
Properties
Idea of technology
• Lack of moisture absorbancy,
Brightness
• Clamminess of fabric in contact with skin, and Copy of natural Lustre
Drape
Shape of cross-section
silk
• Static related problems.
To overcome some of these problems, blending
with natural fibres, particularly cotton, gained a big
market. An extensive work related primarily to
polyester fabrics comfort has been published in
excellent reviews 2 - 6 in the recent past. From the
wearer trials using knit fabrics it was reported that the
comfort of polyester was substantially improved by
cross-section variations, pressure jet treatments and
certain engineering modifications of the ·polyester.
The Japanese industry has also made great strides
in improving the comfort and aesthetic properties of
I
"Sh'mgosen " h as b een
po Iyester. S I'lk - I'k
I e po yester
developed by different technologies? Various
approaches have been tried to develop silky polyester
(trilobal, triangle)
( 1964-)
Rustle of clothes
Copy of silk
touch
(1975-)
Fullness and softness Shrinkage-mix fibres
Drape
Structure of crimps
Delicacy
Persuit for the
aesthetic
properties
(1979-)
Persuit for
micro shape of
cross-section
(1983-)
Silky-spun like
Naturality
Dry touch
Air texturing
False twisting
Thick and thin ya rns
Lustre
Fullness and softness
Drape
Rustle of clothes
Naturality
Tri-petal like crosssection
Microfibres
Cross-sectional shape
Very nice ta ilored
Aim for high
sense and quality fini sh characteristics
(1988-)
Liveliness
Development of
new polymer
80
INDIAN J. FIBRE TEXT. RES., MARCH 1996
Shrinkag~-mix filam~nt - - - - i High shrinkage yarn
t - - - { Difference in
fibre length
High spQed spinning yarn
Spontaneous extension
Polymer modification
------I
Polymer with partic~s
from catalyst residue
Polym~r with added
particles
Brightness
'"r---Fullness and
softn~ss .
)----.Lu~e
r:s-ur--:f:-a-ce-ro-u-g-:-hn-e-s....
s\.--L- Dee p co 10 ur
Vi vid colour
Dry hand
Special spinning - - - - - - - 1
Denier mix
Non-circul~r crosssection
Conjugated yarn
I ' - - - { Shape of (ross - ' f f - - - Soft hand
He<lvy denier
Fine dQnier
I-----{
section
Rustle of (Iothes
Difference of
denier
'c---\--
Spread anti-drap!
Texturing - - - - - - - - - - 1 False twisting
Air tuturing
1----;rr;(o~m;;;m;;ii~ng~l;in;;;g-:-·-~~r\--~ Naturality
Afttr treatment - - - - - - - 1 Twisting
(austic reduction
After finish
Fabric density
l---'~S;;tr~u::-ct:tu:r:e--:of;-""""":----+-~S t iff ness
dagree
fabrics
Springy properties
Drape
Fig. I- Fabric properties of Shingosen and key technologies
51 L~
SI LOOK ROYAL
I
I
1
fI
1\
..... 1...-
\I
/
"
o
SILK
I" / '"
--
I
\../
\V
1/
10
20
30
0
10
20
30
0
10
20
30
Tim~Jms
fr----o
A-Sompl, 'tobric I
B- '" ie rophont
c- W, ight , SOOt 14 em I
0-"'0_ '1Oem Imin I
Fig. 2- Wave of ru stli ng sound of three typical fabrics
the production of silk-like polyester have been
highlighted . Special emphasis has been made on the
saponification or caustic reduction treatments for
prod ucing si lk-like polyester fabrics .
2 Cross-sectional Shape 7 The shape of a silk fibre after removing se ricine
during scouring is triangular. For imitating the
triangular shape of silk fibres, polyester fibres ha ve
<)
been developed with triangular or trilobal
cross-sections. This resulted in lustrous polyester
fibres. The appearance also changed from that of
plastic to a silk eq ui valent.
PET fibres with a tripetal cross-section have also
been developed to provide silky look . There is a
groove at the tip of each lobe oftrilobal cross-section.
This unique cross-section is believed to bring the
rustling so und to polyester fabrics when friction
occurs among them. The wave of rustling sound of
three typical fabrics has been compared (Fig.2) .
