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NONWOVEN

Introduction

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The recent years have been marked by a rapid development of new unconventional techniques in textile production. A common feature of these new technologies has been a partial or complete elimination of conventional textile operations such as weaving, knitting, spinning etc. One of the distinguishing marks of the new products, which cannot be identified by the criteria of conventional textiles, are their particular specific properties and end uses. Nonwoven product is one of them. In textiles, nonwovens represent the highest growth segment and, over a decade, the extent of textile fibre used in nonwoven outlay has exceeded fibre usage in woven, knitted and other outlets.
 


What is Nonwoven Fabric?
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Nonwoven is a fabric made by unconventional method of fabric preparation. Conventional methods are spinning, weaving, knitting where a series of machines are required to make a fabric. But in nonwoven, fabric is prepared directly from fibres by bonding them mechanically, chemically or some other way with the help of a small set of machinery. Different organisations have explained the nonwoven fabrics in different way, but the definition by the American Society for Testing Materials [ASTM D1117.80] includes most fabrics, which most people regard as nonwovens. According to ASTM, the definition is as follows: ‘A nonwoven is a textile structure produced by the bonding or interlocking of fibres, or both, accomplished by mechanical, chemical, thermal or solvent means and combinations thereof. The term does not include paper or fabrics that are woven, knitted or tufted.’
In fibre processing, it is common to make first a web (a thin semi-transparent layer of fibres where fibres are attached by surface cohesion only) and then to lay several webs on top of each other to form a butt, which goes directly to bonding by mechanical, chemical, thermal or solvent means.
 


Why Nonwoven Fabric?
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Nonwovens have many fold advantages over other types of textiles. They are as follows:

The rate of production is very high.
The manufacturing line is shorter than the other textile processes.
It is a continuous process directly from the raw material to the finished fabric,
The labour cost of manufacture is low, because there is no need for material handling as there is in other textile processes,
It produces cheaper fabric for the same area density,
This industry can produce a very wide range of fabric properties from open weddings suitable for insulation containing only 2-3% fibres by volume to stiff reinforcing fabrics where the fibre content may be over 80% by volume.
In many instances, the amount of raw materials per unit of production is decreased, or lower quality materials can be used to achieve an effect similar to that obtainable with superior material with traditional equipment.

Nonwoven fabric has proved its potential in synthetic arena. Nonwoven machinery has reached a high level of engineering quality and design. The continued development of process and its product has allowed nonwoven fabric to become widely used in both domestic and industrial situations. Blankets and floor-coverings are probably the most common domestic application, whereas filtration media, civil engineering substrates and papermaking felts dominate the industrial market.

 


Different Nonwoven Process
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The nonwoven fabric manufacturing process can be divided in two steps:
Butt Production (to lay several webs on top of each other)
Bonding of fibres in different means

Batt production using carding machine
A nonwoven machine usually consists of automatic fibre blending and opening unit (to break, to clean the fibre strands and to mix with other fibres or qualities) feeding automatically to one or more roller and clearer cards (fibre stands are individualised, parallelized and levelled by this part). The output of a card is a thin sheet of fibres called web, where fibres are adhered by frictional contact only. The mass per unit area of card web is too low (about 40 g/m2) to be used directly in a nonwoven machine to make fabric. The uniformity and required mass/unit area can be increased by laying several card webs over each other to form the batt. The fibre orientation in the batt is of three types; parallel laying, cross laying and random laying (Fig 1). The different ways of batt formation are described below.

Parallel-laid    Cross-laid    Random-laid
 


Methods of Bonding

Mechanical Bonding
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Needle punching
    Needle punching is a process for converting batt of fibres into coherent fabric structures, normally by means of barbed needles, which produce mechanical bonds within the web. Parallel laid, cross laid and random laid batts can be used to make a needle punched nonwoven fabric. It is manufactured by continuous penetration of barbed needles through the fibrous batt, in which the fibres can be entangled and form mechanical bonds (Fig 7). Potential of use of jute in this area was explored.

needle

The main disadvantages are that it gives thicker fabric. Finer fabric losses its uniformity. This fabrics are weaker and bulkier in properties.
            Such fabrics are basically used in paddings, insulation media, reinforcing material, packaging etc.

Stitch bonding
    Stitch bonding uses mainly cross-laid and air-laid batts. The batt is taken into a modification of a warp knitting machine and passes between the needles and the guide bars. The batt can be bonded by threads or by fibres. The nature of this fabric is very textile like, soft and flexible. The fabric can be used for insulation and as a decorative fabric. It seems that there is potential of use of jute in this area, which is unexplored till date.

Hydroentanglement
As the name implies the process depends on jets of water working at very high pressures through jet orifices with very small diameters. The jets are arranged in banks and the batt is passed continuously under the jets held up by a perforated screen, which removes most of the water. Fibre ends become twisted together or entangled by the turbulence in the water after it has hit the batt. The supporting screen plays a vital role to the process. This method has not been tried on jute and possibly; this may not be suitable for high hygroscopic property of jute.

 


Adhesive Bonding
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1) Saturation bonding: This wets the whole batt with bonding agents, so that all fibres are covered in a film of binder. Generally, saturation bonded fabrics are compact and relatively thin. Most of the physical properties of saturation-bonded fabric derive from the fact that all the fibres are covered with a film of binder. First, the fabric feels like the binder and not the fibres it is made from. However, in some cases like jute nonwoven, this can be an advantage, because by using either a hydrophobic or a hydrophilic binder the reaction of the fabric to water can be changed regardless of which fibres are used. The uses of such bonded fabric are interlining fabric for textile clothing, filter fabrics, wiping cloths etc. Jute is very much suitable in this process.

