About Nonwovens Textiles

• Nonwoven stuffs are largely describes as piece or web structures bonded simultaneously by entangling fibre or filaments mechanically, thermally or chemically.
  
  
• They are smooth, porous piece prepared directly from part of fibres or from molten plastic or plastic layer.
  
  
• Definition of nonwovens by EDANA

• Felts manufactured by wet milling, this is the reason that they are not categorizes under nonwovens.
• According to EDANA wet laid webs are considers as nonwovens, provided they contain
1. A minimum of 50% of manmade fibres or other fibres of non vegetable origin with a length to diameter ratio equals or superior to 300, or
2. A minimum of 30% of man-made fibres with a length to diameter ratio equals or superior to 600, and
3. The maximum apparent density of 0.40 g/cm³.

• Comparison between different rates of production in the manufacture of textiles & similar materials:

*Average output 5 m2.h-1

Market share of different web laying process:

Non-woven fabric properties

• INDA defines nonwoven fabrics as an engineered fabric that may be a limited life, single-use fabric or a very durable fabric.
• Nonwoven fabrics have various functions such as
  1. Stretch ability,
  2. Flame retardancy,
  3. Wash ability,
  4. Strength,
  5. Absorbency,
  6. Liquid repellency,
  7. Resilience,
  8. Softness,
  9. Cushioning,
  10. Filtering,
  11. Bacterial barrier and
  12. Sterility.
• These characteristics are frequently combined to make fabrics suitable for exact jobs.
• Specific properties can be achieved by
  1. Selecting raw materials and
  2. Applying finishing treatments to nonwovens, such as printing, moulding laminating etc

Production Process

• The manufacturing of nonwovens get place in three stages
• The three stages are:
  1. Web Formation
  2. Web Bonding
  3. Finishing Treatments

Process flowchart for producing nonwoven

• For manufacturing nonwoven fabric very first step is to make web or sheet by the arrangement of fibres or filaments.
• The main raw material may be in the staple fibres jam-packed in bales, or filaments which are extruded from molten polymer chips.
• Four basic methods are used to form a web are:
  1. Dry laid
  2. Spun melt
  3. Wet laid
  4. Other techniques
     
     

A)   Dry laid

• There are two methods of dry laying:
  1. Carding
  2. Air laying

1. A carding machine

• It is a revolving drum or series of drums covered in fine metallic wires or teeth.
• Carding is a mechanical process starting with the opening of fibre bales which are blended and conveyed to the next stage by air transport.
• They are after that combed into a web by a carding machine.
• The exact configuration of cards depends on the fabric weight and fibre properties needed.
• The web can be parallel-laid, or can be random-laid.
• The parallel-laid carded webs result in
  1. Good tensile strength,
  2. Low elongation and
  3. Low tear strength

in the machine direction and the reverse in the cross direction.

2. In air laying:

• Generally tiny fibres are fed into an air flow.
• From here it goes on to a moving belt or perforated drum, where they form a randomly oriented web.
• Air laid webs gives greater adaptability in terms of the fibres and fibre blends that can be used.
• Compared with carded webs, air laid webs has lower density, greater softness and the laminar structure is absent.

B)   Spun Melt

• Spun melt is a generic term describing the manufacturing of nonwoven webs directly from thermoplastic polymers.
• It consists of two processes:
  1. Spun laid
  2. Melt blown
     

1. In spun laid process

• Also known as spun bonded
• Polymer granules are melted and then the molten polymer is extruded throughout spinnerets.
• Then the continuous filaments are chilled and dump on to a conveyor belt to structure a uniform web.
• In the spun laid method, the raw material elasticity is more controlled; however it gives the nonwovens superior strength. Co-extrusion of second components is used in numerous spun laid methods, generally to provide extra properties or bonding potential.

2. In melt blown

• In melt blown process web is formed by comparatively low viscosity polymers which are extruded into a high velocity air stream.
• This distributes the melt, solidifies it and breaks it up into a fibrous web.