'Sillook Royal' has, therefore, not only the lustre of
natural silk, but also a rustling sound similar to that of
the natural sil k.
Polyester fibres wit h petal-like cross-sectio ns ha ve
been produced by conjugate spin ning technologylo.
In this process, small a mounts of easily hydro lysable
components are located at the tips of each lobe.
During saponification or ca ustic trea tment, this
component gets dissolved and grooves a re formed.
The width and depth of each groove can be controlled
at the sub micron level.
3 Differential Shrinkage Polyester Yarn
One o f the techno logies to bring out silk-like bulk
and handle in PET is to use differenti a l shrinkage
polyester component yarn. T wo method s have been
tried to produce different shrinkage levels in mixed
BAJAJ: SILK-LIKE POLYESTER FABRICS
yarns. One is a parallel sort of mixture, just like
Quiana (nylon ya rn produced by Du Pont) and the
other is a se rial kind (Fig. 3).
The parallel structure is made by mixing fibres of
different shrinkage levels either by using different
polymer fibres or by mixing fibres of polyester drawn
at different temperatures. The serial type is produced
by random heat setting along individual fibres during
fibre processing 1 I . The fibres shrink randomly with
TYPE
PARALLEL
Mi Xlld Yarn of
I'ETHOO D~rmt Shrinkage
Lt'it I
SERIAL
Rnndom Hrat- set
AmollJ Individual Fibre
.. _........................................ ... ......
YARN
I--------:--+------:::---~
.~.
'"'-./ .... ..../V.....
--v-..... J"'v... _.
~ ....... "'-." .....
~
""'"
81
the heat treatment. In the parallel structure, higher
shrinkage components form a core, and lower
shrinkage components form waves or loops around
the core. On the other hand , in the serial type
structure, higher and lower shrinkage parts are
di stributed randomy in the yarn and there is no core
(Fig.3). The resulting fabric from serial type
arrangement of different shrinkage level fibres
showed a more natural silk look than the parallel
type.
Uchida 12 has also demonstrated the role of
shrinkage in producing Shingosen. Fukuhara 7 from
Toray Industries has shown that for the production pf
Shingosen, initially dry heat shrink process was tried
and later the wet-heat shrink process. But, a double
shr'unk fabric appears to be closest to silky textiles
(Fig. 4). It has comparatively hi'gher bulkiness and is
more airy and soft. Sillook Sildew, produced recently,
is a double shrunk fabric with large waves or loops on
the surface of the fabric.
For making double shrinkage fibres, the
researchers have to first design the polymers by
selecting a suitable comonomer and its content for
accomplishing the desired shrinkage level. Degree of
polymerization (DP) should also be controlled as a
polymer with higher DP is likely to provide higher
shrinkage.
Parallel yarn str ucture
After screening the polymer with a desired
composition and DP, the fibres can be made from two
, or more polymer components by the same spinneret
from different nozzles. This kind of conjugate
spinning provides fibres with in situ differential
shrinkage. So, additional step for mixing fibres as
discussed earlier is not required and the resulting
Strial yarn structure
mixture directly produced from spinning line is
Fig. 3- Two kinds of shrinkage. Parallel a nd seri al ya rn
uniform.
structures
~I
Double shrin k type
----,..........
I ____~D_r_y_-_he_a_t_s_h_ri~nk~tY_p_e
~ ~~
Grey
fabric
Fig, 4
'-----
__
~_~
1st
2nd
Final
hQat-set
ntat-set
heat-~t
scouring
caustic
dyeing
reduction
Shrinkage d'iagram of polyest .r fab ri c after caustic
treatment
4 Topical Finishes
Finishes also modify the tactile, static and moisture
related properties of polyester fabrics. The
enhancement of polyester properties by treatment
with aqueous sodium hydroxide was recognized soon
after the invention of polyester 13 . Treatment of
untextured yarn fabric with alkali produces softer
tactility with a less synthetic hand . A calendar,
heat-set' and caustic soda saponified fabric was
patented a few.years later as the treatment was said to
produce high fabric lusture without paper-like ,
handle l4 .
