Bioscouring of Cotton- Commercial Applications of Alkaline Stable Pectinase
Transcript of Bioscouring of Cotton- Commercial Applications of Alkaline Stable Pectinase
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Bioscouringof Cotton: Commerical
pplicationsof lkalineStable
ectinase
ByRobert B.Waddell, Dexter Chemical Corp., Charlotte, N.C.
l1
e textile industry continues to
look for new, innovative
methods for improving quality
and production, and also to ad-
dress environmental issues. It is cer-
tain that enzymes will play an impor-
tant role in meeting these objectives.
In recent years, enzymes have become
increasingly useful in the processing of
natural fabrics. Amylases have long
been used as desizing agents for wo-
ven fabrics, and more recently cellu-
lases, lipases, laccases, catalases, and
proteases have found their place in the
production of quality textile fabrics.
The most recent addition to this list is
an alkaline stable pectinase.
Alkaline stable pectinase has proven
to be highly effective for pre-scouring
cotton fabric prior to dyeing. The term
bioscouring has been used to de-
scribe this process. Production results
have shown bioscouring to be an effec-
tive way to improve fabric quality and
at the same time offer a milder, sub-
strate specific scour.
In this paper wewill examine the
objectives of scouring, and the com-
mercial applications of the bioscouring
process.
SCOURINGOBJECTIVES
Cotton fibers consist of approximately
92-96 cellulose and 4-8 impurities
that impede aqueous chemical process-
ing (Fig.I). The primary non-cellulosic
impurities are comprised of waxes,
pectins, proteins, andminerals.1These
components create a hydrophobic
barrier that protects the fiber during
the growth and development stage and
also serves as a lubricant during fiber
AATCC REVIEW
28
ricoThe results from such scours vary
depending on application time, bath
temperature, and chemical concentra-
tions. This type of process covers a
very broad spectrum. It is a non-spe-
cific scour that not only removes the
impurities but can also modify the
cellulosic part of the fiber as well. It
also leaves high levels of alkali in the
fabric that must to be neutralized be-
fore proceeding to the dye bath.
Bioscouring
Bioscouring is a process by which an
alkaline stable pectinase is used to
selectively remove pectin and waxes
from the cotton fiber. By breaking the
pectin interface, which lies between
the waxes and the cellulose fiber, the
waxes are exposed and can be emulsi-
fied when the bath temperature is
brought above their melting point.3
Subsequent rinsing helps to remove
these impurities from the bath. Unlike
alkaline scouring,
this process is sub-
strate specific, and
does not alter the
cellulose compo-
nent. The
bioscouring process
does not swell or
remove the seed
coat fragments
called motes. This
can be beneficial
when scouring for
the natural look.
Because of the mot
and color retention
in cotton fabrics
scoured with this
processing. Most of the waxes should
be removed during the scouring pro-
cess to facilitate fiber wettability and
to ensure level dyeing. These waxes
are found in the outer layers of the
fiber called the primary wall and cu-
ticle(Fig.2 2
SCOURING METHODS
Alkaline Scouring
Traditional scouring of cotton fabrics
has been carried out by the combined
use of alkali, surfactants, and chelating
agents. The alkali, usually caustic
soda, is used to swellmotes and to
saponify oils and waxes. Surfactants
are used to expedite fabric wet out,
emulsify oils and waxes, and to keep
the emulsified material dispersed in
the scour bath and during rinsing.
Chelates are used to formwater-
soluble complexeswith metals, which
facilitates their removal from the fab-
II Cellulose 94.0
. Pectin 1.2
0 Waxes 1.3
0 Protein 0.6
.Ash 1.2
.Other 1.7
Fig. 1. Typical mature cot1on fiber composition. 1
Primary Wall
Cuticle
Secondary Wall
Fig. 2. Cot1on fiber.2
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process, pastel or light shades need to
be bleached prior to dyeing, but me-
dium to dark shades can be dyed di-
rectly after the bioscour.
APPLICATIONS
In mid 1998, scientists and technicians
from Novozymes NA and Dexter
Chemical began working together to
develop a viable process using an
alkaline stable pectinase. Like all en-
zymes, pectinase activity and effi-
ciency is determined by three vari-
ables: time, temperature, and pH. In
designing a product and process that
could be adapted to existing textile
processing equipment, each of these
variables had to be taken into consider-
ation. Processing cost also had to be
carefully monitored to ensure market-
ability.
