Dyeing, Printing & Finishing
Textile World Asia Special Report”Black Magic”BleachingOne of the most significant
innovations in dyeing, printing and finishing developed this year for the textile industry was
presented by Switzerland-based Clariant Ltd. Sometimes referred to as “black magic,” the no-rinse
or NR-prep process is a new exhaustion bleaching process for cellulose fibers and blends. The
technology draws on a patented chemical process called Singulet Bleaching, which uses a regulation
medium for bleaching with hydrogen peroxide. For textile specialists, the main objective is to
obtain a good pre-treatment quality within a shorter cycle and with lower water and energy
consumption.The ProcessThe black magic process is based on a little known property of hydrogen
peroxide bleaching — the progressive exhaustion of the alkaline agent during the oxidation process.
The H2O2 reduction (exhaustion), dependent on the length of process time, is well known; however,
this can’t be said about the pH, which sinks during bleaching. This is the “magic” aspect of the
process.And the magic aspect corresponds to the pH decline to the neutral value in the phase of
alkali peroxide bleaching.The use of SIRRIX SB, which produces a controlled excitation of the
active oxygen during hydrogen peroxide bleaching, thanks to Singulet Bleaching, is also unusual in
that it is an auxiliary that is black in color.Under optimum conditions, the initial pH value for a
bleaching process with a classical recipe lies between 11 and 11.5. After one hour of treatment,
the pH drops by one point to values of about 10 to 10.5. As the pH is a logarithmic value, there is
a 10-time reduction of the alkali quantity between the beginning and the end of the bleaching
operation.On the contrary, with the black magic technology, the initial pH is only 10.5 (the
process requires less alkali at the start), and the final value comes down to a value close to
7.5.This means 3 logarithmic points fewer, and hence a 1,000-time lower quantity of alkali after
only 30 minutes of treatment — including the heating and cooling phases of the bleaching bath. From
the above, it follows that with the classical process, the end of treatment is reached with a very
high pH (from 10 to 10.5), which is brought down to about 9 by the first rinsing bath. It is
therefore necessary to carry out a second wash step, and also to perform neutralization by means of
an acid, in order to “adjust” the dyeing pH close to 6.5 for reactive dyes.In addition, it is
necessary to add the catalase to the bath prior to dyeing to eliminate the residual peroxide
traces. The entire cycle is long and involves high water consumption. The process actually entails
four baths in total (including dyeing), lasting about two hours (including rinsing operations)
before dyeing is started.The black magic process drastically simplifies the cycle — it requires
only two baths and less than one hour of process time. This includes the intermediate emptying and
filling operations, as well as the elimination of peroxide residues by the enzymatic catalase —
Bactosol ARL (Anti-Radicali-Liberi). All things considered, advantages are considerable yielding a
50-percent reduction in time and water, and approximately a 40-percent saving in energy (electric
and thermal) consumption.
Sirrix SB: Regulator Of Singulet BleachingIn terms of efficiency, one can count on improved
hydrophilicity because of the higher saponification of waxes and natural greases (hydrophobic) of
the cotton. Improved hydrophilicity automatically means a better predisposition to dyeing, with the
achievement of deeper, more lively and uniform shades.The degree of whiteness of the cotton
bleached by the black magic process will be high, and without any significant degradation of the
cellulose polymerization degree. Referring to orbital physics, the source of this new chemistry
lies in the capability of causing oxygen “to dance,” knowing its “pitches” of vibration and of
excitation of its active atom, a “softening” (by means of Sirrix SB) is necessary.Sirrix SB enables
the ability to maintain this special “Singulet Oxygen” at its highest energy level. This allows a
quicker and more intense oxidation of the cotton natural pigments, without affecting the textile
fiber. The secret is in the fact that the alkaline agent (NaOH), a powerful activator of the H2O2,
which drops depending on time, allows more moderate bleaching reactions compared to the normal
conditions of a conventional process. In the conventional process, the alkaline agent remains in
high concentration duringthe entire treatment cycle.The most appropriate definition of Sirrix SB
could be a “collapser” of pH. The higher its concentration is raised, the lower the final pH shall
be achieve: a 1.5 concentration in the bleaching bath has demonstrated to be the optimum value.
Given that the Sirrix SB represents the heart of the system, other treatment auxiliaries are worth
mentioning.
The Surfactant Sandoclean JSFThe function of this soaking/detergent agent, selected for the
black magic process, is to break the interface surface tension between the textile substrate and
the bath. This enhances the penetration inside the fiber by exploiting its quick soaking
properties, capable of overcoming the obstacles presented by the hydrophobic natural substances
present in the cotton.The Sandoclean JSF facilitates the saponification of waxes and fats,
obtaining an improved final hydrophilicity. The textile material circulation in jet- or
overflow-type equipment is not adversely effected, in that the product does not foam, does not
contain silicone, and contributes to the prevention of irreparable tears and streaking on the
fabric. Moreover, such a modern auxiliary doesn’t contain organic solvents, and also is
biodegradable.Bactosol ARL:A Powerful “Peroxide-Killer”This “extremephile enzyme,” according to
Clariant’s original definition, is the final result of complex biological reactions, which lead to
a sophisticated bio-catalyst product.This is capable of lowering the reaction energy to the lowest
level of the H2O2 demolition, enhancing the rapid transformation into water compounds and molecular
oxygen. Moreover, this catalase is not an ordinary product — it is active in a large temperature
range (from 20 degrees Celsius to 70 degrees Celsius).It also performs in a vast spectrum of pH
(from 4 to 10). This peculiarity eliminates the need for controlled cooling of the bath at the end
of the cycle, and of carrying out a precise adjustment of the pH. Consequently, in the black magic
process, the socalled “extremephile” properties of Bactosol ARL are strongly appreciated.The
kinetics of the H2O2 demolition is quick and in less than 10 minutes all peroxide residues are
eliminated, thereby avoiding all risks in dyeing with reactive dyestuffs sensitive to trace
oxidizer. Nonetheless, to ensure ideal dyeing conditions and to prevent overrapid dye migration
onto the fiber, it is advisable to bring the pH value close to 6.5. In order to lower the pH from
the 7.5 value present at the end of the black magic process to the 6.5 level (ideal for reactive
dyeing), a special acidification agent is employed.
Sirrix NE:For Effective NeutralizationThe use of this new neutralization agent eliminates the
need for corrosive mineral acids, such as hydrochloric, sulfuric, phosphoric acids, or the use of
volatile organic acids, such as formic and acetic acids.Because the black magic process does not go
through intermediate rinsing before dyeing is carried out, the (light) neutralization agent must
not interfere with dyeing. Nor should it cause the demetallization of certain dyestuffs of the
Ftalocianine type. Ideal for this purpose, Sirrix NE is an acid-type complex that contains neither
phosphorous nor nitrogen, not even chloride ions. It has a strong neutralization power and it is
perfectly biodegradable.In the black magic process, no neutralization is actually carried out;
rather, a slight correction of the pH (which is lowered from 7.5 to 6.5) to ensure a subsequent
safe dyeing. For this purpose, a minimum dose of product (about 0.1 gram per liter) should be
added.Black MagicAround The WorldThe black magic process has been tested around the world and it
has been adopted by many specialists for its operational and qualitative advantages. Black magic
has been applied to the machinery (jets/overflows/ kiers) of many manufacturers, such as Brazzoli,
MCS, Sclavos, Thies, Then, Scholl, Laip, Fong’s, Gaston County, Loris Bellini and others.
Winter 2004