Polyester undergoes nucleophilic substitution and
is hydrolyzed by aqueous sodium hydroxide . The
hydroxyl ions attack the electron-deficient carbonyl
carbons of the polyester to form an intermediate
anion,
82
rNDiAN 1. FIBRE TEXT. RES., MARCH 1996
Table 2- Summary of alkalization processes
SI.No . Materials
2
3
Formulations
Conditions
Remarks
Po lyeste r fa bric
0.3% NaOH in ethano l
50% pick up and
stored
Weight loss 2 1%
Po lyes ter fabric
Kodel IV drawn
P ET fibre &
hea t-set
6% NaOH in 5% ethano l
-do-
-do-
5- 15% sodium hydroxide
lOOT, I h
90 e
Weight loss 12-43 %
OH < t-but ox id e
< sec. pro pox id e
< methoxide
< ethoxide
Wei ght loss
12. 15-29.7 %
4
Terene fibres
1. 5 in . sta ple le ngth
5- 15%
5
Trevi ra fabric
Batch: 1.5-2 % NaOH
0.2% di spersing agent
H .T. beam: 0.05 % accelerator
Pad-ba tch: 19% NaOH
0.2% wetting agent
C ontinuo us: 19% NaOH
0 .2% accelerator
90 g/m2
aOH
0
I h
I lOT, 20 min
Weight loss 18%
R.T. fo r 24 hr
batching
120 e I min
Silk-like handle
Silk-like fini sh
More unce rtain
16-20% weight loss
Weight loss, %
17.5
20.1
21 .9
24.4
Wei ght loss 15 °;.)
Silk:like effec t
0
6
Textured P ET fi la ment
l. 87 oz!ya rn
Celenese
Fortrel 73 1
15% NaOH
0.56 o r 0.87 % quate rnary
Lauryl dimethyl ben zyl
a moniull1 chloride
Bath ratio 10: 1
30-60 min
60 min
30 min
60 min
7
Po lyes ter
3% NaOH
95°C
8
100 % Dacron P ET
fa bri c
10%
w e
9
Li ght weight PET
'68.5 g/m 2
Po lyeste r
4 % aO H
4% NaOH + I % accele ra to r
WY., Na O H
90T. 60 m in
M:L: : 1:60
lOOT. 15 min
II
Po lyester c re pe
100 g/m 2
10% NaOH
n. 1% s url~l c tant
IJOT
M : L::1: 30
12
13
Pol yes ter
Po lyes te r
14
Polyester textured yarn
Polyester textured fabric
Polyester
Polyester yarn
PET fibre , fabric
10
15
16
17
18
PET & POY
fibre s
Heat-set delustred
PET fabric
aO H
120min
30T
70T
Weig ht loss
21-23 % aft e r 60 min
20% afte r 15 min
Strength loss
10-70% warp
WI. loss of tex t > flat > spun yarn
Weight loss
STEG > SD EG > SEG
Fle x. rigidit y
STEG < SDEG < SEG
Weight loss 41 %
Weight loss 27 %
Weight loss 26 .8%
Weight loss 18-25 %
Weight loss 23 %
15 %
90T. I h
Weight loss 20-80%
60T
0-70 h
Weight loss
0-90%
Pad-ba tch
Sodium tri eth ylene gl ycolate (STEG»
Sodium d ie th ylene gl yco late (SDEG ) >
Sodium e th ylene gl yco late (SEG)
3-5 % NaOH
5% NaOH
7. 5% Meth o no lic NaOH
10 % NaOH
15 % Hydrazin hydrade
or ethylene diamine
M:L: : I :20
10% NaOH
M :L:: I: 150
2-8 mol NaOH
I % cet yl trimethy l
ammonium bromide
( 1% w / w)
Weig ht loss 10. 1%
Stre ngth loss 29'10
Weight loss 10.5-1 7.0 %
Stre ngth loss 25%
Weight loss
13.74-14 . 11 %
93-1 2 1°e Ih
104T,. 1 h
2 1°C, I h
59T, 1-6 h
BAJAJ: SILK-LIKE POLYESTER FABRICS
Chain scission follows and results in the production of hydroxyl a nd carboxylate end-gro ups.
83
Table 3- Properties of polyester sa mples sapon ified
pad -steam techniques
[Ca ust ic cone .. 150 gi L; Steaming temp ., 102°C]
Sample
No .
Time of
.steaming
(min)
Weight
loss
(%)
Flexural
ri gidity
(mg. em)
5
10
15
20
12.3
15.7
18.6
2 1.1
24.77
11.99
9.28
8.39
6.55
I
2
3
4
5
by
Strength
loss
(%)
7.3
15.8
17. 1
26.2
The effect of ca ustic solution on a PET fabric
depends on the following parameters 15 - 19:
• Concentration of a lk a li ,
• Time and temperature of alka li treatment,
• Use of surfactants,
40r------------------------------,
• Fibre type (composition and cross-section),
and
o~
• Heat se tting.
- 30
The fibre loses weight as the reaction occurs. Over a
\II
\II
wide range of temperature, the relatio n between
o
weight loss and time or sq uare root of residual weight ~ 20
and time has been found to be linear provided that a
large exee ,; of alka li is used so that the reagent is not
large ly comumed during the treatment time. If an
excess oT alkali is not used and its concentration
decreases as the reaction continues, then the weight
loss/time relation becomes exponential. Various
conditions used for saponification and the weight
Treatment Time (h)
reduction for polyester fabrics with aq ueous sodium
Fig.
5Rdationship
between weight loss and treatment time for
hydroxide are listed in Table 2. It has been concluded
polyester fabric treated with aqueous ca ustic soda [( +) regular
that the influence of temperature on the rate of the polyester, (0) regular pol yester havi ng CTAM, ( x ) AMPET
reaction is greater than that of concentration of alka li,
substituted for regular polyester)
which, in turn , is greater than that of time. Use of
quaternary ammonium salts as accelerators for
saponification has also been recommended 6.20.2 1.
In presence ofCEMDA and CTAM, weight loss of
Samples hydrolyzed using 10% aqueous sodi um 24% co uld be achieved on ly in 40 min at 130°C.
hyd roxide a t 60°C showed linear relationship
Correlation between weight loss, strength loss a nd
between the weight loss and the alkali treatment time flexural rigidity (Table 3) points out that the silk-like
(Fig. 5). Further, the addition of a cationic surfactant, soft handle of polyester can be realised 22 when the
namely certrimmonium bromide (cetyl ammonium fabric loses a weight of about 16% and the flexura l
bromide) CTAM, or the replacement of PET with an rigidity reduces to about 9 mg. cm by trea ting with
anionically modified polyester (AMPET) increases 15% NaOH at 130°C.
the rate of saponi fication considerably. G awish and
End group analysis of saponified polyester
coworkers 21 have shown that the rate of hydrolysis of indicates that with increasing weight loss of
polyester crqe fabric in \0 % NaOH (owl) at 130°C saponified polyester, the number of end groups of
was vcry slow and it required six hours to the [COOH] increased and a valu e of 47.10
theoretical weight loss of 24%. However, with the equivalents/10 6g was achieved at 2 1% weight loss
addition of different quaternary ammonium (Fig.6). The number for control being 32.8
surfactants as accelerators, the rate of hydrolysis equivalents/ I 06 g. The increased number of [COO H)
co ul d be enhanced significantly. The activity of the end groups after the saponification suggests that the
quaternary a mmonium surfactants was in the reaction of a lk a li wi th polyester is of hydrolysis with
scission of polyester chain molecules, resulting in
following order:
Cetyl ethyl methacrylate dimethyl ammoni um more number of [COO H) end groups, and confirms
bromide (CEMDA) > cetyl trimethyl ammonium the mechanism of hydrolysis as shown earlier.
bromide (CT AM) < oleyl bis-(2-hydroxylethyl)The data on sa ponified polyester indicates that
both the acc umula ted charge (acceptance potential )
cetyl ammonium bromide.
84
IN DI A N 1. F IBR E TEXT. R ES., MA RC H 1996
Tah k 4
48
250
Sa mple
No.
46
CII
200
.,
c:
o
">"
90
3
5. 24
160
240
..
4
13.5 1
11 5
;J
5
25 .1 4
90
10
e
40 '"
.
'0
c:
38~
c:
0
0
E
W
.
L....J
Cl.
36 ~
u
-<
ci
z
50
34
°0~------~----~12~----~18~----~~
24
0.31
200
30
2U
u
0. 29
(5)
190
Cl.
.. 100
I
(V)
1.6 1
Cl.
I
(% )
II 2
I
42 "'.
