Non-Formaldehyde Nitrogen-Containing
Fixing Agent For Direct Dyeing
By Yiqi Yang, Edward F. Carman III
Institute of Textile Technology,
Charlottesville, VA
This work was studied to determine if
nitrogen based fixing agents imparted
the same, or increased, fastness properties to direct dyes as a formaldehyde
fixative. Also studied were the effects of
the structures and concentrations of
dyes and fixatives on color fastnesses
of direct dyed cotton. The effect of the
fixlng agents on the fastness properties
of the direct dyed 100 percent cotton
fabric was examined. Fastness properties tested were wash, crock, and light.
Tensile and tear strengths of the fixed
fabrics were also tested.
Introduction
Although direct dyes possess poor
wet fastness properties, they are still
widely used due to their ease of application, comparatively low cost, and
good migration properties.’ in fact,
direct dyes are second only to sulfur
dyes in their textile usage worldwide,
with vat and fiber reactive dyes well
behind.’
The main disadvantage of direct
dyes is their poor wash fastness. The
sorption of direct dye by cotton is not a
permanent irreversible process. The
dye may be removed from the cotton
fiber in successive washings with fresh
Water. Darker shades can be reduced in
depth quickly after only a few water
Washings. How quickly the color change
occurs depends mainly on the affinity of
the dye to the fiber.
Sulfonic acid groups are present on
the direct dye molecule to impart aqueous solubility, thereby facilitating the
application from the aqueous phase.3
Sulfonic groups, however, reduce the
affinity of the dye towards the cellulosic
substrate. This decreased affinity is due
to two factors 1) both the cellulosic fiber
and the direct dye have negative
charges in the aqueous medium, and 2)
the sulfonate group increases the dyeAmerican Dyestuff Reporter
October 1996
water interaction and therefore decreases the dye-fiber attraction.
The wet fastness characteristics of
cellulosic textiles dyed with direct dyes
are rather poor, and to improve the fastness properties of direct dyed fabrics an
aftertreatment may be used. The
aftertreatment follows the completion of
the dyeing process. Although the
improvement in fastness is occasionally
an empirical observation, the aftertreatment process is related to the chemical
constitution of the dye.
To determine the optimal concentration of fixative required for good fastness properties, Etters4 researched the
efficiency of five different fixatives as a
function of the concentration. The efficiency of the fixative was calculated
using the formula: E=D/MV where E is
the efficiency, D is the percent decrease
in dye desorption caused by the fixative,
and MV is the money-value concentration of fixative. The money-value was
calculated from the concentration of the
fixative (%OWG, on the weight of
goods) times the price per pound of the
fixative in dollars. Efficiency is, therefore, the percent decrease in dye desorption that is obtained for one dollar’s
worth of fixative per one hundred
pounds of dyed material after-treated
with a given concentration of fixative.
Within many techniques of aftertreat-
ing, the direct dyed fibers to improve the
wash fastness, the application of
formaldehyde, cationic, and metallic
salts fixatives are the most common
approaches. Formaldehyde improves
colorfastness through crosslinking reactions. Improvement in the fastness
properties occur during the reaction of
two dye molecules with one molecule of
formaldehyde through the formation of a
methylene bridge.3 It is also possible
that one formaldehyde molecule could
react with one dye molecule and one
hydroxyl group of cellulose. Both reactions could decrease the dye desorption
from the fiber. Because of its high reactivity, formaldehyde is one of the most
effective fixatives for direct dyes.
However, because of the health problems associated with formaldehyde,
there is a market demand for nonformaldehyde fixing agents.
An alternative method utilizes nitrogen containing organic compounds that
couple with the dye to increase the molecular weight and reduce solubility of
the dye. The interaction between the
dye and the fixative is mainly the ionic
attraction from the positively charged
nitrogen and the negatively charged dye
ion.6 This salt linkage neutralizes the
negative charge on the dye and
decreases the water solubility of the
dye. Enlargement of the dye molecule
39
inside the fiber also makes it more difficult for the dye to be released by the
fiber.
