Alkaline Dissolution and Dyeing Properties of Sea...
Transcript of Alkaline Dissolution and Dyeing Properties of Sea...
1995
ISSN 1229-9197 (print version)
ISSN 1875-0052 (electronic version)
Fibers and Polymers 2015, Vol.16, No.9, 1995-2002
Alkaline Dissolution and Dyeing Properties of Sea-island Type Polyethylene
Terephthalate Ultramicrofiber Knitted Fabrics
Hodong Kim, Hyun Sung Kim, Young Ki Park, and Jung Jin Lee*
Department of Fiber System Engineering, Dankook University, Yongin 16890, Korea
(Received March 31, 2015; Accepted July 20, 2015)
Abstract: Sea-island type polyethylene terephthalate ultramicrofibers with a single fiber diameter of ca. 600 and 800 nmhave been produced over the last 4 years. Alkaline dissolution behavior and dyeing properties of the ultramicrofiber fabricswere investigated. It was found that the dissolution ratio was dependent upon temperature in the alkali treatment. When thefabric was treated with 1 wt% sodium hydroxide solution at 95 oC, the dissolution ratio reached the theoretical value in about30 min. Alkali dissolution behavior could be monitored indirectly by the cationic dye staining method and observed directlyby SEM analysis. The color yield of the ultramicrofiber fabric dyed with disperse dye was dependent on the dyeingtemperature and K/S value decreased as the dyeing temperature increased. Build-up property was generally good and K/Svalue of dyed fabric from ca. 800 nm fiber was higher than that from ca. 600 nm fiber. Wash fastness was poor to moderatefor ca. 800 nm fabric and poor for ca. 600 nm fabric. Light fastness was very poor.
Keywords: Sea-island type polyethylene terephthalate, Ultramicrofiber, Alkaline dissolution, Cationic dye staining, Disperse dye
Introduction
Polyethylene terephthalate (PET) fibers, which show great
chemical resistance, wash and wear properties, and heat
stability, are used in many applications such as clothing and
tire cords [1]. Microfibers refer to synthetic fibers finer than
about 1 denier per filament (dpf) [2]. Microfiber fabrics are
used in various applications, for example, athletic wear,
suede product, wiping cloth, and industrial filter because of
their specific characteristics including large surface area,
enhanced drape, luster, softness, and water or oil absorbency
[3,4].
Direct spinning and conjugate spinning are two methods
for producing microfibers. Microfibers produced from direct
spinning, in which single component filaments are extruded,
are highly uniformed, although the fibers have limited
fineness, typically in the range of 0.2-0.9 denier [4,5]. In the
case of conjugate spinning, two technologies, namely
separation and dissolution, have been devised. In the separation
technique, bicomponent filaments, typically comprising
polyamide and polyester, are extruded through spinnerets.
After weaving or knitting with filaments of this type, the two
different components separate by physical or chemical
treatment giving microfiber fabrics. Dissolution technique
also involves the spinning of bicomponent filament. The
bicomponent filament contains several ‘island’ components
embedded within a ‘sea’ component. After the filaments are
assembled to a fabric by weaving or knitting, microfiber
fabrics are obtained by dissolving and removing the ‘sea’
component such that only ‘island’ component remains [6-8].
These sea-island type microfibers are known to have finer
denier (<0.01 dpf) than microfibers from other types of
technique.
In the case of sea-island type polyester microfiber, the
regular polyester is commonly used as an ‘island’ while
alkali-soluble polyester is used as ‘sea’ component. When
the alkali-soluble polyester is dissolved out by the treatment
with alkaline solvent, the polyester island remains and forms
the very fine fibers [6]. It is important and difficult to
suitably remove sea component and reveal island component
by alkaline treatment [9].
Several studies on alkaline dissolution and dyeing properties
of sea-island type microfiber have been reported on wide
range of fineness of microfibers (0.01-0.2 dpf). Park et al.
[1] reported the effect of alkaline dissolution on physical
change of 0.01 denier microfiber. Koh et al. [10] or Cho and
Lee [11] reported alkaline dissolution and dyeing behavior
of microfibers, the fineness of which was ranged from 0.2 to
0.01 dpf. In early 2010s, sea-island type PET ultramicrofibers
with the diameter of a single fiber being about 800 nm
(0.007 dpf) or 600 nm (0.004 dpf) have been produced. As
these ultramicrofibers are known to contain more than 330
(800 nm) or 630 (600 nm) island components respectively, it
is expected that the dissolution of the sea component from
the fibers should become more difficult than common
microfibers. For example, Cho and Lee [11] reported that
0.06 and 0.01 dpf sea-island fibers contained 36 and 169
islands respectively. In the previous studies [12,13], we
reported alkaline dissolution behavior and dyeing properties
of knitted fabrics manufactured from sea-island type PET
ultramicrofiber of ca. 800 nm. Up to date, little research has
been reported for the ultramicrofiber of ca. 600 nm.
