PRODUCTION POSIBILITIES OF SILK NON-WOVENS

1. Introduction:

Silk is a natural fibre & is got in a filament form. It has very unique characteristic &

aesthetic appeal like its sheen; its handle; its comfort & its drape which are unmatchable.

This wonderful fibre is spun in the form of a filament by the silkworm larva. India is the

only silk producing country in the world having all the four varieties of silk viz.

Mulberry, Tasar/ Tussah, Eri/Endi, & Muga Silk. The last three silk being categorised

under the Non-Mulberry or VANYA silk.

Silk industry in India, is predominantly decentralised. It is hindered by age old practices

and conventional manufacturing techniques which have limited the range of products and

its uses. Besides, the advances in the synthetic fibre manufacturing technologies have

brought in many challenges for silk fibre industry in several aspects, including the

productivity. Therefore, there is a need to present silk in a new form and in competitive

way. Thus product diversification is the need of the hour, as it not only helps to expand

the market base and adds value to the end product, but also generates additional

employment and income to the Sericulturists.

An attempt has been made to diversify and produce silk non-wovens using silk filament

& silk waste by employing the silkworm to spin the filament in a sheet form (instead of

cocoon) on one hand & on the other, applying the principles of non-woven (bonding &

mechanical) technology and blending it with creativity of the artisans. Special emphasis is

laid on the silk waste generated during the conversion from the cocoon/ pupae stage to

silk fabric. Non-woven is a continuous web sheet or fabric like material composed of

fibres which are mechanically and/or chemically bonded together and is not made by

weaving, knitting or conventional textile process.

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2. Silk production details & Generated Silk Waste Data

Year

Production of raw silk in Tons

Generation of silk waste in Tons

% of silk waste v/s production of raw silk

Mulberry Vanya Total Mulberry Vanya Total Mulberry Vanya Total

1995-96 12884 1025 13909 4022 208 4230 31.2 20.3 30.41996-97 12954 1172 14126 4000 247 4247 30.9 21.1 30.11997-98 14048 1188 15236 4215 235 4450 30.0 19.8 29.21998-99 14260 1284 15544 4250 253 4503 29.8 19.7 29.01999-00 13944 1270 15214 4153 248 4401 29.8 19.5 28.92000-01 14432 1425 15857 4237 305 4542 29.4 21.4 28.62001-02 15842 1509 17351 4655 319 4974 29.4 21.1 28.72002-03 14617 1702 16319 4514 336 4850 30.9 19.7 29.72003-04 13970 1772 15742 3764 373 4137 26.9 21.0 26.32004-05 14620 1880 16500 3587 365 3952 24.5 19.4 24.02005-06 15445 1861 17306 3705 297 4002 24.0 16.0 23.1

0

5

10

15

20

25

30

35

%

Year

% of Silk waste generated in the country over decade

Mulberry Vanya

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4. Waste generated in silk sector:

During the conversion or the processing of Raw silk filament into fabric, generation of

waste at every stage is inevitable. So much so, due to the economic aspect, silk waste is

not discarded & is used in producing yarns such as Spun silk, Noil silk, Ghicha, Matka,

Katia etc. At each stage of processing of silk, inferior yarn in comparison to the previous

stage is produced. Thus generated waste is utilised to the fullest extent in the subsequent

stages. Thus by giving an additional avenue i.e. of producing silk non-wovens, an

opportunity to reap additional financial benefits arises. Being eco friendly, silk can

replace very easily some of the man made fibres due to its lustre, warmth, absorption

property, etc.

Wastes generated in various stages of silk production are:-

a) Floss generated during the deflossing of cocoon

b) From defective cocoons which are sorted out before reeling

c) Cut cocoons which are produced during reproduction

d) Waste generated during cooking, reeling and re-reeling

e) Preparatory twisting and warping waste

f) Weaving waste (shuttle-less loom selvedge waste)

g) Wet processing (degumming) stage.

Thus, using these wastes in an effective way is like fringe benefits to the silk producer.

Additionally, all the secondary & tertiary stage produced yarn could be used for

production of non-wovens.

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5. Production techniques of Non-wovens:

Experiments were initially carried out to see the productivity aspects. Trial production

on a larger scale established the viability of non-wovens especially in arts & artefacts,

fashion designing & upholstery. As already mentioned, utilising the silkworm to

produce a sheet like fabric (or simply called as self bonding of fibres in the fabric) or by

using silk waste & adopting the non-wovens production techniques like chemical

bonding or mechanically interlocking of fibres with help of needle punching, silk non-

wovens can be produced.