Another category of fixative that can
be used to improve the wet fastness
properties of direct dyes is metallic
salts. One of the most common metals
used as an aftertreatment is copper.
The cupric cation, Cu2+, could behave
like the organic nitrogen containing fixatives, forming insoluble copper salts
with the anionic dye molecules. Direct
dyes containing two hydroxyl groups in
he ortho position, adjacent carbon posiions in a benzene ring, can react with
copper salts to produce less-soluble
metallic chelates.
Copper salts are not environmentally
desirable, but the aftertreatments can
be tailored to improve both wash and
light fastness properties of some direct
dyes without producing enough free
copper ion in the effluent to cause problems. Copper salts are used primarily
with heavy browns, navy and black
shades. Although the treated dyestuffs
will have improved light fastness, blue
shades will exhibit a green cast.
Other approaches such as coupling
with diazonium salts, forming metalcomplex with metals other than copper,
or the treatment with potassium bichromate are also used for the improvement
of colorfastness of direct dyed fabrics.
The objectives of this article are to
40
determine the effect of the type and
concentration of nitrogen containing dye
fixing agents on the fastness properties
of direct dyed cotton fabric, and the
effect of the number of sulfonate groups
a dye has on the fastness properties
after fixation. A comparison of the effect
of a formaldehyde condensate dye fixing agent to the non-formaldehyde dye
fixing agents on the fastness properties
of direct dyed cotton fabric is also given.
Material
Dyestuffs
This work used three direct dyestuffs. The main criterion for selection of
the dyestuffs was the solubility of the
dyes. The sulphonate groups were varied from 2 to 4 while keeping a similar
chemical structure. Table I summarizes
the characteristics of the dyes selected.
The dyestuffs were supplied by Aakash
Chemicals & Dye-Stuffs, Inc.
Fixatives
Four different fixatives, donated by
ICI Surfactants, were used for this
experiment, for which three were nonformaldehyde: 1) polyamine condensate (poly), 2) quaternary polyimine
(quat), 3) cationic polyamide (cat), and
4) formaldehyde condensate (form).
The latter fixative was chosen for a
comparison study between it and the
three other non-formaldehyde agents.
Fixatives were chosen for their varying
chemistry, availability, and wide use in
the commercial market. The abbreviations in the parentheses will be used
later on for these four fixing agents.
Fabric
A 7.4 ounces/square yard, 100 percent cotton, 3/1 left-hand twill fabric was
commercially scoured, bleached, and
mercerized for use in this research. Twill
fabric was chosen for its ease of dyeing.
wide usage, and acceptance as a substrate in other direct dyeing experiments, such as the ones by Etters,4 and
Bhattacharyya, et al. The fabric was
donated by Milliken & Company.
Methods
Prescouring
Five approximately 2 by 3 yard samples were washed in a Sears Kenmore
Model 22631 washer set on high load
and cotton/sturdy cycle at 130°F water
temperature with 40 grams of AATCC
detergent, without optical brightener.
After that, the goods were rinsed in distilled water twice with a liquor ratio of
40: 1. The fabric was then air dried.
Dyeing
Ten grams of the fabric was dyed
with a liquor ratio of 20: 1 at a pH of 7.
The dye concentrations were 1 %, 2%
and 4% on the weight of goods (owg)
American Dyestuff Reporter
October 1996
Am
with 5% (owg) of NaCl in each bath. An
Atlas Launderometer was used for
dyeing with 25 steel balls in each can.
The bath was heated to 100°F and held
for S minutes, then the temperature was
raised to 210°F and held for 30 minutes.
The dyebaths were cooled to 70°F in
about 40 minutes. The dye liquor was
dropped, and samples were rinsed in
cool water baths until color bleeding
stopped. The fabric then was centrifuged, and was ready for fixation
treatment.