-
o
Accepta nce
po ten tia l
2
CII
~150
Weight
loss
44CDO
;J
>
Eifec i ofs url;lce sapo ni fica ti o n o n elect ri c cond uct ivit:
of po lyes ter sam pl es
Weig~t Loss
0.33
Mo isture
(~o I
I
0. 35
0. 37
32
I
Regain, 'I,
Tab le 5- Fi ni s hin g stages of po lyes te r fibre fa brics 15
Sa m ple A
Sa m ple B
Loo m sta te
Loom
Relaxa ti o n in washer
( I lOT. 20 min)
Relaxa tion in jet d ye ing
( I l OT. 20 min)
Hea t-se tti ng in hea tsett ing un it
( 190' C 20 s)
Weigh t reduction
( 16'Yo in 40 gi L NaO H )
Hea t-sett ing
Weigh t red uctio n
(25 % in 40 gi L NaO H )
Dye in g in jet dye ing
mac hine (no'c. 30 min)
D yei ng in jet dyein g
mac hine (130'C. 30 min )
Raising
Ra isi ng
SI a te
( 190' C 205)
Fig. 6--Co rrelations betwee n .weigh t loss. [COO H] end gro u ps
and acceptance pote nti a l in saponified po lyes ter
and 11 /2 (the time fo r ha lf the accumul ated charge to
decay) reduce with increasing we ight l oss~ The va lue
of acceptance potentia l red uced from 200 V fo r
control sa mple to 90 V for the saponified sa mple (25%
weight loss) and the di ssipati on time 11 /2 reduced fro m
240 s to lOs. The data also show that up to about 13%
we ight loss the acce pta nce potenti a l dec reased
rapidl y to 11 5 V and with furth er increase in we ight
loss to 25%, it dropped slowly to 90 V (Ta ble 4). The
reducti on in stati c charge acc umul ati on of the
alk ali-t rea ted polyes ter may be attributed to th e
surface saponi fica ti on of polyester as indica ted by the
inc reased nu mbe r of hyd rophili c [COO H] and O H
end gro ups, wick ing a nd , to a limited ex tent , th e
moisture rega in .
T he effect of th e ca usti c solutio n on a po lyester
fa bric depe nds a lso o n th e fi bre type, fa bric
co nstructi on, and hea t-settin g conditi o ns. Bright
fi bres with rou nd cross-section lose we ight slowly
th an de lustred fib res with mult ilobal cross-sectio n.
Reaso ns fo r thi s di ffe rence in the rate of weight loss
co uld be d ue to the fo llowi ng:
• For a give n linea r densit y, a multil obal fib re
wo uld have a large surface area th an a ro un d
fi bre.
• The prese nce of de lustrant may acce lerate th e
we ight loss of the fib re 23 . 24 .
• For peach like effect. hi gh solubility polymers or
ino rga ni c pa rticles are inco rpora ted in PET
melt, which esse nti all y solubilize or leac h out to
give pit effect on surface, thereby affec tin g th e
feel and hand le of th e fa bric. Thi s radi ca l
alterati on in the surface has bee n ensued by
Japanese to prepare dry touch ya rn . Microcraters res ult in low convex-co ncave co nfig urati on.
• Samples ap pea r to lose we ight fas ter after
tex turin g. Fo r exa mple, th e losses in weight of
non-tex tured ya rn and tex tured ya rn when
treated with 5% ca ustic soda at 104°C for I h were
36% anri 41 % respectively.
Ma tsud aira a nd Matsui 25 have al so studied the
effect of various fi nishing stages after the loom state on
th e fa bric handl e. The di ffe rence betwee n sa mples A
and B is in the stage of relaxi ng and we ight reducti on
(Table 5). The effect of relaxing in a washer is expected
to be greater than that in ajet dyeing machine. Overall,
th e polyes ter fi bre fa bric is remark a bl y softe ned and
fa bric hand le by re laxa ti on, whi ch includes desizi ng,
~h rin k i n g of fibres, and relax ing of in te rn al residual
stress. Subseq uent we ight reducti on d ue to alka li
produces "efrecti ve ga p" betwee n the fi bres/o r ya rn s
and th e splitting of fi bres. T be minimum amount of
weight red ucti on necessary to split fi bres is ex pected
to be a pp rox. 10%. By using di scrimi na nt a nalysis
85
BAJAJ: SILK-LIKE POLYESTER FABRICS
with the primary hand values as variables, a
distinctive zone for silk-like and peach-skin type
polyester fabric can be found.