In this study, alkaline dissolution and dyeing properties of
knitted fabric from sea-island type PET ultramicrofiber of
ca. 600 nm or 800 nm were investigated. Alkaline dissolution
behavior was assessed by dissolution ratio measurement,
cationic dye staining method, and scanning electron microscopy
(SEM) analysis. Effect of dyeing temperature on color yield*Corresponding author: [email protected]
DOI 10.1007/s12221-015-5250-9
1996 Fibers and Polymers 2015, Vol.16, No.9 Hodong Kim et al.
was discussed and build-up of 600 nm or 800 nm ultra-
microfiber was compared. Wash and lightfastness were also
evaluated.
Experimental
Materials
Two circular knitted fabrics (interlock) prepared using
100 % sea-island type PET ultramicrofiber were obtained
from KMF Co., South Korea. The composition of each
fabric is shown in Table 1.
Three disperse dyes, Foron Yellow Brown RD-S, Foron
Rubine S-WF, and Foron Blue RD-E were obtained from
Clariant, Co. The cationic dye, Doracryl Orange R 400 %
(C.I Basic Orange 22) (Scheme 1), was obtained from
M.Dohmen Korea, Ltd. and used without purification. All
chemical reagents for alkaline dissolution or dyeing were of
general laboratory grade.
Alkaline Dissolution
Using a 50:1 liquor ratio, a 100 ml alkali bath containing
sodium hydroxide (NaOH, concentration 1 wt%) and
penetrating agent (1 wt%) was prepared. The ultramicrofiber
fabric samples were alkali treated at 95 or 100 oC for 10-
60 min in a laboratory IR-dyeing machine (DTC-6000,
DaeLim Starlet Co., Korea). Each beaker was removed from
the IR-dyeing machine at 10 min intervals and the fabrics
were neutralized with acetic acid and rinsed (Figure 1). After
drying at room temperature for 24 h, the fabrics were
weighed before and after alkali treatment. The dissolution
ratio was calculated by means of equation (1).
Dissolution ratio (%) = (a − b)/a × 100 (1)
where a: weight of fabric before alkali treatment (g) and b:
weight of fabric after alkali treatment (g)
Scanning Electron Microscopy
Scanning electron microscopy (SEM) of the ultramicro-
fiber fabrics before and after alkali treatment with 1 wt%
NaOH aqueous solution at 95 oC was carried out using a
JSM-6700F instrument (JEOL, Japan). The samples were
cryogenically fractured in liquid nitrogen and then coated
with gold by vapor deposition using a vacuum sputter before
SEM observation.
Cationic Dyeing
Dyebath was prepared with the cationic dye (1 % o.w.f)
and buffered at pH 5 with sodium acetate (0.05 M)/acetic
acid. The PET ultramicrofiber fabrics untreated or alkali
treated with 1 wt% NaOH aqueous solution at 95 oC for 10-
Figure 1. Alkaline dissolution profile of sea-island type PET
fabrics.
Scheme 1. Structure of C.I Basic Orange 22.
Table 1. Yarn composition and theoretical dissolution ratio of sea-
island type PET ultramicrofiber fabrics
Sample Yarn composition
Sea-island
ratio
(Co-PET:PET)
Theoretical
dissolution
(%)
N800 Sea-island type PET, 70d/18f,
331 islands, 0.007 dpf
40 : 60 40
N600 Sea-island type PET, 50d/12f,
631 islands, 0.004 dpf
40 : 60 40
Figure 2. Dyeing profile of ultramicrofiber PET fabric with
cationic dye.
Alkaline Dissolution and Dyeing of PET Ultramicrofiber Fabric Fibers and Polymers 2015, Vol.16, No.9 1997
60 min, were dyed in the prepared dyebath with a liquor-to-
goods ratio of 20:1. Dyeing was performed at 80 oC for
20 min in a laboratory dyeing machine (Figure 2). After
dyeing, all the samples were soaped with soaping agent
(Protesol DSL, 1 g/l), rinsed and dried at room temperature.