A. Self bonding of filaments into a fabric:

This happens during the cocoon spinning stage by silk worm larvae. As the silk worm

spins the silk; it produces a gum called Sericin which cements the silk filament known as

Fibroin. The advantage of this gum which is part & parcel of silk spinning is effectively

utilised in the production of non-wovens. Invariably, when silk yarn is used for fabric

production, this Sericin portion is removed during the degumming process. This naturally

adds to the pollution of the environment. With the effective usage of this gum, nearly

25% wastage that would have otherwise occurred is eliminated. During the production,

the silk worms randomly deposit their silk onto a template, each silk worm produces

about one mile of continuous thread. To produce just 100 grams of normal produced silk,

l500 silkworm are killed by stifling. In contrast while adopting this process, the silkworm

continues to live their whole cycle of life, and the silk farmers who tend them, enjoy a

livelihood that is environment friendly. When the spinning is completed, the silkworms

turn into chrysalis and are moved into a safe environment for a fortnight or so when it

metamorphosis to silk moths and these moths could be used for reproduction cycle. After

the life cycle of the silk moth, it is used as fertilizer for cultivation.

Procedure – Plywood of 3’ x 3’ attached on to a pivot arrangement is fixed on a tripod.

Adult silk worms ready for spinning, are kept over the wooden plate and allowed to spin

on the surface. During spinning, the worms move from one end to another and in doing

so, the frame also gets rotated due to the shifting of load on the plate. After 5 to 6 days of

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Production layout

Spinning, the silk sheet thus formed is removed from the plate. The silk sheet thus

produced is cleansed and then immersed in hot water and treated at 80-85 degrees for 15

minutes. The formed sheet is examined & if required, layers are removed in some places

to give uniformity. Depending on the end use, additional layers may be added during this

process. The water is squeezed & pressed by the calendaring process. This moderately

uniform sheet can be taken up for bleaching or dyeing under controlled conditions.

Dyeing process Finished product

Spinning of Filament by the silkworm

Segregating & peeling of layers to achieve uniform sheet

Controlled bleaching & dyeing

Application of finishes

Value add-ons like embroidery, printing, painting etc.

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B. Adhesive bonding of silk fibre got from silk waste:

Procedure:

Preparatory process:

Fibre: Raw material in form of waste comprising of

deflossing waste, reeling waste and basin waste,

cut/pierced/ defective cocoons are thoroughly cleaned.

Importantly silk waste containing pupal parts, dirt &

other impurities are to be separated to obtain clean silk

fibre. After removing the impurities, silk waste may be washed in plain water,

degummed with soap and soda or bleached with Hydrogen Peroxide & Sodium Silicate

and then dyed. Dry and cleaned silk waste is further opened by hand fed onto a fine fillet

machine. 5 to 10 g of hand opened silk waste is processed on fine fillet machine to obtain

a lap (7.5 cm x 1 m) of more or less parallel fibres. The lap of uniform thickness and

weight per unit length, thus prepared, are used for making silk non-wovens or felts.

Adhesive: The construction of a non-woven with suitable adhesive is to achieve improved

characteristics such as strength, firmness, durability & stiffness. Further, depending on

end uses, both fabric & the adhesive need to display fire retardence, hydrophilic,

hydrophobic, anti-microbial properties, organic compatibility, reduced surface tension,

improved dimensional stability to solvent, wash and acid resistance. PVA (poly vinyl

acetate) or PVC (poly vinyl chloride) can be used as adhesives. A solution of PVA (10

g/litre) in plain water is prepared and applied to prepare silk non-wovens.

Production process:

Laying out the fibres: Place a piece of acrylic sheet on the table. Prepare the silk waste

in lap as described above, to be laid on the acrylic sheet. Lay lap horizontally across the

top of the sheet; continue moving downwards creating continuous fibre strips until you

have reached the bottom left corner. Each lap segment of

silk should over lap the other in all directions so as not to

see the acrylic sheet underneath the table.

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A second, third and even fourth layer of silk can be applied. The desired thickness of the

felt will be dependent on the final use. Pieces that will be manipulated or sewed later will

require more than one layer. For maximum sheen, the fibres should be laid out as

smoothly and as parallel as possible. A certain amount of skill is required to do this.