After much consideration it was
determined that batch processed cotton
and poly/cotton knits would be the
most applicable candidate for this new
enzyme process. The three variables;
time, temperature, and pH could be
easily controlled to meet the enzyme s
requirements in jets and other batch
equipment. Applications such as multi-
stage continuous, and pad-batch woven
processing would follow as more expe-
rience with the alkaline stable pecti-
nase was gained and as other enzymes
are developed to work in combination
with the pectinase.
Check pH
8.5-9.5 ~
i
Load Fabric
Add
Chelate
Detergent
Sodium Carbonate Buffer
Lubricant Defoarner Optional)
Fig. 3. Bioscour process profi le.
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Cotton Knit Application
Trials on production scale equipment
started in January 1999at Cross Creek
Apparel in Mt. Airy, N.C. Initial work
was done to compare the bioscour
process to the plant s then current
production process for prescouring
cotton knits. Loads of the same fabric
and color were run on the same equip-
ment and the fabrics compared. Trials
were run on navy and hunter green
colors successfully.The bioscoured
fabrics had very level, on-shade
dyeings with excellent wettability and
extractables. The control process used
was an extensive, high alkaline scour.
This control process had been running
for an extended period with little qual-
ity problems. As a result of the first
trial s success, a follow-up set of pro-
duction trials was scheduled.
The next trials were conducted by
injecting the bioscour process directly
into the plant s production. One jet
1000 Ib) was set aside to run the
bioscour, for a period of one week.
During this period 13lots were suc-
cessfully scoured and dyed. The fiber
reactive colors evaluated on this trial
consisted of royal blue, medium blue,
navy, black, and red. All of the lots,
regardless of the style, weight, or
color, met or exceeded quality expec-
tations.
Following these successful trials,
the bioscour process was adopted and
200F/5 min.
135F/
10 min.
Fill 140F
Add
Dextrol Bioscour
implemented May 1999). Since that
time, no production problems have
occurred as a result of the bioscour
process. Over the last year several
other knit dyehouses have adopted the
process. A typical process profile can
be seen in Fig. 3.
With this procedure the batch
equipment, usually a jet, is filled at
any temperature up to 135F.The fabric
is loaded, either before or after the
first chemical tank add. The bath is
circulated, sampled, and the pH
checked before addition of the second
chemical tank. The temperature is
brought to 135Fand held for 10min-
utes. This is the actual bioscour part of
the procedure. The bath is then heated
to 200F to melt and emulsify waxes,
and held for five minutes. The scour is
followedby at least one 180Frinse
before proceeding to the dyebath.
The latest modifications include
reducing the time used in the rinse
procedure by skipping the drain step
and going directly to an overflow
wash. Other procedure modifications,
such as adding a 120Frinse prior to
the bioscour process, have proven to
be effective in helping remove knitting
oils and reducing foam levels.
Cotton Woven brics
Most traditional cotton woven fabrics
are wet processed by one of three
methods: pad batch, batch, or continu-
180F/5 min.
Overt low rinse at 140F/1 0 min.
----
Proceed to Dyeing Procedure
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ous preparation. Pad batch processing
usually consists of a saturator and a
storage method for extended applica-
tion time or dwell, followedby a
washer. Batch processing can be car-
ried out in a variety of equipment such
as becks, jigs, kiers, and soft-flowjets.
Continuous preparation can be broken
down into two types-rope and open-
width ranges. Both rope and open-
width ranges vary in the number of
consecutive processes or stages, de-
pending on the desired result.
Pad Batch Bioscour
The adaptation of the bioscour proce-
dure to a pad batch process is rela-
tively easy. The fabric is wet out in the
saturator, passed through a nip roller to
get a controlled wet pickup, held at
room temperature for 12-24 hours, and
then washed. Due to an extended
amount of dwell time the temperature
of the saturator can be maintained at
the enzyme optimum of 135For lower.
The pH is set at 8.5-9.5 in the satura-
tor bath by the addition of a buffer.
