Introduction
Biotechnology
can be defined as “the application of scientific and engineering principles to
the processing of materials by biological agents to provide goods and services".
The earliest evidence of biotechnology include baking of bread using yeast by
the ancient Egyptians and brewing. Today enzymes have been used
on a large scale in medicine, food analysis, genetically modified food,
transgenic animals and plants and also in the domestic detergent fields. The
discovery of chemical structure of DNA has led to genetic engineering, DNA
finger-printing, rapid gene sequencing and host of related technologies such as
process engineering, fermentation, enzymology, downstream processing, microbiology,
biochemistry, process control, reactor design, immobilized cells and enzymes,
biosensors, biopolymers and biotransformation
In
textile application, the knowledge of specific action of enzymes-amylases for
starch splitting began around 1857, when malt extract was used to remove size from
fabrics before printing . The
use of enzyme in pre-treatment processes of textiles has found much broader
acceptence. At present the priority areas are scouring and bleaching of
cellulosic fibres and carbonising, bleaching and shrink-resist treatment of
wool. Enzymes have traditionally been used for stone washing and bio-polishing
of cotton fabrics and garments. Also enzymes have been incorporated in
detergents to remove fibre fuzz and brighten the colour of the fabric.
Enzymes
are naturally-occuring proteins capable of catalysing specific chemical reactions
and being catalysts, facilitate the reaction without being consumed. After catalysing
the chemical reaction, therefore the enzyme is released and is able to catalyse
another reaction-and so on. factors).
The textile and clothing sector is now a major user of enzymes during
manufacturing and after-care. Cellulases
are widely used in textile application. Cellulases are high molecular colloidal
protein catalysts in metabolic form and are commonly produced by soil-dwelling
fungi and bacteria .
Fig 1, Synergistic action of enzyme on cellulosics
Fig
2. Enzymatic Hydrolysis of cotton
Fig
2. shows the reducing and non-reducing
end groups by the action of cellulase on 1,4-[3-glycoside bond of the cellulose
molecule. [3-glucosidases hydrolase small chain oligomers, such as cellobiose
into glucose. The three types of cellulase component act synergistically in
degrading cellulose to glucose
Treatment of Cotton with
Enzymes
Enzymatic desizing
of cotton
Malt extract was used originally for the desizing of
amylaceous sizes from the fabric.
Later, around 1900, Diastafor was found more efficient for starch desizing. Rapidases were introduced in 1919 and cause the
liquefaction of starch in compounds soluble in water. At present a variety of these
products are available commercially. They are mainly based on amylopectic enzymes. These
enzymes do not damage the
cellulose. These enzymes are effective at various temperatures ranging from 20 to 115~ covering all means of applications .
Now-a-days special attention
is paid towards the development of simultaneous desizing and scouring in an alkaline medium replacing two-stage process.
The use of enzymes in
mercerization
The
effect and action of enzymes seems to be very limited because of the stronger conditions
of alkali of mercerizing strength. Enzymatic hydrolysis is accelerated when
mercerization is carried out without tension . The greater
accessibility and lower crystallinity of cellulose mercerized without tension
is a decisive factor in the enzymatic hydrolysis process. Mercerized cotton is
generally more prone to enzymatic modification than untreated cotton
Enzymatic degumming of
silk
Degumming
of silk to remove the sericin is an important step. Soda-ash and sulphides used
in conventional degumming process not only reduces the fabric strength but also
causes pollution problem. On the other hand enzymatic degumming is a very safe
and simple method of degumming. Apart from sericin the silk fabric also contain
about 2% oil to facilitate weaving. Enzymes not only dissolved the gummy
portion but also dissolved the oil at the same time
Recipe:
Papain- 6%
Sodium phosphate- 2%
Formic acid- 1%
Temperature- 60 degree Celsius
Time- 1h
PH- 6
MLR- 1:20
After
from Papen pepsin, tropism, pectinase may be used as a proteolytic enzymes for
degumming of silk. Degumming of silk can also be carried out with the help of
cellulolytic enzyme (cellulose).