Disperse Dyeing
The PET ultramicrofiber fabrics alkali treated with 1 wt%
NaOH aqueous solution at 95 oC for 40 min, were dyed with
three disperse dyes in a laboratory dyeing machine. The
dyebaths were prepared with disperse dye (0.5-5.0 % o.w.f.)
and dispersant (1 g/l), and buffered at pH 5 with sodium
acetate (0.05 M)/acetic acid. Liquor-to-goods ratio was 20:1.
Dyeing was commenced at 40 oC. The dyebath temperature
was raised at a rate of 1 oC/min to 130 oC, maintained at the
temperature for 40 min and cooled (Figure 3). Instead of
130 oC, different dyeing temperature such as 110 or 120 oC
was applied to investigate the effect of dyeing temperature
on color yield. The dyed fabrics were then reduction-cleared
at 80 oC for 20 min with NaOH (2 g/l) and sodium hydrosulfite
(Na2S2O4, 2 g/l).
Measurement of Color Yield and Fastness
The K/S values of the dyed fabric were measured on a
spectrometer (Coloreye 3100, Gretag-Macbeth, USA) with
D65 standard illuminant and a 10 o standard observer.
According to the Kubelka-Munk theory, K/S value from
surface reflectance of the maximum absorption wavelength
is given by equation (2).
K/S = (1 − R)2/2R (2)
where K: absorption coefficient, S: scattering coefficient,
and R: reflectance (0<R≤1).
The dyed fabrics were heat-set at 180 oC for 60 s and
tested for fastness to washing (ISO 105-C06/C1S) and light
(ISO 105-B02). The shade change, together with the staining
of adjacent fabrics, was rated according to the appropriate
ISO grey scale and light fastness was rated using ISO blue
scale.
Results and Discussion
As shown in Table 1, the sea-island type ultramicrofiber in
the present study is composed of regular PET (60 %) as an
island component and alkali-soluble PET (40 %) as a sea
component. The alkali-soluble PET, or Co-PET, is a copolymer
containing 10-15 wt% sulfonated isophthalate, as shown in
Scheme 2. The sulfonate group is considered to assist the
dissolution of polymer by NaOH aqueous solution and
disrupt the crystallinity of the polymer by the bulky group,
which results in easier dissolution when compared to the
Figure 3. Dyeing profile of PET fabric with disperse dye.
Scheme 2. Structure of alkali-soluble PET.
Figure 4. Cross-section of sea-island type PET ultramicrofibers;
(a) N800 and (b) N600.
1998 Fibers and Polymers 2015, Vol.16, No.9 Hodong Kim et al.
regular PET [10,14,15].
The cross-section of the sea-island type PET ultramicrofiber
is shown in Figure 4. The filament of N800 and N600
contained 331 and 631 island components, respectively.
Dissolution Ratio
The effect of alkali treatment temperature on the dissolution
ratio of N600 is shown in Figure 5. The dissolution ratio of
N600 at 100 oC increased more rapidly with increasing
treatment time than the dissolution ratio at 95 oC. It is well
known that alkali hydrolysis of the sea component readily
occurs at higher temperature. The theoretical dissolution
ratio required for the completion of dissolution of the sea
component in N600 is 40 % as given in Table 1. The
dissolution ratio of alkali-treated N600 at 100 oC reached its
theoretical value between 20 and 30 min, while that of
alkali-treated N600 at 95 oC reached in 30 min. The practical
dissolution ratio continued to increase after reaching the
theoretical values in both cases. This suggests that the island
component should also have been dissolved in the excess
treatment time. Again, it is important to find an optimum
condition of alkaline treatment in order not only to obtain
well-revealed island ultramicrofiber but also to avoid
undesirable damage to the island component.
The alkaline dissolution behavior of N600 was found to be
similar to that of N800 from the previous report [13]. Thus,
dissolution ratio of alkali-treated ultramicrofiber fabric was
dependent on alkaline treatment temperature as well as
treatment time.