C)   Wet laid

• The method of wet laying is similar to paper manufacturing but with synthetic fibres.
• Dilute slurry of water and fibres is dumped on a moving wire screen and drained to form a web.
• After that with the help of pressing between rollers the web is dewatered, consolidated and then dried out. Impregnation with binders is frequently integrated in a later phase of the progression.

D)   Other techniques

• This consists of a no of specialize technologies, in which the fibre manufacture, web construction and bonding generally take place at the same time and in the similar position.
• As specified above specialize technology the most important is the electrostatic spinning, where mainly fibrillation takes place to form the web.
• With the development in technology now machine manufacturer are thinking of merging two or more web forming technology simultaneously to increase the productivity & advance end use properties. For e.g. the spun laid/melt blown process are combined to make the SMS composite nonwoven fabric.

• As soon as the web is formed it has a little strength which doesn’t match the requirement of the customers. So it becomes very necessary to bond the web & for that method many choice are available.
• The main criterion of choice of any web bonding technology entirely depends on the functional properties.
• There are three basic types of bonding:
  1. Chemical
  2. Thermal
  3. Mechanical
     

A)   Chemical bonding

• In chemical bonding normally web is bonded with the help of some binding agent generally refer as binder.
• Three groups of materials are commonly used as binders:
  1. Acrylate polymers and copolymers
  2. Styrene-butadiene copolymers
  3. Vinyl acetate ethylene copolymers.
• The method of applying binder are
  1. Impregnating
  2. Coating
  3. Spraying
• The binders should necessary to apply homogeneously for better property gaining.

B)   Thermal bonding (cohesion bonding)

• In thermal bonding the controlled heat is applied for bonding the non woven fabrics. And this type of bonding is applied to raw materials which are thermoplastic in nature.
• Here a low melt fibre or bicomponent fibre is introduced at the web formation stage to perform the binding function later in the process but the web fibre itself can be used.
• There are several thermal bonding systems in use:
  1. Calendar bonding.
  2. Through-air thermal bonding.
  3. Drum and blanket systems.
  4. Sonic bonding.
     

C)   Mechanical bonding

• There are three major types of mechanical bonding:
  1. Needle punching
  2. Hydro-entanglement
  3. Stitch bonding

1. Needle punching is usually used for manufacturing geo-textiles. Especially designed needles are hard-pressed and pulled throughout the web to entangle the fibres for proper bonding.
   
   
2. Hydro entanglement uses high pressure jets of water to cause the fibres to interlace. It is mainly applied to carded or wet laid webs. The water jet pressure used has a direct bearing on the strength of the web, but system design also plays a part. Hydro entanglement is sometimes known as spun lacing.
   
   
3. Stitch bonding is a third type of mechanical bonding. It can be done with or without the addition of a thread. When no thread is added, the process is often referred to a loop formation.

• A range of different chemical material are in use before or after binding, or various mechanical processes are applied to the nonwoven after binding for modifying or adding to existing properties.
• By applying this above chemical nonwovens can be made
  1. Flame retardant,
  2. Water repellent,
  3. Conductive,
  4. Porous,
  5. Antistatic,
  6. Breathable,
  7. Absorbent and various other properties can be achieved.
• For proper lamination nonwoven can be coated, printed or dyed.
• Based upon the industry where it is used different methods are selected from above which will be applied.
• But mainly the following trends have been observed:
  1. Traditional textile industry uses Dry Form process
  2. The synthetic fibre industry uses the Spun-bond and Melt-blown methods
  3. The paper industry uses the wet process

Defects of nonwoven fabrics

There are different type of defects comes in nonwoven fabrics

• Fabric defects
• Roll defects
• Physical property defects

Application Categories

• Nonwoven fabric manufacturers usually manufacture the fabric in a roll form.
• It is then sent to various other industries where it has end applications, where is it cut and given different form depending upon the use.
• The application of nonwoven are: