Origin - Jute is a natural vegetable fibre under the category of bast fibres like flax, hemp, kenaf and ramie. Since ancient times, it has been traditionally grown in the eastern part of the Indian subcontinent, which make up of the present day West Bengal of India and plains of Bangladesh. Jute is an annually renewable plant belonging to the genus Corchorus of the order Tiliacea. Normally, two species viz. Corchorus Olitorious and Corchorus capsularis, commonly known as Tossa and White jute respectively are produced in commercial scale. Another bast fibre crop commonly known as Mesta has two cultivated species – Hibiscus cannabinus and Hibiscus Sabdariffa.
The word jute was first published by Roxburg, the then Superintendent of Botanical Garden, Shibpur, West Bengal in the year 1795, in his letter addressed to the Board of Directors of East India Company. The first jute mill in India was set up in the year 1855 at Rishra, near Kolkata.
Jute Cultivation – A Brief Over view
Land – Jute can grow in wide range of soil but fertile loamy alluvial soil is better suitable.
Soil pH – 6 -7.5 is ideal soil pH where jute is cultivated.
Climate – Relative humidity between 40-90% and temperature between 17° C and 41°C, along with well distributed rainfall over 1200 mm is ideal for cultivation and growth of jute.
Harvesting & Retting – Jute crop can be harvested between 100 – 120 days. After harvesting the jute bundles are kept in the field for 2 -3 days to allow leaf shedding. The bundles of jute stems after defoliation are placed in retting tank in ‘Jak’ and weighed down under water and places at a depth of 10 cm. Retting is a microbial process by which the fibre from the woody core (stick) is loosened. Bacteria and fungi act upon the soft tissues of the stem, which on dissolution makes it easy to separate the fibre from the core (stick). At normal temperature of 34° C, it taken generally 8-10 days for complete retting.
Jute Grading - Jute cultivation is confined to West Bengal, Eastern Bihar, Assam, Orissa, Tripura and Andhra Pradesh where mostly Mesta is grown. Out of these states, West Bengal, Bihar and Assam contribute about 80% of the total production. Again, these three states may be further classified quality-wise in five principal jute growing areas, i.e. South Bengal, Semi-Northern, Northern, Assam and Junglee (Purnea region). The places of origin, i.e. Mokam was the basic guiding factor in the old system of grading, whereas in the new grading system introduced by BIS in 1975, six characteristics viz. strength, defects, root content, color, fineness and bulk density have been considered for grading Tossa and White jute. The raw jute have been classified into eight grades (08), starting from TD1 / W1 (most superior) to TD8/W8 (most inferior). Mesta on the other hand has been classified into six grades (M1 to M6).
Jute Processing – An overview.
- Selection or Batching: The word ‘selection’ means segregation of jute fibre according to quality and formulation of batch mix for different end products with reference to availability, cost and processing convenience. The selection process followed in the mill is subjective in nature.
- Softening: In this process, the jute reeds are passed through a series of spirally fluted heavy rollers and are simultaneously subjected to an oil-water emulsion application with an objective to soften the rigid jute fibres as well as the fibre joints in the meshy jute reeds (strands of fibre) and also to clean the fibres from loosely adhered extraneous matter. Then emulsion added jute reeds are piled under a cover for 1 – 3 days, softening of the jute reeds take place due to some biological phenomenon. This process is known as ‘piling’. Softening is carried out by Softener machine or Spreader machine, the latter being more economical due to lower man-power requirement.
- Carding: Jute carding is a critical processing stage. The breaker card is considered to be the heart of the jute processing system. The generation of spinnable fibres from long meshy jute reeds starts at this stage. This process changes the input material into sliver (tapes / ribbons) of desired linear density composed of fragments of original mesh after transverse breaking and longitudinal splitting of the jute reeds. This process is generally done in two stages, Breaker and Finisher Card, with occasional Inter Carding done in case of very coarse fibres used for sacking variety.
- Breaker Card: After piling, the hard barky root portions of jute reeds are cut and their soft and pliable portions are manually fed to a card, called the Breaker Card, since it breaks the meshy structure of jute to generate individual filaments.
- Finisher Card: For the sake of satisfactory spinning performance and producing yarn of acceptable quality, another carding operation with the help of more denser and finer pins as compared to those of breaker card is felt necessary to split further the fibres longitudinally into finer elements.
- Drawing: By the process of drawing, the card slivers are made more thin with improved parallelization and thereby more suitable for spinning. Thinning (attenuation) of sliver and improvement of fibre parallelization are progressively done with the help of 2 or 3 drawing passages.
- Spinning: In the spinning frame, the sliver delivered from the last (finisher) drawing frame is further elongated by drafting to the specified linear density of the final yarn and is finally twisted to form the yarn. Each of the jute spinning frame has 3 simultaneous and essential functions namely drafting, twisting and winding. Generally flyer spinning frames are used for spinning of jute yarn.
- Winding: One of the main objectives of winding is to remove faulty places in the yarn like large thick places and slubs to assure better performance of the yarns during post – winding operations like weaving. Winding of warp and weft are done separately in spool winding and cop winding machine respectively.
- Beaming: The warp yarn packages (or spools) are placed in the creel of the beaming machine which delivers the warp beam or better known as the weaver’s beam.
- Weaving: It is basically the process of interlacement of the warp and the weft and is carried out in the loom for fabric manufacturing. The looms used in the jute industry for producing conventional products are shuttle looms, though shuttle-less looms are also used for producing finer fabrics for value added products.
- Finishing: It consists of a sequence of steps to convert the ex-loom fabric into final sellable product. The processes along with their brief function is given below:
- Damping / Unwinding: Unwinding of cloth rolls and moistening prior to calendaring operation.
- Calendaring: Flattening of the constituent threads of the cloth mechanically to produce better cover and surface finish.
- Lapping (used for hessian only): Folding of the fabric into desired length to make is suitable for packing.
- Cutting (used for sacking only): The cloth is cut by rotary or guillotine type cutting machine for manufacturing bags of pre-fixed lengths.
- Sewing (used for sacking only): It involves sewing the cut length of the sacking fabric to produce a sack (bag) of desired dimension. Stitching of the raw edges of the bag is called hemming and stitching at the sides is done by Herakle machine.
- Safety stitching: This type of stitching is provided additionally during bag manufacture, to provide additional safety against seam failure.
- Branding: Bags are branded manually by screen printing method.
- Bundling (used for sacking only): Bundles of 25 bags are made prior to baling.
- Baling: Bales are formed with these bundles with the help of a baling press. For A Twill and B Twill 400 and 500 bags are packed per bale.