Recipe:
Cellulase-
6%
Sodium bi-carbonate-
7.5%
Temperature- 70 degree Celsius
Time- 2h
PH- 8.5
MLR- 1:20
Enzymatic scouring of
cotton
To achieve good absorbancy of cotton, dirt, sizes and
natural impurities are usually removed by alkaline scouring. If these
impurities are not removed, can lead to the formation of AOX in the effluent
when NaOCl is used as a bleaching agent. Enzymatic treatment of
unscoured cotton fabric can be done with pectinase,cellulase, protease, lipase
and other enzymes. Cellulases are especially suited to scouring of cotton fabrics [12]. The
degree of whiteness of a cotton sample treated with cellulases only is lower by 8-10% than
the degree of whiteness of alkaline
boiled-off treatment. Pectinolytic enzymes can be used for enzymatic
degradation of pectin
adhering to cotton. Cotton fibres or their blends with other fibres can be treated with aqueous solutions
containing protopectinases for 18 h at 40~ to give scoured yams with good tensile strength
retention. The change in the water absorbancy of cotton is rapidly catalysed by
pectinases, cellulases or their mixtures. Pectinases can destroy the cuticle
structure by digesting the pectins in the cuticle of cotton. Cellulases can
destroy the cuticle structure by digesting the primary wall cellulose
immediately under the cuticle of cotton. By combining the enzyme treatment (a simultaneous treatment of
pectinase and cellulase), or
the alkaline boiled-off, with an alkaline peroxide bleaching, the total degree
of
whiteness is higher in combination with enzyme
treatment. Cellulases break the linkage from the cellulose side and the
pectinases break the linkage from the cuticle side. The result of the synergism is a more effective
scouring in both the speed and the
evenness of the treatment.
Enzymatic
Bleaching
The enzyme Glucose-Oxidase is used in enzymatic
bleaching of cotton(Bio-Bleaching).
Recipe:
Glucose oxidase - 0.125gpl
d-glucose - 20gpl
Magnesium Sulphate (peroxide activator) - 2gpl
Non-ionic surfactant (triton-x-100) – 1gpl
Time
- 120 min
Temperature – 85oC
MLR –
1:20
pH –
10
Biopolishing
Surface
modification of cellulosic fabrics to improve their cleaner surface conferring
cooler feel, brighter luminosity of colours, softer feel and more resistance to
pilling using cellulases is often known as bio-polishing.This
treatment can be applied to knit and woven cellulosic fabrics such as cotton,
viscose and linen and their blends. The elimination of
superficial micro fibrils of the cotton fibre through the action of cellulase
enzymes is obtained by the controlled hydrolysis of cellulose leaving the
surface of the fibres free and conferring a more even look. The
effect of cellulase enzymes on the fabric is hairiness. After enzyme treatment
the fabric improved their permanent softness and smoothness property. Further
the water regain is not decreased by the enzymatic treatment. Although
bio-polishing may be carried out at any time during wet processing, it is most
conveniently performed after bleaching. Fabric may be treated in either piece
or garment form and the treatment can be combined with another process or kept
as a single operation. Controlled finishing with cellulase enzymes optimises
the surface properties of the fabric, but decrease in tensile strength.
Effect of cellulase treatment in washing processes
There
are three methods to remove surface fibres from 100% cotton woven and knit
goods, namely singeing in the greige state and bio-polishing. The third method
is home laundering the fabrics using detergent that contains a cellulase
enzyme. Laundering of knit fabrics with detergent containing cellulase enzymes
help to maintain a clean surface appearance and the appearance of the fabric
look better even after multiple launderings.