Sodium hydroxide treatment reduces electrostatic
charge generation from 280 V to 100 V and the halflife
from 5 to 2.5 s. Sol brig and Obendorf2 6 have reported
the considerable weight loss after sapon ifying
polyester fibre containi ng 2% Ti0 2 (Fig.7) and the
pitting on the surface, obsefved through SEM, mainly
axiall y oriented a long the fibre surface. Treating
polyester fibre with 10% aq. NaOH at 100°C (by
steaming) for 45 min produced hygroscopic polyester
fibre.
In another study, a wide range of particles have been
used for creating microvoids on the fibre surface. A
common method is to remove microparticles blended
in the polyester polymer by a lka li treatment. By
applying this method to vario us polyester fibres
containing differt'nt types of particles, fibres with
vario us patterns of voids on surface are obtained.
Originally, this modification was carried out to give
depth of colour.
30
Dull
25
Bright
Serri().jll
~
0
- 20
Clear
'"'"
.3
15
.....
~
.~
'"
~
10
5
OE-__L -_ _L -_ _L -_ _
~
_ _ ~ _ _ ~_ _ _ _ ~
Treatment Time
Fig. 7-Change in weight of clear. bright. semi-dull ai1d dull PET
yarns over 6 h of treatment with \0 % NaOH solution
A method of forming a controlled microcrater on
the fibre surface is proposed. The fibre pretreated by a
;pecific resist is exposed to a laser beam and then
treated again with chemicals. This process can control
the dimensions of voids such as depth , length and
height, and their density.
A blend containing PET and 4% BaS04 (~ 2%, av o
jiam. :::; 9 /-1m) was melt sp un at 1800 m/min to give
290% elongation at Kuraray Co. The fibre wa~ used as
sheath and later on textured by Taslan process and
causticized to give 30% weight loss.
For improved lustre, polyester fibres containing :::;
0.04% inorganic oxide particles and having
birefringence 0.03-0.08 were draw twisted for ~ 0.15 s
at 130-170° and then untwi sted to give textured yarn
with very good lustre 2 7 .
The effect of BaS04 on the extent of saponification
has a lso been studied in o ur laboratories 28 . As the
treatment time and concentration of NaOH
progressively increased from I to 2 h and from 5 to
10% respectively , the loss in weight of the polyester
fibre increased from 3.03% (Po, 5% NaOH , I h) to
15.2% (Po, 10 % NaOH , 2 h) at 90°C bath
temperature.
It can be seen from Table 6 that PoSi loses more
weight over Po or P oSiF 5. This is perhaps due to th e
formation of sodium si licate in the presence of a lk ali.
due to si li cone oil coati ng on PET, which see ms to
acce lerate the sapon ificat ion process. The reduction
in diam.is a lso maximum in PllSi fibres.
After hydrolysis, elongated pits, o ri ented in the
direction of the fibre ax is, on the surface of PllSi F "
sample were noticed . However. unfilled fibres did not
show a ny pits. It was found that the size of the pits
depended on the length of expowre to alk ali, while the
number of pits depended on the concentration of
BaS04 in the fibre (Fig.8). As the treatment time and
a lk a li concentration increased from I to 2 h and 5 to
10% respectively, the pits en larged mainly in the fibre
axis direction. Longer treatment increased th e size of
the pits without changi ng their numbers. H ydro lyt ic
Table 6-Change in weight and diameter of BaSO.-filled polyester fibres after saponification
5% NaOH
Sample
\0% NaOH
2h
I h
Wt loss
%
Ih
Diameter
Wt loss
Diameter
~m
%
~m
39.4
3.03
Po
6.4
. 38.6
PoSi ·
4.{)5
39.1
PoSiF s
Diameter of Po (unsaponified). 40 ~m; PoSi -
38.9
5.0
38 .3
8.3
5.52
38.8
silane coated; PoSiF s -
Wt loss
%
2h
Diameter
Wt loss
~m
'1.