Cationic Dye Staining
Sea component of sea-island type PET ultramicrofiber is a
copolymer containing sulfonated isophthalate. This sulfonate
anionic group has a substantivity to cationic dyes so that the
sea component can be dyed or stained with cationic dyes by
electrostatic attraction. On the other hand, the island component,
which is a 100 % hydrophobic PET homopolymer, is hardly
dyed by cationic dyes. Therefore, it is possible to monitor
the dissolution behavior of the sea component by cationic
dye staining after alkali treatment [6]. Untreated or alkali-
treated PET ultramicrofiber fabric with 1 wt% NaOH aqueous
solution at 95 oC for 10-60 min, were dyed with a cationic
dye. Figure 6 shows the K/S values of N600 according to
alkali treatment time. The untreated fabrics exhibited high
K/S values by cationic dye staining, which suggested that
there should be lots of sea component in the fabric. The K/S
values decreased as alkali treatment time increased, and
finally levelled off after ca. 30 min. The decline in K/S
values suggests that the sea component would be dissolved
out by alkali treatment and only a small amount of cationic
dye could be adsorbed to the fiber. There was no marked
decrease in K/S value after 30 min which might indicate that
only the island component should remain, with almost all of
the sea component being removed from the fiber. The
levelling-off point was ca. 30 min, which coincided with the
optimum time of alkaline treatment at 95 oC from dissolution
ratio measurement in Figure 5. Thus, the cationic dye staining
method was found to be a good method for monitoring alkali
dissolution behavior of sea-island type ultramicrofiber fabric.
Surface and Cross-sectional Morphology
Figure 7 shows SEM images of ultramicrofiber fabrics
(N600) before and after alkali treatment with 1 wt% NaOH
at 95 oC. As the alkali treatment time increased, the island
components were gradually separated from one another.
After 20 min of alkali treatment, several island components,
especially outer part of the sea-island fiber, were separated
in the cross-sectional view, which should be attributed to
dissolution of the sea component. However, inside of the
fiber, a large portion of sea and island components remained
Figure 5. Effect of alkali treatment temperature on the dissolution
ratio of N600.Figure 6. Cationic dye staining of PET ultra-microfiber fabric
(N600) as a function of alkaline treatment time.
Alkaline Dissolution and Dyeing of PET Ultramicrofiber Fabric Fibers and Polymers 2015, Vol.16, No.9 1999
Figure 7. SEM images of N600 before and after alkaline treatment with 1 wt% NaOH at 95 oC; (a) untreated, (b) 20 min treatment, (c) 30 min
treatment, and (d) 40 min treatment.
2000 Fibers and Polymers 2015, Vol.16, No.9 Hodong Kim et al.
without separation. More island components were separated
after 30 min, although still some island components appeared
not to be separated from a surface and cross-sectional view.
From the results of dissolution ratio and cationic dye
staining, optimum alkaline treatment time was 30 min when
using 1 wt% NaOH at 95 oC. However, sea components
were not found to be completely dissolved from SEM data.
It seems that there are so many and highly packed island
components (631 islands) that the alkaline solution cannot
permeate the inside of every single fiber and dissolve all the
sea component in 30 min at this condition. After 40 min,
much more island components were separated when compared
to 30 min. But island components did not seem to be fully
separated. In case of N800 which has less island components
(331 islands) than N600, island components was completely
split after 40 min with the same alkaline treatment condition
(1 wt% NaOH at 95 oC) as shown in Figure 8.
Dyeing Properties
In order to investigate the dyeing properties, the sea-island
type PET ultramicrofiber fabrics were firstly alkali treated
with 1 wt% NaOH aqueous solution at 95 oC for 40 min, and
then dyed with commercial disperse dyes. Figure 9 shows
the K/S values of the ultramicrofiber fabric, N600, from
different dyeing temperature. It was found that K/S values
slightly decreased as dyeing temperature increased from 110
up to 130 oC. Generally, the higher dyeing temperature is,
the more dye migration or dye diffusion from the surface
into the core part of the fiber will occur. At 110 oC, it seems
that a large portion of dye molecules would exist at the
surface rather than the core part of the fiber owing to the
very small diameter. When dyed at higher temperature such
as 130 oC, more dye molecules might diffuse within the fiber
which would result in low K/S values. Another explanation
can be made by considering that dyeing is thermodynamically
exothermic process so that dye-fiber adsorption will preferably
occur at relatively low temperature while reverse reaction or
desorption might occur at a very high temperature.