The saturator also contains a wetter/
emulsifier to facilitate good fabric wet
out and removal of waxes during
washing.A chelate may be added to
the saturator bath or metered into the
first wash box to avoid a buildup of
hard soaps.Wash temperatures of
180For above are required for good
wax emulsification and removal.
If the fabric has been sized with
starch, an amylase should be added to
the saturator mix to, in effect, desize
and scour simultaneously.Care must
be taken in selection of the amylase to
ensure compatibility and effectiveness
at the 8.5-9.5 pH range.
Wovens on Batch Equipment
Processing woven fabrics on batch
equipment is similar to the method
used for knits. This process can be
adapted to all of the batch equipment
including jigs, becks, kiers, or soft-
flowjets. The main difference between
wovens and knits is the need for the
addition of an amylase to remove
starch sizing.
AATCC REVIEW
Continuous Bioscouring of
Wovens
On single stage continuous rope ranges
such as a I-box steamer, it is possible
to get excellent scouring and desizing
without major modifications to tradi-
tional procedures. By adjusting the
saturator pH down to 8.0-8.5 the alka-
line stable pectinase becomes more
stable and is less sensitive to tempera-
ture. Because the fabric being intro-
duced into the I-box does not see full
temperature for 10-15minutes, the
alkaline stable pectinase has time to
work before exceeding its deactivation
temperature. This allows the steam
temperature in the I-box to be held at
an easier to maintain a temperature of
190-200F.In this procedure, a ther-
mally stable amylase should be used to
maximize dwell time efficiency. The
saturator bath should contain wetter,
emulsifier, buffer, amylase, and pecti-
nase. Chelate is then metered into the
first hot wash box. This type of equip-
ment can be used very effectively to
scour fabrics for the natural look or
to scour yarn dyed fabrics that need
improvedwettability, such as towels.
On multiple stage ranges, the
bioscour process can be used in a
variety of ways. On a two-stage range
the alkaline stable pectinase can be
combined with amylase to give the
results of a desize and scour.On three-
stage ranges the bioscour procedure
may be able to replace the traditional
caustic scour. Due to variations in
continuous ranges, the bioscour proce-
dure must be customized to accommo-
date each set of conditions.
CONCLUSION
As experience with the bioscour proce-
dure was gained, many advantages
surfaced. Some were obvious, while
others were a bit more subjective and
case specific. The bioscour process fits
within the traditional prescour time
frame, and the chemical cost is compa-
rable. In some cases, the scour time
has been reduced and the scouring
efficiency has been improved. Due to
more uniform wax removal and better
wettability, bioscoured fabrics have
yielded smoother dyeings. Many of the
streaks and the motley appearance
associated with heavy shades are re-
duced or eliminated. In some cases,
bioscoured fabrics dye heavier than
traditionally prescoured fabrics. This
can translate into dye cost savings and
reduced color in the effluent. Because
of the low alkalinity of the bioscour
procedure, no acid neutralization is
required before dyeing can start. This
can reduce the amount of water used
by a few thousand gallons per load.
Bioscoured fabrics maintain a high
mote count unlike caustic scoured
fabrics. This is an advantage when the
natural look is desired. A high leve
of wettability can be achieved without
affecting the fabric appearance. This
cannot be done with traditional alka-
line scours.
In many dyehouses caustic soda is
manually weighed, carried, and dis-
pensed by operators. The alkaline
stable pectinase described is much
safer to handle than caustic. This pecti
nase, unlike caustic, will not harm
human tissue, which in turn reduces
personal risk to the operator. Also, the
quantity used is only a fraction of the
caustic use level, therefore eliminating
the heavy lifting associated with buck-
ets of caustic.
References
Lange, N. E. K., Book of Papers
AATCC International Conference
Exhibition, Philadelphia, 1998,p463.
2 Hardin, 1.R. and J. Kim,
Book of
Papers
AATCC International Confer-
ence Exhibition, Philadelphia, 1998
p319.
3. Etters, J.N., P. A. Husain, and N. E. K
Lange,
BioPreparation The New Ad
vanced Way of Preparing Fabric
Yarn 1999,pp4,6.
uthor s ddress
Robert B.Waddell,Dexter Chemical
Corp., P.O.Box 7403, Charlotte, N.C.
28241-7403; telephone 704-588-3991;
fax 704-588-4049; e-mail
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