Mercerization
Mercerization is a chemical treatment of cotton with a strong caustic alkaline solution in
order to improve the luster, hard feel and to impart a greater affinity for dyes and various
chemical finishes.
This is the process applicable only on cellulosic fibers especially cotton. John Mercer
invented this process in 1844.
Objectives
improved luster
increased ability to absorb dye
improved reactions with a variety of chemicals
improved strength/elongation
improved smoothness & hand feel
Changes after Mercerization
Before After
Changes after Mercerization
UNTREATED COTTON MERCERIZED COTTON
General Process of mercerization
The mercerizing involves Following subsequent steps
Application of NaOH solution around 55-60°TW ( 31-35% ) at a
Temperature of 15 to 18°C.
A dwell period of 55 sec on an average, to permit diffusion of
alkali into the fiber.
Stretching (specially warp) while the material is impregnated
in the caustic solution
Washing off the caustic soda from the material while keeping
the material still in the stretch state (specially weft) to prevent
shrinkage
WHEN MERCERIZATION CAN BE CARRIED OUT ?
At Grey stage
After Desizing
After Scouring
After Scouring and bleaching
Every stage of mercerizing has its own advantages
and dis-advantages. It is suggested to carry out
Mercerizing preferably after Scouring to get best of
the process.
Mercerization methods
Tension Mercerization (treatment under tension)
Slack Mercerization (treatment without tension)
CLASSIFICATION OF MERCERIZATION PROCESS
Mercerization can be carried out on yarn, hanks, and in fabric form for both woven and knitted
fabric
Classification according to the form of the product
A) Yarn mercerization
Batch: Hank mercerization
Cheese mercerization
Continuous:Single end mercerization
Tow mercerization
Warp mercerization
B) Knit Mercerization
Open mercerization
Closed mercerization (Round mercerization, tubular knit mercerization)
C) Cloth mercerization
Chainless mercerization (Roller mercerization)
Chain mercerization (Stenter mercerization)
Batch-up mercerization
WHAT ARE THE PARAMETERS OF
MERCERIZATION ?
• Concentration of NaOH
• Time of Treatment
• Tension applied
• Temperature
• Impurities of NaOH
Advantages
If you asked to design a cotton apparel which has following
requirements
Highly Luster
High tensile strength
Highly smooth surface
A silky look & better dimensional stability
Highly moisture absorbent
Better crease recovery
Uniform dyeing & good color yield.
Then you have mercerized the fabric from which you design the
apparels because mercerization offer you above advantages over
normal fabric.
Bio-polishing
Pretreatment processes lead to the formation of pile on fabric
surface due to friction between fabric, machine parts & liquor
which lowered the fabric quality & reduce dyeing brightness. The
appearance and handle of cotton knits can be significantly
improved by treatment with enzyme namely cellulase, and such
treatment leads to the removal of surface hairs from fabric and
improve brightness of dyed fabric.
Bio-polishing removes protruding fibers and slubs from fabrics,
significantly reduces pilling, softens fabric hand and provides a
smooth fabric appearance, especially for knitwear and as a
pretreatment for printing
Pilling
After Bio-polishing
After Bio-polishing
Process of Bio-polishing :
There are two process of Bio-polishing
Dyeing followed by bio-polishing.
Bio-polishing before Dyeing .
Process Variables :
To achieve optimum bio-polishing, the process variables have been varied
as mentioned below ......
Concentration : Concentration of enzyme: 0.5%, 1%, 2%, 2.5%, 3% & 4%.
Temperature : Temperatures are 40 0C, 45 0C, 50 0C, 55 0C & 60 0C.
pH : 3 - 4, 4 - 5 & 5 - 6.
M : L : 1:5, 1:10, 1:15 & 10.
Mechanical Agitation: Vigorous Stirring, Medium Stirring & Without
Stirring
Advantages & Disadvantages :
Depth of shade increases when enzyme treatment is
given before dyeing but the depth decreases when
enzyme treatment is given after dyeing.
Wash fastness of the enzyme treated sample after
dyeing is good but Wash fastness of the enzyme
treated sample before dyeing is very poo .
One bath application saves energy, time & cost but
the bio-polishing effect is not as good as the two bath
method .
Decreases the Pilling tendency .
Loss in weight.
Loss in strength.
Whiteness
The standard ceramic tile (Made of MgSO4) is
measured and set to equal 100. The other specimen
are rated against this standard.
Unbleached fabrics will give values in the 50 to 60
range.
Well breached fabrics will rank more than 85 or better.
Optical Brightening Agent
There is a yellowish tint in textile apparels due to following
reasons.
1. Textile fibers specially natural fiber generally absorb blue light
in visible spectrum as they contain impurities (Natural pigment)
results yellow tint on apparels even after bleaching.
2. Daylight has slight yellowish tint which increase yellow portion
in reflected light
3. Human eye contain yellow colored pigment which is
responsible to observe the yellowness in apparels.
Whiteness in these substrates can be improved by the action of
products named optical brighteners, fluorescent brightening
agents or fluorescent whitening agents (FWA). It increase blue in
Optical brighteners, are chemical compounds that absorb light in
the ultraviolet and violet region (usually 340-370 nm) of
the electromagnetic spectrum, and re-emit light in the blue region
(typically 420-470 nm) by fluorescence. It is also known as physical
bleaching agent.
Why is it called physical bleaching agent:
• It introduce complementary color to that of natural coloring
matter resulting in uniform distribution of reflected light
• It involves no chemical reaction
How OBA works
The effectiveness of fluorescent brighteners is dependent on
several factors:
Nature of textile goods
Temperature
Addition of salt
Liquor ratio
Concentration of fluorescent brightener
pH of bath
Time
OBA treated fabric appears more white only in the illuminates
containing ultra-violet radiation.
Application Method
a) Exhaust method: for knit goods mainly & it is done with
scouring bleaching simultaneously.
b) Padding: Either with bleaching or in finishing
What have you learned