Fixing
Six levels of concentrations, 0.5, 1 .O,
2.0, 3.0, 4.0, and 5.0 percent (owg), of
each fixative were tested for each dyed
sample with a liquor ratio of 20: 1. The
experiment was performed in the
Laundrometer, with 25 steel balls in
each can. The temperature was elevated to 120°F and held for 20 minutes.
Then the bath was cooled to 70°F and
the fabric was removed from the cans,
rinsed with distilled water, centrifuged,
and air dried at ambient conditions. To
minimize the processing error, three
replicas for each test condition were
run. The mean values were reported.
Color Measurement
The major concern for this work was
the color change or color fastness under
different conditions. The visual method
used was the AATCC standard Gray
Scales for Evaluating Staining and
Change in Color. Both scales have
assessment values from one to five, as
Well as half values. The value of 5
means no shade difference between the
control and the test sample. The smaller the value, the more the color difference or the fading. The instrumental
measurement was Efmc2\8 on the BYK
Gardner Spectrophotometer, using a
10 CIE Standard Observer and a D65
Illuminant. E FMC2 is a quantitative
American Dyestuff Reporter
October 1996
description of the total color difference
between two substrates and a value of
about 0.5 to 1 .O is detectable by the
human eyes. The larger the value, the
more the color difference or the fading.
Co/or Fastness Tests
Wash fastness tests were performed
using the AATCC Test Method 61-1989,
Test 2A. Crock fastness. both dry and
wet, were examined according to the
AATCC Test Method 8-1989. Light fastness tests were conducted at Ciba’s
laboratory in Greensboro. NC. The 40
hour tests were conducted under the
guidelines of AATCC Test Method 16E1987, using an Atlas Ci65 Weatherometer water-cooled Xenon-Arc light. All
the tests are the standard tests from the
Technical Manual of the Association of
Textile Chemists and Colorists.
Fabric Strength
Tensile strength was tested using the
Scott Tensile Tester according to ASTM
D1 682-75. Tear strength was examined
by Elmendorf Tear Tester based on
ASTM D1424-83. Both methods were
from the American Society for Testing
and Materials.
Results And Discussion
To evaluate the effect of fixatives on
wash fastness, the dyed and finished
samples were washed and the color
fadings were assessed by both the
E FMC2 and gray scale Values. Figures
1, 2, and 3 presents the color fastness
results of the fabrics dyed with 1.0%
(owg) of Direct Red 83, Direct Red 62
and Direct Orange 26, respectively, and
finished with all four fixatives at concentration levels from 0.5 to 5.O%(owg). As
shown in the figures, the nonformaldehyde fixatives could achieve the same
or better fixation results than a
formaldehyde fixing agent.
For Direct Red 83, the best nitrogen
containing fixative was polyamine condensate. For Direct Red 62 and Orange
26, the best was cationic polyamide.
Quaternary polyimine was always the
least effective fixative for the dyes
examined.
Considering the dye characteristics
listed in Table I, it is possible that
polyamine condensate is better for dyes
with high water solubility and cationic
polyamide is better for those with lower
solubility. Because of the charge neutralizing mechanism, the more positive
charges a fixative has could more efficiently neutralize the negative charges
on direct dyes and decrease the dye
42
solubility. However, if the fixative carries
too many positive charges, the solubility
in water of itself and the solubility of the
dye-fixative complex after finishing will
be high. This in turn will decrease the
effectiveness of the fixative. Due to the
limited size, a fixative could only cover
certain number of dye molecules no
matter how many charges it has.
Therefore, if a fixative carries more
charges than the charges of the dye
molecule it could cover after fixation,
some net positive charges will be left
and, later, increase the solubility of the
dye-fixative complex. Other factors,
such as the similar distance between
two charges of the fixative and that of
the dye, are also important to the effectiveness of the fixatives.
The results in Figures 1 to 3 also
demonstrate that the most improvement
of wash colorfastness are at fixative
concentrations lower than 1%. Further
increase of the fixative concentrations
could not improve the wash fastness
with the same proportion as it did at
concentrations below 1%. A possible
explanation is that at concentrations
below l%, there are already enough fixative molecules on the fabric to neutralize most of the dyes. Increase of the fixative concentration would not further
decrease the solubility of the dyes on
the fabric.