Build-up property of N600 with three disperse dyes was
evaluated and compared to that of N800 (Figure 10). When
dyeing temperature was fixed to 130 oC, K/S values of both
ultramicrofiber fabrics continuously increased as the dye
concentration increased, suggesting that build-up properties
of both fabric should be generally good. The result might be
attributed to the larger surface area of ultramicrofiber and
bigger capability of dye adsorption when compared to the
regular fiber. On the other hand, overall K/S values of N800
or N600 are not so high and maximum K/S value of N800
was not more than 10 when using 5 % o.w.f of Foron Blue
RD-E. K/S value of N600 was always lower than that of
N800. These results are due to the low linear density of the
ultramicrofiber. It is well known that the specific surface
area increases markedly with decreasing filament linear
density, which results in reduced depth of shade of dyed
fabric. Finer fiber would appear lighter in shade than coarser
fiber because greater amount of incident light would be
scattered or reflected at the surface of the dyed substrate
resulting from larger surface area [4].
Figure 8. SEM images of N800 after alkaline treatment with 1 wt% NaOH at 95 oC for 40 min.
Figure 9. Effect of dyeing temperature on color yield of N600
dyed with disperse dyes (3 % o.w.f).
Alkaline Dissolution and Dyeing of PET Ultramicrofiber Fabric Fibers and Polymers 2015, Vol.16, No.9 2001
Fastness Properties
Table 2 shows the results of wash and light fastness test for
ultramicrofiber fabric dyed with commercial disperse dyes
(3 % o.w.f.). In wash fastness of rubine and blue dyes,
staining of adjacent acetate, nylon, or PET for N800 was
poor to moderate and that for N600 was poor. During the
heatsetting, dye molecule would migrate from interior to the
surface of the fiber. This thermomigration would occur more
easily in finer fiber resulting in lower wash fastness.
Light fastness of N800 or N600 was very poor. This is
Figure 10. Build-up properties of N800 and N600 dyed with disperse dyes; (a) Foron Yellow Brown RD-S, (b) Foron Rubine S-WF, and
(c) Foron Blue RD-E.
Table 2. Wash and light fastness of dyed ultramicrofiber fabric
Sample Dye
Wash fastness
LightChange
Staining
Acetate Cotton Nylon PET Acrylic Wool
N800
Yellow browna 4 3 4-5 4 4 4-5 4-5 2
Rubineb 4 2 4 3 3-4 4-5 4 1
Bluec 4 2 3 3 3-4 4-5 4 1
N600
Yellow browna 4 3 4-5 3-4 4 4-5 4-5 1
Rubine b 4 2 3-4 2 2 4 3-4 1
Bluec 4-5 2 3 2 2 4 3-4 1aForon Yellow Brown RD-S,
bForon Rubine S-WF, and
cForon Blue RD-E.
2002 Fibers and Polymers 2015, Vol.16, No.9 Hodong Kim et al.
similar to the previous result in which light fastness of fabric
containing 800 nm ultramicrofiber was very poor (grade 1)
while that of microfiber fabric was poor to moderate (grade
2-3) [12]. It seems that, in ultramicrofiber having larger
surface area, the more dye molecules should be exposed to
external light than in coarser fiber.
Conclusion
Alkaline dissolution and dyeing properties of knitted
fabric from sea-island type PET ultramicrofiber of ca. 600 nm
or 800 nm were investigated. The dissolution ratio of fabric
from ca. 600 nm ultramicrofiber was found to be dependent
upon temperature in the alkali treatment. The dissolution
ratio increased more rapidly with increasing treatment time
at higher temperature. When the fabric was treated with
1 wt% NaOH aqueous solution at 95 oC, the dissolution ratio
reached the theoretical value in 30 min. Alkali dissolution of
the sea component could be monitored by the cationic dye
staining method. While the K/S value of untreated fabric was
high by cationic dyeing, that of alkali-treated fabric decreased
as the treatment time increased, and finally levelled off.
Morphological change of sea-island type ultramicrofiber before
and after alkali treatment was observed directly by SEM
analysis. Although island components with a diameter of ca.
800 nm could be completely separated when treated with
1 wt% NaOH at 95 oC for 40 min, those with a diameter of
ca. 600 nm could not.
The color yield of the disperse dye on the ultramicrofiber
fabric was found to be dependent on the dyeing temperature.
K/S values decreased as dyeing temperature increased from
110 up to 130 oC. K/S value of dyed fabric from ca. 600 nm
ultramicrofiber was lower than that from ca. 800 nm
ultramicrofiber. The wash fastness of ca. 800 nm fabric was
poor to moderate and that of ca. 600 nm fabric was poor.
The light fastness of both fabrics was very poor. Efforts to
improve the wash and light fastness of the ultramicrofiber
are needed.
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