~m
15.2
22.2
18.8
36.8
35 .2
36.04
8.4
38.2
13.4
37.22
10.5
37.94
5% BaS04-filled PET
Diameter
00
0'1
z
o
);
z
;-
::!l
0:1
"
tTl
rri
><
:-i
fii
y')
!:
»
":t
(j
'"'"
0\
Fig. 8- SEM of saponified BaSO"-fi lled PET [( a) No rm al PET, (b) PET fill eu wilh 5% B"SO", (e) PET tilled wilh to'Yt, B"SO", (d)
Saponified norma l PET. (e) Saponified PET ti lled wi th SU!c, 8:ISO", alld (n Saponified PET fi lled with IO'y', 13aSO"1
87
BAJAJ : SILK-LIKE POLYESTER FA BRICS
Table 7- Te nsile properti es of sa ponified po lyeste r fibres
[NaOH conc .. 5% ]
Treatment time
Sample
code
I h
Tenacity
cN /tex
2h
Strength
r<: tenti on
%
Brea king
elongati o n
%
M odulu s
N ' tex
P"
P"Si
38
96.5
21
10
34
87. 1
IH
8.3
P"SiF,
36
97.0
18
11. 2
degrada ti on of the polyester begins a t the surface o f
the fibre an d continues until a BaS04 particle is
exposed (Fig.8). Pits appear to develop from
preferential hydrol ysis of polymer aro und the fill er
particle, locations where alkali can diffuse more easil y
due to hyd rophilic nature of the fill er. Thi s action
leaves an axially-oriented elli ptica l voi d around the
filler particle, forming an entry point for the alkaline
solution to attack polymer beneath the original
surface. Possibl y, the drawin g process used in th e
production of fibres ca uses the pi ts to be ellip tical.
Strength
ret ent ion
Te nacity
eN / tex
36.3
29 .5
35. 1
19
9.5
75. 6
14
7.8
94 ..8
17
10.6
.5:.'../:,
POlyester..q;~t.".
. :rf~(/"
J. •
..,
.h
• ..,ft:· .•
{
. .l "'f'
.....
,f
/-
ct>
'i"
:J!.t!Jzo
Sil ica ~.i"'~
f R','N'
New
$;Jji.~
~("~
The effect of silica particles on the lustre and handle
of po lyester fibres after saponification has a lso been
st udied by Yamaguchi 29. The fine concave and
convex structure is formed by a difference in solubility
in alk al i between the pol yeste r and the particles
uniformly dispe rsed in polyester. For making a fine
concave and convex st ructure of a specific size, firstly
ultrafine particles, which have a-similar refraction
rate to fibrcs and an average di ameter below 100 nm .
are uniforml y di spersed in polyester fibre wi th out
co hesion. Silica has a tendency to cohesion by
hydrogen bond of silica surface. So , silica in water is
stabilized by Na + cation as silica solution. To prevent
silica particles cohesion or agglomeration , silica sol is
mixed with et hylene glycol and particles are stabili zed
and PET is mad e by direct estc rifica ti on method.
92.1
'~':
~.
5 Te nsile Properties
The tenacity, breaking elonga ti on a nd initial
modulus decrease wi th the increase in weight loss due
to sa ponification (Table 7). Tensi le strength retention
in Po fibres is 92% and 73.6% at 5% and 15.2% weight
loss res pectivel y. However, under the same condition s of treatment the percentage strength retenti on
for P"SiF 5 samples is slig htl y better, i.e. 94.8% and
75.4% at 5.5 % and 18.8% weight loss due to
sa ponification .
Modulus
N/tex
%
Brea king
elongation
ala
surface
Alkaline
treatment
Fig. 9- Pieture of the fine concave a nd convex mechanism after
alkaline treatment
Sol-dispe rsed silica as selected particles
P ro[)enics
Silica
So lubilit y rati o a gainst alkali
80
Index of refract ion
1.55
Oi <l me te r( pill)
0.05
Pol yester
1.62
10
~
10
The fibre s containing silica are treated with an
etc hi ng meth od using alkali . Their surfaces are peeled
ofr. Silica's solubili ty ratio against alkali is so ra pid
that a fin e concave and convex structure is formed
(Fig.9).