Staining of the color removed from
dyed goods onto other textiles is also a
major consideration of the wash colorfastness The relation between fixative
and staining was consistent with that
between fixative and wash fastness. An
example of the staining onto cotton stop
of the standard AATCC multifiber test
fabric of polyamine condensate fixed
fabric is illustrated in Figure 4. The best
improvement was for the Direct Red 83
dyed fabric, about 3 gray scale classes.
while both the Red 62 and Orange 26
were 1 class improved.This result was
similar to the improvement of wash fastness by polyamine condensate presented in Figures 1 to 3, in which polyamine
condensate improved colorfastness of
Direct Red 83 dyed fabric about 2.5
classes but only 0.5 to 1 class for Direct
Red 62 and Orange 26 dyed ones.
No remarkable improvement in both
dry and wet crock fastnesses was
encountered for any of the three
dyestuffs examined with any of the four
fixatives. Figure 5 illustrated the charge
of crock fastness of fabrics finished with
polyamine condensate. Figure 6 shows
the crock fastness of the fabric finished
with all four fixatives. As shown in the
figures, the maximum improvement was
only 0.5 class based on the S-class
American Dyestuff Reporter
October 1996
gray scale for staining. This is probably
because crock fastness examines the
strength of the interaction between the
dye and the fiber, not the affinity which
is related to the relative attraction
between dye-fiber and dye-water. The
nitrogen containing fixatives mainly
decrease the dye-water attraction and
have little effect on dye-fiber attraction.
Therefore, they could not markedly
improve crock fastness.
Using fixatives sacrifices some of the
light fastness of direct dyes due to the
poorer light fastness of the fixatives
than of the dyes. The decomposition of
the fixatives and the formation of free
radicals and other chemicals promote
the decomposition and fading of the
dyes. The effects of different fixatives on
fastness light of all three dyes are illustrated in Figures 7 to 9. As shown, fixatives decreased the lightfastness of the
dyes and the extent of such decrease
increased with increasing concentrations of fixatives. At 0.5% (owg) fixative
level, the concentration which gave the
most wash fastness improvement, lightfastness decreased 0.5 to 1.0 class
more than the control fabric, dyed but
unfinished, after 40-hour exposure in
the standard lightfastness chamber.
Nevertheless, the decrease of the lightfastness due to the application of nitrogen containing nonformaldehyde fixatives was similar to, or less than, those
finished with the conventional formaldehyde fixative.
The influence of shade depth on the
effectiveness of the fixatives were also
studied by testing all the above properties of fabrics dyed with 2% and 4%
(owg) of the direct dyes. Examples of
wash fastness of fabrics dyed with 1, 2,
and 4% of Direct Red 83 and Direct
orange 26 and then finished with
cationic polyamide and polyamine con-
densate are illustrated in Figures 10 and
11. The ordinates in both figures were
color changes before and after laundering. As shown, no matter what depth of
shade a fabric had, polyamine condensate was better than cationic polyamide
fixative for the Red 83 dyed fabric, while
cationic polyamide was better for the
fabric dyed with Orange 26.
The crock fastness of fabrics dyed
with higher shade depths (2% and 4%)
were also similar to 1% shade depth.
Crock fastness of fabric did not improve
remarkably after fixation. As shown in
Figure 12, the maximum improvemen
of the wet crock fastness of Direct Red
83 dyed fabric was only 0.5 class no
matter what fixative and what shade
depth were tested.
Figure 13 illustrates the effect c
shade depth on light fastness of Direct
Red 83 dyed fabrics finished with differ
ent fixatives. It is very interesting that
the degree of reduction of light fastness.
due to the use of the fixatives actually
deceased with increasing shade depth.