Proteases, lipases and amylases are generally used to increase the
efficacy of removal of stains. Cellulases assist in the removal of par-
tabulate soils by removing microfibril from the cotton fibres, which initially
form the pills and which scatter incident light. The short fibre ends emerging
from the fabric surface is enzymatically hydrolysed, but an additional
mechanical treatment is necessary to complete the process, to remove the fibres
normally leading to pilling for example, rotating drum washers and jets. Prior
mechanical agitation makes cellulosic chains more accessible for cellulase
hydrolysis. The cellobiohydrolase rich enzyme mixtures produce more soluble
reducing sugars, which can also reduce the indigo clue and increase back
staining. In the two-step process of washing, the total loss of colour is about
20%, while the one step washing process yields a loss of colour of about 40%,
under the same conditions
Stone Washing
In
the stone washing process, the finished garments, whose fabric had been dyed
with sulphur, or reactive dyes or indigo are subject to the eroding action of
pumice stone in a washing machine in the presence of an oxidiser, usually
potassium permanganate. The treatment results in uneven decolourisation,
without excessive loss of fabric strength. The blue denim is faded by the
abrasion action of pumice stones. wash-out and stone-wash effects can be
produced on dyed jeans by subjecting piece goods to a bio-finish process with
suitable cellulase complexes without pumice stone and bleaching agents. Complete
or partial replacement of pumice stones by cellulase enzymes for the effect of
stone-washing on denim is well established and hundreds of looks can be
generated from any piece of standard denim fabric. The enzymes or combination
of enzymes eliminate partially projecting dyed fibres, exposing the undyed
material underneath. This forms the uneven, colour-flecked surface of wash-out
article, but with no material surface damage and with an elegent fabric
appearance. The surface frictions play an important role in the enzymatic
decolourisation of cellulosic fabric]. The mechanical action opens the
outermost layers of the cellulosic crystal, thus increasing the part of the
cellulose accessible to enzymes, and allowing the enzymatic removal of the dye.
The use of acid cellulases are recommended for fast treatments and neutral
cellulases for more severe treatments when marked effects are required.
Endoenriched acid cellulase is found to be best for easily weekened fabrics
such as linen and viscose rayon. Standard whole acid cellulases are best for
sturdy fabrics such as lyocell, modal rayon and heavy weight cotton .
Application of
enzymes in pre-treatment processing of jute
The cellulase, xylanase and pectinase enzymes have
tremendous effect on processing of jute. The treatment of enzyme before
bleaching of jute improve whiteness whereas due to backstaining at optimum pH, there is
decrease in whiteness and
increase in yellowness index, if treatment is carried out after bleaching. The enzyme action is more on 4% NaOH scoured fabric.
Scouring causes higher hemicellulose loss producing open structure and thus larger surface
area of lignin is accessible
to hydrogen peroxide resulting in higher whiteness.
Treatment of Protein Fibres with Enzyme
Wool Carbonisation
Vegetable
matters of wool are normally removed by a process known as carbonising.
Carbonisation of wool with inorganic acid may cause some degradation of the
fibre. The replacement ofcarbonisation by the use of enzymes, such as
cellulases, ligninases, hydrolases, lyases and oxidoreductases are reported. A
biochemical alternative using complex combination of enzymes to the chemical
process of carbonising with sulphuric acid is also reported. The amount of
sulphuric acid required for carbonisation can be reduced by the action of
cellulolytic and pectinolytic enzymes.
Wool bleaching
Bleaching
of wool is necessary for the enhancement of whiteness and lustre. Using
proteolytic enzymes alone or in combination with peroxide, the degree of
whiteness and hydrophilicity of the fibres are increased, compared with the
oxidative treatment alone. Serine protease stable to hydrogen peroxide is
active in an alkaline medium and its activity increases with increasing
peroxide level. Higher whiteness index is caused by the decolourising action
ot" the enzyme on natural colorants present in the wool fibre.
Shrinkproofing and hand
modification of wool
Wool
fibres have a tendency to felt and shrink due to its scaly structure. The
differential frictional effect (DFE) causes the fibre to move towards their
root end when mechanical action is applied in the wet state. Generally
shrinking of wool is done either by oxidative or reductive methods and/or by
application of resin. The most frequently used commercial process consists of
chlorination, followed by dechlorination and polymer application. Among the
various processes, nickelcatalysed surface degradation by hypochlorite and the
use of second generation' chlorination equipment are
commercialised. Though such descaling is expected to improve the handle of the
wool fibres by making them smoother, the handle is actually made harsher,
perhaps because the fibres become sized by degraded protein. However, the
softness of the fabric can be improved as a final application of a silicone
microemulsion but expensive equipment are needed.
Conclusion
Environment
friendly pre-treatment processes of textiles are the need of the day due to
tremendous awareness of chemical pollution and mounting legislation to limit
the chemical burden of the factory effluent. Biotechnology can be used for the treatment
of wastes which can solve the problem either partially or totally. The use of
enzymes in the pre treatment process can deliver the requirement of being
eco-friendly as it easily degradable. Also there us no residul remaing in the
fabrics after treatment process which in turn does not cause stains in the
fabrics. Moreover, the use of enzymes is also time consuming.