2) Foam bonding: One of the problems of saturation bonding is that too much water is used and it increases the cost of drying as well as risk of binder migration. The method of foam bonding is almost same as saturation bonding; only binder foam is used in place of adhesive solution.

3) Print bonding: Print bonding involves applying the same types of binder to the batt but the application is on limited areas and in a set pattern. The batt is first saturated with water and then printed with either a printing roller or a rotary screen printer. The binder formulation must contain some thickener to prevent the binder migration from the printed area. Print bonded fabrics are much softer in feel and also much more flexible, but weaker than saturation bonded fabrics.
It is used in disposable /protective clothing, cover stock and domestic wiping cloths.

4) Spray bonding: The binder may also be applied by spraying, using spray guns similar to those used in printing, which may be operated by compressed air. The product is a thick, open and lofty fabric used widely as the filling in quilted fabrics, for some upholstery and also some types of filter media.

 


Thermal Bonding
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Jute nonwoven can be made using thermal bonding process. A blend of fusible fibre having very low melting point, with jute fibre can be used. Thermal bonding is used with all the methods of batt production. The uses are in some upholstery, some filter media and filling in quilted fabrics. The low-pressure thermal bonded products used as insulation, as rather expensive packaging, or for filtration. The main uses of calendared high pressure thermal bonded nonwoven are in some geotextiles, stiffeners in some clothing and in shoes, some filtration media and in roofing membranes. Thermoplastic powders may be used as an alternative to thermoplastic fibres for bonding in the methods of thermo-bonding. The uses are in high bulk applications, protective apparel and cover stock areas.
 


Solvent Bonding
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In one application of the method, a spunlaid polyamide batt is carried through an enclosure containing the solvent gas, NO2 which softens the skin of the filaments. On leaving the enclosure bonding is completed by cold calendar rolls and the solvent is washed from the fabric with water using traditional textile equipment.  The other application uses a so-called latent solvent (not a solvent in room temperature but becomes a solvent at higher temperatures). This liquid latent solvent is used in conjunction with carding and cross laying. The batt is passed to a hot air oven, which first activates the solvent and later evaporates it. This form of bonding is rarely used but it is interesting in the point of view that the solvent can be recycled.
 


Uses of Nonwovens
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  • Waddings and paddings: Sanitary articles, Apparel paddings, Furniture paddings.
  • Thermal insulation materials: Packing and wrapping materials, Industrial and building thermal insulations, Apparel warmth retaining interlinings.
  • Acoustics insulation : Industrial and building insulations
  • Reinforcing material: Shoes and leather wear interlining, bookbinding, Shirt collars, Apparel interlining,
  • Decorative Textiles : Curtains, Ribbons,
  • Household textiles: Upholstery fabrics, Carpets, Towels, Table cloths , Napkins, Bed linen,
  • Industrial material: Covers, Tarpaulins, felts, Filters, Protective clothing,
  • Apparels :Underwear, Blankets, Coat, Ladies dress fabric, Childrens dress fabrics.

 


Use of Jute in Nonwoven
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Nonwoven technology is considered to be a forward technology and is one of the promising alternatives very much suited to the jute industry. Nonwoven technology appears to be particularly relevant to the jute industry in view of its high productivity and low wage component of the production cost associated with it. Besides, this offers a means of diversifying into various value-added products which would fetch better returns to the industry using even waste fibres. Today production of jute nonwoven fabrics is limited to a few thousand tons of needled felts used mainly for packaging, cushioning, carpet underlaying. Thus much of the jute nonwoven textiles remain untapped. Jute needle punched nonwoven products offer cost effective and market oriented diversification for jute. However, more extensive research, intensive production and marketing expertise has to be built into the jute sector to make jute nonwovens a commercial success for jute diversification.
In ‘Jute Nonwoven’, jute is the only fibre used in the nonwoven bonded by mechanical or chemical means, whereas if some other fibres (natural or synthetic) used along with jute in major proportion, it is called ‘Jute-based Nonwoven Fabrics’.
National Institute of Research on Jute and Allied Fibre Technology (NIRJAFT), Kolkata (Previously, Jute Technological Research Laboratories (JTRL)) of Indian Council of Agricultural Research (ICAR) has done pioneering work since last 30 years in the development of jute nonwoven textiles for various applications. The researches have been carried out in following broad areas: (a) use of unspinnable fibre wastes, (b) to identify and characterise the different uses, (c) blending of jute with other natural or synthetic fibres, (d) to study the structure-property relations. Out of various systems of nonwoven preparation, parallel laid, cross laid and air laid batts are appears to be suitable in fabric preparation with needle punched and adhesive bonded nonwoven technologies, particularly with relevant to jute. The appropriate technology of manufacturing jute nonwovens, which is the outcome of different research projects of NIRJAFT, not only produces the diversified products from jute but also creates the value addition. This book highlighted the research outputs on needle punched nonwoven fabrics, products and their uses.
 


Why jute?
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Unique natural colour; smooth and glossy fibre surface.
High strength, modulus and dimension stability.
Moderate draping.
Good moisture absorption and breath ability.
Good bleach ability, dye ability and printability.
Low cost
Annually renewable and abundantly grown in India.
Biodegradability and eco-friendliness, vegetation and bio-technical support with enhancement of organic matters and nutrient levels to the soil after degredation.
Resistance to weather and microbial attack better than cotton.