Kurara y Company ha s dcveloped this fibre as the
super microcrator polyester fibre '-' SN 2000" . Fig.1 0
shows the relation between fibre surface area (BET
method) and alk aline weight reduction . The effect of
microcrator due to alkali treatment o n the depth of
black colour has also been shown. So, at high alkaline
weight reduction , polyester fibre of fine surface
provides not only a deeper colour shade but an
improvement in lustre and ha ndl e of the fabrics .
Toray Industr ies 30 prepared polyester fibres with
mild silk-like luster by polycondensing glyco l slu rries
co ntainin g particles with (RI 1.3-2.0) and average
88
-
INDIAN J.FIBRE TEXT. RES., MARCH 1996 .
1.2 r-- - -- - - -- - -- - - - - - , 1 5
.
...'"
Table 8- Moisture regain , st rength retention and the durability
to washing of the chitosan-treated fabrics 33
~~-.--------r_
Micro-crater polyu.ter
Fabric
E
-0
0
.c;
Add-on
(%)
1. 0
16
E'"
>....
co
'"'"
OJ
d
~
.q:
17
0·8
d
QI
u
..&-._ ._ ._ . - - 0
d
~
::>
Vl
c:
-'"
u
-..vt-
.-:: ...a.-r
..&. .............. __
----------r
J.
co
Untreated
Chitosan-treated
without curing
Chitosan-trea ted
with c uring"
6.6
15.3
6.4
16.7
Moisture Strengt~ Durability to
regain retenti on washing
(%)
(°lc,)
(weight
remained, % )
0.4
I.7
2.4
1.6
2.4
100
75.6
87.6
138.0
150.0
2.5
2.3
95.0
84.4
Alkali trea tment: 10% Sodium hyd roxide, 90 min, 60' C
C uring condition: 130' C, 90 min
Regular polyesf~r
Alkaline
Weight Reduction
(%)
Fig. I O-Relationships between the surface area, blackness and
a lkaline weight reduction (Black dyed Georgette fabric)
primary particle diam.45 J.1m and average secondary
particle ciiam.350 J.1m with polyacids to form PET,
melt-spun and drawn to give trilobal fibres with silica
content of 0.01-0.4% .
For rapidly hydrolyzable PET fibres , melt blending
of PET with 2-10% sulfo containing aromatic diol(l)
was carried out by Teijin Ltd 3J .
H-t 0 C2H4)mO ----@{-OC C2H4 0
(I)
~H
S03 M
.
application and the nature of amine. Amide
formation results in chain scission. Amines were
found to reac t and attack amorphous as well as
crystalline regions. It appears, according to Zironian,
that the weight loss/time curves are affected by the fine
structure of the polymer and the location of attack.
7 Aftereffects
o Deterioration in tensile properties
o Broadens dye class for PET
o Improved wettability
o Oily soi l release improved
o Good antistatic property
o Increased moisture regain
o Cracks developed on fibre surface
o Brittleness increased
o Flex life decreased
o Shift in endothermic melting peak to lower
temperature
o Improved pilling resistance.
References
A woven fabric of the fibre showed weight
reduction rate of 41 % / h in boiling aqueous NaOH.
Ester Co. Ltd has developed polyester fibre with
superior softness and gloss by dispersing 0.5-20%
EPR in PET fibre. M~lt kneading was carried out and
then spun into fibre 32 •
Matsukawa et al. 33 have shown the recovery in
tensile strength of alkali-treated polyester fabrics by
subsequent treatment with chitosan (Table 8). The
chitosan was fixed to the surface of saponified PET hy
the reaction of the carboxyl groups .arid the amino
groups of the chitosan molecu·les.
6 Weight Reduction by Amines 1s
The reaction is similar to that by NaOH . The
location of attack varies and depends on the mode of
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5 Zeronian S H & Collins M J, Text Chern C%r . 20(4) (1988)
25 .
6 Matsumoto M, Indian Text l . (Jan. 1991) 'J4 .
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14 Gajjar N J , U S Pat 2,828,528; I April 1958.
BAJAJ: SILK-UKE POLYESTER FABRICS
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16
17
18
19
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21
22
23
24
25
Zeronian S H & Collins M J, Text Prog, 20(2) (1989) 70.
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26 Kurara y.£:"o .. Jap Po/ 07,90,736; C/refll Airs/I', 123 (1995)
I I 5250g.
27 Toray Ind, Jap Pat 06,322.625; Chem Abstr, 122 (1995)
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190257x.
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