Wetting: Before applying adhesive, the laid lap sheet should be wetted thoroughly, so the

silk accepts the adhesive. Silk sheet is wetted by sprinkling

plain water or soap solution over it. It takes more water and

time to penetrate the fibres than one might anticipate. The

silk sheet changes to a darker colour and becomes very flat

with no air pockets once the water has been soaked. Use a

smooth glass or stainless steel rod of 2cms diameter and apply pressure by rolling it over

the sheet. This will help the water or solution to penetrate uniformly and the sheet

becomes still flat and excess water is wiped out.

Application of adhesive: Pre-prepared adhesive (depending on the end use of the non-

wovens) is spread all over the wetted silk sheet, slowly and evenly. Pressure is applied by

rolling the steel rod over the sheet as done during wetting.

Applying of adhesive Pressing

Drying: The felt prepared on acrylic sheet is dried under the shade, as the sun rays have

destructive action on the silk fibre. It takes about 3-4 hours to dry.

Peeling of non-wovens: When the fusion is completed, felts are slowly removed from the

acrylic sheet.

Curing: For final setting of the adhesive, the non-wovens must be heat set. Ironing also

helps to flatten or remove fluffy surface. Always use a press cloth while ironing the felts

to avoid gumming up of the iron surface. The acrylic sheet is washed with warm water

and wiped, dried and kept ready for next batch of silk non-wovens preparation.

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Raw material (Cleaned Silk Waste)

Degumming/ Bleaching/Dyeing

Washing

Drying & Opening by Hand

Mechanical opening & web formation in lap form

Lap laying & bonding with Adhesives (Chemical bonding)

Pressing (steel rods), Drying (under shade) and Curing (ironing)

Finishing techniques (printing, embroidery & finishes etc)

It is observed that the softness and lustre of mulberry fibre is well reflected in the non-

woven sample, though the concentration of binder used, weight of the fibre taken and the

process followed were identical for all varieties of silk.

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C. Mechanical bonding of silk fibre got from silk hard waste:

This waste especially hard waste generated during twisting and weaving can be more

effectively utilised for development of silk non-woven fabrics for increased value

addition besides diversified application. It is observed that the hard waste generated to the

extent of 300 MT in silk twisting and weaving (Shuttle less looms) is not being used for

any purpose. Apart from this, even silk waste, fibres obtained from non-reelable cocoons,

filature yarn, fabric selvedge etc can also be used.

The procedure for opening & cleaning of the fibres followed here are similar to chemical

bonding. Here the mechanical methods i.e. the use of needle punching machine to

entangle the fibre into web like structure is employed.

The preparation of the raw material is done as follows:-

Between two layers of fibre webs (got in a lap form), cotton net is used. If required,

additional fibre webs are laid in a sandwich fashion. This is then fed into the needle

punching machine.

Selection of Raw material

Preparation of fibre (Degumming/stripping of colour)Opening and lap formation

Web formation

Web bonding (Mechanical)

Dyeing, Drying and Curing

Finishing techniques

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Line diagram of needle punching machine

Z I- Fibrous web feeding and compression zone; Z II – Needle punching zone; Z III- Drawing-off zone;

1 - Needle beam; 2 - Needle board; 3 – Needles; 4 - Feed table; 5 - Draw-in rollers; 6 - Bed plate (lower hole plate); 7 - Stripper plate (upper hole plate)8 - Drawing-off rollers.

Selvedge waste Needle Punched Fabric

Non-woven care:-

Yes, you can wash all products in Luke warm water or dry cleaning is the best option.

Some natural dyed samples

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6. Uses/applications

Appliqué for clothing, Appliqué work on hand crafted items

Inner lining for warm garments

Head caps, ties, garments & blankets

Furnishing and home apparels

Handicrafts items like wall paintings, wall hangings, wall coverings, gift tags,

bags, purse/wallets, table mats, matting for pictures, journal/book/album covers

greeting/invitation/business cards, lamp shades & many many more …..

Imagination is the limit.

Technical & Medical textiles

Embroidery & appliqué work

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6. Conclusions:

The objective of developing non-woven product out of all the 4 varieties of silk

fibre is possible.

The manufacturing technology evolved suits the decentralised sector also.

It is a low cost technology

The product standardisation would automatically lead to standardisation of

process parameters and would be within the capacity of targeted stake holders.

A systematic approach for its marketing would generate sustainable self

employment for the villagers.

Silk lovers get a new product in a competitive way.

Effective utilisation of silk & its produced waste.

Embroidery Work

References:

Dr. V. K. Kothari: Non-wovens and their application in filtration

www.livesilkrevolution.com

Indian Silk – Nov 05 to Apr 06

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