With heavier shade, the decrease c
light fastness due to the use of fixative
were not large. The similar results from
the study on the fabric dyed with Direct
Orange 26 as presented in Figure 14
further confirmed such a statement.
Because of the possible interactions
between cellulosic fiber and the fixatives or other chemicals in the fixation
bath, the strength of the fabric after fixation was tested to examine whether
there was any fiber damages due to the
fixation. As illustrated in Figures 15 and
16, there were no notable decrease in
either tensile or tear strengths after fixation. The nitrogen containing nonformaldehyde fixation is the fiber safe
process.
Conclusions
Formaldehyde containing fixing
agents for direct dyeing could be substituted by nitrogen containing nonformaldehyde fixatives without sacrificing the performance properties of the
finished goods. Choosing the suitable
nonformaldehyde fixatives could actually produce better products than using
the formaldehyde fixative. Using the
nonformaldehyde fixatives at 0.5%
(owg) level, wash fastness could be
improved as much as 2.5 classes based
on AATCC Grey Scale. Crock fastness
had no marked improvement after using
fixing agents. The best improvement
44
was about 0.5 class for the wet crock
fastness. The nonformaldehyde fixatives studied decreased the fastness
light of direct dyes. At 0.5% (owg) fixative level, the decrease was 0.5 to 1.0
class more than untreated control for 40
hours test for the fabric dyed with 1 %
(owg) of dyes. However, the lightfastness decrease due to the application of
nonformaldehyde fixatives were similar
or less than that caused by the
formaldehyde fixative.
For the fabrics dyed with 2% and
4% (owg) of dyes, the maximum
decrease of lightfastness caused by the
addition of the nonformaldehyde fixatives was only 0.5 classes. The tensile
and tear strengths of the fabric were not
affected by fixation. It is possible that
the polyamine condensate tested is better for the dyes with higher water solubility and cationic polyamide studied is
better for those dyes with lower water
solubility.
Acknowledgments
The authors would like to thank Neil
Stewart, and Dennis Balmforth of the
institute of Textile Technology, Nelson
Houser and Tim Little of Ciba, and John
Cooney of ICI Rayca for their he/p during this
research. The donation of the fabric by
Milliken & Company, the use of light fastness
tester of Ciba are gratefully acknowledged.
References
(1) Bhattacharyya, N., Doshi. B.A.
Sahasrabudhe, AS., & Mistry, P.R. (1990).
Improved fastness of direct dyed cotton.
American Dyestuff Reporter, 79, 3, 24-37.
(2) SDC Reports (1987). Sulphur dyes are
important. Society of Dyers and Colourists
103, 297-298.
(3) Houser, N. E., & White, M. (1976)
Direct dyes for high temperature application to
polyester/cotton. AATCC Book of Papers. 105.
112.
(4) Etters, J.N., (1989). How to evaluate
direct-dye fixatives. American Dyestuff
Reporter, 78, 9, 19-22, 91.
(5) Varghese, J., Bhattacharyya, N., &
Sahasrabudhe, A. S. (1989). Aftertreatments
on cellulosic textiles dyed with direct dyes -- a
review. Colourage. 6, 15-21.
(6) Bhattacharyya, N., & Chouhan. S
(1991). Interaction of direct dyes with cation
fixing agents. Indian Journal of Fibre & Textile
Research, 16, 2, 140-145.
(7) Aspland. J.R. (1991). Chapter 2: Direct
dyes and their application. Textile Chemists
and Colorists, 23, 11, 41-45.
(8) Billmeyer and Smith. (1967). Optimized
equation for MacAdam color differences. Color
Engineering. Nov/Dec, 28-31.
(9) American Association of TextlIe
Chemists and Colorists. (1985). AATCC
Technical Manual. Research Triangle Park, NC
American Association of Textile Chemists and
Colorists.
(10) American Society for Testing and
Materials. (1989). Annual book of ASTM
standards. D 13 on textile. section 7.
Philadelphia, PA: American Society for
Testing and Materials.
American Dyestuff Reporter
October 1996